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  • richardmitnick 2:09 pm on February 14, 2017 Permalink | Reply
    Tags: , An exceptional result on a very rare decay of a particle called Bs0, , CERN LHCb,   

    From CERN: “The Standard Model stands its ground” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    14 Feb 2017
    Stefania Pandolfi

    1
    Event display of a typical Bs0 decay into two muons. The two muon tracks from the Bs0 decay are seen as a pair of green tracks traversing the whole detector. (Image: LHCb collaboration)

    Today, in a seminar at CERN, the LHCb collaboration has presented an exceptional result on a very rare decay of a particle called Bs0. This observation marks yet another victory for the Standard Model (SM) of particle physics – the model that explains, to the best of our knowledge, the behaviour of all fundamental particles in the universe – over all its principal theoretical alternatives.

    CERN/LHCb
    CERN/LHCb

    The LHCb collaboration has reported the observation of the decay of the Bs0 meson – a heavy particle made of a bottom anti-quark and a strange quark – into a pair of muons. This decay is extremely rare, the rarest ever seen: according to the theoretical predictions, it should occur about 3 times in every billion total decays of that particle.

    3
    Event display from the LHCb experiment shows examples of collisions that produced candidates for the rare decay of the Bs0 meson. Image credit: LHCb Collaboration.

    The decay of the Bs0 meson has been long regarded as a very promising place to look for cracks in the armour of the Standard Model, which, despite being our best available description of the subatomic world, leaves some questions unanswered. Therefore, over time, physicists came up with many alternatives or complementary theories. A large class of theories that extend the Standard Model into new physics, such as Supersymmetry, predicts significantly higher values for the Bs0 decay probability. Therefore, an observation of any significant deviation from the SM predicted value would suggest the presence of new, yet unknown, physics.

    The experimental value found by the LHCb collaboration for this probability is in an excellent agreement with the one predicted by the theory, and the result is confirmed to a very high level of reliability, at the level of 7.8 standard deviations: that is, the scientists are extremely sure that it hasn’t occurred just by chance. The LHCb collaboration obtained the first evidence of this phenomenon in November 2012, with a significance of 3.5 standard deviations. Three years later, together with the CMS collaboration, LHCb obtained the first confirmed observation in May 2015, with a significance of 6.2 standard deviations (for more information read the CERN Press release and the paper published on Nature ).

    This new finding limits the room for action of other models of physics beyond the SM: all candidate models will have to demonstrate their compatibility with this important result.

    Further reading on the LHCb website.

    See the full article here.

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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

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  • richardmitnick 1:33 pm on January 14, 2017 Permalink | Reply
    Tags: , , CERN LHCb, , ,   

    From CERN Courier: “Run 2 promises a harvest of beauty for LHCb” 

    CERN Courier

    1
    New measurement

    The first b-physics analysis using data from LHC Run 2, which began in 2015 with proton–proton collisions at an energy of 13 TeV, shows great promise for the physics programme of LHCb. During 2015 and 2016, the experiment collected a data sample corresponding to an integrated luminosity of about 2 fb^–1. Although this value is smaller than the total integrated luminosity collected in the three years of Run 1 (3 fb^–1), the significant increase of the LHC energy in Run 2 has almost doubled the production cross-section of beauty particles. Furthermore, the experiment has improved the performance of its trigger system and particle-identification capabilities. Once such an increase is taken into account, along with improvements in the trigger strategy and in the particle identification of the experiment, LHCb has already more than doubled the statistics of beauty particles on tape with respect to Run 1.

    The new analysis is based on 1 fb–1 of available data, aiming to measure the angle γ of the CKM unitarity triangle using B– → D0K*– decays. While B– → D0K– decays have been extensively studied in the past, this is the first time the B– → D0K*– mode has been investigated. The analysis, first presented at CKM2016 (see Triangulating in Mumbai in Faces & Places), allows the LHCb collaboration to cross-check expectations for the increase of signal yields in Run 2 using real data. A significant increase, roughly corresponding to a factor three, is observed per unit of integrated luminosity. This demonstrates that the experiment has benefitted from the increase in b-production cross-section, but also that the trigger of the detector performs better than in Run 1. Although the statistical uncertainty on γ from this measurement alone is still large, the sensitivity will be improved by the addition of more data, as well as by the use of other D-meson decay modes. This bodes well for future measurements of γ to be performed in this and other decay modes with the full Run 2 data set.

    Measurements of the angle γ are of great importance because it is the least well-known angle of the unitarity triangle. The latest combination from direct measurements with charged and neutral B-meson decays and a variety of D-meson final states, all performed with Run 1 data, yielded a central value of 72±7 degrees. LHCb’s ultimate aim, following detector upgrades relevant for LHC Run 3, is to determine γ with a precision below 1°, providing a powerful test of the Standard Model.

    See the full article here .

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

    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:

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    THE FOUR MAJOR PROJECT COLLABORATIONS

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    CERN ATLAS New

    ALICE
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    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

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  • richardmitnick 1:50 pm on September 28, 2016 Permalink | Reply
    Tags: , CERN LHCb, ,   

    From CERN: “Looking for charming asymmetries” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    28 Sep 2016
    Stefania Pandolfi

    1
    A view of the LHCb experimental cavern. (Image: Maximilien Brice/CERN)
    CERN LHCb New

    One of the biggest challenges in physics is to understand why everything we see in our universe seems to be formed only of matter, whereas the Big Bang should have created equal amounts of matter and antimatter.

    CERN’s LHCb experiment is one of the best hopes for physicists looking to solve this longstanding mystery.

    At the VIII International Workshop on Charm Physics (link is external), which took place in Bologna earlier this month, the LHCb Collaboration presented the most precise measurement to date of a phenomenon called Charge-Parity (CP) violation among particles that contain a charm quark.

    CP symmetry states that laws of physics are the same if a particle is interchanged with its anti-particle (the “C” part) and if its spatial coordinates are inverted (P). The violation of this symmetry in the first few moments of the universe is one of the fundamental ingredients to explain the apparent cosmic imbalance in favour of matter.

    Until now, the amount of CP violation detected among elementary particles can only explain a tiny fraction of the observed matter-antimatter asymmetry. Physicists are therefore extending their search in the quest to identify the source of the missing anti-matter.

    The LHCb collaboration made a precise comparison between the decay lifetime of a particle called a D0 meson (formed by a charm quark and an up antiquark) and its anti-matter counterpart D0 (formed by an charm antiquark and up quark), when decaying either to a pair of pions or a pair of kaons. Any difference in these lifetimes would provide strong evidence that an additional source of CP violation is at work. Although CP violation has been observed in processes involving numerous particles that contain b and s quarks, the effect is still unobserved in the charm-quark sector and its magnitude is predicted to be very small in the Standard Model.

    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.

    Thanks to the excellent performance of CERN’s Large Hadron Collider, for the first time the LHCb collaboration is accumulating a dataset large enough to access the required level of precision on CP-violating effects in charm-meson decays. The latest results indicate that the lifetimes of the D0 and D0 particles, measured using their decays to pions or kaons, are still consistent, thereby demonstrating that any CP violation effect that is present must indeed be at a tiny level.

    However, with many more analyses and data to come, LHCb is looking forward to delving even deeper into the possibility of CP violation in the charm sector and thus closing in on the universe’s missing antimatter. “The unique capabilities of our experiment, and the huge production rate of charm mesons at the LHC, allow us to perform measurements that are far beyond the sensitivity of any previous facility,” says Guy Wilkinson, spokesperson for the LHCb collaboration. “However, nature demands that we dig even deeper in order to uncover an effect. With the data still to come, we are confident of responding to this challenge,” he adds.

    More information is available on the LHCb website.

    See the full article here.

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  • richardmitnick 4:00 pm on June 29, 2016 Permalink | Reply
    Tags: , , CERN LHCb, , , , , 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 4:14 pm on September 15, 2015 Permalink | Reply
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    From livescience: “Could Physics’ Reigning Model Finally Be Dethroned?” 

    Livescience

    September 10, 2015
    Tia Ghose

    CERN LHCb chamber
    The LHCb detector at CERN. Credit: CERN

    Trouble is brewing in the orderly world of subatomic physics.

    New evidence from the world’s largest atom smasher, the Large Hadron Collider in Geneva, Switzerland, suggests that certain tiny subatomic particles called leptons don’t behave as expected.

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

    So far, the data only hint at these misbehaving leptons. But if more data confirm their wayward behavior, the particles would represent the first cracks in the reigning physics model for subatomic particles, researchers say.

    Reigning model

    A single model, called the Standard Model, governs the bizarre world of the teensy tiny.

    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.

    It dictates the behavior of every subatomic particle, from ghostly neutrinos to the long-sought Higgs boson (discovered in 2012), which explains how other particles get their mass.

    CERN CMS Event
    Higgs at CMS

    CERN CMS Detector
    CMS at CERN

    In hundreds of experiments over four decades, physicists have confirmed over and over again that the Standard Model is an accurate predictor of reality.

    But the Standard Model isn’t the whole picture of how the universe operates. For one, physicists haven’t found a way to reconcile the microcosm of the Standard Model with [Albert] Einstein’s theory of general relativity, which describes how mass warps space-time on a larger scale. And neither theory explains the mysterious substance called dark matter, which makes up most of the universe’s matter, yet emits no light. So physicists have been on the hunt for any results that contradict the Standard Model’s basic premises, in the hopes that it could reveal new physics.

    Cracks in the foundation

    Physicists may have found one such contradiction at the Large Hadron Collider (LHC), which accelerates beams packed with protons around a 17-mile-long (27 kilometers) underground ring and smashes them into one another, creating a shower of short-lived particles.

    While sifting through the alphabet soup of short-lived particles, scientists with the LHC’s beauty experiment (LHCb) noticed a discrepancy in how often B mesons — particles with mass five times that of the proton — decayed into two other types of electron like particles, called the tau lepton and the muon.

    The LHCb scientists noticed slightly more tau leptons than they expected, which they first reported earlier this year. But that result was very preliminary. From LHCb data alone, there was a high chance — about 1 in 20 — that a statistical fluke could explain the findings.

    “This is a small hint, and you would have not been supremely excited until you see more of it,” said Hassan Jawahery, a particle physicist at the University of Maryland in College Park, who works on the LHCb experiment.

    But this same discrepancy in the tau-lepton-muon ratio has cropped up before, at Stanford University’s BaBar experiment, which tracked the fallout from electrons colliding with their antimatter partners, positrons.

    SLAC Babar
    SLAC Babar

    With both data sources combined, the odds that the tau-lepton-muon discrepancy is a byproduct of random chance drops significantly. The new results are at a certainty level of “4-sigma,” which means there is a 99.993 percent chance the discrepancy between tau leptons and muons represents a real physical phenomenon, and is not a byproduct of random chance, the researchers reported Sept. 4 in the journal Physical Review Letters. (Typically, physicists announce big discoveries, such as that of the Higgs boson, when data reaches a 5-sigma level of significance, meaning there’s a 1 in 3.5 million chance that the finding is a statistical fluke.)

    “Their values are totally in line with ours,” said Vera Luth, a physicist at Stanford University in California who worked on the BaBar experiment. “We’re obviously thrilled that it doesn’t look totally like a fluctuation. It may actually be right.”

    Strange new worlds?

    Of course, it’s still too early to say with absolute certainty that something fishy is going on in the world of the very small. But the fact that similar results have been found using completely different experimental models bolsters the LHCb findings, said Zoltan Ligeti, a theoretical physicist at Lawrence Berkeley National Laboratory in California, who was not involved in the current experiments. In addition, the B-factory at the atom-smashing KEK-B experiment in Japan has found a similar deviation, he added.

    KEK Belle detector
    KEK Belle Detctor

    If the phenomenon they’ve measured holds up with further testing, “the implications for theory and how we view the world would be extremely substantial,” Ligeti told Live Science. “It’s really a deviation from the Standard Model in a direction that most people would not have expected.”

    For instance, one of the top contenders to explain dark matter and dark energy is a class of theories known as supersymmetry, which posits that each known particle has a superpartner with slightly different characteristics. But the most popular versions of these theories cannot explain the new results, he said.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    Still, the new results aren’t confirmed yet. That will have to wait until the team begins analyzing data from the newest run of the LHC, which ramped up to nearly double the energy levels in April, Jawahery said.

    “The uncertainties are still large, and we would like to do better,” Luth said. “I’m sure the LHCb will do that.”

    See the full article here .

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  • richardmitnick 11:53 am on August 27, 2015 Permalink | Reply
    Tags: , , CERN LHCb, , , ,   

    From U Maryland: “Evidence Suggests Subatomic Particles Could Defy the Standard Model” 

    U Maryland bloc

    University of Maryland

    August 26, 2015
    Matthew Wright
    301-405-9267
    mewright@umd.edu

    Large Hadron Collider team finds hints of leptons acting out against time-tested predictions

    The Standard Model of particle physics, which explains most of the known behaviors and interactions of fundamental subatomic particles, has held up remarkably well over several decades.

    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.

    This far-reaching theory does have a few shortcomings, however—most notably that it doesn’t account for gravity. In hopes of revealing new, non-standard particles and forces, physicists have been on the hunt for conditions and behaviors that directly violate the Standard Model.

    Now, a team of physicists working at CERN’s Large Hadron Collider (LHC) has found new hints of particles—leptons, to be more precise—being treated in strange ways not predicted by the Standard Model. The discovery, scheduled for publication in the September 4, 2015 issue of the journal Physical Review Letters, could prove to be a significant lead in the search for non-standard phenomena.

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

    1
    In this event display from the LHCb experiment at CERN’s Large Hadron Collider, proton-proton collisions at the interaction point (far left) result in a shower of leptons and other charged particles. The yellow and green lines are computer-generated reconstructions of the particles’ trajectories through the layers of the LHCb detector. Image credit: CERN/LHCb Collaboration

    3
    LHCb Detector

    The team, which includes physicists from the University of Maryland who made key contributions to the study, analyzed data collected by the LHCb detector during the first run of the LHC in 2011-12. The researchers looked at B meson decays, processes that produce lighter particles, including two types of leptons: the tau lepton and the muon. Unlike their stable lepton cousin, the electron, tau leptons and muons are highly unstable and quickly decay within a fraction of a second.

    According to a Standard Model concept called “lepton universality,” which assumes that leptons are treated equally by all fundamental forces, the decay to the tau lepton and the muon should both happen at the same rate, once corrected for their mass difference. However, the team found a small, but notable, difference in the predicted rates of decay, suggesting that as-yet undiscovered forces or particles could be interfering in the process.

    “The Standard Model says the world interacts with all leptons in the same way. There is a democracy there. But there is no guarantee that this will hold true if we discover new particles or new forces,” said study co-author and UMD team lead Hassan Jawahery, Distinguished University Professor of Physics and Gus T. Zorn Professor at UMD. “Lepton universality is truly enshrined in the Standard Model. If this universality is broken, we can say that we’ve found evidence for non-standard physics.”

    The LHCb result adds to a previous lepton decay finding, from the BaBar experiment at the Stanford Linear Accelerator Center, which suggested a similar deviation from Standard Model predictions.

    SLAC Babar
    SLAC/BaBaR

    (The UMD team has participated in the BaBar experiment since its inception in 1990’s.) While both experiments involved the decay of B mesons, electron collisions drove the BaBar experiment and higher-energy proton collisions drove the LHC experiment.

    “The experiments were done in totally different environments, but they reflect the same physical model. This replication provides an important independent check on the observations,” explained study co-author Brian Hamilton, a physics research associate at UMD. “The added weight of two experiments is the key here. This suggests that it’s not just an instrumental effect—it’s pointing to real physics.”

    “While these two results taken together are very promising, the observed phenomena won’t be considered a true violation of the Standard Model without further experiments to verify our observations,” said co-author Gregory Ciezarek, a physicist at the Dutch National Institute for Subatomic Physics (NIKHEF).

    “We are planning a range of other measurements. The LHCb experiment is taking more data during the second run right now. We are working on upgrades to the LHCb detector within the next few years,” Jawahery said. “If this phenomenon is corroborated, we will have decades of work ahead. It could point theoretical physicists toward new ways to look at standard and non-standard physics.”

    With the discovery of the Higgs boson—the last major missing piece of the Standard Model—during the first LHC run, physicists are now looking for phenomena that do not conform to Standard Model predictions.

    Higgs Boson Event
    Higgs Boson event at CMS

    CERN CMS Detector
    CMS Detector in the LHC at CERN

    Jawahery and his colleagues are excited for the future, as the field moves into unknown territory.

    “Any knowledge from here on helps us learn more about how the universe evolved to this point. For example, we know that dark matter and dark energy exist, but we don’t yet know what they are or how to explain them. Our result could be a part of that puzzle,” Jawahery said. “If we can demonstrate that there are missing particles and interactions beyond the Standard Model, it could help complete the picture.”

    ###

    In addition to Jawahery and Hamilton, UMD Graduate Assistants Jason Andrews and Jack Wimberley are co-authors on the paper. The UMD LHCb team also includes Research Associate William Parker and Engineer Thomas O’Bannon, who are not coauthors on the paper.

    The research paper, “Measurement of the ratio of branching fractions…,” The LHCb Collaboration, is scheduled to appear online August 31, 2015 and to be published September 4, 2015 in the journal Physical Review Letters.

    See the full article here.

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    U Maryland Campus

    Driven by the pursuit of excellence, the University of Maryland has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

    The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

    Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

     
  • richardmitnick 7:53 pm on August 18, 2015 Permalink | Reply
    Tags: , CERN LHCb, , ,   

    From Don Lincoln at FNAL: “Pentaquarks” 

    CERN LHCb NewFNAL II photo

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

    FNAL Don Lincoln
    Don Lincoln

    Scientific research isn’t always simple; in fact, it’s often like rummaging around an unfamiliar room in the dark while wearing a blindfold. Under such conditions, it is inevitable that we have to make guesses about what we encounter. Sometimes those guesses turn out to be right and sometimes they don’t.

    This kind of exploratory research is especially true at the very frontier of human understanding and a recent announcement at the LHC [LHCb Collaboration] about a new form of matter called pentaquarks exemplifies this sort of investigation. The history of the search for pentaquarks involves previous observations that eventually faded under the light of more study. So what’s the deal with this recent announcement? Fermilab’s Dr. Don Lincoln tells us of the history of this interesting possible particle and gives us an idea of what we can expect in the near future.

    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 8:21 am on July 29, 2015 Permalink | Reply
    Tags: , , CERN LHCb, , , ,   

    From NOVA: “What the Heck is a Pentaquark?” 

    PBS NOVA

    NOVA

    28 Jul 2015
    FNAL Don Lincoln
    Don Lincoln

    What do you get when you combine four quarks and an antiquark?

    If you think this sounds like the opening of a particle physicists’ riddle, you aren’t too far off. Hypothetically, this particular quark combo makes a “pentaquark.” Despite decades of searching, physicists haven’t been able to actually find a pentaquark. Now, though, there’s a hint that two pentaquarks have unexpectedly come out of hiding.

    2
    Illustration of a possible layout of the quarks in a pentaquark particle such as those discovered at LHCb. © CERN

    If the new result holds up—a big if—the unexpected discovery would add a new species of particle to the standard model’s menagerie. But the measurements, recently announced by the team collaborating on the LHCb experiment, are truly perplexing.

    2
    LHCb on the LHC at CERN

    While the results were submitted for publication a couple of days ago, the first discussion in a large public conference occurred on July 23 at the 2015 meeting of the high energy physics division of the European Physical Society, where I had the opportunity to hear Sheldon Stone, who led the analysis, talk about the result. It’s certainly a topic of both excited and skeptical discussion here at the conference.

    Pentaquarks were first predicted in 1964 by Murray Gell-man and George Zweig in the separate and competing papers in which they first hypothesized the existence of quarks. (Gell-man’s name “quark” has stood the test of time, while Zweig independently proposed the now-defunct “aces.”) Physicists have looked for pentaquarks for a long time, unsuccessfully. We don’t know why there has been no evidence for their existence for so long. Maybe they don’t exist. Or maybe they do and the LHCb experiment has finally found them.

    Quarks are the building blocks of protons and neutrons and, as far as we know, they are the smallest basic units of matter. Quarks combine with other quarks according to the rules of quantum chromodynamics (QCD), which is the theory describing the behavior of the strong nuclear force, which is the strongest of the known subatomic forces. Pair a quark with an antiquark, and you’ve got a particle called a meson; three quarks make a baryon, like a proton or neutron. The new pentaquark—if it really is a pentaquark—seems to be made up of two up quarks, a down quark, and a charm quark/antiquark pair.

    The announcement is the latest chapter in a somewhat dubious story of now-you-see-now-you-don’t discovery. In 2002, scientists in Japan announced the discovery of a particle with a mass about 1.5 times that of a proton. They called it the Θ+, and argued that it was a kind of pentaquark. This announcement triggered a flurry of searches by other groups of experimenters, with some groups confirming the Θ+ and finding other particles that were claimed to be different pentaquark candidates, while other researchers found no evidence for any new particles at all. The excitement continued for three years until 2005, when the community decided that the original announcement was wrong. The death knell of the Θ+ sounded when a group of scientists at the Thomas Jefferson National Accelerator Facility (TJNAF) in Newport News, Virginia, repeated the initial Japanese measurement with far more data. The TJNAF scientists saw no evidence for the existence of the Θ+, and the community consigned it to the dustbin of history as one of many particle “discoveries” that ultimately didn’t pan out.

    The particles recently announced by the LHCb experiment aren’t the Θ+. Instead, the new particles have a mass of about 4.5 times that of the proton. The LHCb team wasn’t actually searching for pentaquarks when they made their measurements. Instead, they were studying how a particle called the Λb baryon decays. To their surprise, they found that a fraction of the time, some of the “daughter” particles left behind by the decay seemed to be coming from an unknown parent particle. So what the heck was it?

    3
    The LCHb team found the potential pentaquarks while investigating how a Λb baryon decays into a J/ψ meson and a Λ* baryon, which in turn decays into a K- meson and a proton (p+). In such a complicated decay mode, it is customary to look at the three daughter particles two at a time and calculate what the mass of the parent particle could have made them. In the case of the K- meson and a proton, you’d expect to see that they preferentially came from a particle with a mass of a Λ* baryon. Since the J/ψ and the proton weren’t thought to come from the decay of a single particle, you’d expect to see no particular mass looking special—but, as seen here, the researchers saw that a fraction of the time, these two particles seemed to come from a parent with a specific mass. Could pentaquarks be the culprit? Image adapted by Don Lincoln.

    The LHCb team was unable to reconcile their measurements with any of the known or predicted particles of the Standard Model.

    3
    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.

    They seemed to need something new. After testing out lots of hypotheses, they considered the discredited pentaquarks. (Remember that pentaquarks are a prediction of the theory of QCD, they’ve just never been seen before.) One pentaquark wasn’t enough to fit their data, but two did the trick. When they included two new pentaquark particles in their calculations, the data and theory agreed.

    The two new particles have an unusual amount of quantum mechanical spin, specifically 3/2 and 5/2. (Protons, neutrons and electrons are all spin ½.) Like all particles that are bound by the strong nuclear force and decay under its rules, they live for a very short time, specifically about 10-23 seconds.

    Given the checkered history of previous pentaquark searches, physicists are naturally skeptical. So it is worth dissecting the claim. The first question is whether scientists are confident that they’ve discovered some kind of new particle. Here, the claim is on firmer ground: the two detections have significance of nine and 12 standard deviations respectively. (The usual standard in particle physics to claim the discovery of a phenomenon is five standard deviations, and larger numbers mean more certainty. Nine and 12 are very strong numbers.)

    It’s less certain whether the new particles are really pentaquarks. There are good reasons for skepticism: For one thing, the makeup of the new pentaquarks—two ups, a down, and a charm quark/antiquark pair—seems improbable. It should be easier to make a pentaquark consisting of only up and down quarks, which are lighter than charm quarks, and such a particle has never been discovered. Discovering a charm pentaquark first feels like going fishing and pulling up two sharks and no trout. A second possibility is that the new discovery is actually a sort of “molecule”: a particle called a J/ψ attached to a proton, roughly similar to how a deuteron is a proton and neutron bound together. Both have the same quark content, but only “five things in a bag” qualifies as a “real” pentaquark.

    When I caught up with Sheldon Stone during the coffee break after his talk at the conference, he speculated that the higher mass of the charm quarks could make the resulting pentaquark more stable or perhaps somehow makes this sort of pentaquark more likely to form. He cautioned, however, that this was speculation on his part and more work would be required to substantiate these ideas.

    Theoretical physicists are likewise skeptical. Frank Wilczek, professor of physics at MIT and winner of the Nobel Prize in physics for his contributions to the development of the theory of QCD was excited about the possibility of the existence of the pentaquark, but cautious about the measurement.

    So what will it take for the community to embrace this exciting development? Well, as Carl Sagan is famous for noting, extraordinary claims require extraordinary evidence. It is also true that independent confirmation is key. Accordingly, other LHC experiments will try to repeat the analysis approach reported by the LHCb collaboration in order to see if their measurement can be replicated. In addition, theorists will try to see if they can find a mechanism within QCD that will explain why pentaquarks containing charm quarks are more likely to form than ones with lighter quarks.

    Now, taking a more personal perspective, what do I think? First, Sheldon Stone made a persuasive and thorough case at his talk. I think the LHCb experiment is a world class collaboration, with some of the finest minds on the planet and ample experience in the subject matter. Further, they are well aware of the history of the pentaquark and would not lightly propose this hypothesis without adequate care. However, I am very cautious of claims of this nature, especially without confirmation from other experiments. I think the only sensible approach is to view the claim charitably, but critically. Taking a phrase from President Ronald Reagan, I “trust, but verify.” I think the next few months will be very interesting.

    See the full article here.

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

     
  • richardmitnick 11:58 am on July 14, 2015 Permalink | Reply
    Tags: , CERN LHCb, , ,   

    From CERN: “CERN’s LHCb experiment reports observation of exotic pentaquark particles” 

    CERN New Masthead

    14 Jul 2015
    No Writer Credit

    Today, the LHCb experiment at CERN’s Large Hadron Collider has reported the discovery of a class of particles known as pentaquarks. The collaboration has submitted a paper reporting these findings to the journal Physical Review Letters.

    “The pentaquark is not just any new particle,” said LHCb spokesperson Guy Wilkinson. “It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over fifty years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we’re all made, is constituted.”

    Our understanding of the structure of matter was revolutionized in 1964 when American physicist, Murray Gell-Mann, proposed that a category of particles known as baryons, which includes protons and neutrons, are comprised of three fractionally charged objects called quarks, and that another category, mesons, are formed of quark-antiquark pairs. Gell-Mann was awarded the Nobel Prize in physics for this work in 1969. This quark model also allows the existence of other quark composite states, such as pentaquarks composed of four quarks and an antiquark. Until now, however, no conclusive evidence for pentaquarks had been seen.

    LHCb researchers looked for pentaquark states by examining the decay of a baryon known as Λb (Lambda b) into three other particles, a J/ψ- (J-psi), a proton and a charged kaon. Studying the spectrum of masses of the J/ψ and the proton revealed that intermediate states were sometimes involved in their production. These have been named Pc(4450)+ and Pc(4380)+, the former being clearly visible as a peak in the data, with the latter being required to describe the data fully.

    “Benefitting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states”, says LHCb physicist Tomasz Skwarnicki of Syracuse University.

    “More precisely the states must be formed of two up quarks, one down quark, one charm quark and one anti-charm quark.”

    Earlier experiments that have searched for pentaquarks have proved inconclusive. Where the LHCb experiment differs is that it has been able to look for pentaquarks from many perspectives, with all pointing to the same conclusion. It’s as if the previous searches were looking for silhouettes in the dark, whereas LHCb conducted the search with the lights on, and from all angles. The next step in the analysis will be to study how the quarks are bound together within the pentaquarks.

    “The quarks could be tightly bound,” said LHCb physicist Liming Zhang of Tsinghua University, “or they could be loosely bound in a sort of meson-baryon molecule, in which the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei.”

    More studies will be needed to distinguish between these possibilities, and to see what else pentaquarks can teach us. The new data that LHCb will collect in LHC run 2 will allow progress to be made on these questions.

    3
    2
    Illustration of the possible layout of the quarks in a pentaquark particle such as those discovered at LHCb. The five quarks might be tightly bonded (left). They might also be assembled into a meson (one quark and one antiquark) and a baryon (three quarks), weakly bound together. © CERN

    See the full article here.

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    Meet CERN in a variety of places:

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    THE FOUR MAJOR PROJECT COLLABORATIONS

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