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  • richardmitnick 5:31 pm on September 15, 2016 Permalink | Reply
    Tags: , CERN CMS, , Pixel detector, U.S. CMS FPIX team   

    From FNAL: “The world’s latest (and greatest) pixel detector” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    September 14, 2016
    Steve Nahn

    This article, and the work it represents, is dedicated to our dear friend and colleague Gino Bolla.

    There’s a new pixel detector in the world, and it’s one of our own.

    1
    This close-up shows three disks in one half cylinder, a quarter of the full FPIX detector.

    The Forward Pixel detector, part of the CMS Phase 1 upgrade, is taking shape out at SiDet. The new device lies at the heart of the CMS detector, providing micron-scale resolution on charged particle trajectories, which in turn provides precision position measurements of the proton-proton collisions. This detector is composed of 672 modules, each of which has 16 readout chips. Each chip reads out the signal from charge deposited on one of an array of 52×80 pixels.

    That means nearly 45 million pixels to sample at 100 kHz, the nominal trigger rate of CMS. The modules are mounted onto inner and outer custom carbon fiber “half-disks,” and three inner-outer pairs are mounted in the custom carbon fiber support structure, called a “half-cylinder.” The half-cylinder also brings the innovative dual-phase carbon dioxide cooling fluid and power to the half-disks and carries the data away via optical fibers.

    In addition to the physical detector, there are also the external components, such as the power supply and interlock system and the Data Acquisition system. To say it is a complex apparatus is a rather gross understatement. Though it is based on the original detector, this version supplies an extra layer of tracking with less mass and is more capable of handling the increased instantaneous luminosity expected in LHC Run 2 and Run 3, which will bring us up to 2023.

    Over the last three years, the U.S. CMS FPIX team, including contributions from 21 institutions, has designed, prototyped, extensively tested, and fabricated the detector components. They are in the last stages of assembly and on time for installation during the upcoming winter technical stop of the LHC. The entire enterprise exploited the unique strengths of this dispersed team. For example, the sensors were procured by the University of Kansas; the data-concentrator ASIC was designed by Rutgers University; the modules were assembled at Purdue University and the University of Nebraska and tested by x-ray exposure at Kansas State University and the University of Illinois-Chicago.

    Kansas State, Vanderbilt University, the University of Mississippi and Cornell University are developing data acquisition and control systems, while Fermilab has focused on mechanical structure, microelectronics and integration. And right now it is all coming together at SiDet.

    Over the past six months, modules have been arriving at SiDet, where a small army of students, postdocs, faculty (and even a project manager, when they let him) have been testing the modules at 17 degrees and at -20 degrees Celsius. In parallel a team of talented technicians and engineers has been assembling the mechanical structure. It hasn’t been without hiccups, notably the initially low yield of modules due to splinters (from cutting up wafers) damaging readout chips and the discovery of a whole new (to us, anyway) potential failure mode. This mode, known as “hot cracking,” is when impurities in the small stainless steel tubing spread out around stress lines during the molten cooling phase of laser welding, forming cracks only a handful of microns wide but several hundred long, which initially withstand pressure testing but may fail after extended thermal cycling.

    However, due to the dedication and talents of the teams involved, these problems have been overcome. We are well on the way to sending this new detector to CERN. If you have time, you should head out to SiDet to see it before it goes and gets buried deep in the heart of CMS, but you’ll have to hurry! The first of four half-cylinders complete with modules has been tested and is at CERN already, with the second one following this week, and the third and fourth within the next few weeks. Look for one of the people in the photo above, who will be happy to show you the fruits of their labor.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 4:00 pm on June 29, 2016 Permalink | Reply
    Tags: , CERN CMS, , , , , , Tetraquarks? For real?   

    From Symmetry: “LHCb discovers family of tetraquarks” 

    Symmetry Mag

    Symmetry

    06/29/16
    Sarah Charley

    1
    LHCb. Courtesy of CERN

    Researchers found four new particles made of the same four building blocks.

    It’s quadruplets! Syracuse University researchers on the LHCb experiment confirmed the existence of a new four-quark particle and serendipitously discovered three of its siblings.

    Quarks are the solid scaffolding inside composite particles like protons and neutrons. Normally quarks come in pairs of two or three, but in 2014 LHCb researchers confirmed the existence four-quark particles and, one year later, five-quark particles.

    The particles in this new family were named based on their respective masses, denoted in mega-electronvolts: X(4140), X(4274), X(4500) and X(4700). Each particle contains two charm quarks and two strange quarks arranged in a unique way, making them the first four-quark particles composed entirely of heavy quarks. Researchers also measured each particle’s quantum numbers, which describe their subatomic properties. Theorists will use these new measurements to enhance their understanding of the formation of particles and the fundamental structures of matter.

    “What we have discovered is a unique system,” says Tomasz Skwarnicki, a physics professor at Syracuse University. “We have four exotic particles of the same type; it’s the first time we have seen this and this discovery is already helping us distinguish between the theoretical models.”

    Evidence of the lightest particle in this family of four and a hint of another were first seen by the CDF experiment at the US Department of Energy’s Fermi National Accelerator Lab in 2009.

    FNAL/Tevatron CDF detector
    FNAL/Tevatron machine
    FNAL/Tevatron map
    CDF; Tevatron; Tevtron map

    However, other experiments were unable to confirm this observation until 2012, when the CMS experiment at CERN reported seeing the same particle-like bumps with a much greater statistical certainty.

    CERN/CMS Detector
    CERN/CMS Detector

    Later, the D0 collaboration at Fermilab also reported another observation of this particle.

    FNAL/Tevatron DZero detector
    D0/FNAL

    “It was a long road to get here,” says University of Iowa physicist Kai Yi, who works on both the CDF and CMS experiments. “This has been a collective effort by many complementary experiments. I’m very happy that LHCb has now reconfirmed this particle’s existence and measured its quantum numbers.”

    The US contribution to the LHCb experiment is funded by the National Science Foundation.

    LHCb researcher Thomas Britton performed this analysis as his PhD thesis at Syracuse University.

    “When I first saw the structures jumping out of the data, little did I know this analysis would be such an aporetic saga,” Britton says. “We looked at every known particle and process to make sure these four structures couldn’t be explained by any pre-existing physics. It was like baking a six-dimensional cake with 98 ingredients and no recipe—just a picture of a cake.”

    Even though the four new particles all contain the same quark composition, they each have a unique internal structure, mass and their own sets of quantum numbers. These characteristics are determined by the internal spatial configurations of the quarks.

    “The quarks inside these particles behave like electrons inside atoms,” Skwarnicki says. “They can be ‘excited’ and jump into higher energy orbitals. The energy configuration of the quarks gives each particle its unique mass and identity.”

    According to theoretical predictions, the quarks inside could be tightly bound (like three quarks packed inside a single proton) or loosely bound (like two atoms forming a molecule.) By closely examining each particle’s quantum numbers, scientists were able to narrow down the possible structures.

    “The molecular explanation does not fit with the data,” Skwarnicki says. “But I personally would not conclude that these are definitely tightly bound states of four quarks. It could be possible that these are not even particles. The result could show the complex interplays of known particle pairs flippantly changing their identities.”

    Theorists are currently working on models to explain these new results—be it a family of four new particles or bizarre ripple effects from known particles. Either way, this study will help shape our understanding of the subatomic universe.

    “The huge amount of data generated by the LHC is enabling a resurgence in searches for exotic particles and rare physical phenomena,” Britton says. “There’s so many possible things for us to find and I’m happy to be a part of it.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:37 pm on April 8, 2016 Permalink | Reply
    Tags: , , CERN CMS, , , , ,   

    From FNAL: “Heavy neutrinos: Leave no stone unturned” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    April 8, 2016
    Bo Jayatilaka

    While the discovery of the Higgs boson at the LHC yielded considerable evidence that the Higgs mechanism is responsible for some particles having mass and others not, it does not help explain why massive particles have the specific masses they do. Over a decade prior to the discovery of the Higgs boson, experiments studying neutrinos produced by the sun and by particle accelerators made the astounding discovery that neutrinos have mass, albeit in incredibly tiny amounts. The question du jour about neutrino masses shifted immediately from “Do neutrinos have mass?” to “Why are neutrino masses what they are?”

    Physicists naturally attack this question from as many angles as possible. A significant focus of the scientific efforts of Fermilab center on studying neutrinos produced by the Fermilab accelerator complex in order to probe this question. An experiment like CMS, designed to measure highly interactive particles, can’t directly detect neutrinos at all and might seem to be left on the sidelines in this quest. However, a popular family of theories suggests that there is an additional family of neutrino linked to the garden-variety neutrinos we know of. This linking mechanism between the known neutrinos and their exotic cousins is known as a “seesaw mechanism,” as it forces one type to become massive when the others become lightweight. Searching for unknown but massive particles is exactly what the CMS detector was designed to do.

    CERN/CMS Detector
    CERN/CMS Detector

    The CMS experiment has searched for such heavy neutrinos, focusing on the case where the heavy neutrino is of the Majorana type, meaning that it is its own antiparticle. As Don Lincoln explains about one of the first such searches, the production and decay of a heavy Majorana neutrino results in the signature of two leptons (electrons or muons) of the same electric charge along with jets. A more recent search at CMS used the full 8-TeV data set and focused on events in which the same-charged leptons were muons.

    To ensure that no stone remains unturned in the search for heavy Majorana neutrinos, the analysis of 8-TeV data has been updated* to include events with like-charged electron pairs and like-charged pairings of an electron and a muon.-

    Unfortunately, as with the previous searches, no evidence of a heavy neutrino was seen. However, the inclusion of electron and electron-muon pair events allowed CMS physicists to place significantly more stringent limits on the possible masses of heavy Majorana neutrinos. With Run 2 of the LHC under way, you can expect searches for Majorana neutrinos to push into ever higher masses.

    *Search for heavy Majorana neutrinos in e+/- e+/- plus jets and e+/- mu+/- plus jets events in proton-proton collisions at sqrt(s) = 8 TeV
    CMS Collaboration

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 5:35 pm on March 18, 2016 Permalink | Reply
    Tags: , , CERN CMS, , , ,   

    From CERN: “CMS hunts for supersymmetry in uncharted territory” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    Mar 18, 2016

    The CMS collaboration is continuing its hunt for signs of supersymmetry (SUSY), a popular extension to the Standard Model that could provide a weakly interacting massive-particle candidate for dark matter, if the lightest supersymmetric particle (LSP) is stable.

    Standard model of Supersymmetry Illustration: CERN & IES de SAR
    The Standard Model of Supersymmetry Illustration: CERN & IES de SAR

    With the increase in the LHC centre-of-mass energy from 8 to 13 TeV, the production cross-section for hypothetical SUSY partners rises; the first searches to benefit are those looking for the strongly coupled SUSY partners of the gluon (gluino) and quarks (squarks) that had the most stringent mass limits from Run 1 of the LHC. By decaying to a stable LSP, which does not interact in the detector and instead escapes, SUSY particles can leave a characteristic experimental signature of a large imbalance in transverse momentum.

    Searches for new physics based on final states with jets (a bundle of particles) and large transverse-momentum imbalance are sensitive to broad classes of new-physics models, including supersymmetry. CMS has searched for SUSY in this final state using a variable called the “stransverse mass”, MT2, to measure the transverse-momentum imbalance, which strongly suppresses fake contributions due to potential hadronic-jet mismeasurement. This allows us to control the background from copiously produced QCD multi-jet events. The remaining background comes from Standard Model processes such as W, Z and top-quark pair production with decays to neutrinos, which also produce a transverse-momentum imbalance. We estimate our backgrounds from orthogonal control samples in data targeted to each. To cover a wide variety of signatures, we categorise our signal events according to the number of jets, the number of jets arising from bottom quarks, the sum of the transverse momenta of hadronic jets (HT), and MT2. Some SUSY scenarios predict spectacular signatures, such as four top quarks and two LSPs, which would give large values for all of these quantities, while others with small mass splittings produce much softer signatures.

    Unfortunately, we did not observe any evidence for SUSY in the 2015 data set. Instead, we are able to significantly extend the constraints on the masses of SUSY partners beyond those from the LHC Run 1. The gluino has the largest production cross-section and many potential decay modes. If the gluino decays to the LSP and a pair of quarks, we exclude gluino masses up to 1550–1750 GeV, depending on the quark flavour, extending our Run 1 limits by more than 300 GeV. We are also sensitive to squarks, with our constraints summarised in figure 1. We set limits on bottom-squark masses up to 880 GeV, top squarks up to 800 GeV, and light-flavour squarks up to 600–1260 GeV, depending on how many states are degenerate in mass.

    Even though SUSY was not waiting for us around the corner at 13 TeV, we look forward to the 2016 run, where a large increase in luminosity gives us another chance at discovery.

    See the full article here.

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    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 11:34 am on March 11, 2016 Permalink | Reply
    Tags: , , CERN CMS, , , Joel Butler, ,   

    From Symmetry: “Fermilab scientist elected next CMS spokesperson” 

    Symmetry Mag

    Symmetry

    03/10/16
    Sarah Charley

    Joel Butler will lead the LHC experiment starting in September.

    CMS spokesman Joel Butler from FNAL
    Joel Butler

    Long before the start-up of the Large Hadron Collider, physicist Joel Butler was helping shape the path of particle physics research in the United States.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    He led experiments at the Department of Energy’s Fermilab, was one of the co-founders of the lab’s Computing Division, and served on the High Energy Physics Advisory Panel.

    Now, more than 30 years into his career as an experimental physicist, Butler’s responsibilities will become global as he takes the helm of one of the world’s largest physics experiments: the CMS experiment based at CERN.

    CERN CMS New
    CERN CMS Event
    CMS with possible Higgs event

    “I am very happy, but I also feel a great sense of responsibility,” Butler says. “It’s a huge collaboration and I am humbled that our collaborators trust me to lead them.”

    The CMS (Compact Muon Solenoid) collaboration designed, constructed and is currently operating one of the two LHC detectors that co-discovered the Higgs boson in 2012.

    Higgs Boson Event

    The CMS experiment is now searching at an even higher energy for phenomena beyond the Standard Model of particle physics, such as dark matter and new fundamental particles.

    Standard model with Higgs New
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The collaboration consists of roughly 180 collaborating institutions and 3,000 scientists.

    As the spokesperson, Butler will be responsible for guiding the technical and scientific endeavors performed by universities and laboratories in more than 40 countries. He will also represent CMS in its interactions with other organizations and the public.

    Tiziano Camporesi is the current spokesperson of CMS experiment. He will lead the collaboration through the LHC’s spring start up and a summer of data collection before passing the baton to Butler in September 2016. He is looking forward to working with Butler through the challenges ahead.

    “We are all hoping to see some nice surprises from our data over the course of the next few years,” Camporesi says. “Butler is extremely hardworking and I’m confident he will do a good job leading the collaboration during this exciting time.”

    Butler joined the CMS collaboration in 2005. He oversaw the construction of the US-funded forward pixel detector and managed the US CMS Operations Program between 2007 and 2013. He is currently helping develop upgrades that will enable the CMS detector to handle higher collision rates in the future.

    During his term, Butler’s main goal is to understand the needs and abilities of CMS’s contributing institutions to maximize the scientific output of the CMS experiment and prepare the detector for the high-luminosity LHC run in 2020.

    “Different nations and institutes face different challenges,” Butler says. “We are going to take a huge amount of data and will have a big workload preparing the upgrades for the next generation of the LHC, which is why we need to increase our engagement with all of our collaborators to ensure that everyone is able to contribute effectively.”

    Even though Butler has spent nearly a third of his scientific career working on the CMS experiment, he admits that there is still a lot left to learn about the experiment and its collaborators.

    “I talked with nearly all of our institutions and explained plans, answered questions and discussed the experiment,” Butler says. “These meetings were incredibly valuable. No matter how much I think I know about CMS, there’s always a lot more to learn.”

    Butler’s term will start this fall and bring the CMS collaboration up to the end of LHC Run II in 2018, when the LHC will shut down for another round of upgrades before ramping up for Run III. Butler says he is looking forward to working with a large and diverse population of scientists at an important moment in physics history.

    “It’s a fantastic group of people, and my assignment is to help them all do the best job they can for CMS,” he says.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 6:08 pm on January 27, 2016 Permalink | Reply
    Tags: , CERN CMS, , , , Unparticles   

    From FNAL: “Particles and unparticles” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    January 27, 2016

    FNAL Don Lincoln
    Don Lincoln

    The LHC accelerator is in the business of discovering new things, from particles that are expected (like the Higgs boson) to particles that are sort of expected (like the panoply of particles predicted by supersymmetric models) to particles from something entirely unexpected (like the what-the-heck-is-that moment that changes our theories forever).

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Supersymmetry standard model
    Standard Model of Supersymmetry

    The commonality of all of these potential discoveries is that they include particles. All particles have a fixed mass. So all electrons in the universe have the same mass, as do all muons, pions, protons or any other subatomic particle you can name.

    (This is true no matter how fast the particles are moving, and it’s worth emphasizing this point, as it may not jibe with some readers’ understanding of what happens when a particle’s velocity approaches light speed [in a vacuum]. You may have heard that the mass of a particle changes as velocity increases. We teach this to people first encountering relativity, but the statement is an illustrative one. What actually changes is the particle’s inertia, which is equivalent to mass at low velocities. You can read more about this in a previous column. So, for a particle, no matter what energy and momentum it has, it must also have a single and specific mass.)

    However, in 2007 scientist Howard Georgi had an idea: Suppose there was a kind of particle that had a mass that wasn’t constant. If you doubled the particle’s energy and momentum, you would double its mass. If you halved the energy, you’d halve the mass. Such a particle wouldn’t have a well-defined mass at all. This kind of particle is called an unparticle.

    Unparticles are governed by fractal mathematics and are highly speculative. In fact, there is no hint in the data that they must exist, nor is there a compelling theoretical reason why they should. On the other hand, they are possible, and given that we don’t know what theory will supplant the Standard Model, we should be open to all sorts of improbable ideas. We do know that unparticles, if they exist, must interact via known forces only weakly.

    Standard model with Higgs New
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in a fifth row.

    So, of course, CMS went looking for them.

    CERN CMS Detector
    CMS

    In a recent analysis that looked for both unparticles and dark matter, scientists studied events in which a Z boson was created, as well as undetected energy that would be the signal of either a dark matter particle or unparticle escaping.

    Sadly, no evidence was observed for either phenomenon. Truthfully, it would have been shocking if unparticles had been observed, but the fact that LHC experiments are looking for even such bizarre possibilities highlights that the scientific community is exploring all viable ideas, hoping to find something that gives us a huge advance in our understanding of the nature of reality.

    See the full article here .

    Please help promote STEM in your local schools.

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 8:29 pm on December 16, 2015 Permalink | Reply
    Tags: , , , CERN CMS, , ,   

    From CERN: “ATLAS and CMS present their 2015 LHC results” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    16 Dec 2015
    Corinne Pralavorio

    1
    A 13 TeV collision recorded by ATLAS. The yellow and green bars indicate the presence of particle jets, which leave behind lots of energy in the calorimeters. (Image: ATLAS)

    2
    A 13 TeV proton collision recorded by CMS. The two green lines show two photons generated by the collision. (Image: CMS)

    Particles circulated in the Large Hadron Collider (LHC) on Sunday for the last time in 2015, and, two days later, the two large general-purpose experiments, ATLAS and CMS, took centre stage to present their results from LHC Run 2. These results were based on the analysis of proton collisions at the previously unattained energy of 13 TeV, compared with the maximum of 8 TeV attained during LHC Run 1 from 2010 to 2012.

    The amount of data on which the two experiments’ analyses are based is still limited – around eight times less than that collected during Run 1 – and physicists need large volumes of data to be able to detect new phenomena. Nonetheless, the experimentalists have already succeeded in producing numerous results. Each of the two experiments has presented around 30 analyses, about half of which relate to Beyond-Standard-Model research. The Standard Model is the theory that describes elementary particles and their interactions, but it leaves many questions unanswered. Physicists are therefore searching for signs of Beyond-Standard-Model physics that might help them to answer some of those questions.

    The new ATLAS and CMS results do not show any significant excesses that could indicate the presence of particles predicted by alternative models such as supersymmetry. The two experiments have therefore established new limits for the masses of these hypothetical new particles. Advances in particle physics often come from pushing back these limits. For example, CMS and ATLAS have established new restrictions for the mass of the gluino, a particle predicted by the theory of supersymmetry. This is just one of the many results that were presented on 15 December.

    The two experiments have also observed a slight excess in the diphoton decay channel. Physicists calculate the mass of hypothetical particles that decay to form a pair of photons, and look at how often different masses are seen. If the distribution does not exactly match that expected from known processes, or in other words a bump appears at a specific mass not corresponding to any known particle, it may indicate a new particle being produced and decaying. However, the excess is too small at this stage to draw such a conclusion. We will have to wait for more data in 2016 to find out whether this slight excess is an inconsequential statistical fluctuation or, alternatively, a sign of the existence of a new phenomenon. Find out next time: season 2 is only just beginning.

    The presentations by ATLAS and CMS are available here.

    See the full article here.

    Please help promote STEM in your local schools.

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    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New

    LHC

    CERN LHC New
    CERN LHC Grand Tunnel

    LHC particles

    Quantum Diaries

     
  • richardmitnick 8:11 pm on December 16, 2015 Permalink | Reply
    Tags: , , , CERN CMS, , , ,   

    From Pauline Gagnon at Quantum Diaries: “If, and really only if…” 

    12.16.15

    Pauline Gagnon
    Pauline Gagnon

    On December 15, at the End-of-the-Year seminar, the CMS and ATLAS experiments from CERN presented their first results using the brand new data accumulated in 2015 since the restart of the Large Hadron Collider (LHC) at 13 TeV, the highest operating energy so far.

    CERN CMS Detector
    CMS

    CERN ATLAS New
    ATLAS

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC

    Although the data sample is still only one tenth of what was available at lower energy (namely 4 fb-1 for ATLAS and 2.8-1 fb for CMS collected at 13 TeV compared to 25 fb-1 at 8 TeV for each experiment), it has put hypothetical massive particles within reach. If the LHC were a ladder and particles, boxes hidden on shelves, operating the LHC at higher energy is like having a longer ladder giving us access to higher shelves, a place never checked before. ATLAS and CMS just had their first glimpse at it.

    Both experiments showed how well their detectors performed after several major improvements, including collecting data at twice the rate used in 2012. The two groups made several checks on how known particles behave at higher energy, finding no anomalies. But it is in searches for new, heavier particles that every one hopes to see something exciting. Both groups explored dozens of different possibilities, sifting through billions of events.

    Each event is a snapshot of what happens when two protons collide in the LHC. The energy released by the collision materializes into some heavy and unstable particle that breaks apart mere instants later, giving rise to a mini firework. By catching, identifying and regrouping all particles that fly apart from the collision point, one can reconstruct the original particles that were produced.

    Both CMS and ATLAS found small excesses when selecting events containing two photons. In several events, the two photons seem to come from the decay of a particle having a mass around 750 GeV, that is, 750 times heavier than a proton or 6 times the mass of a Higgs boson.

    CERN ATLAS Higgs Event
    Higgs event at ATLAS

    Since the two experiments looked at dozens of different combinations, checking dozens of mass values for each combination, such small statistical fluctuations are always expected.

    2
    Top part: the combined mass given in units of GeV for all pairs of photons found in the 13 TeV data by ATLAS. The red curve shows what is expected from random sources (i.e. the background). The black dots correspond to data and the lines, the experimental errors. The small bump at 750 GeV is what is now intriguing. The bottom plot shows the difference between black dots (data) and red curve (background), clearly showing a small excess of 3.6σ or 3.6 times the experimental error. When one takes into account all possible fluctuations at all mass values, the significance is only 2.0σ

    What’s intriguing here is that both groups found the same thing at exactly the same place, without having consulted each other and using selection techniques designed not to bias the data. Nevertheless, both experimental groups are extremely cautious, stating that a statistical fluctuation is always possible until more data is available to check this with increased accuracy.

    3
    CMS has slightly less data than ATLAS at 13 TeV and hence, sees a much smaller effect. In their 13 TeV data alone, the excess at 760 GeV is about 2.6σ, 3σ when combined with the 8 TeV data. But instead of just evaluating this probability alone, experimentalists prefer take into account the fluctuations in all mass bins considered. Then the significance is only 1.2σ, nothing to write home about. This “look-elsewhere effect” takes into account that one is bound to see a fluctuation somewhere when ones look in so many places.

    Theorists show less restrain. For decades, they have known that the Standard Model, the current theoretical model of particle physics, is flawed and have been looking for a clue from experimental data to go further.

    4
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Many of them have been hard at work all night and eight new papers appeared this morning, proposing different explanations on which new particle could be there, if something ever proves to be there. Some think it could be a particle related to Dark Matter, others think it could be another type of Higgs boson predicted by Supersymmetry or even signs of extra dimensions. Others offer that it could only come from a second and heavier particle. All suggest something beyond the Standard Model.

    Two things are sure: the number of theoretical papers in the coming weeks will explode. But establishing the discovery of a new particle will require more data. With some luck, we could know more by next Summer after the LHC delivers more data. Until then, it remains pure speculation.

    This being said, let’s not forget that the Higgs boson made its entry in a similar fashion. The first signs of its existence appeared in July 2011. With more data, they became clearer in December 2011 at a similar End-of-the-Year seminar. But it was only once enough data had been collected and analysed in July 2012 that its discovery made no doubt. Opening one’s gifts before Christmas is never a good idea.

    See the full article here .

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    Participants in Quantum Diaries:

    Fermilab

    Triumf

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    CERN

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  • richardmitnick 2:30 pm on September 26, 2015 Permalink | Reply
    Tags: , , CERN CMS, , , Leptoquarks, ,   

    From FNAL- “Frontier Science Result: CMS Subatomic gryphons” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Sept. 25, 2015
    FNAL Don Lincoln
    This article is written by Don Lincoln

    1
    The gryphon is a mythical beast with the head of an eagle and the hindquarters of a lion. Physicists look for a proposed particle hybrid of a quark and a lepton. This theoretical particle is called a leptoquark.

    Mythology is replete with creatures that are exotic blends of more familiar animals, for example gryphons, mermaids and centaurs. Finding ordinary animals is commonplace, but discovering one of these blended ones would be a true triumph of science.

    There are similarities in particle physics. For instance, the Standard Model contains the very familiar quarks and leptons.

    2
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    These two classes of particles have very different properties. Quarks feel all of the known subatomic forces and are found in the center of atoms. Leptons feel only two of the three known subatomic forces (they do not react via the strong nuclear force), and the most familiar lepton, the electron, orbits far from the atomic nucleus. Further, a single quark cannot convert into a single lepton, and vice versa. These really are quite different beasties.

    However, the goal of particle physics is unification. We hope one day to generate a single, overlapping theory that contains but one type of particle and one type of force. We are very far from that goal and will need to somehow account for the existence of the very different quarks and leptons.

    One possibility is that a quark and lepton can fuse to make a hybrid particle called a leptoquark. Leptoquarks would contain all the properties of quarks and leptons and would be a step on the path to building a unified theory.

    Leptoquarks are speculative particles, and they pop up in many proposed theories. And, like any good researchers, CMS scientists studied their data to see if they could find evidence that supported the particle’s existence.

    CERN CMS ICON
    CMS in the LHC at CERN

    After considerable effort, the CMS experiment submitted for publication not one, but two papers reporting on a leptoquark search. One paper looked for leptoquarks produced individually, while the other looked for leptoquarks produced in pairs.

    No evidence was observed for the existence of leptoquarks, which means either that the idea is wrong or that the measurement didn’t have enough energy to make them. These two papers were reported using LHC data recorded in 2012 at an energy of 8 trillion electronvolts. CMS is recording data now at a much higher energy, and researchers are refining their analyses to dig into this new possible treasure trove. The hunt for leptoquarks isn’t over yet.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 10:35 am on August 21, 2015 Permalink | Reply
    Tags: , CERN CMS, , , , ,   

    From FNAL: LHC Run II: first analysis 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Aug. 21, 2015
    FNAL Don Lincoln
    Don Lincoln

    CERN CMS Detector
    CMS Detector

    It was Lao-Tzu who said, “A journey of a thousand miles begins with a single step.” While this proverb from the Tao Te Ching is universally true, it has an especially apropos meaning for scientists working at the LHC.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN
    LHC at CERN

    Our journey isn’t always a physical one, but rather travels into intellectual realms never before investigated. We look to understand the behavior of matter at the highest energies ever achieved and to explore the conditions of the universe a tenth of a trillionth of a second after it began.

    Our one-step-at-a-time approach served us well using the data recorded from 2010–12 (what scientists called LHC Run I), in which the Higgs boson was discovered, vast swaths of ideas for new theories were ruled out and the most energetic collisions ever achieved were characterized.

    2
    Proposed Higgs event at CMS

    This was an enormous success, leading to about 1,000 separate publications from the four big LHC experiments. During this period, scientists thoroughly explored the behavior of matter at collision energies of 7 and then 8 trillion electronvolts.

    After two years downtime, the LHC resumed operations in 2015 (which we are calling Run II) and is now delivering beams of protons that collide at even higher energies, specifically 13 trillion electronvolts. There is no way to know what we will discover, as this is truly intellectual terra incognito.

    As it happens, not all collisions occur with equal probability. Glancing collisions can occur a billion times more often than, for example, ones in which Higgs bosons are made. This allows scientists to quickly study certain data while waiting for enough data to accumulate for the rarer collisions. In addition, in the rarer collisions, two of the protons’ constituents collide energetically, but the remainder experience only glancing interactions. Thus understanding the physics of glancing collisions is important even for events in which the discovery potential is much higher.

    On July 21, CMS submitted for publication the first physics paper using the Run II data. The analysis studied the most common collisions to characterize both the number and direction of charged particles created in the collisions. Even in these gentlest of collisions, more than 20 charged particles are created on average. Further, it is always possible when exploring a new energy regime that surprises might arise, so the researchers compared their measurement to those taken at lower collision energies and observed no real surprises.

    The real message is the LHC publication juggernaut has pounced on Run II data with a vengeance. This paper is the first, but it won’t be the last.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
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