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  • richardmitnick 3:56 pm on February 17, 2017 Permalink | Reply
    Tags: Accelerator Science, Bjorken x variable, , , HERA collider, How strange is the proton?, , , , , , Strong interactions   

    From CERN ATLAS: “How strange is the proton?” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    25th January 2017
    ATLAS Collaboration

    1
    Figure 1: The data ellipses illustrate the 68% CL coverage for the total uncertainties (full green) and total excluding the luminosity uncertainty (open black). Theoretical predictions based on various PDF sets are shown with open symbols of different colours. (Image: ATLAS Collaboration/CERN)

    The protons collided by the LHC are not elementary particles, but are instead made up of quarks, antiquarks and gluons. The theory of the strong interactions – quantum chromodynamics (QCD) – does not allow physicists to calculate the composition of protons from first principles. However, QCD can connect measurements made in different processes and at different energy scales such that universal “parton density functions” (PDFs) can be extracted. These determine the dynamic substructure of the proton.

    The discovery of quarks as the elements of the partonic structure of the proton dates about 50 years. Soon after QCD was born and the existence of gluons inside the proton was established. Much has since been learned through a combination of new experimental data and theoretical advances. At the LHC, reactions involve quarks or gluons that carry a certain fraction x of the proton’s momentum, expressed through the Bjorken x variable. Below x of 0.01, the proton constituents are mainly gluons and a sea of quark-antiquark pairs.

    Electron-proton scattering data from the HERA collider has constrained the gluon and the sum of all quarks weighted by the square of their electric charge.

    3
    Data from the HERA collider live on (Image: DESY Hamburg)

    4
    DESY map

    But the low x sea-quark composition – expressed in terms of the lighter quarks named up, down and strange quarks – is still not well understood. New data from the ATLAS experiment shows, with unprecedented precision, the production of W and Z bosons through the weak interaction. This sheds new light on the question: how “strange” the proton is at small x?

    The W production is detected through its decay into a charged lepton (electron or muon) and a neutrino, while the Z boson produces an electron-positron (or muon-antimuon) pair. The experimental detection of electrons and muons poses different challenges and thus the simultaneous measurement in both channels provides an important cross-check of the results, thus improving the final precision achieved. The integrated cross sections for Z boson and W boson production are measured with a precision of 0.3% and 0.6%, respectively, and with an additional common normalisation uncertainty from the luminosity determination of 1.8%. Differential cross sections are also measured in a variety of kinematic regions and about half of the measurement points have a precision of 1% or better.

    2
    Figure 2: Determination of the relative strange-to-light quark fraction R_s. Bands: Present result and its uncertainty contributions from experimental data, QCD fit, and theoretical uncertainties. Closed symbols with horizontal error bars: predictions from different NNLO PDF sets. Open square: previous ATLAS result. (Image: ATLAS Collaboration/CERN)

    The measurements are then compared to state-of-the-art QCD expectations using different PDF sets. Because the production of W and Z bosons through the weak interaction has a different dependence on the specific quark flavours compared to the electromagnetic interaction seen in electron-positron scattering at HERA, analysing both data sets gives new access to the strange quark content of the proton.

    As is shown in Figure 1, the measured production rate of W bosons is very similar for all PDF sets, in good agreement with the data. In contrast, the rate for Z boson production is underestimated significantly for most PDF sets. A dedicated analysis enables this deficit to be attributed to a too small strange quark contribution in most PDF sets. The new PDF set, which this paper presents, requires the strange quark sea to be of a similar size as the up and down quark sea. This is summarised by the quantity RS, which is the ratio of the strange quark sea to the up and down quark sea, and which is found to be close to one, as shown in Figure 2. This result is a striking confirmation of the hypothesis of a light-flavour symmetry of proton structure at low x. This result will generate many further studies, because hitherto there had been indications from low energy neutrino-scattering data that favoured a suppressed strange-quark contribution with respect to the up and down quark parts, leading to an RS close to 0.5.

    The analysis also shows that the potential to which precise W and Z cross sections can provide useful constraints on PDFs is not limited by the now very high experimental precision, but rather by the uncertainty of the currently available theory calculations. The salient results of this paper are thus of fundamental importance for forthcoming high-precision measurements, such as the mass of the W boson, and also represent a strong incentive for further improving the theory of Drell-Yan scattering in proton-proton collisions.

    Links:

    Precision measurement and interpretation of inclusive W+, W− and Z/γ∗ production cross sections with the ATLAS detector, https://arxiv.org/abs/1612.03016

    See the full article here .

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

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  • richardmitnick 10:17 am on February 16, 2017 Permalink | Reply
    Tags: Accelerator Science, , , , , , , SCOAP³,   

    From The Conversation: “How the insights of the Large Hadron Collider are being made open to everyone” 

    Conversation
    The Conversation

    January 12, 2017 [Just appeared in social media.]
    Virginia Barbour

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    If you visit the Large Hadron Collider (LHC) exhibition, now at the Queensland Museum, you’ll see the recreation of a moment when the scientist who saw the first results indicating discovery of the Higgs boson laments she can’t yet tell anyone.

    It’s a transitory problem for her, lasting as long as it takes for the result to be thoroughly cross-checked. But it illustrates a key concept in science: it’s not enough to do it; it must be communicated.

    That’s what is behind one of the lesser known initiatives of CERN (European Organization for Nuclear Research): an ambitious plan to make all its research in particle physics available to everyone, with a big global collaboration inspired by the way scientists came together to make discoveries at the LHC.

    This initiative is called SCOAP³, the Sponsoring Consortium for Open Access in Particle Physics Publishing, and is now about to enter its fourth year of operation. It’s a worldwide collaboration of more than 3,000 libraries (including six in Australia), key funding agencies and research centres in 44 countries, together with three intergovernmental organisations.

    It aims to make work previously only available to paying subscribers of academic journals freely and immediately available to everyone. In its first three years it has made more than 13,000 articles available.

    Not only are these articles free for anyone to read, but because they are published under a Creative Commons attribution license (CCBY), they are also available for anyone to use in anyway they wish, such as to illustrate a talk, pass onto a class of school children, or feed to an artificial intelligence program to extract information from. And these usage rights are enshrined forever.

    The concept of sharing research is not new in physics. Open access to research is now a growing worldwide initiative, including in Australasia. CERN, which runs the LHC, was also where the world wide web was invented in 1989 by Tim Berners-Lee, a British computer scientist at CERN.

    The main purpose of the web was to enable researchers contributing to CERN from all over the world share documents, including scientific drafts, no matter what computer systems they were using.

    Before the web, physicists had been sharing paper drafts by post for decades, so they were one of the first groups to really embrace the new online opportunities for sharing early research. Today, the pre-press site arxiv.org has more than a million free article drafts covering physics, mathematics, astronomy and more.

    But, with such a specialised field, do these “open access” papers really matter? The short answer is “yes”. Downloads have doubled to journals participating in SCOAP³.

    With millions of open access articles now being downloaded across all specialities, there is enormous opportunity for new ideas and collaborations to spring from chance readership. This is an important trend: the concept of serendipity enabled by open access was explored in 2015 in an episode of ABC RN’s Future Tense program.

    Greater than the sum of the parts

    There’s also a bigger picture to SCOAP³’s open access model. Not long ago, the research literature was fragmented. Individual papers and the connections between them were only as good as the physical library, with its paper journals, that academics had access to.

    Now we can do searches in much less time than we spend thinking of the search question, and the results we are presented with are crucially dependent on how easily available the findings themselves are. And availability is not just a function of whether an article is free or not but whether it is truly open, i.e. connected and reusable.

    One concept is whether research is “FAIR”, or Findable, Accessible, Interoperable and Reusable. In short, can anyone find, read, use and reuse the work?

    The principle is most advanced for data, but in Australia work is ongoing to apply it to all research outputs. This approach was also proposed at the November 2016 meeting of the G20 Science, Technology and Innovation Ministers Meeting. Research findings that are not FAIR can, effectively, be invisible. It’s a huge waste of millions of taxpayer dollars to fund research that won’t be seen.

    There is an even bigger picture that research and research publications have to fit into: that of science in society.

    Across the world we see politicians challenging accepted scientific norms. Is the fact that most academic research remains available only to those who can pay to see it contributing to an acceptance of such misinformed views?

    If one role for science is to inform public debate, then restricting access to that science will necessarily hinder any informed public debate. Although no one suggests that most readers of news sites will regularly want to delve into the details of papers in high energy physics, open access papers are 47% more likely to end up being cited in Wikipedia, which is a source that many non-scientists do turn to.

    Even worse, work that is not available openly now may not even be available in perpetuity, something that is being discussed by scientists in the USA.

    So in the same way that CERN itself is an example of the power of international collaboration to ask some of the fundamental scientific questions of our time, SCOAP³ provides a way to ensure that the answers, whatever they are, are available to everyone, forever.

    See the full article here .

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    The Conversation US launched as a pilot project in October 2014. It is an independent source of news and views from the academic and research community, delivered direct to the public.
    Our team of professional editors work with university and research institute experts to unlock their knowledge for use by the wider public.
    Access to independent, high quality, authenticated, explanatory journalism underpins a functioning democracy. Our aim is to promote better understanding of current affairs and complex issues. And hopefully allow for a better quality of public discourse and conversation.

     
  • richardmitnick 2:30 pm on February 14, 2017 Permalink | Reply
    Tags: Accelerator Science, , , ,   

    From CERN ALICE: “QGP: 17 years after the public announcement…” 

    CERN
    CERN New Masthead

    CERN ALICE Icon HUGE

    31 January 2017
    Virginia Greco

    Interview with Luciano Maiani, DG of CERN from 1999 to 2003, who gave the announcement talk of the discovery of QGP at the SPS.

    CERN  Super Proton Synchrotron
    CERN Super Proton Synchrotron

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    About 25 years after its first theoretical prediction, the new state of matter called quark-gluon plasma (QGP) was observed at CERN’s SPS. The public announcement was made on the 10th of February 2000 by Luciano Maiani, Director General of CERN back then. At the event organized by ALICE to celebrate the 30-year anniversary of the first heavy-ion collisions at the SPS, Maiani gave his account of this piece of history of physics.

    We had an interview with him after the seminar.

    After one year of mandate as DG of CERN you had the honour and the responsibility to announce that evidence of the existence of QGP had been found at the SPS. How did you live these happenings?

    At that time I was not an expert in heavy ion physics, because I hadn’t worked in the field. Nevertheless, I was aware of the phase transition issue and of the two existing visions about what happens to nuclear matter at very high temperature. On one side there was the theory that matter would break down into a gas of quarks and gluons (and temperature could be freely increased), on the other side the model of Hagedorn about the existence of an upper limit of the temperature reachable, which could be estimated from the hadron spectrum to be 170-180 MeV.

    With the development of QCD it was possible to combine these two models. In particular, in 1975 Nicola Cabibbo and Giorgio Parisi suggested that the Hagedorn limit temperature is just the critical temperature of a phase transition from a gas of hadrons, made of confined quarks, to a gas of deconfined quarks and gluons (the QGP). These works had convinced the experts in the field.

    When the moment came to decide whether to make a public announcement about what the SPS had found, I discussed with many of the people involved, such as Claude Detraz, who was Director for Fixed Target and Future Programmes during my mandate, Reinhard Stock and Hans Specht. After examining the data and collecting opinions, I concluded that we had convincing signals that what we were observing was indeed the quark-gluon plasma.

    But the public announcement was cautious, wasn’t it? Was there still some doubt?

    I think that the announcement was quite clear. I have the text of it with me, it reads: “The data provide evidence for colour deconfinement in the early collision stage and for a collective explosion of the collision fireball in its late stages. The new state of matter exhibits many of the characteristic features of the theoretically predicted Quark-Gluon Plasma.” The key word is “evidence”, not discovery, and the evidence was there, indeed.

    In the talk I gave at that time I also described the concept of quark deconfinement using an analogy with the snow on the Jura Mountain, which I particularly like. We can consider a quark as a skier: when the temperature is not very low, on the mountain there are only patches of snow in which the skier can move. When the temperature decreases and the snow increases, the skier can move along bigger and bigger spaces, up to a point where he or she can freely sweep long distances. The same can be said for a quark confined in a hadron (the patch), which becomes free when temperature increases.

    Of course at that moment the idea still popular was that we were dealing with a phase transition to a gaseous state in which quarks and gluons would be asymptotically free. Later RHIC showed that the situation is more complicated and that this new state is much more like a liquid with very low viscosity rather than like a gas.

    The announcement came just a few months before the start of the programme of RHIC. Were there some polemics about this “timing”?

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    The Solenoidal Tracker at the Relativistic Heavy Ion Collider (RHIC)

    We were almost at the conclusion of a long and accurate experimental programme at the SPS, so making a summing up was needed. In addition, as I said, we thought there were the elements for a public announcement. And this has been proved right by later experiments.

    Somebody thought that it would make RHIC, which was going to enter in operation, appear useless. But that was not the case, since much more was left to study. Indeed in the same announcement talk I said: “the higher energies of RHIC and LHC are needed to complete the picture and provide a full characterization of the Quark-Gluon Plasma”.

    In your opinion, what is the future of this branch of research?

    Well, there are still many open problems, things that need to be studied further.

    It is very important to explore the properties of this new state of matter and the connected phenomena, to get a more precise physical picture of the new state.

    Personally, I think that there is also another possible line of research in this field: to study the production of those exotic hadronic resonances that are not included in the scheme of baryons and mesons (i.e. three quarks or quark-antiquark structures). These resonances have been observed in CMS and LHCb in pp collisions, and it would be interesting to study how they are produced in heavy-ion collisions. It could give us indications about what these objects are, tell us if they are molecules made of colourless hadrons or new states which are configurations of quarks and antiquarks (different from mesons) that include subcomponents connected by colour bounds.

    ALICE could provide an important contribution to this research. It is not easy to observe such exotic states in heavy-ion collisions but I think it is worth trying.

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    No image caption. No image credit.

    An iconic view of the universe
    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    See the full article here .

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    Meet CERN in a variety of places:

    CernCourier
    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

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

    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.

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    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

    Cern Courier

    CernCourier
    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 2:36 pm on February 10, 2017 Permalink | Reply
    Tags: Accelerator Science, , , , Electron-Ion Collider possibly opening a new frontier in nuclear physics., Exploring the Matter that Filled the Early Universe, , , , Quark Matter 2017 conference (QM17), , Ultrarelativistic heavy-ion collisions   

    From BNL: “Exploring the Matter that Filled the Early Universe” 

    Brookhaven Lab

    February 6, 2017
    Karen McNulty Walsh
    kmcnulty@bnl.gov

    (631) 344-8350
    Peter Genzer
    (631) 344-3174
    genzer@bnl.gov

    1
    Credit for conference logo design: Anjali Chandrashekar, student, Pratt Institute

    Theorists and scientists conducting experiments that recreate matter as it existed in the very early universe are gathered in Chicago this week to present and discuss their latest results. These experiments, conducted at the world’s premier particle colliders — the Relativistic Heavy Ion Collider (RHIC) at the U.S. Department of Energy’s Brookhaven National Laboratory, and the Large Hadron Collider (LHC) at the European Center for Nuclear Research (CERN) — are revealing intriguing information about the building blocks of visible matter and the force that holds them together in the universe today.

    BNL RHIC Campus
    BNL/RHIC Star Detector
    RHIC map and STAR detector

    CERN/LHC Map
    CERN LHC Grand TunnelCERN LHC particles
    LHC at CERN

    The Quark Matter 2017 conference (QM17) will feature new results describing the particles created as atomic nuclei smash into one another at nearly the speed of light at RHIC and the LHC. These “ultrarelativistic heavy-ion collisions” melt ordinary protons and neutrons, momentarily setting free their inner constituents — quarks and gluons — so scientists can study their behavior and interactions. The physicists want to sort out the detailed properties of the hot “quark-gluon plasma” (QGP), and understand what happens as this primordial soup cools and coalesces to form the more familiar matter of today’s world.

    The two scientific collaborations conducting nuclear physics research at RHIC—STAR and PHENIX, named for their house-sized detectors—will present findings that build on earlier discoveries at this DOE Office of Science User Facility.

    Brookhaven Phenix
    Brookhaven Phenix

    The two collaborations perform cross-checking analyses to verify results, while also exploiting each detector’s unique capabilities and strengths for independent explorations. The QM17 presentations will showcase precision measurements made possible by recent detector upgrades.

    “These results illustrate how a global community of dedicated scientists is taking full advantage of RHIC’s remarkable versatility to explore in depth the structure of nuclear matter over a wide range of temperatures and densities to better understand the dynamic behavior of quarks and gluons and the strong nuclear force,” said Berndt Mueller, Associate Laboratory Director for Nuclear and Particle Physics at Brookhaven Lab. “The latest RHIC findings indicate that RHIC sits at the ‘sweet spot’ for probing the most interesting questions about the quark-gluon plasma and its transition to matter as we know it.”

    The meeting will also feature talks on the planned upgrade of the PHENIX experiment to a new RHIC detector known as sPHENIX, which will have greatly increased capabilities for tracking subatomic interactions.

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    The solenoid magnet that will form the core of the sPHENIX detector. No image credit

    In addition, at least one talk will focus on the scientific rationale for building an Electron-Ion Collider, a proposed future facility that would enable an in-depth exploration of gluons in protons and other nuclei, opening a new frontier in nuclear physics.

    In addition, at least one talk will focus on the scientific rationale for building an Electron-Ion Collider, a proposed future facility that would enable an in-depth exploration of gluons in protons and other nuclei, opening a new frontier in nuclear physics.

    Select QM 2017 Highlights from RHIC

    Does size really matter?

    Before RHIC began operations in 2000, nuclear physicists suspected it would take collisions of large nuclei such as gold to produce enough heat to create quark-gluon plasma. Since then, RHIC’s gold-gold smashups (and later collisions of lead nuclei at the LHC) have reliably recreated a soup of quarks and gluons that flows like a nearly “perfect” liquid with extraordinarily low viscosity. Scientists detect the flow by observing correlations in certain characteristics of particles streaming from the collisions even when they are relatively far apart. More recently, smashups of smaller nuclei such as helium and even single protons with the large nuclei have produced correlation patterns that suggest that smaller drops of QGP might be possible. The latest results, to be presented by PHENIX, come from collisions of protons with aluminum nuclei, and also from deuteron-gold collisions over a range of collision energies. Lowering the energy changes how long the QGP phase lasts, which should change the strength of the correlations. The new results also include the first analysis of particles emerging closest to the colliding beams in the forward and rearward directions, as tracked by the recently installed Forward Silicon Vertex Tracker. Adding this tracker to detector components picking up particles emerging more centrally, perpendicular to the colliding beams, gives the physicists a way to test in three dimensions how the correlations vary with the pressure gradients created by the asymmetrical collisions.

    Discerning differences among heavy quarks


    A virtual tour of the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC).

    PHENIX’s Central Barrel and Forward Silicon Vertex Tracker and STAR’s high precision Heavy Flavor Tracker (HFT) give RHIC physicists access to studying the behavior of so-called heavy quarks, which go by the exotic names of “charm” and “bottom.” These particles, produced in the QGP, start to decay into other particles a short distance from the collision zone, but those decay products eventually strike the trackers. By tracing their tracks, scientists can identify precisely where the decay took place. And since charm and bottom quarks have slightly different lifetimes before decaying, and therefore different travel distances, this method gives the scientists a way to tell them apart.

    Going with the flow

    One way scientists will use this data is to see how heavy quarks are affected by the QGP, and whether there are differences among them. Earlier indirect findings by PHENIX, later confirmed by STAR, already indicated that heavy quarks get swept up in the flow of the QGP, somewhat like a rock getting pulled along by a stream instead of sinking to the bottom. These observations formed part of the motivation for the construction of the STAR HFT. New data from the HFT to be presented by STAR provide the first direct evidence of heavy quark flow, and show that the interactions of these heavy particles with the QGP medium are strong. STAR’s HFT is the first application of the silicon based Monolithic Active Pixel Sensor technology in a collider environment. The measurements show that the flow of a type of heavy particles called D0s, which contain a charm quark, follows the same trend as seen for lighter particles and can be described by the same viscous hydrodynamics. The unprecedented precision in this measurement will pave the path towards precisely determining one of the intrinsic transport properties of the QGP and tell us how quarks interact with it.

    PHENIX will present precision results from its Central Barrel Vertex Detector showing that some heavy quarks are more affected by the QGP than others. The results show that charm quarks lose more energy in the QGP than heavier bottom quarks. With this high statistics data set, PHENIX will now be able to study how the energy-loss is affected by how central, or head-on, the collisions are. PHENIX will also present its first heavy-quark result from the Forward Silicon Vertex Tracker, measuring the total cross section of bottom quarks emerging in the forward and rearward directions in collisions between copper and gold ions.

    Learning how particles grow


    A virtual tour of the STAR detector at the Relativistic Heavy Ion Collider (RHIC).

    The STAR HFT has also made it possible to make the first measurements of a particle called Lambda c emerging from RHIC collisions. Lambda c is made of three quarks—just like protons and neutrons—but with one of the three being a heavy quark. These Lambda c particles are extremely difficult to tease out from the data. But because they can only be created in energetic particle collisions, they carry unique information about the conditions within. Studying this “sentry” information carried by the Lambda c should help scientists learn how relatively “free” quarks that populate the early-stage QGP eventually coalesce and combine to form the more familiar composite particles of ordinary matter.

    Tracking high-momentum jets

    Observing how jets of particles springing from individual quarks or gluons lose energy, or get “quenched,” as they interact with the medium has been one major sign that RHIC’s energetic collisions of gold on gold were forming QGP. STAR will present several new jet studies that provide further insights into both how this quenching occurs and how the lost energy re-emerges, In addition, PHENIX will present new results exploring the question of whether collisions of smaller particles with gold, which appear to create the flow patterns of QGP, also show evidence of jet quenching. Their results include data on jet energy loss in a variety of collision systems, both large and small. The method uses photons emitted opposite the jet to calibrate how much energy the jet should have to determine whether or not there was quenching. The data show some modifications to the jet structure and the yield of high-momentum particles inside the jets, but it is not yet clear how to interpret these results.

    Taking the QGP’s temperature

    Tracking heavy quarks and particles made from them gives RHIC physicists a new way to zero in on a more precise temperature of the QGP—already known to be more than 250,000 times hotter than the center of the sun. The new precision comes from measuring how different bound states of heavy quark-antiquark pairs, held together with different amounts of energy, melt in the plasma. STAR counts up different types of these particles (for example, Upsilons, pairs of bottom and anti-bottom quarks, that come in several binding varieties) using another recently upgraded detector component called the Muon Telescope Detector. Muons are the decay products of the Upsilons. STAR uses these counts to look for a deficit of one type of Upsilon relative to another to set boundaries on the QGP temperature. The physicists are eager to compare their results with those from the LHC, where with higher collision energies, they expect to see higher temperatures.

    PHENIX’s measurements of temperature have relied on tracking photons, particles of light, emitted from the hot matter (think of the glow of an iron bar in a blacksmith’s fire, where the color of the light is related to how hot the iron is). But PHENIX’s photon data have uncovered something unusual: While collisions initially emit photons equally in all directions, fractions of a second later the emitted photons appear to have a directional preference that resembles the elliptical flow pattern of the perfect liquid QGP. This is intriguing because photons shouldn’t interact with the matter—or even be produced in such measurable quantities as the matter produced in the collisions cools and expands. To explore this mystery, PHENIX measured thermal direct photons at different gold-gold collision energies (39, 62, and 200 billion electron volts, or GeV), as well as in the smaller collision system. The results they present will shed light on the sources of these direct photons.

    Disentangling the effects of cold nuclear matter

    RHIC physicists are also learning more about “cold” nuclear matter—the state of the nucleus, filled with a field of gluons, before it collides—and how to account for its effects when studying the hot QGP. In order to disentangle the effects of cold nuclear matter, PHENIX is comparing the suppression of the excited state of the bound charm-anti-charm particle known as Psi to its ground state. They are studying collisions of protons and helium with gold or aluminum—small systems where cold nuclear matter predominates—and will use these as a baseline for better understanding the sequential melting of the bound states in the hot QGP. Their findings indicate that the less tightly bound version of the Psi is more than twice as susceptible to the effects of cold nuclear matter than the more tightly bound version. This effect must be accounted for in analyzing the data from QGP-creating collisions where the presence of both cold and hot nuclear matter influences the results.

    New way to turn down the energy

    STAR has exploited RHIC’s ability to collide nuclei over a wide range of collision energies, conducting a Beam Energy Scan to explore the creation of QGP and its transition to ordinary nuclear matter over a wide range of conditions. At QM17 they’ll present data from collisions at the lowest energy yet. Instead of colliding one beam into the beam coming into the detector from the opposite direction, as occurs in most RHIC experiments, STAR placed a stationary target (a foil of gold) within the beam pipe inside STAR and aimed just one beam at the target. Like a collision in which one moving car crashes into one that is parked, this fixed-target collision lowered the impact compared to what would occur if both beams (or cars) were moving and colliding head on. Data from these low energy collisions will be an integral part of phase two of the Beam Energy Scan, which is enabled by improvements to the RHIC accelerator complex that allow for higher collision rates.

    Research at RHIC is funded primarily by the U.S. Department of Energy’s Office of Science and by these agencies and organizations.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition
    BNL Campus

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

     
  • richardmitnick 2:31 pm on February 5, 2017 Permalink | Reply
    Tags: Accelerator Science, , , , , , ,   

    From CERN via futurism: “Scientists May Have Solved the Biggest Mystery of the Big Bang” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    1

    futurism

    February 2, 2017
    Chelsea Gohd

    The Unanswered Question

    The European Council for Nuclear Research (CERN) works to help us better understand what comprises the fabric of our universe. At this French association, engineers and physicists use particle accelerators and detectors to gain insight into the fundamental properties of matter and the laws of nature. Now, CERN scientists may have found an answer to one of the most pressing mysteries in the Standard Model of Physics, and their research can be found in Nature Physics.

    According to the Big Bang Theory, the universe began with the production of equal amounts of matter and antimatter. Since matter and antimatter cancel each other out, releasing light as they destroy each other, only a minuscule number of particles (mostly just radiation) should exist in the universe. But, clearly, we have more than just a few particles in our universe. So, what is the missing piece? Why is the amount of matter and the amount of antimatter so unbalanced?


    Access mp4 video here .

    The Standard Model of particle physics does account for a small percentage of this asymmetry, but the majority of the matter produced during the Big Bang remains unexplained.

    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.

    Noticing this serious gap in information, scientists theorized that the laws of physics are not the same for matter and antimatter (or particles and antiparticles). But how do they differ? Where do these laws separate?

    This separation, known as charge-parity (CP) violation, has been seen in hadronic subatomic particles (mesons), but the particles in question are baryons. Finding evidence of CP violation in these particles would allow scientists to calculate the amount of matter in the universe, and answer the question of why we have an asymmetric universe. After decades of effort, the scientists at CERN think they’ve done just that.

    Using a Large Hadron Collider (LHC) detector, CERN scientists were able to witness CP violation in baryon particles. When smashed together, the matter (Λb0) and antimatter (Λb0-bar) versions of the particles decayed into different components with a significant difference in the quantities of the matter and antimatter baryons. According to the team’s report, “The LHCb data revealed a significant level of asymmetries in those CP-violation-sensitive quantities for the Λb0 and Λb0-bar baryon decays, with differences in some cases as large as 20 percent.”


    Access mp4 video here .

    What Does This Mean?

    This discovery isn’t yet statistically significant enough to claim that it is definitive proof of a CP variation, but most believe that it is only a matter of time. “Particle physics results are dragged, kicking and screaming, out of the noise via careful statistical analysis; no discovery is complete until the chance of it being a fluke is below one in a million. This result isn’t there yet (it’s at about the one-in-a-thousand level),” says scientist Chris Lee. “The asymmetry will either be quickly strengthened or it will disappear entirely. However, given that the result for mesons is well and truly confirmed, it would be really strange for this result to turn out to be wrong.”

    This borderline discovery is one huge leap forward in fully understanding what happened before, during, and after the Big Bang. While developments in physics like this may seem, from the outside, to be technical achievements exciting only to scientists, this new information could be the key to unlocking one of the biggest mysteries in modern physics. If the scientists at CERN are able to prove that matter and antimatter do, in fact, obey separate laws of physics, science as we know it would change and we’ll need to reevaluate our understanding of our physical world.

    See the full article here.

    Please help promote STEM in your local schools.

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    Meet CERN in a variety of places:

    Cern Courier
    CernCourier
    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 1:58 pm on January 27, 2017 Permalink | Reply
    Tags: Accelerator Science, Fermilab achieves milestone beam power for neutrino experiments, , , Main Injector, , , ,   

    From FNAL: “Fermilab achieves milestone beam power for neutrino experiments” 

    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.

    January 26, 2017
    Ricarda Laasch

    1
    Thanks to recent upgrades to the Main Injector, Fermilab’s flagship accelerator, Fermilab scientists have produced 700-kilowatt proton beams for the lab’s experiments. Photo: Peter Ginter

    Fermilab’s accelerator is now delivering more neutrinos to experiments than ever before.

    The U.S. Department of Energy’s Fermi National Accelerator Laboratory has achieved a significant milestone for proton beam power. On Jan. 24, the laboratory’s flagship particle accelerator delivered a 700-kilowatt proton beam over one hour at an energy of 120 billion electronvolts.

    The Main Injector accelerator provides a massive number of protons to create particles called neutrinos, elusive particles that influence how our universe has evolved. Neutrinos are the second-most abundant matter particles in our universe. Trillions pass through us every second without leaving a trace.

    Because they are so abundant, neutrinos can influence all kinds of processes, such as the formation of galaxies or supernovae. Neutrinos might also be the key to uncovering why there is more matter than antimatter in our universe. They might be one of the most valuable players in the history of our universe, but they are hard to capture and this makes them difficult to study.

    “We push always for higher and higher beam powers at accelerators, and we are lucky our accelerator colleagues live for a challenge,” said Steve Brice, head of Fermilab’s Neutrino Division. “Every neutrino is an opportunity to study our universe further.”

    With more beam power, scientists can provide more neutrinos in a given amount of time. At Fermilab, that means more opportunities to study these subtle particles at the lab’s three major neutrino experiments: MicroBooNE, MINERvA and NOvA.

    FNAL/MicrobooNE
    FNAL/MicrobooNE

    FNAL/MINERvA
    FNAL/MINERvA

    FNAL/NOvA experiment
    FNAL/NOvA map

    FNAL NOvA Near Detector
    FNAL NOvA Near Detector

    “Neutrino experiments ask for the world, if they can get it. And they should,” said Dave Capista, accelerator scientist at Fermilab. Even higher beam powers will be needed for the future international Deep Underground Neutrino Experiment, to be hosted by Fermilab. DUNE, along with its supporting Long-Baseline Neutrino Facility, is the largest new project being undertaken in particle physics anywhere in the world since the Large Hadron Collider.

    FNAL DUNE Argon tank at SURF
    FNAL DUNE Argon tank at SURF
    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA
    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    “It’s a negotiation process: What is the highest beam power we can reasonably achieve while keeping the machine stable, and how much would that benefit the neutrino researcher compared to what they had before?” said Fermilab accelerator scientist Mary Convery.

    “This step-by-step journey was a technical challenge and also tested our understanding of the physics of high-intensity beams,” said Fermilab Chief Accelerator Officer Sergei Nagaitsev. “But by reaching this ambitious goal, we show how great the team of physicists, engineers, technicians and everyone else involved is.” The 700-kilowatt beam power was the goal declared for 2017 for Fermilab’s accelerator-based experimental program.

    Particle accelerators are complex machines with many different parts that change and influence the particle beam constantly. One challenge with high-intensity beams is that they are relatively large and hard to handle. Particles in accelerators travel in groups referred to as bunches.

    Roughly one hundred billion protons are in one bunch, and they need their space. The beam pipes – through which particles travel inside the accelerator – need to be big enough for the bunches to fit. Otherwise particles will scrape the inner surface of the pipes and get lost in the equipment.

    2
    The Main Injector, a 2-mile-circumference racetrack for protons, is the most powerful particle accelerator in operation at Fermilab. It provides proton beams for various particle physics experiments as well as Fermilab Test Beam Facility. Photo: Reidar Hahn

    Such losses, as they’re called, need to be controlled, so while working on creating the conditions to generate a high-power beam, scientists also study where particles get lost and how it happens. They perform a number of engineering feats that allow them to catch the wandering particles before they damage something important in the accelerator tunnel.

    To generate high-power beams, the scientists and engineers at Fermilab use two accelerators in parallel. The Main Injector is the driver: It accelerates protons and subsequently smashes them into a target to create neutrinos. Even before the protons enter the Main Injector, they are prepared in the Recycler.

    The Fermilab accelerator complex can’t create big bunches from the get-go, so scientists create the big bunches by merging two smaller bunches in the Recycler. A small bunch of protons is sent into the Recycler, where it waits until the next small bunch is sent in to join it. Imagine a small herd of cattle, and then acquiring a new herd of the same size. Rather than caring for them separately, you allow the two herds to join each other on the big meadow to form a big herd. Now you can handle them as one herd instead of two.

    In this way Fermilab scientists double the number of particles in one bunch. The big bunches then go into the Main Injector for acceleration. This technique to increase the number of protons in each bunch had been used before in the Main Injector, but now the Recycler has been upgraded to be able to handle the process as well.

    “The real bonus is having two machines doing the job,” said Ioanis Kourbanis, who led the upgrade effort. “Before we had the Recycler merging the bunches, the Main Injector handled the merging process, and this was time consuming. Now, we can accelerate the already merged bunches in the Main Injector and meanwhile prepare the next group in the Recycler. This is the key to higher beam powers and more neutrinos.”

    Fermilab scientists and engineers were able to marry two advantages of the proton acceleration technique to generate the desired truckloads of neutrinos: increase the numbers of protons in each bunch and decrease the delivery time of those proton to create neutrinos.

    “Attaining this promised power is an achievement of the whole laboratory,” Nagaitsev said. “It is shared with all who have supported this journey.”

    The new heights will open many doors for the experiments, but no one will rest long on their laurels. The journey for high beam power continues, and new plans for even more beam power are already under way.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    FNAL Icon
    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 3:11 pm on January 26, 2017 Permalink | Reply
    Tags: Accelerator Science, , CERN Robots, , TIM - Train Inspection Monorail   

    From Symmetry: “The robots of CERN” 

    Symmetry Mag

    Symmetry

    01/26/17
    Sarah Charley

    1
    Mario di Castro, CERN
    TIM and other mechanical friends tackle jobs humans shouldn’t.

    The Large Hadron Collider is the world’s most powerful particle accelerator. Buried in the bedrock beneath the Franco-Swiss boarder, it whips protons through its nearly 2000 magnets 11,000 times every second.

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

    As you might expect, the subterranean tunnel which houses the LHC is not always the friendliest place for human visitors.

    “The LHC contains 120 tons of liquid helium kept at 1.9 Kelvin,” says Ron Suykerbuyk, an LHC operator. “This cooling system is used to keep the electromagnets in super conducting state capable of carrying up to 13,000 Amps of current through its wires. Even with all the safety systems we have in place, we prefer to limit our underground access when the cryogenic systems are on”.

    But as with any machine, sometimes the LHC needs attention: inspections, repairs, tuning. The LHC is so secure that even with perfect conditions, it takes 30 minutes after the beam is shut off for the first humans to even arrive at the entrance to the tunnel.

    But the robotics team at CERN asks: Why do we need humans for this job anyway?

    Enter TIM—the Train Inspection Monorail. TIM is a chain of wagons, sensors and cameras that snake along a track bolted to the LHC tunnel’s ceiling. In the 1990s, the track held a cable car that transported machinery and people around the Large Electron-Position Collider, the first inhabitant of the tunnel.

    CERN LEP Collider
    CERN LEP Collider

    With the installation of the LHC, there was no longer room for both accelerator and the cable car, so the monorail was reconfigured for the sleeker TIM robots.

    There are currently two TIM robots and plans to install two more in the next couple of years. These four TIM robots will patrol the different quadrants of the LHC, enabling operators to reach any part of the 17-mile tunnel within 20 minutes. As TIM slithers along the ceiling, an automated eye keeps watch for any changes in the tunnel and a robotic arm drops down to measure radiation. Other sensors measure the temperature, oxygen level and cell phone reception.

    “In addition to performing environmental measurements, TIM is a safety system which can be the eyes and ears for members of the CERN Fire Brigade and operations team,” says Mario Di Castro, the leader of CERN’s robotics team. “Eventually we’d like to equip TIM with a fire extinguisher and other physical operations so that it can be the first responder in case of a crisis.”

    TIM isn’t alone in its mission to provide a safer environment for its human coworkers. CERN also has three teleoperated robots that can assess troublesome areas, provide assessments of hazards and carry tools.

    The main role of these three robots is to access radioactive areas.

    Radiation is a type of energy carried by free-moving subatomic particles. As protons race around CERN’s accelerator complex, special equipment called collimators constrict their passage and absorb particles that have wondered away from the center of the beam pipe. This trimming process ensures that the proton stream is compact and tidy.

    After a couple weeks of operation, the collimators have absorbed so many particles that they will reemit their energy—even after the beam is shut off. There is no radiation hazard to humans unless they are within a few meters of the collimators, and because the machine is fully automated, humans rarely need to perform check-ups. But occasionally, material in these restricted areas required attention.

    By replacing humans with robots, engineers can quickly fix small problems without needing to wait long periods of time for the radiation to dissipate or sending personnel into potentially unsafe environments.

    “CERN robots help perform repetitive and dangerous tasks that humans either prefer to avoid or are unable to do because of hazards, size constraints or the extreme environments in which they take place, such CERN experimental areas,” Di Castro says.

    About half the time, these tasks are very simple, such as performing a visual assessment of the area or taking measurements. “Robots can replace humans for these simple tasks and improve the quality and timeliness of work,” he says.

    Last year the SPS accelerator (which starts the acceleration process for particles that eventually move to the LHC) needed an oil refill to keep its parts running smoothly.
    But the accelerator itself was too radioactive for humans to visit, so one of the CERN robotics team’s robots rolled in gripping an oil can in its flexible arm.

    In June 2016, scientists needed to dispose of radioactive Cobalt, Cesium and Americium they had used to calibrate radiation sensors. Two CERN robots cycled in with several tools, extracted the radioactive sources and packed them in thick protective containers for removal.

    Over the last two years, these two robots have performed more than 30 interventions, saving humans both time and radiation doses.

    As the LHC increases the power and particle collisions over the next decade, Di Castro and his team are preening these robot companions to increase their capabilities. “We are putting a strong commitment to adapt and develop existing robotic solutions to fit CERN’s evolving needs,” Di Castro says.


    Access mp4 video here .

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:30 pm on January 25, 2017 Permalink | Reply
    Tags: Accelerator Science, , HERA at DESY, Parton density functions (PDFs), ,   

    From CERN ATLAS: “How strange is the proton?” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    25th January 2017
    ATLAS Collaboration

    1
    Figure 1: The data ellipses illustrate the 68% CL coverage for the total uncertainties (full green) and total excluding the luminosity uncertainty (open black). Theoretical predictions based on various PDF sets are shown with open symbols of different colours. (Image: ATLAS Collaboration/CERN)

    The protons collided by the LHC are not elementary particles, but are instead made up of quarks, antiquarks and gluons. The theory of the strong interactions – quantum chromodynamics (QCD) – does not allow physicists to calculate the composition of protons from first principles. However, QCD can connect measurements made in different processes and at different energy scales such that universal “parton density functions” (PDFs) can be extracted. These determine the dynamic substructure of the proton.

    The discovery of quarks as the elements of the partonic structure of the proton dates about 50 years. Soon after QCD was born and the existence of gluons inside the proton was established. Much has since been learned through a combination of new experimental data and theoretical advances. At the LHC, reactions involve quarks or gluons that carry a certain fraction x of the proton’s momentum, expressed through the Bjorken x variable. Below x of 0.01, the proton constituents are mainly gluons and a sea of quark-antiquark pairs.

    Electron-proton scattering data from the HERA collider has constrained the gluon and the sum of all quarks weighted by the square of their electric charge.

    3
    The electron(positron)-proton collider HERA was shut down at the end of June 2007. HERA was a unique instrument which made a major contribution to high energy particle physics and, in particular, to confirming aspects of quantum chromodynamics (QCD). The knowledge obtained with HERA will be essential for discovering the meaning of data obtained from the large hadron Collider (LHC) at CERN in Geneva. http://www.desy.de/~mpybar/endofHERA.html

    But the low x sea-quark composition – expressed in terms of the lighter quarks named up, down and strange quarks – is still not well understood. New data from the ATLAS experiment shows, with unprecedented precision, the production of W and Z bosons through the weak interaction. This sheds new light on the question: how “strange” the proton is at small x?

    The W production is detected through its decay into a charged lepton (electron or muon) and a neutrino, while the Z boson produces an electron-positron (or muon-antimuon) pair. The experimental detection of electrons and muons poses different challenges and thus the simultaneous measurement in both channels provides an important cross-check of the results, thus improving the final precision achieved. The integrated cross sections for Z boson and W boson production are measured with a precision of 0.3% and 0.6%, respectively, and with an additional common normalisation uncertainty from the luminosity determination of 1.8%. Differential cross sections are also measured in a variety of kinematic regions and about half of the measurement points have a precision of 1% or better.

    2
    Figure 2: Determination of the relative strange-to-down sea quark fractions r_s (left) and R_s (right). Bands: Present result and its uncertainty contributions from experimental data, QCD fit, and theoretical uncertainties. Closed symbols with horizontal error bars: predictions from different NNLO PDF sets. Open square: previous ATLAS result. (Image: ATLAS Collaboration/CERN)

    The measurements are then compared to state-of-the-art QCD expectations using different PDF sets. Because the production of W and Z bosons through the weak interaction has a different dependence on the specific quark flavours compared to the electromagnetic interaction seen in electron-positron scattering at HERA, analysing both data sets gives new access to the strange quark content of the proton.

    As is shown in Figure 1, the measured production rate of W bosons is very similar for all PDF sets, in good agreement with the data. In contrast, the rate for Z boson production is underestimated significantly for most PDF sets. A dedicated analysis enables this deficit to be attributed to a too small strange quark contribution in most PDF sets. The new PDF set, which this paper presents, requires the strange quark sea to be of a similar size as the up and down quark sea. This is summarised by the quantity RS, which is the ratio of the strange quark sea to the the up and down quark sea, and which is found to be close to one, as shown in Figure 2. This result is a striking confirmation of the hypothesis of a light-flavour symmetry of proton structure at low x. This result will generate many further studies, because hitherto there had been indications from low energy neutrino-scattering data that favoured a suppressed strange-quark contribution with respect to the up and down quark parts, leading to an RS close to 0.5.

    The analysis also shows that the potential to which precise W and Z cross sections can provide useful constraints on PDFs is not limited by the now very high experimental precision, but rather by the uncertainty of the currently available theory calculations. The salient results of this paper are thus of fundamental importance for forthcoming high-precision measurements, such as the mass of the W boson, and also represent a strong incentive for further improving the theory of Drell-Yan scattering in proton-proton collisions.

    Links:

    Precision measurement and interpretation of inclusive W+, W− and Z/γ∗ production cross sections with the ATLAS detector, https://arxiv.org/abs/1612.03016

    See the full article here .

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

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  • richardmitnick 1:53 pm on January 19, 2017 Permalink | Reply
    Tags: Accelerator Science, , , , , ,   

    From Symmetry: “Matter-antimatter mystery remains unsolved” 

    Symmetry Mag
    Symmetry

    01/19/17
    Sarah Charley

    1
    Maximilien Brice, CERN

    Measuring with high precision, physicists at CERN found a property of antiprotons perfectly mirrored that of protons.

    There is little wiggle room for disparities between matter and antimatter protons, according to a new study published by the BASE experiment at CERN.

    cern-base-collaboartion-bloc

    Charged matter particles, such as protons and electrons, all have an antimatter counterpart. These antiparticles appear identical in every respect to their matter siblings, but they have an opposite charge and an opposite magnetic property. This recalcitrant parity is a head-scratcher for cosmologists who want to know why matter triumphed over antimatter in the early universe.

    “We’re looking for hints,” says Stefan Ulmer, spokesperson of the BASE collaboration. “If we find a slight difference between matter and antimatter particles, it won’t tell us why the universe is made of matter and not antimatter, but it would be an important clue.”

    Ulmer and his colleagues working on the BASE experiment at CERN closely scrutinize the properties of antiprotons to look for any miniscule divergences from protons. In a paper published today in the journal Nature Communications, the BASE collaboration at CERN reports the most precise measurement ever made of the magnetic moment of the antiproton.

    “Each spin-carrying charged particle is like a small magnet,” Ulmer says. “The magnetic moment is a fundamental property which tells us the strength of that magnet.”

    The BASE measurement shows that the magnetic moments of the proton and antiproton are identical, apart from their opposite signs, within the experimental uncertainty of 0.8 parts per million. The result improves the precision of the previous best measurement by the ATRAP collaboration in 2013, also at CERN, by a factor of six. This new measurement shows an almost perfect symmetry between matter and antimatter particles, thus further constricting leeway for incongruencies which might have explained the cosmic asymmetry between matter and antimatter.

    The measurement was made at the Antimatter Factory at CERN, which generates antiprotons by first crashing normal protons into a target and then focusing and slowing the resulting antimatter particles using the Antiproton Decelerator. Because matter and antimatter annihilate upon contact, the BASE experiment first traps antiprotons in a vacuum using sophisticated electromagnetics and then cools them to about 1 degree Celsius above absolute zero. These electromagnetic reservoirs can store antiparticles for long periods of time; in some cases, over a year. Once in the reservoir, the antiprotons are fed one-by-one into a trap with a superimposed magnetic bottle, in which the antiprotons oscillate along the magnetic field lines. Depending on their North-South alignment in the magnetic bottle, the antiprotons will vibrate at two slightly different rates. From these oscillations (combined with nuclear magnetic resonance methods), physicists can determine the magnetic moment.

    The challenge with this new measurement was developing a technique sensitive to the miniscule differences between antiprotons aligned with the magnetic field versus those anti-aligned.

    “It’s the equivalent of determining if a particle has vibrated 5 million times or 5 million-plus-one times over the course of a second,” Ulmer says. “Because this measurement is so sensitive, we stored antiprotons in the reservoir and performed the measurement when the antiproton decelerator was off and the lab was quiet.”

    BASE now plans to measure the antiproton magnetic moment using a new trapping technique that should enable a precision at the level of a few parts per billion—that is, a factor of 200 to 800 improvement.

    Members of the BASE experiment hope that a higher level of precision might provide clues as to why matter flourishes while cosmic antimatter lingers on the brink of extinction.

    “Every new precision measurement helps us complete the framework and further refine our understanding of antimatter’s relationship with matter,” Ulmer says.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.


     
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