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  • richardmitnick 4:25 pm on December 6, 2016 Permalink | Reply
    Tags: 2016: an exceptional year for the LHC, , , , , CERN CMS, ,   

    From CERN: “2016: an exceptional year for the LHC” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    6 Dec 2016
    Corinne Pralavorio

    1
    This proton-lead ion collision in the ATLAS detector produced a top quark – the heaviest quark – and its antiquark (Image: ATLAS)

    It’s the particles’ last lap of the ring. On 5 December 2016, protons and lead ions circulated in the Large Hadron Collider (LHC) for the last time. At exactly 6.02am, the experiments recorded their last collisions (also known as ‘events’).

    When the machines are turned off, the LHC operators take stock, and the resulting figures are astonishing.

    The number of collisions recorded by ATLAS and CMS during the proton run from April to the end of October was 60% higher than anticipated. Overall, all of the LHC experiments observed more than 6.5 million billion (6.5 x 1015) collisions, at an energy of 13 TeV. That equates to more data than had been collected in the previous three runs combined.

    3
    One of the first proton-lead ion collisions at 8.16 TeV recorded by the ALICE experiment. (Image: ALICE/CERN)

    In technical terms, the integrated luminosity received by ATLAS and CMS reached 40 inverse femtobarns (fb−1), compared with the 25fb−1 originally planned. Luminosity, which measures the number of potential collisions in a given time, is a crucial indicator of an accelerator’s performance.

    “One of the key factors contributing to this success was the remarkable availability of the LHC and its injectors,” explains Mike Lamont, who leads the team that operates the accelerators. The LHC’s overall availability in 2016 was just shy of 50%, which means the accelerator was in ‘collision mode’ 50% of the time: a very impressive achievement for the operators. “It’s the result of an ongoing programme of work over the last few years to consolidate and upgrade the machines and procedures,” Lamont continues.

    4
    An event recorded by the CMS experiment during the LHC’s proton-lead ion run for which no fewer than 449 particles tracks were reconstructed. (Image: CMS/CERN)

    For the last four weeks, the machine has turned to a different type of collision, where lead ions have been colliding with protons. “This is a new and complex operating mode, but the excellent functioning of the accelerators and the competence of the teams involved has allowed us to surpass our performance expectations,” says John Jowett, who is in charge of heavy-ion runs.

    With the machine running at an energy of 8.16 TeV, a record for this assymetric type of collision, the experiments have recorded more than 380 billion collisions. The machine achieved a peak luminosity over seven times higher than initially expected, as well as exceptional beam lifetimes. The performance is even more remarkable considering that colliding protons with lead ions, which have a mass 206 times greater and a charge 82 times higher, requires numerous painstaking adjustments to the machine.

    The physicists are now analysing the enormous amounts of data that have been collected, in preparation for presenting their results at the winter conferences.

    6
    A proton-lead ion collision recorded by the LHCb experiment in the last few days of the LHC’s 2016 run. (Image: LHCb)

    Meanwhile, CERN’s accelerators will take a long break, called the Extended Year End Technical Stop (EYETS) until the end of March 2017. But, while the accelerators might be on holiday, the technical teams certainly aren’t. The winter stop is an opportunity to carry out maintenance on these extremely complex machines, which are made up of thousands of components. The annual stop for the LHC is being extended by two months in 2017 to allow more major renovation work on the accelerator complex and its 35 kilometres of machines to take place. Particles will return to the LHC in spring 2017.

    7
    The integrated luminosity of the LHC with proton-proton collisions in 2016 compared to previous years. Luminosity is a measure of a collider’s efficiency and is proportional to the number of collisions. The integrated luminosity achieved by the LHC in 2016 far surpassed expectations and is double that achieved at a lower energy in 2012. (Image : CERN)

    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 10:59 am on November 4, 2016 Permalink | Reply
    Tags: , CERN CMS, , , The buzz from CMS   

    From FNAL: “The buzz from CMS” 

    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.

    November 4, 2016
    Vivan O’Dell

    CERN/CMS Detector
    CERN/CMS Detector

    The CMS experiment at CERN’s Large Hadron Collider is buzzing with activity.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC st CERN

    The first year of Run 2 is ending, and as we near the end of 2016, we have our work cut out for us.

    CMS is upgrading its inner tracking detector over the winter during a 21-week temporary halt of beams. We’re preparing for more upgrades during the second LHC long shutdown in 2018-19. We’re also finalizing designs for a major upgrade, targeting the 10-year running period from 2026-3035. CMS is like three experiments at once: one collecting and analyzing data, one in the final stages of building and installing, and one in the early design phase.

    The major upgrade, the High-Luminosity LHC upgrades, targets the detectors as well as the accelerator, and Fermilab has major responsibilities in both of these areas. Fermilab is the host lab for U.S. contributions to CMS and is home to the CMS HL-LHC upgrade project office. We are also a major player in the upgrades of tracking, calorimetry and trigger. These upgrades will allow CMS to run efficiently in a high-collision-rate and high-radiation environment.

    Last year, CERN officially approved the CMS and ATLAS detector upgrades to move from proposal phase to detailed technical designs, which is similar to a project “baselining” phase. This was followed in April with both NSF and DOE officially recognizing the U.S. contributions to the HL-LHC CMS upgrades: We received CD-0 approval for the detector upgrades from DOE and the official approval to move into the preliminary-design phase from NSF. The U.S. contributions to the accelerator also achieved CD-0 in April.

    The next year will be a busy year for the CMS HL-LHC upgrades: In the United States we are planning for DOE CD-1 in the fall and the NSF Preliminary Design Review at the end of the year. Internationally, CMS is working on delivering four detailed technical design reports, which cover all aspects of the upgrades, their costs, and the planned international contributions to build and maintain them. Luckily the sun never sets on the CMS collaboration, and the CMS Center at Fermilab offers unlimited espresso.

    Both upgrades, which will be installed over the next couple of years, will enable CMS to collect nearly 100 times more data at its current center-of-mass collision energy, which is roughly 14 TeV. That boost in data volume increases the potential for making significant discoveries of new phenomena to complete our understanding of particle physics and allows more precise measurements of Higgs boson properties and other tests of Standard Model processes.

    Vivian O’Dell is the U.S. CMS Phase II upgrade project manager.

    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 11:47 am on October 17, 2016 Permalink | Reply
    Tags: , , CERN CMS, Dr Michel Della Negra, Dr Peter Jenni, , Sir Tejinder (Jim) Virdee, W.K.H. Panofsky Prize   

    From ICL: “Fathers of Higgs boson detectors awarded particle physics prize” 

    Imperial College London
    Imperial College London

    17 October 2016
    Hayley Dunning

    1
    Professor Sir Tejinder Virdee (L) and Dr Michel DellaNegra (R)

    2
    Dr Peter Jenni

    Two Imperial physicists share in a prize for experimental physics for their work masterminding the CMS and ATLAS experiments

    The W.K.H. Panofsky Prize in Experimental Particle Physics, awarded by the American Physical Society, has this year been given to three scientists, “For distinguished leadership in the conception, design, and construction of the ATLAS and CMS detectors, which were instrumental in the discovery of the Higgs boson.”

    Receiving the honours are Professor Sir Tejinder (Jim) Virdee FRS from the Department of Physics at Imperial, Dr Michel Della Negra from CERN, who is also a Distinguished Research Fellow at Imperial, and Dr Peter Jenni from CERN and Albert-Ludwigs-University Freiburg.

    In July 2012, scientists using the Compact Muon Solenoid (CMS) and A Toroidal LHC Apparatus (ATLAS) experiments operating at the Large Hadron Collider (LHC) at CERN announced the discovery of the Higgs boson.

    CERN/CMS Detector
    CERN/CMS Detector

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN/ATLAS detector
    CERN/ATLAS detector

    CERN ATLAS Higgs Event
    CERN ATLAS Higgs Event

    This new particle, whose associated field gives mass to the fundamental particles, is the last missing link of the Standard Model of particle physics.

    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 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

    Professor Jordan Nash, head of the Department of Physics at Imperial, said: “I’m delighted to see that Jim and Michel have been awarded this year’s Panofsky prize. Their dedication for more than two decades to the design, construction, and operation of the CMS detector has been essential to enabling the wonderful science and discoveries we have seen at the LHC.”

    Hayley Dunning talked to Professor Virdee about his latest award, chasing the Higgs and the future of the Large Hadron Collider.

    You’ve won a few prizes for your work – how does it feel to win the W.K.H. Panofsky Prize?

    It is a great honour to receive this prize and it is particularly pleasing to get this recognition from our peers. Even though the past 25 years have been long and not without many difficulties, it has nevertheless led to a fantastic result for all of us at the LHC – the discovery of the Higgs boson.

    This award is also acknowledgement of the huge experimental effort that led to the discovery of the Higgs boson. This wouldn’t have been possible without the contributions of thousands of scientists and engineers from around the world. On a personal note, I have enjoyed the enormous support of my exceptional colleagues at Imperial as well as the many others in the CMS Collaboration.

    What attracted you to particle physics and big experiments like the LHC?

    Particle physics is a modern-day name for the centuries-old effort to understand the fundamental laws of nature. I was intrigued to find out more: how nature really works at the most fundamental level, and I’ve always felt that this has to be one of the most exciting of human endeavours.

    Particle physicists didn’t really set out to do ‘big’ experiments. I, like my colleagues, were not attracted by the magnitude of the experiment, but by the magnitude and importance of the questions for which we were searching answers. CMS has the size it has due to the huge power of its ‘microscope’ to examine physics at the smallest distance scales offered for study by the highest accelerator energy so far achieved.

    And this can be seen in the history of this endeavour: twenty-five years ago, we started CMS with a handful of physicists and engineers. The enormity of the detectors that were necessary to answer these enormous questions meant that the collective talents and resources of a worldwide effort would be necessary. Now, CMS has over 3,000 scientists and engineers and involves 40 countries.

    Did you always believe you would be able to find the Higgs boson with CMS and ATLAS?

    In retrospect, and not overlooking the open mind that we all physicists have to have, I did believe, that if the Higgs boson were a true constituent particle of nature, we would find it sooner or later at the LHC. It has to be remembered that mass is a fundamental attribute of fundamental particles and is what gives our universe substance.

    At the time of conception of the CMS detector, a few of us paid particular attention to conjectures that suggested the mass of the Higgs boson could lie in the range where, years later, in 2012, it was eventually found. In this range the electromagnetic calorimeter, which I pioneered, played a vital role. Similarly, other parts of CMS were conceived, designed and constructed so as to ensure that the Higgs boson would be found if it were at other masses.

    Luckily, it turned out that the Higgs boson is a choice of nature. What was less of a stroke of luck is that we found it – given that it is a real element of nature.

    What are you working on now, and what do you hope for the future of the LHC experiments?

    My current work involves the in-depth study of the properties of the newly found Higgs boson, the search for widely anticipated physics beyond the Standard Model, and the design of the upgrades to the CMS detector for very high luminosity (implying very high proton-proton interaction rate) LHC running, due to start in the mid-2020s.

    In the context of this upgrade, a year or so ago I began another exciting project to develop a novel technique to replace a part of CMS. The goal is to increase the physics reach of the next phase of the LHC and take us into the 2030s. In 2015 I was awarded an EU-ERC Advanced grant to carry out the research, development and prototyping of this novel project.

    See the full article here .

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    Imperial College London

    Imperial College London is a science-based university with an international reputation for excellence in teaching and research. Consistently rated amongst the world’s best universities, Imperial is committed to developing the next generation of researchers, scientists and academics through collaboration across disciplines. Located in the heart of London, Imperial is a multidisciplinary space for education, research, translation and commercialisation, harnessing science and innovation to tackle global challenges.

     
  • richardmitnick 8:00 am on October 8, 2016 Permalink | Reply
    Tags: , CERN CMS, , , , ,   

    From Don Lincoln at FNAL: “Eight is enough” 

    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.

    October 7, 2016

    FNAL Don Lincoln
    Don Lincoln

    1
    In the search for new physics, no stone can be left unturned. In this analysis, scientists looked for a new particle that underwent a cascade of decays, resulting in eight distinct particles. No image credit.

    While the LHC was built for many purposes, one of the key reasons it was created was to investigate the most energetic collisions possible. The basic idea is that high-energy collisions have the best chance of unveiling phenomena never before observed.

    In particle physics, low-energy things happen all the time, while high-energy things are extremely rare. To give a sense of scale, the lowest-energy collisions that we study occur about a billion times more often than the highest-energy collisions we can create.

    Now if you want to study very high-energy things, you want to use the strongest force available to you. That’s because a strong force makes many collisions, and if you make many collisions, you are more likely to see the rare and very high-energy type of event you are looking for. In particle physics terminology, that means that you need to use events that use the strong nuclear force.

    That works out as a good strategy at the LHC because the LHC collides protons together, and protons are full of quarks and gluons, both of which interact via the strong force. The basic idea is that a quark or gluon from one proton will interact with a quark or gluon from the other proton, merge into some new and undiscovered particle, and then decay and be observed in the detector. Now the CMS experiment has already looked into the case where this new particle decayed directly into two ordinary particles.

    CERN/CMS Detector
    CERN/CMS Detector

    It has also looked into the case where the new particle decayed into two new (but different) particles that then each decayed into two ordinary particles. In this scenario, there would be four ordinary particles hitting the detector. Neither of these analyses led to the discovery of new physics.

    However, there is no reason that these should be the only two possible scenarios. It could be that LHC collisions would make one new particle, which then decayed into two new but lower-mass particles, each of which subsequently decayed into two more new and even lighter particles, resulting in four, which each finally decayed into two ordinary particles, producing eight. Thus the CMS experiment went looking for events in which eight ordinary particles simultaneously hit the detector.

    CMS was searching for particles called “jets,” which are actually collections of even more particles, but we can use algorithms to reduce a jet to looking like a single particle. So they were looking for events that produced eight jets.

    So far so good. The problem with this analysis arises because, even without new physics, the strong nuclear force makes lots of events in which there are eight or more jets, so it is pretty hard to identify events with eight jets that are made by new physics. But there is one saving grace. The collisions in which eight jets are made by ordinary physics have the same basic distribution of total energy as the ones in which only two jets are made. So they use the well-understood two-jet data to make predictions of eight-jet data and then compare it to the measurements all eight-jet data. If too many eight-jet events are found, then maybe they’ve made a discovery.

    Sadly, no excess was found. But this was a clever technique and one that might well be worth pursuing in the future. The most recent paper was for data recorded at a collision energy of eight trillion electronvolts of energy (back in 2012), and we’ve recorded data with 13 trillion electronvolts. Maybe with the new data, this technique will lead to a different result.

    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 5:31 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.

    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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