Stephen Sekula

Dallas, TX, USA

Husband; Associate Professor of Physics; I teach at SMU in Dallas, TX; I study the Higgs Particle with the ATLAS Experiment at the Large Hadron Collider at CERN; writer and blogger; drummer; programmer; teacher; scientist; traveler; runner; gardener; open-source aficionado.

  • LHC experiments present new Higgs results at 2019 EPS-HEP conference

    ParticleNews at 2019-07-15T16:28:23Z

    "LHC experiments present new Higgs results at 2019 EPS-HEP conference"

    LHC experiments present new Higgs results at 2019 EPS-HEP conference achintya Mon, 07/15/2019 - 15:18

    Combined image showing Higgs candidates from ATLAS (left) and CMS (right)
    (Image: CERN)

    Geneva and Ghent. At the 2019 European Physical Society’s High-Energy Physics conference (EPS-HEP) taking place in Ghent, Belgium, the ATLAS and CMS collaborations presented a suite of new results. These include several analyses using the full dataset from the second run of CERN’s Large Hadron Collider (LHC), recorded at a collision energy of 13 TeV between 2015 and 2018. Among the highlights are the latest precision measurements involving the Higgs boson. In only seven years since its discovery, scientists have carefully studied several of the properties of this unique particle, which is increasingly becoming a powerful tool in the search for new physics.

    The results include new searches for transformations (or “decays”) of the Higgs boson into pairs of muons and into pairs of charm quarks. Both ATLAS and CMS also measured previously unexplored properties of decays of the Higgs boson that involve electroweak bosons (the W, the Z and the photon) and compared these with the predictions of the Standard Model (SM) of particle physics. ATLAS and CMS will continue these studies over the course of the LHC’s Run 3 (2021 to 2023) and in the era of the High-Luminosity LHC (from 2026 onwards).

    The Higgs boson is the quantum manifestation of the all-pervading Higgs field, which gives mass to elementary particles it interacts with, via the Brout-Englert-Higgs mechanism. Scientists look for such interactions between the Higgs boson and elementary particles, either by studying specific decays of the Higgs boson or by searching for instances where the Higgs boson is produced along with other particles. The Higgs boson decays almost instantly after being produced in the LHC and it is by looking through its decay products that scientists can probe its behaviour.

    In the LHC’s Run 1 (2010 to 2012), decays of the Higgs boson involving pairs of electroweak bosons were observed. Now, the complete Run 2 dataset – around 140 inverse femtobarns each, the equivalent of over 10 000 trillion collisions – provides a much larger sample of Higgs bosons to study, allowing measurements of the particle’s properties to be made with unprecedented precision. ATLAS and CMS have measured the so-called “differential cross-sections” of the bosonic decay processes, which look at not just the production rate of Higgs bosons but also the distribution and orientation of the decay products relative to the colliding proton beams. These measurements provide insight into the underlying mechanism that produces the Higgs bosons. Both collaborations determined that the observed rates and distributions are compatible with those predicted by the Standard Model, at the current rate of statistical uncertainty.

    Higgs Candidates,Proton Collisions,Event Displays,Physics,ATLAS
    An event recorded by ATLAS showing a candidate for a Higgs boson produced in association with two top quarks. The Higgs boson decays to four muons (red tracks). There is an additional electron (green track) and four particle jets (yellow cones) (Image: ATLAS/CERN)

    Since the strength of the Higgs boson’s interaction is proportional to the mass of elementary particles, it interacts most strongly with the heaviest generation of fermions, the third. Previously, ATLAS and CMS had each observed these interactions. However, interactions with the lighter second-generation fermions – muons, charm quarks and strange quarks – are considerably rarer. At EPS-HEP, both collaborations reported on their searches for the elusive second-generation interactions.

    ATLAS presented their first result from searches for Higgs bosons decaying to pairs of muons (H→μμ) with the full Run 2 dataset. This search is complicated by the large background of more typical SM processes that produce pairs of muons. “This result shows that we are now close to the sensitivity required to test the Standard Model’s predictions for this very rare decay of the Higgs boson,” says Karl Jakobs, the ATLAS spokesperson. “However, a definitive statement on the second generation will require the larger datasets that will be provided by the LHC in Run 3 and by the High-Luminosity LHC.”

    CMS presented their first result on searches for decays of Higgs bosons to pairs of charm quarks (H→cc). When a Higgs boson decays into quarks, these elementary particles immediately produce jets of particles. “Identifying jets formed by charm quarks and isolating them from other types of jets is a huge challenge,” says Roberto Carlin, spokesperson for CMS. “We’re very happy to have shown that we can tackle this difficult decay channel. We have developed novel machine-learning techniques to help with this task.”

    Real Events,For Press
    An event recorded by CMS showing a candidate for a Higgs boson produced in association with two top quarks. The Higgs boson and top quarks decay leading to a final state with seven jets (orange cones), an electron (green line), a muon (red line) and missing transverse energy (pink line) (Image: CMS/CERN)

    The Higgs boson also acts as a mediator of physics processes in which electroweak bosons scatter or bounce off each other. Studies of these processes with very high statistics serve as powerful tests of the Standard Model. ATLAS presented the first-ever measurement of the scattering of two Z bosons. Observing this scattering completes the picture for the W and Z bosons as ATLAS has previously observed the WZ scattering process and both collaborations the WW processes. CMS presented the first observation of electroweak-boson scattering that results in the production of a Z boson and a photon.

    “The experiments are making big strides in the monumental task of understanding the Higgs boson,” says Eckhard Elsen, CERN’s Director of Research and Computing. “After observation of its coupling to the third-generation fermions, the experiments have now shown that they have the tools at hand to address the even more challenging second generation. The LHC’s precision physics programme is in full swing.”

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  • at 2019-07-15T23:00:06Z

    Congratulations to Dr. Dan Jardin for the successful defense of his PhD thesis! #SuperCDMS

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  • Alexandre Oliva at 2019-07-03T17:51:30Z

    hacker!  tinkerer!
    awesome! :-)

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  • Astronomy Picture of the Day for 2019-07-02 12:30:02.403922

    Astronomy Picture of the Day (Unofficial) at 2019-07-02T17:30:03Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 July 2
    See Explanation.  Clicking on the picture will download
 the highest resolution version available.

    NGC 1566: The Spanish Dancer Spiral Galaxy
    Image Credit: NASA, ESA, Hubble; Processing & Copyright: Leo Shatz

    Explanation: If not perfect, then this spiral galaxy is at least one of the most photogenic. An island universe containing billions of stars and situated about 40 million light-years away toward the constellation of the Dolphinfish (Dorado), NGC 1566 presents a gorgeous face-on view. Classified as a grand design spiral, NGC 1566's shows two prominent and graceful spiral arms that are traced by bright blue star clusters and dark cosmic dust lanes. Numerous Hubble Space Telescope images of NGC 1566 have been taken to study star formation, supernovas, and the spiral's unusually active center. Some of these images, stored online in the Hubble Legacy Archive, were freely downloaded, combined, and digitally processed by an industrious amateur to create the featured image. NGC 1566's flaring center makes the spiral one of the closest and brightest Seyfert galaxies, likely housing a central supermassive black hole wreaking havoc on surrounding stars and gas.

    Today: Total solar eclipse visible in parts of South America
    Tomorrow's picture: titanian moon copter

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    Sort of like: 💃

    JanKusanagi at 2019-07-02T22:35:35Z

  • JanKusanagi at 2019-06-22T14:27:00Z

    You're off to a good start 😁

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  • The proton, a century on

    ParticleNews at 2019-06-13T13:28:14Z

    "The proton, a century on"

    The proton, a century on abelchio Thu, 06/13/2019 - 10:11

    It is 100 years since Ernest Rutherford published his results proving the existence of the proton. For decades, the proton was considered an elementary particle. But ever since researchers at the SLAC and DESY laboratories began firing electrons into protons, beginning in the 1960s, experiments have revealed that the proton has a complex internal structure, one that depends on how you look at it, or rather on how hard you hit it. A century on, however, much remains to be learnt about the proton. Check out the latest edition of the CERN Courier and read in-depth articles about what we know and don’t know about the proton.

    In “Rutherford, transmutation and the proton”, you’ll find an account of the historical events leading to Ernest Rutherford’s discovery of the proton, published in 1919. In “The proton laid bare”, you can read about scientists’ evolving knowledge of the proton, how a deeper understanding may be key to the search for new physics phenomena, and what remains to be learnt – including the origin of the proton’s spin, whether or not the proton decays on long timescales, and the puzzling, although soon-to-be resolved, value of its radius.

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  • Lock the Planck: the kilogram has a new definition

    ParticleNews at 2019-05-20T12:27:55Z

    "Lock the Planck: the kilogram has a new definition"

    Lock the Planck: the kilogram has a new definition

    achintya Mon, 05/20/2019 - 14:01
    METAS Kibble balance (BWM II)
    The Kibble balance (a.k.a. watt balance) built by the Swiss Federal Institute of Metrology (METAS) to measure the Planck constant with ultra-high precision (Image: CERN)

    Until today, a kilogram was defined as the mass of the International Prototype Kilogram (IPK), a platinum–iridium cylinder located in Paris, France. While all the other base units of the International System of Units (SI) had been redefined over the years based on fundamental constants of nature or atomic properties, the kilogram had remained since the late 19th century the only one to rely on a human-made artefact.

    This changes today, and metrologists – those who study measurement – are excited. On the occasion of World Metrology Day, which commemorates the signing of the Metre Convention back in 1875, the kilogram has been given a new definition. From now on, it will be defined based on the most precise measurement ever made of the Planck constant, which can be expressed in terms of the SI units kilogram, metre and second. Since the latter two units are already defined by constants of nature, the value of a kilogram can be obtained without relying on comparing it with a physical reference block.

    But measuring the Planck constant to a suitably high precision of ten parts per billion required decades of work by international teams across continents, and CERN played a small part in the endeavour.

    In 1975, British physicist Bryan Kibble proposed a device, then known as a watt balance and now called the Kibble balance in his honour, which would allow the Planck constant to be measured precisely based on the IPK. Once the precision was achieved, the Planck constant’s value could be fixed and the definitions inverted, removing the kilogram’s dependence on the IPK. Several Kibble balances around the world were constructed to compare measurements, including one in Switzerland. METAS, the Swiss Federal Institute of Metrology, has been working on their Kibble balance project for almost two decades, the activity being led by Ali Eichenberger and Henri Baumann. Knowing CERN’s expertise in magnet systems, Eichenberger and Baumann reached out to the Laboratory to help prepare the required magnets.

    “I am extremely proud to have participated in this adventure,” says Davide Tommasini from CERN’s Magnets, Superconductors and Cryostats group, who was directly involved in the project. “I do not know if the redefinition of the kilogram has a direct impact on the experiments at CERN, but the past teaches us that there are many new advancements which, at their initial moment, may not appear in their whole potential.”

    In 2018, the Kibble balance in Canada measured the Planck constant with necessary ultrahigh precision, allowing a combination of measurements from around the world to help fix its value. But does it affect the value of the kilogram itself? Not really. “The Plank constant has been fixed at 6.626070150 × 10−34 kg⋅m2/s using the IPK as standard,” explains Eichenberger. “So from today, one kilogram will stay the same. If the IPK drifts further with time then its value will change, but any mass calibration will have an uncertainty of the order of 20 parts per billion.”

    So while it is a momentous occasion worthy of celebration, you won’t have to recalibrate your bathroom scales just yet.

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    Ah, so I still weight the same? 😌

    JanKusanagi at 2019-05-20T14:08:33Z

  • LS2 report: The Proton Synchrotron’s magnets prepare for higher energies

    ParticleNews at 2019-02-13T11:27:36Z

    "LS2 report: The Proton Synchrotron’s magnets prepare for higher energies"

    LS2 report: The Proton Synchrotron’s magnets prepare for higher energies

    achintya Wed, 02/13/2019 - 09:35
    PS Magnets consolidation during LS2
    PS Magnets consolidation during LS2 (Image: CERN)

    The Proton Synchrotron (PS), which was CERN’s first synchrotron and which turns 60 this year, once held the record for the particle accelerator with the highest energy. Today, it forms a key link in CERN’s accelerator complex, mainly accelerating protons to 26 GeV before sending them to the Super Proton Synchrotron (SPS), but also delivering particles to several experimental areas such as the Antiproton Decelerator (AD). Over the course of Long Shutdown 2 (LS2), the PS will undergo a major overhaul to prepare it for the higher injection and beam intensities of the LHC’s Run 3 as well as for the High-Luminosity LHC.

    One major component of the PS that will be consolidated is the magnet system. The synchrotron has a total of 100 main magnets within it (plus one reference magnet unit outside the ring), which bend and focus the particle beams as they whizz around it gaining energy. “During the last long shutdown (LS1) and at the beginning of LS2, the TE-MSC team performed various tests to identify weak points in the magnets,” explains Fernando Pedrosa, who is coordinating the LS2 work on the PS. The team identified 50 magnets needing refurbishment, of which seven were repaired during LS1 itself. “The remaining 43 magnets that need attention will be refurbished this year.”

    Specifically, one of the elements, known as the pole-face windings, which is located between the beam pipe and the magnet yoke, needs replacing. In order to reach into the magnet innards to replace these elements, the magnet units have to be transferred to a workshop in building 151. Once disconnected, each magnet is placed onto a small locomotive system that drives them to the workshops. The locomotives themselves are over 50 years old, and their movement must be delicately managed. It takes ten hours to extract one magnet. So far, six magnets have been taken to the workshop and this work will last until 18 October 2019.

    The workshop where the magnets are being treated is divided into two sections. In the first room, the vacuum chamber of the magnets is cut so as to access the pole-face windings. The magnet units are then taken to the second room, where prefabricated replacements are installed.

    As mentioned in the previous LS2 Report, the PS Booster will see an increase in the energy it imparts to accelerating protons, from 1.4 GeV to 2 GeV. A new set of quadrupole magnets will be installed along the Booster-to-PS injection line, to increase the focusing strength required for the higher-energy beams. Higher-energy beams require higher-energy injection elements; therefore some elements will be replaced in the PS injection region as part of the LHC Injectors Upgrade (LIU) project, namely septum 42, kicker 45 and five bumper magnets.

    Other improvements as part of the LIU project include the new cooling systems being installed to increase the cooling capacity of the PS. A new cooling station is being built at building 355, while one cooling tower in building 255 is being upgraded. The TT2 line, which is involved in the transfer from the PS to the SPS, will have its cooling system decoupled from the Booster’s, to allow the PS to operate independent of the Booster schedule. “The internal dumps of the PS, which are used in case the beam needs to be stopped, are also being changed, as are some other intercepting devices,” explains Pedrosa.

    The LS2 operations are on a tight schedule,” notes Pedrosa, pointing out that works being performed on several interconnected systems create constraints for what can be done concurrently. As LS2 proceeds, we will bring you more news about the PS, including the installation of new instrumentation in wire scanners that help with beam-size measurement, an upgraded transverse-feedback system to stabilise the beam and more.

    More pictures of the PS magnets are available on CDS:

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  • Build The Peach!

    Jason Self at 2019-02-01T14:37:58Z

    Build the peach! Build the peach!

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  • Astronomy Picture of the Day for 2019-01-26 12:30:01.764936

    Astronomy Picture of the Day (Unofficial) at 2019-01-26T18:30:03Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 January 26
    See Explanation.  Clicking on the picture will download
the highest resolution version available.

    The Umbra of Earth
    Image Credit & Copyright: Antonio Finazzi

    Explanation: The dark, inner shadow of planet Earth is called the umbra. Shaped like a cone extending into space, it has a circular cross section most easily seen during a lunar eclipse. For example, on January 21 the Full Moon slid across the northern half of Earth's umbral shadow, entertaining moonwatchers around much of the planet. In the total phase of the eclipse, the Moon was completely within the umbra for 63 minutes. Recorded under clear, dark skies from the hills near Chiuduno, Italy this composite eclipse image uses successive pictures from totality (center) and partial phases to trace out a large part of the umbra's curved edge. Reflecting sunlight scattered by the atmosphere into Earth's shadow, the lunar surface appears reddened during totality. But close to the umbra's edge, the limb of the eclipsed Moon shows a distinct blue hue. The blue eclipsed moonlight originates as rays of sunlight pass through layers high in the upper stratosphere, colored by ozone that scatters red light and transmits blue.

    Tomorrow's picture: crossing the sky

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  • Astronomy Picture of the Day for 2019-01-23 12:30:02.300728

    Astronomy Picture of the Day (Unofficial) at 2019-01-23T18:30:03Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 January 23
    See Explanation.  Clicking on the picture will download
the highest resolution version available.

    Orion over the Austrian Alps
    Image Credit & Copyright: Luk Vesel

    Explanation: Do you recognize this constellation? Through the icicles and past the mountains is Orion, one of the most identifiable star groupings on the sky and an icon familiar to humanity for over 30,000 years. Orion has looked pretty much the same during the past 50,000 years and should continue to look the same for many thousands of years into the future. Orion is quite prominent in the sky this time of year, a recurring sign of (modern) winter in Earth's northern hemisphere and summer in the south. Pictured, Orion was captured recently above the Austrian Alps in a composite of seven images taken by the same camera in the same location during the same night. Below and slightly to the right of Orion's three-star belt is the Orion Nebula, while the four bright stars surrounding the belt are, clockwise from the upper left, Betelgeuse, Bellatrix, Rigel, and Saiph.

    New: Instagram page features cool images recently submitted to APOD
    Tomorrow's picture: the cold eclipse

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  • Doug Whitfield at 2019-01-22T20:55:35Z

    Who should I be following? No one has posted anything in 3 hours. Last comment appears to have been 2 hours ago...

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    I got nothing. :-)

    My feed has been fairly quiet of late as well. That said, and have been chatty of late.

    Stephen Sekula at 2019-01-23T00:32:14Z

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  • The @Debian 10 'buster' release freeze has begun --

    Debian Project at 2019-01-21T00:15:07Z

    The @Debian 10 'buster' release freeze has begun --

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  • JanKusanagi at 2019-01-17T19:03:10Z

    I feel relaxed already! 😌

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  • Astronomy Picture of the Day for 2019-01-14 12:30:02.260530

    Astronomy Picture of the Day (Unofficial) at 2019-01-14T18:30:03Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 January 14
    See Explanation.  Clicking on the picture will download
the highest resolution version available.

    Meteor and Milky Way over the Alps
    Image Credit & Copyright: Nicholas Roemmelt (Venture Photography)

    Explanation: Now this was a view with a thrill. From Mount Tschirgant in the Alps, you can see not only nearby towns and distant Tyrolean peaks, but also, weather permitting, stars, nebulas, and the band of the Milky Way Galaxy. What made the arduous climb worthwhile this night, though, was another peak -- the peak of the 2018 Perseids Meteor Shower. As hoped, dispersing clouds allowed a picturesque sky-gazing session that included many faint meteors, all while a carefully positioned camera took a series of exposures. Suddenly, a thrilling meteor -- bright and colorful -- slashed down right next the nearly vertical band of the Milky Way. As luck would have it, the camera caught it too. Therefore, a new image in the series was quickly taken with one of the sky-gazers posing on the nearby peak. Later, all of the images were digitally combined.

    Tomorrow's picture: heart & soul

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  • Jason Self at 2019-01-14T02:05:49Z

    I removed 15 of the 16 RAM modules and the computer boots into the Trisquel installer just fine. It would appear the problems can be explained away with bad memory. Time to break out Memtest86+...

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    at 2019-01-15T00:05:23Z

    What? You don't know what a TARDIS is?

    Don't you have a plain old dictionary? 😆

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  • This weekend we have a Debian Bugsquashing Party in Venlo #Debian #BSP #Party

    Debian Project at 2019-01-11T22:15:05Z

    This weekend we have a Debian Bugsquashing Party in Venlo #Debian #BSP #Party

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  • JanKusanagi at 2019-01-11T19:18:58Z

    Some giant took a bite out of the Sun!!!!! 😱

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  • JanKusanagi at 2019-01-08T04:48:14Z

    Gifted. But the thing about the Navier-Stokes problem was just a background thing. It was just funny to see it mentioned 😆

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