The Global Community of Particle Physics

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  • Race and disease risk and Berlin’s singing nightingales

    2019-04-25T19:28:07Z via NavierStokesApp To: Public

    "Race and disease risk and Berlin’s singing nightingales"

    Noncancerous tumors of the uterus—also known as fibroids—are extremely common in women. One risk factor, according to the scientific literature, is “black race.” But such simplistic categories may actually obscure the real drivers of the disparities in outcomes for women with fibroids, according to this week’s guest. Host Meagan Cantwell speaks with Jada Benn Torres, an associate professor of anthropology at Vanderbilt University in Nashville, about how using interdisciplinary approaches— incorporating both genetic and cultural perspectives—can paint a more complete picture of how race shapes our understanding of diseases and how they are treated. In our monthly books segment, book review editor Valerie Thompson talks with David Rothenberg, author of the book Nightingales in Berlin: Searching for the Perfect Sound, about spending time with birds, whales, and neuroscientists trying to understand the aesthetics of human and animal music. This week’s episode was edited by Podigy. Listen to previous podcasts. About the Science Podcast [Image: Carlos Delgado/Wikipedia; Matthias Ripp/Flickr; Music: Jeffrey Cook]

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  • It takes a village

    2019-04-25T15:28:59Z via NavierStokesApp To: Public

    "It takes a village"

    Building a particle physics laboratory requires more than physicists.

    Valerie Higgins in the archives

    On the third floor of the central high-rise building at Fermi National Accelerator Laboratory, archivist Valerie Higgins’ office is full of odd treasures. There’s a wizard hat once worn by Nobel laureate and former lab director Leon Lederman, and a plaster bust of Manhattan Project physicist Robert Oppenheimer made by Fermilab’s founding director, Robert Wilson. There’s a trophy-shaped samovar of unknown origin—possibly a gift from tea-drinking Russian scientists.

    Stacked along one wall of shelves are around 30 humble green or brown boxes, each containing about 30 cassette tapes: oral histories that date back to the founding of the archives 40 years ago.

    The tapes contain interviews with people that have been instrumental in building the lab and the experiments that run there. Most of the interviews are with physicists. But some venture outside the detector halls to speak with the technical and support staff that make sure the physicists’ research takes place. Higgins, who has conducted around 50 oral history interviews herself, has been consciously adding to this category in her six years as Fermilab archivist. 

    Higgins has authored a paper available in the online physics repository, arXiv, and earlier this month published an op-ed for Physics World on the importance of capturing perspectives from all parts of the laboratory. She sat down with Symmetry writer Lauren Biron to discuss her thoughts.

    What kinds of perspectives do you look to capture in your work?


    Since scientific research often involves such large numbers of people, and the experiments or projects can become like institutions unto themselves, you have to approach documenting things with an eye towards the entire project.

    You need to document the contributions not just of the scientists who were working on the experiment, accelerator or project you are interested in, but also other technical staff who may not be physicists—people like computer scientists, engineers and technicians—and then also people who might be considered non-technical, such as administrative assistants. 

    I don’t think I fully understood or appreciated how many people are involved in making modern scientific research happen until I started my position here. In the paper, I listed some of the positions from Fermilab’s directory in 1969, and they include things like a nurse and an artist and a director of public information—positions someone unfamiliar with the lab might not expect to find here. We have accountants, the roads and grounds crew, the security staff. There are all sorts of different positions it takes to make the lab run. The site is 6800 acres and there are thousands of employees and scientists from collaborating institutions, so of course there are these sorts of positions. But until you stop to think about what it takes to run the lab, that might not occur to you.

    I try to get as broad a slice as I can. For instance, when I started, we hadn’t documented as much of the computing as we would have liked to, but former lab archivist Adrienne Kolb and I worked together to start to remedy that. We have interviews with people from the education office, human resources, directors, assistant directors, high level administrators, administrative assistants, technicians. I would like to get more technicians and engineers.

    What are the benefits of capturing information from non-scientific staff in oral histories, particularly compared to more traditional records?


    You don’t want to think of oral histories as a replacement for other records. They definitely have their limitations. There’s the fallibility of human memory. Sometimes people will just be flat out inaccurate, like on dates. Some things are more subjective and people will remember them different ways. 

    What makes oral histories valuable is actually that subjectivity. There are things you can capture in an oral history interview that you just don’t get from the records, or that never made it into the records. There are the reasons decisions were made or ways in which things were done. It’s the day-to-day stuff that isn’t written down anywhere or formalized in such a way that won’t make it into the records. 

    Sometimes everyone just knows that stuff, so it’s not written down, but then 20 or 30 years later, not everyone knows that assumed knowledge. 

    Fermilab has a very strong oral history program in the archives that dates back to the beginning of the archives in 1978. Right off the bat they were doing oral history interviews with people. We have over 1000 tapes of interviews, and now we have digital files of more recent interviews. 

    While we’ve focused on interviewing non-scientific people more recently, they did some of that even in the early days. I’ve found those interviews to have very interesting content and to be unique perspectives on the early history of the lab. 

    One of the things that can be valuable, particularly with people such as administrative assistants, is they can provide more of an outside view on what’s happening in the experiment or project. They often are not involved in a highly specialized area—they often have more general knowledge and know more about how the different areas interact.

    One thing I found with the oral history interviews was that a lot of people I interviewed who were non-technical have really appreciated that I wanted to interview them and saw their contributions to the lab as valuable. I’ve encountered some staff who are baffled and say, “Why do you want to talk to me, I haven’t done anything that important.” But then when I interview them, it always turns out that they did important things that were key to the success of the lab.

    Valerie Higgins in the archives
    Photo by Reidar Hahn, Fermilab

    What kinds of things are you missing from the early days of the lab?


    One example is the bubble chamber film scanners, the teams of mostly women who looked through images for potentially interesting particle events from a detector. So far, I have not found any interviews with the bubble chamber film scanners. I haven’t found anything other than the articles written about them. 

    That would be interesting if we had it—an interview with someone explaining what their day to day work was like, and what they did, and how they interacted with physicists. As far as I can tell, that doesn’t seem to exist. There wouldn’t have been any other records that documented something like that. That’s the sort of thing you’re only going to get from an oral history interview.

    Have you found things that surprised you?


    I’ve found very interesting things, like the interview with Robert Wilson’s first primary administrative assistant, Priscilla Duffield, who had also been assistant to Ernest Lawrence [who won the Nobel Prize for inventing the cyclotron particle accelerator] and Robert Oppenheimer [who led Los Alamos National Laboratory during the Manhattan Project and later advocated against nuclear proliferation]. 

    One of the frustrations with oral histories is you sometimes hear something really interesting and wish you could ask for more detail. She only gives a few sentences about it, but Duffield briefly talks about the different leadership and decision-making styles that she saw in Wilson versus Oppenheimer versus Lawrence, and I thought that was a really cool thing to find.  

    I don’t know if this is surprising, but it’s fun to hear about some of the cultural events that went on at the lab. You might have some photos from an event, but you don’t usually have many records that tell you about the games or food or funny things that people did or said. I suppose it might sound frivolous, but some of those things give you insight into what the life at the lab was like at that time.

    What do you hope people will learn from your recent work?


    I think the most relevant thing for anyone to be aware of is the importance of people who are in the support roles. Be aware of their importance if you’re an archivist trying to document modern scientific research, if you’re a historian writing about this work, if you’re a scientist involved in the work. Remember that these people are also making that research happen. 

    And if you are a support person, be aware that your work is important and valuable. It’s not just scientists who make these experiments happen and who make this lab run—it also takes people with other interests and talents that align.

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  • XENON1T Scientists Observe the Rarest Decay Process Ever Measured in the Universe

    2019-04-24T17:28:13Z via NavierStokesApp To: Public

    "XENON1T Scientists Observe the Rarest Decay Process Ever Measured in the Universe"

    XENON1T Scientists Observe the Rarest Decay Process Ever Measured in the UniversePress Releasexeno Wed, 04/24/2019 - 11:512219

    The universe is almost 14 billion years old. An inconceivable length of time by human standards – yet compared to some physical processes, it is but a moment. There are radioactive nuclei that decay on much longer time scales. An international team of scientists has now directly measured the rarest decay process ever recorded in a detector. Using the XENON1T detector which mainly searches for dark matter at the INFN Gran Sasso National Laboratory, the researchers were able to observe the decay of Xenon-124 atomic nuclei for the first time. The half-life of a process is the time after which half of the radioactive nuclei present in a sample have decayed away. The half-life measured for Xenon-124 is about one trillion times longer than the age of the universe. This makes the observed radioactive decay, the so-called double electron capture of Xenon-124, the rarest process ever seen happening in a detector. 

    “The fact that we managed to observe this process directly demonstrates how powerful our detection method actually is – also for signals which are not from dark matter,” says Prof. Christian Weinheimer from the University of Münster (Germany) whose group lead the study. 

    In addition, the new result provides information for further investigations on neutrinos, the lightest of all elementary particles whose nature is still not fully understood. XENON1T is a joint experimental project of about 160 scientists from Europe, the US and the Middle East. The results were published in the science journal “Nature”.

    A sensitive dark matter detector

    The Gran Sasso Laboratory of the National Institute for Nuclear Physics (INFN) in Italy, where scientists are currently searching for dark matter particles is located about 1,400 meters beneath the Gran Sasso massif, well protected from cosmic rays which can produce false signals. Theoretical considerations predict that dark matter should very rarely “collide” with the atoms of the detector. This assumption is fundamental to the working principle of the XENON1T detector: its central part consists of a cylindrical tank of about one meter in length filled with 3,200 kilograms of liquid xenon at a temperature of –95° C. When a dark matter particle interacts with a xenon atom, it transfers energy to the atomic nucleus which subsequently excites other xenon atoms. This leads to the emission of faint signals of ultraviolet light which are detected by means of sensitive light sensors located in the upper and lower parts of the cylinder. The same sensors also detect a minute amount of electrical charge which is released by the collision process. 

    The new study shows that the XENON1T detector is also able to measure other rare physical phenomena, such as double electron capture. To understand this process, one should know that an atomic nucleus normally consists of positively charged protons and neutral neutrons, which are surrounded by several atomic shells occupied by negatively charged electrons. Xenon-124, for example, has 54 protons and 70 neutrons. In double electron capture, two protons in the nucleus simultaneously “catch” two electrons from the innermost atomic shell, transform into two neutrons, and emit two neutrinos. The other atomic electrons reorganize themselves to fill in the two holes in the innermost shell. The energy released in this process is carried away by X-rays and so-called Auger electrons. However, these signals are very hard to detect, as double electron capture is a very rare process which is hidden by signals from the omnipresent natural radioactivity.

    The measurement

    This is how the XENON collaboration succeeded with this measurement: The X-rays from the double electron capture in the liquid xenon produced an initial light signal as well as free electrons. The electrons were moved towards the gas-filled upper part of the detector where they generated a second light signal. The time difference between the two signals corresponds to the time it takes the electrons to reach the top of the detector. Scientists used this interval and the information provided by the sensors measuring the signals to reconstruct the position of the double electron capture. The energy released in the decay was derived from the strength of the two signals. All signals from the detector were recorded over a period of more than one year, however, without looking at them at all as the experiment was conducted in a “blind” fashion. This means that the scientists could not access the data in the energy region of interest until the analysis was finalized to ensure that personal expectations did not skew the outcome of the study. Thanks to the detailed understanding of all relevant sources of background signals it became clear that 126 observed events in the data were indeed caused by the double electron capture of Xenon-124. 

    Using this first-ever measurement, the physicists calculated the enormously long half-life of 1.8×1022 years for the process. This is the slowest process ever measured directly. It is known that the atom Tellurium-128 decays with an even longer half-life, however, its decay was never observed directly and the half-life was inferred indirectly from another process. The new results show how well the XENON1T detector can detect rare processes and reject background signals. While two neutrinos are emitted in the double electron capture process, scientists can now also search for the so-called neutrino-less double electron capture which could shed light on important questions regarding the nature of neutrinos. 

    Status and outlook

    XENON1T acquired data from 2016 until December 2018 when it was switched off. The scientists are currently upgrading the experiment for the new “XENONnT” phase which will feature a three times larger active detector mass. Together with a reduced background level this will boost the detector’s sensitivity by an order of magnitude.


    The XENON1T Experiment
    The XENON Experiment at INFN Gran Sasso National Laboratory
    Short movie of the XENON1T construction at LNGS


    INFN Communications Office | Antonella Varaschin
    +39 349 5384481

    LNGS-INFN Outreach Office | Roberta Antolini
    +39 0862 437216

    The XENON spokesperson

    Prof. Elena Aprile, Columbia University, New York, US

    Tel. +39 3494703313 Tel. +1 212 854 3258 

    In Italy

    XENON National Leader for INFN

    Marco Selvi, INFN Bologna
    Tel. +39 3283178626 Tel. +39 0512091120

    Laboratori Nazionali del Gran Sasso - INFN

    INFN Gran Sasso National Laboratory. (Courtesy: INFN)

    INFN Gran Sasso National Laboratory. (Courtesy: INFN)

    Gran Sasso National Laboratory (LNGS) is one of the four national laboratories of INFN (National Institute for Nuclear Physics).

    The other laboratories of INFN are based in Catania, Frascati (Rome) and Legnaro (Padua); the whole network of laboratories house large equipment and infrastructures available for use by the national and international scientific community.

    The National Institute for Nuclear Physics (INFN) is the Italian research agency dedicated to the study of the fundamental constituents of matter and the laws that govern them, under the supervision of the Ministry of Education, Universities and Research (MIUR). It conducts theoretical and experimental research in the fields of subnuclear, nuclear and astroparticle physics.

    Via G. Acitelli, 22
    67100Assergi AQ

    + 39 0862 4371

    XENON spokesperson
    Prof. Elena Aprile, Columbia University, New York, US.
    Tel. +39 3494703313
    Tel. +1 212 854 3258

    INFN spokesperson
    Roberta Antolini
    + 39 0862 437216


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  • Serbian flag raised at CERN

    2019-04-23T15:28:04Z via NavierStokesApp To: Public

    "Serbian flag raised at CERN"

    Serbian flag raised at CERN

    cmenard Tue, 04/23/2019 - 09:49
    The Serbian flag was raised in the presence of the President of the CERN Council, Prime Minister of the Republic of Serbia, CERN Director-General, Serbian Minister of Education, Science and Technological Development and the Serbian Ambassador to the UN Office in Geneva. (Image: Maximilien Brice/CERN)

    The Serbian flag was raised today at a ceremony on the Esplanade des Particules to mark the country’s accession as CERN’s 23rd Member State. The ceremony was attended by the Prime Minister of the Republic of Serbia, Ana Brnabić, the President of the CERN Council, Ursula Bassler, and the CERN Director-General Fabiola Gianotti, together with representatives of CERN’s Member and Associate Member States and the CERN community.

    “The 23rd of April is a great day for Serbia and its science, as the flag of the Republic of Serbia is officially hoisted in front of CERN in Geneva, marking Serbia’s accession as its 23rd full Member. This will allow our researchers to work in higher capacity and on a global level with their colleagues from CERN, while enabling our economy to participate in CERN projects on a larger scale. Membership in CERN presents Serbia in the best light, as a modern, competitive country whose economic development increasingly relies on science and innovation, driven by our young scientists and innovators,” said Ana Brnabić, Prime Minister of the Republic of Serbia.

     “This is the moment when the commitment of a new Member State becomes visible: the commitment to support fundamental science, to foster peaceful collaboration and to engage in multilateral initiatives for the benefit of all. We are pleased to raise the Serbian flag among those of our Member States,” said Ursula Bassler, President of the CERN Council.

    “It is a great pleasure to welcome Serbia to the CERN family. This day recognises the long history of fruitful scientific cooperation between Serbia and CERN, and Serbia’s commitment to fundamental research. We look forward to strengthening our collaboration in particle physics, innovation, and training and education of the young generations, with Serbia as a Member State,” said Fabiola Gianotti, CERN Director-General.

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  • Falsifiability and physics

    2019-04-23T14:27:52Z via NavierStokesApp To: Public

    "Falsifiability and physics"

    Can a theory that isn’t completely testable still be useful to physics?

    Scientists look on as giant hand comes down with shape that will fit into any available holes.

    What determines if an idea is legitimately scientific or not? This question has been debated by philosophers and historians of science, working scientists, and lawyers in courts of law. That’s because it’s not merely an abstract notion: What makes something scientific or not determines if it should be taught in classrooms or supported by government grant money.

    The answer is relatively straightforward in many cases: Despite conspiracy theories to the contrary, the Earth is not flat. Literally all evidence is in favor of a round and rotating Earth, so statements based on a flat-Earth hypothesis are not scientific. 

    In other cases, though, people actively debate where and how the demarcation line should be drawn. One such criterion was proposed by philosopher of science Karl Popper (1902-1994), who argued that scientific ideas must be subject to “falsification.” 

    Popper wrote in his classic book The Logic of Scientific Discovery that a theory that cannot be proven false—that is, a theory flexible enough to encompass every possible experimental outcome—is scientifically useless. He wrote that a scientific idea must contain the key to its own downfall: It must make predictions that can be tested and, if those predictions are proven false, the theory must be jettisoned. 

    When writing this, Popper was less concerned with physics than he was with theories like Freudian psychology and Stalinist history. These, he argued, were not falsifiable because they were vague or flexible enough to incorporate all the available evidence and therefore immune to testing. 

    But where does this falsifiability requirement leave certain areas of theoretical physics? String theory, for example, involves physics on extremely small length scales unreachable by any foreseeable experiment. Cosmic inflation, a theory that explains much about the properties of the observable universe, may itself be untestable through direct observations. Some critics believe these theories are unfalsifiable and, for that reason, are of dubious scientific value.

    At the same time, many physicists align with philosophers of science who identified flaws in Popper’s model, saying falsification is most useful in identifying blatant pseudoscience (the flat-Earth hypothesis, again) but relatively unimportant for judging theories growing out of established paradigms in science.

    “I think we should be worried about being arrogant,” says Chanda Prescod-Weinstein of the University of New Hampshire. “Falsifiability is important, but so is remembering that nature does what it wants.”

    Prescod-Weinstein is both a particle cosmologist and researcher in science, technology, and society studies, interested in analyzing the priorities scientists have as a group. “Any particular generation deciding that they’ve worked out all that can be worked out seems like the height of arrogance to me,” she says.

    Tracy Slatyer of MIT agrees, and argues that stringently worrying about falsification can prevent new ideas from germinating, stifling creativity. “In theoretical physics, the vast majority of all the ideas you ever work on are going to be wrong,” she says. “They may be interesting ideas, they may be beautiful ideas, they may be gorgeous structures that are simply not realized in our universe.”

    Particles and practical philosophy

    Take, for example, supersymmetry. SUSY is an extension of the Standard Model in which each known particle is paired with a supersymmetric partner. The theory is a natural outgrowth of a mathematical symmetry of spacetime, in ways similar to the Standard Model itself. It’s well established within particle physics, even though supersymmetric particles, if they exist, may be out of scientists’ experimental reach. 

    SUSY could potentially resolve some major mysteries in modern physics. For one, all of those supersymmetric particles could be the reason the mass of the Higgs boson is smaller than quantum mechanics says it should be.

    “Quantum mechanics says that [the Higgs boson] mass should blow up to the largest mass scale possible,” says Howard Baer of the University of Oklahoma. That’s because masses in quantum theory are the result of contributions from many different particles involved in interactions—and the Higgs field, which gives other particles mass, racks up a lot of these interactions. But the Higgs mass isn’t huge, which requires an explanation.

    “Something else would have to be tuned to a huge negative [value] in order to cancel [the huge positive value of those interactions] and give you the observed value,” Baer says. That level of coincidence, known as a “fine-tuning problem,” makes physicists itchy. “It's like trying to play the lottery. It's possible you might win, but really you're almost certain to lose.”

    If SUSY particles turn up in a certain mass range, their contributions to the Higgs mass “naturally” solve this problem, which has been an argument in favor of the theory of supersymmetry. So far, the Large Hadron Collider has not turned up any SUSY particles in the range of “naturalness.” 

    However, the broad framework of supersymmetry can accommodate even more massive SUSY particles, which may or may not be detectable using the LHC. In fact, if naturalness is abandoned, SUSY doesn’t provide an obvious mass scale at all, meaning SUSY particles might be out of range for discovery with any earthly particle collider. That point has made some critics queasy: If there's no obvious mass scale at which colliders can hunt for SUSY, is the theory falsifiable?

    A related problem confronts dark matter researchers: Despite strong indirect evidence for a large amount of mass invisible to all forms of light, particle experiments have yet to find any dark matter particles. It could be that dark matter particles are just impossible to directly detect. A small but vocal group of researchers has argued that we need to consider alternative theories of gravity instead.

    Slatyer, whose research involves looking for dark matter, considers the criticism partly as a problem of language. “When you say ‘dark matter,’ [you need] to distinguish dark matter from specific scenarios for what dark matter could be,” she says. “The community has not always done that well.” 

    In other words, specific models for dark matter can stand or fall, but the dark matter paradigm as a whole has withstood all tests so far. But as Slatyer points out, no alternative theory of gravity can explain all the phenomena that a simple dark matter model can, from the behavior of galaxies to the structure of the cosmic microwave background.

    Prescod-Weinstein argues that we're a long way from ruling out all dark matter possibilities. "How will we prove that the dark matter, if it exists, definitively doesn’t interact with the Standard Model?" she says. "Astrophysics is always a bit of a detective game. Without laboratory [detection of] dark matter, it’s hard to make definitive statements about its properties. But we can construct likely narratives based on what we know about its behavior."

    Similarly, Baer thinks that we haven’t exhausted all the SUSY possibilities yet. “People say, ‘you've been promising supersymmetry for 20 or 30 years,’ but it was based on overly optimistic naturalness calculations,” he says. “I think if one evaluates the naturalness properly, then you find that supersymmetry is still even now very natural. But you're going to need either an energy upgrade of LHC or an ILC [International Linear Collider] in order to discover it.” 

    Beyond falsifiability of dark matter or SUSY, physicists are motivated by more mundane concerns. “Even if these individual scenarios are in principle falsifiable, how much money would [it] take and how much time would it take?” Slatyer says. In other words, rather than try to demonstrate or rule out SUSY as a whole, physicists focus on particle experiments that can be performed within a certain number of budgetary cycles. It's not romantic, but it's true nevertheless.

    A hand reaches in the dark for an object representing super symmetry.
    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    Is it science? Who decides?

    Historically, sometimes theories that seem untestable turn out to just need more time. For example, 19th century physicist Ludwig Boltzmann and colleagues showed they could explain many results in thermal physics and chemistry if everything were made up of "atoms"—what we call particles, atoms, and molecules today—governed by Newtonian physics. 

    Since atoms were out of reach of experiments of the day, prominent philosophers of science argued that the atomic hypothesis was untestable in principle, and therefore unscientific. 

    However, the atomists eventually won the day: J. J. Thompson demonstrated the existence of electrons, while Albert Einstein showed that water molecules could make grains of pollen dance on a pond’s surface.

    Atoms provide a case study for how falsifiability proved to be the wrong criterion. Many other cases are trickier. 

    For instance, Einstein’s theory of general relativity is one of the best-tested theories in all of science. At the same time, it allows for physically unrealistic “universes,” such as a "rotating" cosmos where movement back and forth in time is possible, which are contradicted by all observations of the reality we inhabit. 

    General relativity also makes predictions about things that are untestable by definition, like how particles move inside the event horizon of a black hole: No information about these trajectories can be determined by experiment. 

    Yet no knowledgeable physicist or philosopher of science would argue that general relativity is unscientific. The success of the theory is due to enough of its predictions being testable.

    Another type of theory may be mostly untestable, but have important consequences. One such theory is cosmic inflation, which (among other things) explains why we don’t see isolated magnetic monopoles and why the universe is a nearly uniform temperature everywhere we look. 

    The key property of inflation—the extremely rapid expansion of spacetime during a tiny split second after the Big Bang—cannot be tested directly. Cosmologists look for indirect evidence for inflation, but in the end it may be difficult or impossible to distinguish between different inflationary models, simply because scientists can’t get the data. Does that mean it isn’t scientific?

    “A lot of people have personal feelings about inflation and the aesthetics of physical theories,” Prescod-Weinstein says. She’s willing to entertain alternative ideas which have testable consequences, but inflation works well enough for now to keep it around. “It’s also the case that the majority of the cosmology community continues to take inflation seriously as a model, so I have to shrug a little when someone says it’s not science.”

    On that note, Caltech cosmologist Sean M. Carroll argues that many very useful theories have both falsifiable and unfalsifiable predictions. Some aspects may be testable in principle, but not by any experiment or observation we can perform with existing technology. Many particle physics models fall into that category, but that doesn’t stop physicists from finding them useful. SUSY as a concept may not be falsifiable, but many specific models within the broad framework certainly are. All the evidence we have for the existence of dark matter is indirect, which won't go away even if laboratory experiments never find dark matter particles. Physicists accept the concept of dark matter because it works.

    Slatyer is a practical dark matter hunter. “The questions I'm most interested asking are not even just questions that are in principle falsifiable, but questions that in principle can be tested by data on the timescale of less than my lifetime,” she says. “But it's not only problems that can be tested by data on a timescale of ‘less than Tracy's lifetime’ are good scientific questions!”

    Prescod-Weinstein agrees, and argues for keeping an open mind. “There’s a lot we don’t know about the universe, including what’s knowable about it. We are a curious species, and I think we should remain curious.”

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  • Week 14 at the Pole

    2019-04-19T15:27:51Z via NavierStokesApp To: Public

    "Week 14 at the Pole"

    The sky was still bright enough last week to take a photo of an ozone balloon launch, the first one to send up a special plastic balloon in the hopes of a better survival as it ascends in the cold atmosphere.

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  • How dental plaque reveals the history of dairy farming, and how our neighbors view food waste

    2019-04-18T19:27:50Z via NavierStokesApp To: Public

    "How dental plaque reveals the history of dairy farming, and how our neighbors view food waste"

    This week we have two interviews from the annual meeting of AAAS in Washington D.C.: one on the history of food and one about our own perceptions of food and food waste.  First up, host Sarah Crespi talks with Christina Warinner from the Max Planck Institute for the Science of Human History in Jena, Germany, about the history of dairying. When did people first start to milk animals and where? It turns out, the spread of human genetic adaptations for drinking milk do not closely correspond to the history of consuming milk from animals. Instead, evidence from ancient dental plaque suggests people from all over the world developed different ways of chugging milk—not all of them genetic. Next, Host Meagan Cantwell speaks with Sheril Kirshenbaum, co-director of the Michigan State University Food Literacy and Engagement Poll, about the public’s perception of food waste. Do most people try to conserve food and produce less waste? Better insight into the point of view of consumers may help keep billions of kilograms of food from being discarded every year in the United States. This week’s episode was edited by Podigy. Listen to previous podcasts. About the Science Podcast [Image:  Carefull in Wyoming/Flickr; Music: Jeffrey Cook]

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  • What gravitational waves can say about dark matter

    2019-04-18T16:27:51Z via NavierStokesApp To: Public

    "What gravitational waves can say about dark matter"

    Scientists think that, under some circumstances, dark matter could generate powerful enough gravitational waves for equipment like LIGO to detect.

    An illustration representing gravitational waves

    In 1916, Albert Einstein published his theory of general relativity, which established the modern view of gravity as a warping of the fabric of spacetime. The theory predicted that objects that interact with gravity could disturb that fabric, sending ripples across it.

    Any object that interacts with gravity can create gravitational waves. But only the most catastrophic cosmic events make gravitational waves powerful enough for us to detect. Now that observatories have begun to record gravitational waves on a regular basis, scientists are discussing how dark matter—only known so far to interact with other matter only through gravity—might create gravitational waves strong enough to be found. 

    The spacetime blanket

    In the universe, space and time are invariably linked as four-dimensional spacetime. For simplicity, you can think of spacetime as a blanket suspended above the ground. Jupiter might be a single Cheerio on top of that blanket. The sun could be a tennis ball. R136a1—the most massive known star—might be a 40-pound medicine ball. 

    Each of these objects weighs down the blanket where it sits: the heavier the object, the bigger the dip in the blanket. Like objects of different weights on a blanket, objects of different masses have different effects on the fabric of spacetime. A dip in spacetime is gravitational field.

    The gravitational field of one object can affect another object. The other object might fall into the first object’s gravitational field and orbit around it, like the moon around Earth, or Earth around the sun. 

    Alternatively, two bodies with gravitational fields might spiral toward each other, getting closer and closer until they collide. As this happens, they create ripples in spacetime—gravitational waves. 

    On September 14, 2015, scientists used the Laser Interferometer Gravitational-Wave Observatory, or LIGO, to make the first direct observation of gravitational waves, part of the buildup to the crash between two massive black holes. 

    Since that first detection, the LIGO collaboration—together with the collaboration that runs a partner gravitational-wave observatory called Virgo—has detected gravitational waves from at least 10 more mergers of black holes and, in 2017, the first merger between two neutron stars. 

    Dark matter is believed to be five times as prevalent as visible matter. Its gravitational effects are seen throughout the universe. Scientists think they have yet to definitively see gravitational waves caused by dark matter, but they can think of numerous ways this might happen.  

    Primordial black holes 

    Scientists have seen the gravitational effects of dark matter, so they know it must be there—or at least, something must be going on to cause those effects. But so far, they’ve never directly detected a dark matter particle, so they’re not sure exactly what dark matter is like.

    One idea is that some of the dark matter could actually be primordial black holes.

    Imagine the universe as an infinitely large petri dish. In this scenario, the Big Bang is the point where matter-bacteria begins to grow. That point quickly expands, moving outward to encompass more and more of the petri dish. If that growth is slightly uneven, certain areas will become more densely inhabited by matter than others. 

    These pockets of dense matter—mostly photons at this point in the universe—might have collapsed under their own gravity and formed early black holes. 

    “I think it’s an interesting theory, as interesting as a new kind of particle,” says Yacine Ali-Haimoud, an assistant professor of physics at New York University. “If primordial black holes do exist, it would have profound implications on the conditions in the very early universe.” 

    By using gravitational waves to learn about the properties of black holes, LIGO might be able to prove or constrain this dark matter theory. 

    Unlike normal black holes, primordial black holes don’t have a minimum mass threshold they need to reach in order to form. If LIGO were to see a black hole less massive than the sun, for example, it might be a primordial black hole. 

    Even if primordial black holes do exist, it’s doubtful that they account for all of the dark matter in the universe. Still, finding proof of primordial black holes would expand our fundamental understanding of dark matter and how the universe began. 

    Neutron star rattles

    Dark matter seems to interact with normal matter only through gravity, but, based on the way known particles interact, theorists think it’s possible that dark matter might also interact with itself. 

    If that is the case, dark matter particles might bind together to form dark objects that are as compact as a neutron star.  

    We know that stars drastically “weigh down” the fabric of spacetime around them. If the universe were populated with compact dark objects, there would be a chance that at least some of them would end up trapped inside of ordinary matter stars. 

    A normal star and a dark object would interact only through gravity, allowing the two to co-exist without much of a fuss. But any disruption to the star—for example, a supernova explosion—could create a rattle-like disturbance between the resulting neutron star and the trapped dark object. If such an event occurred in our galaxy, it would create detectable gravitational waves

    “We understand neutron stars quite well,” says Sanjay Reddy, University of Washington physics professor and senior fellow with the Institute for Nuclear Theory. “If something ‘odd’ happens with gravitational waves, we would know there was potentially something new going on that might involve dark matter.” 

    The likelihood that any exist in our solar system is limited. Chuck Horowitz, Maria Alessandra Papa and Reddy recently analyzed LIGO’s data and found no indication of compact dark objects of a specific mass range within Earth, Jupiter or the sun. 

    Further gravitational-wave studies could place further constraints on compact dark objects. “Constraints are important,” says Ann Nelson, a physics professor at the University of Washington. “They allow us to improve existing theories and even formulate new ones.”

    Axion stars

    One light dark matter candidate is the axion, named by physicist Frank Wilczek after a brand of detergent, in reference to its ability to tidy up a problem in the theory of quantum chromodynamics.

    Scientists think it could be possible for axions to bind together into axion stars, similar to neutron stars but made up of extremely compact axion matter. 

    “If axions exist, there are scenarios where they can cluster together and form stellar objects, like ordinary matter,” says Tim Dietrich, a LIGO-Virgo member and physicist. “We don’t know if axion stars exist, and we won’t know for sure until we find constraints for our models.” 

    If an axion star merged with a neutron star, scientists might not be able to tell the difference between the two with their current instruments. Instead, scientists would need to rely on electromagnetic signals accompanying the gravitational wave to identify the anomaly. 

    It’s also possible that axions could bunch around a binary black hole or neutron star system. If those stars then merged, the changes in the axion “cloud” would be visible in the gravitational wave signal. A third possibility is that axions could be created by the merger, an action that would be reflected in the signal. 

    This month, the LIGO-Virgo collaborations began their third observing run and, with new upgrades, expect to detect a merger event every week. 

    Gravitational-wave detectors have already proven their worth in confirming Einstein’s century-old prediction. But there is still plenty that studying gravitational waves can teach us. “Gravitational waves are like a completely new sense for science,” Ali-Haimoud says. “A new sense means new ways to look at all the big questions in physics.”

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  • Successful tests of a cooler way to transport electricity

    2019-04-18T16:27:50Z via NavierStokesApp To: Public

    "Successful tests of a cooler way to transport electricity"

    Successful tests of a cooler way to transport electricity

    camonnin Thu, 04/18/2019 - 14:52

    Like a metal python, the huge pipe snaking through a CERN high-tech hall is actually a new electrical transmission line. This superconducting line is the first of its kind and allows vast quantities of electrical current to be transported within a pipe of a relatively small diameter. Similar pipes could well be used in towns in the future.

    This 60-metre-long line has been developed for CERN’s future accelerator, the High-Luminosity LHC, which is due to come into operation in 2026. Tests began last year and the line has transported 40 000 amps. This is 20 times more than what is possible at room temperature with ordinary copper cables of a similar cross-section. The line is composed ofsuperconducting cables made from magnesium diboride (MgB2) and offers no resistance, enabling it to transport much higher current densities than ordinary cables, without any loss. The snag is that, in order to function in a superconducting state, the cables must be cooled to a temperature of 25 K (-248°C). It is therefore placed inside a cryostat, a thermally insulated pipe in which a coolant, namely helium gas, circulates. The real achievements are the development of a new, flexible superconducting system and the use of a new superconductor (MgB2).

    The line is more compact and lighter than its copper equivalent, and it is cryogenically more efficient than a classical low temperature superconducting link that must be cooled to 4.5 K. 

    Amalia Ballarino, the project leader

    Having proven that such a system is feasible, at the end of March the team tested the connection to the room temperature end of the system. In the High-Luminosity LHC, these lines will connect power converters to the magnets. These converters are located at a certain distance from the accelerator. The new superconducting transmission lines, which measure up to 140 m in length, will feed several circuits and transport electrical current of up to 100 000 amps.

    “The magnesium diboride cable and the current leads that supply the magnets are connected by means of high-temperature ReBCO (rare-earth barium copper oxide) superconductors, also a challenging innovation for this type of application,” explains Amalia Ballarino.  These superconductors are called “high-temperature” because they can operate at temperatures of up to around 90 kelvins (-183 °C), as opposed to just a few kelvins in the case ofclassical low-temperature superconductors. They can transport very high current densities, but are very tricky to work with, hence the impressiveness of the team’s achievement.

    Tests of the line with its new connection represent an important milestone in the project, as it proves that the whole system works correctly. “We have new materials, a new cooling system and unprecedented technologies for supplying the magnets in an innovative way,” says Amalia Ballarino. 

    The project has also caught the attention of the outside world. Companies are using the work done at CERN to study the possibility of using similar transmission lines (at high voltage), instead of conventional systems, to transport electricity and power over long distances. 

    Credit: CERN

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  • A new edition of the IceCube Masterclass makes new connections with students

    2019-04-17T15:27:41Z via NavierStokesApp To: Public

    "A new edition of the IceCube Masterclass makes new connections with students"

    The sixth edition of the IceCube Masterclass hosted over 150 students at 13 institutions in Belgium, Germany, Switzerland, and the United States. The masterclasses were held on January 30, March 20, April 4 and April 11.

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  • A collision of light

    2019-04-16T14:27:50Z via NavierStokesApp To: Public

    "A collision of light"

    One of the latest discoveries from the LHC takes the properties of photons beyond what your electrodynamics teacher will tell you in class.

    Long-exposure photo showing many colors of light

    Professor Anne Sickles is currently teaching a laboratory class at the University of Illinois in which her students will measure what happens when two photons meet.

    What they will find is that the overlapping waves of light get brighter when two peaks align and dimmer when a peak meets a trough. She tells her students that this is process called interference, and that—unlike charged particles, which can merge, bond and interact—light waves can only add or subtract.

    “We teach undergraduates the classical theory,” Sickles says. “But there are situations where effects forbidden in the classical theory are allowed in the quantum theory.”

    Sickles is a collaborator on the ATLAS experiment at CERN and studies what happens when particles of light meet inside the Large Hadron Collider. For most of the year, the LHC collides protons, but for about a month each fall, the LHC switches things up and collides heavy atomic nuclei, such as lead ions. The main purpose of these lead collisions is to study a hot and dense subatomic fluid called the quark-gluon plasma, which is harder to create in collisions of protons. But these ion runs also enable scientists to turn the LHC into a new type of machine: a photon-photon collider.

    “This result demonstrates that photons can scatter off each other and change each other’s direction,” says Peter Steinberg, and ATLAS scientist at Brookhaven National Laboratory.

    When heavy nuclei are accelerated in the LHC, they are encased within an electromagnetic aura generated by their large positive charges.

    As the nuclei travel faster and faster, their surrounding fields are squished into disks, making them much more concentrated. When two lead ions pass closely enough that their electromagnetic fields swoosh through one another, the high-energy photons which ultimately make up these fields can interact. In rare instances, a photon from one lead ion will merge with a photon from an oncoming lead ion, and they will ricochet in different directions.

    However, according to Steinberg, it’s not as simple as two solid particles bouncing off each other. Light particles are both chargeless and massless, and must go through a quantum mechanical loophole (literally called a quantum loop) to interact with one another.

    “That’s why this process is so rare,” he says. “They have no way to bounce off of each other without help.”

    When the two photons see each other inside the LHC, they sometimes overreact with excitement and split themselves into an electron and positron pair. These electron-positron pairs are not fully formed entities, but rather unstable quantum fluctuations that scientists call virtual particles. The four virtual particles swirl into each other and recombine to form two new photons, which scatter off at weird angles into the detector.

    “It’s like a quantum-mechanical square dance,” Steinberg says.

    When ATLAS first saw hints of this process in 2017, they had only 13 candidate events with the correct characteristics (collisions that resulted in two low-energy photons inside the detector and nothing else).

    After another two years of data taking, they have now collected 59 candidate events, bumping this original observation into the statistical certainty of a full-fledged discovery.

    Steinberg sees this discovery as a big win for quantum electrodynamics, a theory about the quantum behavior of light that predicted this interaction. “This amazingly precise theory, which was developed in the first half of the 20th century, made a prediction that we are finally able to confirm many decades later.”

    Sickles says she is looking forward to exploring these kinds of light-by-light interactions and figuring out what else they could teach us about the laws of physics. “It’s one thing to see something,” she says. “It’s another thing to study it.”

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  • Cinque studenti abruzzesi tra i ragazzi dei raggi cosmici al Gran Sasso

    2019-04-15T10:28:33Z via NavierStokesApp To: Public

    "Cinque studenti abruzzesi tra i ragazzi dei raggi cosmici al Gran Sasso"

    Sono 29 studenti di scuole superiori, arrivano all’Aquila da 14 regioni italiane, per conoscere e approfondire la fisica dei raggi cosmici.

    Read More ...

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  • Week 13 at the Pole

    2019-04-12T21:28:29Z via NavierStokesApp To: Public

    "Week 13 at the Pole"

    There’s still just a bit of sunlight lingering, as seen in the image—what’s not so easily discernible in the image are the stars, but the winterovers report having seen them for the first time in months.

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  • A new species of ancient human and real-time evolutionary changes in flowering plants

    2019-04-11T19:28:28Z via NavierStokesApp To: Public

    "A new species of ancient human and real-time evolutionary changes in flowering plants"

    The ancient humans also known as the “hobbit” people (Homo floresiensis) might have company in their small stature with the discovery of another species of hominin in the Philippines. Host Sarah Crespi talks to Contributing Correspondent Lizzie Wade about what researchers have learned about this hominin from a jaw fragment, and its finger and toe bones and how this fits in with past discoveries of other ancient humans. Also this week, host Meagan Cantwell speaks with Florian Schiestl, a professor in evolutionary biology at the University of Zurich in Switzerland, about his work to understand the rapid evolution of the flowering plant Brassica rapa over the course of six generations. He was able to see how the combination of pollination by bees and risk of getting eaten by herbivores influences the plant’s appearance and defense mechanisms. This week’s episode was edited by Podigy. Listen to previous podcasts. About the Science Podcast [Image: Florian Schiestl; Music: Jeffrey Cook]

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  • LHCb results add clues to pentaquark mystery

    2019-04-11T16:28:27Z via NavierStokesApp To: Public

    "LHCb results add clues to pentaquark mystery"

    A re-examination of a particle discovered in 2015 has scientists debating its true identity.

    Illustration showing the pentaquark as a molecule

    Syracuse professor Tomasz Skwarnicki has been a physicist for 30 years. He and his  collaborators have measured rare processes and even discovered new particles. But he says their recent re-examination of a particle they discovered in 2015 was one the few analyses that made him exclaim, “Oh my gosh.”

    Skwarnicki has been working on the LHCb experiment at CERN for more than a decade. He uses the collisions generated by the Large Hadron Collider to search for exotic combinations of quarks.

    Quarks are fundamental particles that bond together to form hadrons—the most common ones being the protons and neutrons found in the atoms that make up almost everything around us.

    For decades scientists had only ever seen hadrons containing three quarks, or a quark and an antiquark. Recent observations of particles made from four and five quarks have begun to challenge this paradigm. A question that remains about these exotic particles, however, is how the quarks are structured within them.

    This interest in how quarks bond stems from the study of a fundamental property of quarks called color charge.

    A splash of color

    Color charge is similar to the electric charge in that it induces an attractive force between particles. Just as magnets with opposite electromagnetic charges stick together, quarks with different color charges stick together. There are three possible color charges: red, blue and green. (And for antiquarks, anti-red, anti-blue and anti-green.)

    It’s not a coincidence that quarks prefer to bond into groups of two and three. In nature, scientists have found only color-neutral objects. They have found hadrons made up of a quark and an antiquark of opposite color charges (for example, red and anti-red), and hadrons made up of three quarks of different color charges (a red quark, a blue quark and a green quark, which also neutralize one another).

    For decades scientists have been looking for new kinds of quark combinations that break this mold—specifically, two matter-quarks bound together into a diquark.

    Because the force between color-charged quarks is orders of magnitude stronger than that of an electric field, most experts think that only hadrons which are completely color neutral are possible. But some theorists hold out hope that with the right combination, pockets that maintain a non-neutral color charge could momentarily exist.

    If they could find a combination of quarks that are not completely color-neutral, “it would open a new world,” says Ahmed Ali, a theoretical physicist at DESY.

    And if they could find a way to harness that charge, he says, “the implications could be far-reaching.” The last time scientists figured out how to separate the charges fundamental particles, the result was electricity.

    Scientists think it’s physically impossible to isolate a non-neutral quark cluster. But some hope that in the collisions generated by the LHC, one of these theoretical diquark combinations could momentarily manifest itself. “Finding that experimentally would be a breakthrough,” Ali says.

    Scientists have made some promising observations that show complex combinations of quarks. Since 2003, numerous experiments have observed particles that appear to be made up of four quarks. And in 2015, LHCb announced the discovery of the first particle made up of five quarks—a pentaquark.

    But this latest analysis by the LHCb collaboration raises questions about the identity of this pentaquark—and may have taken scientists back to square one in the search for a particle that could shed light on questions about color.

    Seeing triple

    The first time Skwarnicki saw LHCb’s pentaquark, it appeared as a large and broad bump that unexpectedly showed up in data from collisions that produced protons and particles called J-psi. It wasn’t especially clear, he says: “It was like looking at an image that was far away and out of focus.”

    This year, Skwarnicki and his colleagues redid the analysis using 10 times as much data, and the difference was striking. “I was the first person to see the data,” he says. “It was beautiful.”

    And startling. Rather than a single bump, Skwarnicki was suddenly looking at three: three distinct pentaquarks. “The peaks were so sharp and narrow,” he says. “Each pentaquark has the same quark content, but they are in different quantum states, which gives them different masses.”

    The new result has reignited a debate about what pentaquarks actually look like. “The key question is how the quarks organize themselves,” Ali says.

    “There is a certain latent—but not so latent—competition between the different theoretical camps.”

    The atom camp

    Theorist Marek Karliner at Tel Aviv University, and his colleague Jon Rosner at the University of Chicago, were not surprised at the appearance of three separate pentaquarks.

    “The three masses just happen to sit right where you would expect them,” Karliner says.

    That is, right where you would expect them if the pentaquark isn’t a tightly bound pentaquark, but rather a new type of atomic nucleus, formed from two well-understood, color-neutral hadrons—one made up of two quarks, and one made up of three.

    Their reasoning? Simple addition. “We expect the mass of a nucleus to be very close to the sum of its constituent parts,” he says.

    The mass of the lightest pentaquark is suspiciously close to the combined masses of a two-quark particle called a D-meson and a three-quark particle called a Sigma-C baryon. The heavier two pentaquarks could be made of the same two particles, but with their internal quarks misaligned—a configuration that slightly bumps up their energy and therefore bumps up the overall mass of the pentaquark.

    Another feature that jumped out at Karliner is the lifetime of these particles. In this nuclear interpretation of the pentaquark, the two clusters of quarks are distinct and feel only a weak pull towards each other, forming a new type of meta-stable atomic nucleus.

    “They are long-lived compared to what we normally observe in composite unstable states made out of quarks,” Karliner says. “In the nuclear picture, the long lifetime is natural and very easy to understand.”

    Illustration showing a tightly bound pentaquark

    Some scientists think a tightly bound pentaquark could have pockets of non-neutral color charge.


    The clustered quark camp

    To put it simply, Ali finds the nuclear model of the pentaquark a bit disappointing. Even though a molecular pentaquark is still a new discovery, “no new no new color structures are involved,” he says. “They are formed by the recombination of known hadrons.”

    What he really wants to find is evidence of a tightly bound pentaquark, in which the five quarks are held close together by the strong force. Ali suspects that within a true tightly bound pentaquark, the quark colors could mix in a way that would allow for some non-neutral color charge.

    He remains optimistic that more complex quark combinations are possible, he says. “The theory which describes quark behavior is rich, and there are many forms and representations which could still show themselves.”

    The LHC is currently shut down for upgrades that will allow the experiments to collect even more data, letting scientists take a closer look at the pentaquark. “I anticipate that this is not the end of the story,” Ali says. “It’s the beginning. We’re entering a new hadronic world, and I suspect that more objects will be found.”

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  • Assegnato a Lorenzo Pagnanini il premio Bruno Rossi

    2019-04-10T14:28:15Z via NavierStokesApp To: Public

    "Assegnato a Lorenzo Pagnanini il premio Bruno Rossi"

    Assegnato a Lorenzo Pagnanini il premio Bruno Rossi per una delle due migliori tesi di dottorato in fisica delle astroparticelle incentrata sull’esperimento CUPID-0 situato presso i Laboratori Nazionali del Gran Sasso dell’INFN.

    Read More ...

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  • Astronomers capture first image of a black hole

    2019-04-10T13:28:36Z via NavierStokesApp To: Public

    "Astronomers capture first image of a black hole"

    The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster.

    Glowing ring that is the first image of light at the event horizon of a black hole

    The Event Horizon Telescope—a planet-scale array of eight ground-based radio telescopes forged through international collaboration—was designed to capture images of a black hole.

    Today, in coordinated press conferences across the globe, EHT researchers reveal that they have succeeded, unveiling the first direct visual evidence of a supermassive black hole and its shadow.

    This breakthrough was announced in a series of six papers published in a special issue of The Astrophysical Journal Letters. The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5 billion times that of the Sun.

    “This is a huge day in astrophysics,” says NSF Director France Córdova. “We’re seeing the unseeable. Black holes have sparked imaginations for decades. They have exotic properties and are mysterious to us. Yet with more observations like this one they are yielding their secrets. This is why NSF exists. We enable scientists and engineers to illuminate the unknown, to reveal the subtle and complex majesty of our universe.”

    The EHT links telescopes around the globe to form an Earth-sized virtual telescope with unprecedented sensitivity and resolution. The EHT is the result of years of international collaboration and offers scientists a new way to study the most extreme objects in the universe predicted by Einstein’s general relativity during the centennial year of the historic experiment that first confirmed the theory.

    “We have taken the first picture of a black hole,” says EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian. “This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.”

    The National Science Foundation played a pivotal role in this discovery by funding individual investigators, interdisciplinary scientific teams and radio astronomy research facilities since the inception of EHT. Over the last two decades, NSF has directly funded more than $28 million in EHT research, the largest commitment of resources for the project.

    Black holes are extraordinary cosmic objects with enormous masses but extremely compact sizes. The presence of these objects affects their environment in extreme ways, warping spacetime and super-heating any surrounding material.

    “If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow—something predicted by Einstein’s general relativity that we’ve never seen before,” says chair of the EHT Science Council Heino Falcke of Radboud University, the Netherlands. “This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and allowed us to measure the enormous mass of M87’s black hole.”

    Multiple calibration and imaging methods have revealed a ring-like structure with a dark central region—the black hole’s shadow—that persisted over multiple independent EHT observations.

    “Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well,” says Paul T.P. Ho, EHT Board member and Director of the East Asian Observatory. “This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass.”

    Creating the EHT was a formidable challenge that required upgrading and connecting a worldwide network of eight pre-existing telescopes deployed at a variety of challenging high-altitude sites. These locations included volcanoes in Hawaii and Mexico, mountains in Arizona and the Spanish Sierra Nevada, the Chilean Atacama Desert, and Antarctica.

    The EHT observations use a technique called very-long-baseline interferometry (VLBI). which synchronizes telescope facilities around the world and exploits the rotation of our planet to form one huge, Earth-size telescope observing at a wavelength of 1.3 mm. VLBI allows the EHT to achieve an angular resolution of 20 micro-arcseconds—enough to read a newspaper in New York from a sidewalk café in Paris.

    The telescopes contributing to this result were ALMA, APEX, the IRAM 30-meter telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope. Petabytes of raw data from the telescopes were combined by highly specialized supercomputers hosted by the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory.

    The construction of the EHT and the observations announced today represent the culmination of decades of observational, technical, and theoretical work. This example of global teamwork required close collaboration by researchers from around the world. Thirteen partner institutions worked together to create the EHT, using both pre-existing infrastructure and support from a variety of agencies. Key funding was provided by the US National Science Foundation, the EU’s European Research Council, and funding agencies in East Asia.

    “We have achieved something presumed to be impossible just a generation ago,” says Doeleman. “Breakthroughs in technology, connections between the world’s best radio observatories, and innovative algorithms all came together to open an entirely new window on black holes and the event horizon.”

    Editor's note: This text is adapted from a press release by the National Science Foundation.

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  • LS2 Report: SPS receives major facelift for new beam dump

    2019-04-09T15:28:42Z via NavierStokesApp To: Public

    "LS2 Report: SPS receives major facelift for new beam dump"

    LS2 Report: SPS receives major facelift for new beam dump

    achintya Tue, 04/09/2019 - 11:46
    The new SPS beam dump and the cavern in which it will be placed
    The SPS will receive a new beam dump after LS2, placed in the old cavern of the UA1 experiment. (Image: CERN)

    The Super Proton Synchrotron (SPS) is undergoing an overdue overhaul. Its beam dump, which was previously at point 1 of the SPS, will be replaced by a new one located across the ring at SPS point 5. The new beam dump being constructed requires extensive civil-engineering work to house and operate it, which is one of the primary tasks for the SPS team during the second long shutdown (LS2) of CERN’s accelerator complex.

    When a beam of protons or heavy ions accelerating through the SPS needs to be brought to a stop, it is redirected into a beam dump that absorbs the particle beam, terminating its flight. “We need a bigger dump for the SPS due to the higher energies of circulating particles following the LHC Injector Upgrade (LIU) project,” explains Jonathan Meignan, who is coordinating the project to replace the SPS beam dump. After scouting for a suitable location, it was decided to install the new beam dump at an opposite point in the SPS ring, where there is sufficient space for the dump and the additional infrastructure it needs.,Accelerators
    Jonathan Meignan in front of part of the shielding for the new SPS beam dump (Image: Achintya Rao/CERN)

    The task is however a difficult one, involving several related works. The underground cavern that will house the new beam dump, known as ECX5, was the location of the erstwhile UA1 detector, which discovered the W and Z bosons in 1983 when the SPS was operated as a proton–antiproton collider. It will need to be drastically modified to incorporate the services needed for the modifications to the SPS. For example, the transport zone next to the SPS tubes, which is used by both personnel and equipment, will have to be rerouted so it skirts the voluminous beam dump and its large shielding. The SPS tunnel will therefore undergo digging to widen a section of it by about one metre to accommodate the new shape of the transport zone.

    Kicker magnets, which are responsible for deflecting the travelling particles into the dump-bound trajectories, have to be installed in Long Straight Section 5 of the SPS leading up to the beam dump. “To prepare for this installation, the beamlines within LSS5 had to be completely removed,” remarks Meignan. Simultaneously with this removal, an intense decabling campaign was conducted to free space for the new cables. More than 135 km of obsolete cables were removed, notes Meignan. New cables, including high-voltage cables for the kickers, have been installed, snaking all the way from LSS5 to the service cavern adjacent to ECX5, where their instrumentation and control systems will be located.

    The crane suspended from the roof of ECX5, which can be used to move the large blocks making up the beam dump, has been upgraded as well. “The crane was fitted with cameras during the last year-end technical stop,” says Meignan, “and equipped for remote control from the service cavern, to minimise the radiation exposure of the operators.”

    As of early April, ECX5 has been isolated from the rest of the SPS to conduct these civil-engineering activities, which are expected to be finished in December. At the same time, the dump and its shielding, which is made of steel, concrete and marble surrounding the inner core, is being assembled on the surface above its future home. In the new year, the beamline will be reconnected and the dump will be installed before being commissioned.

    We will return to the SPS and its many LS2 activities in a future report.

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  • All hands on deck

    2019-04-09T14:28:32Z via NavierStokesApp To: Public

    "All hands on deck"

    Some theorists have taken to designing their own experiments to broaden the search for dark matter.

    An illustration depicting experimental theorists

    From a young age, Philip Schuster knew he wanted to go into particle physics. As an undergraduate, he became involved in a number of research projects with experimentalists. But, like many other students pursuing a career in physics, he reached a point when he had to narrow his path.

    “When you’re going into graduate school, you have to make a very stark choice between going in the direction of theory or experiment,” says Schuster, now a theorist at SLAC National Accelerator Laboratory. “One of the reasons for that is that either one takes a tremendous investment and commitment of time. It’s just not practical to do both simultaneously.”

    As much as he enjoyed the hands-on feeling of experiments, Schuster felt a stronger pull down the theory route. But he continued to keep an eye on what was happening in the world of experiment.

    Falling through the cracks

    Toward the end of his graduate education around 2007, Schuster wound up embedded with an experimental group working with data from the Large Hadron Collider. Although his work was still theoretical, this experience rekindled an interest in experimental physics that carried through into his postdoctoral fellowship.

    Together with Natalia Toro, also a theorist SLAC, and Rouven Essig, a theorist at Stony Brook University, Schuster began developing a series of ideas for an experiment that could leverage existing equipment to look for new forces that might be related to dark matter. The three teamed up with Bogdan Wojtsekhowski, an experimentalist at Thomas Jefferson National Accelerator Facility, to co-lead the experiment, called A Prime Experiment, or APEX.

    At the time, spearheading experiments was considered a dangerous move for theorists. Many feared that physicists could end up falling into the cracks between theory and experiment, landing in a place where their work would be unappreciated by both sides. But the seemingly impossible hunt for dark matter called for new approaches.

    “We knew we were taking a risk,” Schuster says. “And because so few people were doing it at the time, the risk felt even more vivid.

    “I remember being a little worried about it from time to time. But whenever I stood back, I could see that we had this physics problem that was going to require both theory and new experiments to answer.”

    A deepening divide

    There wasn’t always so much distinction between experiment and theory in physics. From Galileo Galilei to Isaac Newton, many of the great physicists had to use both theory and experiment. But as the field expanded, so did the scale of the experiments and the complexity of the theory. The larger and more challenging the experiments grew, and the more elaborate the theories became, the higher the level of specialization and expertise scientists required to work on them.  

    “At first it wasn't so much a split as it was just a sharpening of roles,” Schuster says. “People who tended to be a little bit more inclined to mathematical modeling versus actually tinkering. But with the discovery and development of quantum mechanics, you really had to specialize in something to make any sort of progress. The divide deepened out of a necessity, and it just became much more entrenched with time.” 

    New perspectives

    But in the past decade, a new trend has emerged. In the scramble to detect dark matter particles, more and more theorists have been dreaming up experiments that can tackle the problem from new perspectives.

    “Over the last few years, we’ve been going back to the drawing board,” says Mariangela Lisanti, a theorist at Princeton University. “There has been a renaissance in dark matter science that calls for a much closer collaboration between the two communities, so people have been moving closer to that boundary as a result.”

    A large part of this, Essig says, is that physicists have been expanding the type of dark matter candidates they’re interested in, requiring new ideas on how to find them. 

    “Most of us go into science because we want to understand the world,” says David Spergel, a theoretical astrophysicist at Princeton University. “We want to be able to compare theoretical ideas with experiments, and there's no better way to do that than to be directly involved in the experiment. I think it's very valuable for us to ask the question, ‘What types of new experiments should be done to advance our knowledge of fundamental physics?’”

    Back to the basics

    To broaden the search for dark matter, physicists have gone back to the basics, in a way—designing smaller-scale experiments that can often fit on tabletops. These smaller and less expensive experimental setups and collaborations provide a perfect avenue for theorists to explore new ideas.

    “These little experiments are kind of moving into the mainstream, and that's been a really good thing,” says Jonathan Feng, a theorist at University California, Irvine. “There are some really interesting ideas out there, and any one of them can actually discover dark matter or some new particle and just change our whole view of what's going on.”

    Many of these small experiments are fueled by collaboration between theorists and experimentalists. Recently, Feng worked with experimentalists to design FASER, a small dark matter experiment sitting in the LHC tunnel that looks for exotic weakly interacting particles produced in collisions. David Casper, an experimentalist involved in the project, says that Feng and the other theorists have been instrumental in the process.

    “This experiment was really their idea,” Casper says. “This wasn’t theorists becoming involved in experiment. It was experimentalists joining theorists to make their idea a reality.”

    Flooding the field

    This synergy between theorists and experimentalists in the hunt has been a driving force for why many physicists do what they do. Lisanti says she’s always been interested in flying close to the interface between the two disciplines.

    “Collaborating closely with experimentalists and thinking of new ways to shed light on patterns in the data is what I love spending my days doing,” she says. “I can't imagine any other thing that would be more fun.” 

    Now, the trend of theorists proposing experiments has become so common that it’s almost expected of new students entering the field. The hope is that flooding the field with new ideas could finally lead to the discovery of dark matter.

    “I was at a conference a few months ago and I heard a few people joking that you’re not a real theorist until you’ve done an experiment,” Feng says. “For a while people had this idea that theorists were only meant to devise high-minded, beautiful thoughts and theories of everything. But sometimes we need to get our hands dirty and make sure we’re covering as many bases as we can.”

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  • Week 12 at the Pole

    2019-04-08T20:28:54Z via NavierStokesApp To: Public

    "Week 12 at the Pole"

    Although the sun has set and winter has begun, it takes a while before it actually gets dark at the South Pole. Twilight is a prolonged process there, lasting weeks. Here there’s still plenty of daylight to see the station as it starts to look nice and frosty without direct sunlight.

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