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  • richardmitnick 7:59 am on July 17, 2019 Permalink | Reply
    Tags: "Bottomonium particles don’t go with the flow", , , CERN ALICE, , , ,   

    From CERN: “Bottomonium particles don’t go with the flow” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    16 July, 2019
    Ana Lopes

    The first measurement, by the ALICE [below] collaboration, of an elliptic-shaped flow for bottomonium particles could help shed light on the early universe.

    A few millionths of a second after the Big Bang, the universe was so dense and hot that the quarks and gluons that make up protons, neutrons and other hadrons existed freely in what is known as the quark–gluon plasma. The ALICE experiment at the Large Hadron Collider (LHC) can recreate this plasma in high-energy collisions of beams of heavy ions of lead. However, ALICE, as well as any other collision experiments that can recreate the plasma, cannot observe this state of matter directly. The presence and properties of the plasma can only be deduced from the signatures it leaves on the particles that are produced in the collisions.

    In a new article, presented at the ongoing European Physical Society conference on High-Energy Physics, the ALICE collaboration reports the first measurement of one such signature – the elliptic flow – for upsilon particles produced in lead–lead LHC collisions.

    The upsilon is a bottomonium particle, consisting of a bottom (often also called beauty) quark and its antiquark. Bottomonia and their charm-quark counterparts, charmonium particles, are excellent probes of the quark–gluon plasma. They are created in the initial stages of a heavy-ion collision and therefore experience the entire evolution of the plasma, from the moment it is produced to the moment it cools down and gives way to a state in which hadrons can form.

    One indication that the quark–gluon plasma forms is the collective motion, or flow, of the produced particles. This flow is generated by the expansion of the hot plasma after the collision, and its magnitude depends on several factors, including: the particle type and mass; how central, or “head on”, the collision is; and the momenta of the particles at right angles to the collision line. One type of flow, called elliptic flow, results from the initial elliptic shape of non-central collisions.

    In their new study, the ALICE team determined the elliptic flow of the upsilons by observing the pairs of muons (heavier cousins of the electron) into which they transform, or “decay”. They found that the magnitude of the upsilon elliptic flow for a range of momenta and collision centralities is small, making the upsilons the first hadrons that don’t seem to exhibit a significant elliptic flow.

    The results are consistent with the prediction that the upsilons are largely split up into their constituent quarks in the early stages of their interaction with the plasma, and they pave the way to higher-precision measurements using data from ALICE’s upgraded detector, which will be able to record ten times more upsilons. Such data should also cast light on the curious case of the J/psi flow. This lighter charmonium particle has a larger flow and is believed to re-form after being split up by the plasma.

    See the full article here.


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    Meet CERN in a variety of places:

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    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS


    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

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  • richardmitnick 3:55 pm on March 20, 2019 Permalink | Reply
    Tags: , , CERN ALICE, , , ,   

    From ALICE at CERN: “The subterranean ballet of ALICE” 

    From From ALICE at CERN

    19 March, 2019
    Corinne Pralavorio

    During the long shutdown of CERN’s accelerators, the ALICE experiment at the LHC is removing and refurbishing or replacing the majority of its detectors.

    CERN ALICE Time Projection Chamber (Image: Maximilien Brice/CERN)

    The experiment caverns of the Large Hadron Collider (LHC) are staging a dazzling performance during Long Shutdown 2 (LS2). The resplendent sub-detectors, released from their underground homes, are performing a fascinating ballet. At the end of February, ALICE removed the two trackers, the inner tracker system and the time projection chamber, from the detector. At the very start of the long shutdown, on 3 December 2018, the teams began disconnecting the dozens of sub-detectors. And finally, on 25 February, the two trackers were ready to be removed.

    The trackers are located around the collision points and are used to reconstruct the tracks of the particles produced in the collisions. The data they generate are essential for identifying the particles and understanding what happened during the collision. ALICE’s inner tracker is a 1.5-metre-long tube, 1 metre in diameter. It will be replaced with a new, much more precise detector closer to the collision point, formed of seven pixel layers and containing a total of 12.5 billion pixels. The current detector is still in the cavern and could spend its retirement as a museum piece in an exhibition above ground.

    CERN ALICE internal tracker system (Image: Maximilien Brice/ Julien Ordan CERN)

    The time projection chamber is an imposing cylinder, measuring 5.1 metres in length and 5.6 metres in diameter, weighing an enormous 15 tonnes. The huge sub-detector was nonetheless hoisted out in just four hours, to be transferred to a building where it will undergo a complete metamorphosis. The current detector is based on multiwire proportional chamber technology. To increase the detector’s acquisition speed by a factor of 100, the readout system will be equipped with much faster components called gas electron multipliers (GEMs), and the electronics will be completely replaced. The teams have started the renovation work, which should take around 11 months.

    At present, the removal process is continuing in the cavern. Most of the calorimeters have been removed for refurbishment. Around 50 people are hard at work at the experiment.

    4
    After the removal of the two trackers, ALICE’s heart is now empty. (Image: Julien Ordan/CERN)

    To find out more about the major work in progress at ALICE, see these articles on the website and in the CERN Courier.

    See the full article here .


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  • richardmitnick 3:42 pm on February 13, 2019 Permalink | Reply
    Tags: "Building a billion pixel detector for the Large Hadron Collider, , , CERN ALICE, , , , , STFC’s Daresbury Laboratory   

    From Science and Technology Facilities Council: “Building a billion pixel detector for the Large Hadron Collider” 


    From Science and Technology Facilities Council

    13 February 2019

    Wendy Ellison
    STFC Communications
    Daresbury Laboratory
    Sci-Tech Daresbury
    WA4 4AD
    Tel: 01925 603232

    Scientists, engineers and technicians at Daresbury Laboratory are playing a key role in building ground-breaking new technologies that will enable a major upgrade of the ALICE experiment, one of the four main detectors at the Large Hadron Collider at CERN.

    STFC Daresbury Laboratory-Hub for Pioneering Research


    CERN/ALICE Detector

    1
    Gary Markey and Terry Lee, mechanical technicians at Daresbury Laboratory, building the staves that are now on their way to ALICE at CERN.
    (Credit: STFC)

    3
    University of Liverpool Physicist, Dr Giacomo Contin, prepares the staves for shipment from Daresbury to CERN.
    (Credit: STFC)

    Weighing more than the Eiffel Tower and sitting in a vast cavern 56m below the ground, ALICE acts like a giant microscope that is used to observe and study a state of matter that was last present in the universe just billionths of a second after the Big Bang. The LHC is used to create this matter, which has a temperature around 400,000 times that of the sun, by accelerating and then colliding heavy nuclei of lead. Research at ALICE allows us to reconstruct and provide new insights into the physics of the early universe when, 13.8 billion years ago, in the moments after the Big Bang, the Universe consisted of a primordial soup of particles called Quark-Gluon Plasma.

    Quark-Gluon Plasma from BNL RHIC

    ‘Perfect liquid’ quark-gluon plasma is the most vortical fluid from phys.org

    The ALICE upgrade is a significant international project, and the team at STFC’s Daresbury Laboratory, in collaboration with the University of Liverpool, has been developing and building ground-breaking new technologies as part of a new Inner Tracking System. Extremely thin and highly-pixelated sensors, together with ultra-light support structures will boost the tracking performance of ALICE by a factor of a hundred. It will be the thinnest, most pixelated tracker at the LHC, capable of identifying and measuring the energy of particles created by the LHC’s collisions at lower energies than any of the other LHC experiments.

    The Daresbury-Liverpool team is building 30 staves of this new generation of sensor, each containing millions of pixels. The staves, which frame and support the sensors, are now being carefully transported to CERN in batches every six weeks until the end of September, where they will be tested before being installed, officially making ALICE a billion pixel detector.

    Dr Roy Lemmon, physicist and lead for the ALICE upgrade project at STFC’s Daresbury Laboratory, which is located at Sci-Tech Daresbury, said: “This project highlights the skills and significant role of the UK’s researchers in the development of new generations of technology for, in this case, ALICE, part of the world’s largest science experiment. It’s very exciting to be part of something that will not only help solve our science challenges, but which could also impact our lives in a really positive way, such as through improvements in medical imaging, through the development of new technologies.”

    “The ALICE upgrade is taking place during the scheduled two-year shutdown for the LHC. The newly-upgraded experiment will start taking data in 2021.

    Further information about ALICE at the CERN website.

    Further information about Daresbury Laboratory at the STFC website.

    See the full article here .

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    STFC Hartree Centre

    Helping build a globally competitive, knowledge-based UK economy

    We are a world-leading multi-disciplinary science organisation, and our goal is to deliver economic, societal, scientific and international benefits to the UK and its people – and more broadly to the world. Our strength comes from our distinct but interrelated functions:

    Universities: we support university-based research, innovation and skills development in astronomy, particle physics, nuclear physics, and space science
    Scientific Facilities: we provide access to world-leading, large-scale facilities across a range of physical and life sciences, enabling research, innovation and skills training in these areas
    National Campuses: we work with partners to build National Science and Innovation Campuses based around our National Laboratories to promote academic and industrial collaboration and translation of our research to market through direct interaction with industry
    Inspiring and Involving: we help ensure a future pipeline of skilled and enthusiastic young people by using the excitement of our sciences to encourage wider take-up of STEM subjects in school and future life (science, technology, engineering and mathematics)

    We support an academic community of around 1,700 in particle physics, nuclear physics, and astronomy including space science, who work at more than 50 universities and research institutes in the UK, Europe, Japan and the United States, including a rolling cohort of more than 900 PhD students.

    STFC-funded universities produce physics postgraduates with outstanding high-end scientific, analytic and technical skills who on graduation enjoy almost full employment. Roughly half of our PhD students continue in research, sustaining national capability and creating the bedrock of the UK’s scientific excellence. The remainder – much valued for their numerical, problem solving and project management skills – choose equally important industrial, commercial or government careers.

    Our large-scale scientific facilities in the UK and Europe are used by more than 3,500 users each year, carrying out more than 2,000 experiments and generating around 900 publications. The facilities provide a range of research techniques using neutrons, muons, lasers and x-rays, and high performance computing and complex analysis of large data sets.

    They are used by scientists across a huge variety of science disciplines ranging from the physical and heritage sciences to medicine, biosciences, the environment, energy, and more. These facilities provide a massive productivity boost for UK science, as well as unique capabilities for UK industry.

    Our two Campuses are based around our Rutherford Appleton Laboratory at Harwell in Oxfordshire, and our Daresbury Laboratory in Cheshire – each of which offers a different cluster of technological expertise that underpins and ties together diverse research fields.

    The combination of access to world-class research facilities and scientists, office and laboratory space, business support, and an environment which encourages innovation has proven a compelling combination, attracting start-ups, SMEs and large blue chips such as IBM and Unilever.

    We think our science is awesome – and we know students, teachers and parents think so too. That’s why we run an extensive Public Engagement and science communication programme, ranging from loans to schools of Moon Rocks, funding support for academics to inspire more young people, embedding public engagement in our funded grant programme, and running a series of lectures, travelling exhibitions and visits to our sites across the year.

    Ninety per cent of physics undergraduates say that they were attracted to the course by our sciences, and applications for physics courses are up – despite an overall decline in university enrolment.

     
  • richardmitnick 3:17 pm on January 21, 2019 Permalink | Reply
    Tags: 'New' ALICE coming to life during LS2, , CERN ALICE, , High-Luminosity LHC (HL-LHC), Novel Muon Forward Tracker (MFT), , ,   

    From ALICE at CERN: “‘New’ ALICE coming to life during LS2” 

    CERN
    CERN New Masthead

    From From ALICE at CERN

    21 January 2019
    Virginia Greco

    With the conclusion of Run 2, ALICE has entered a new phase, during which a major upgrade of its detector, data-taking and data-processing systems will be implemented.

    At 6 a.m. on December 3, 2018, the LHC expert team switched off the engine of the biggest particle accelerator in the world, which will rest for the next two years before entering a new phase of operation. Starting in March 2021, in fact, the LHC will deliver collisions at increased luminosity, allowing the experiments to collect much more data in less time and, thus, to study rare phenomena.

    The higher luminosity will certainly benefit ALICE, the LHC experiment dedicated to the study of the strong interaction and of the Quark-Gluon-Plasma (QGP), a state of matter which prevailed in the first instants of the universe and is recreated in droplets at the LHC by colliding lead ions. During Run 3, indeed, the interaction rate of lead ions will be increased to reach about 50 kHz, i.e. an instantaneous luminosity of L= 6×1027 cm-2s-1. This will allow ALICE to accumulate more than 10nb-1 of Pb-Pb collisions. Data samples of pp and p-Pb collisions will also be collected to measure the same observables in different interaction systems.

    To exploit the extraordinary scientific potential of Run 3 and subsequent High-Luminosity LHC (HL-LHC) operations and to be able to study rare processes, the ALICE collaboration is currently implementing a major upgrade of its detector, data-taking and data-processing systems.

    The current Inner Tracking System (ITS), which is located at the heart of the detector, will be replaced by a brand-new one composed of seven layers of silicon pixel detectors. A compact pixel sensor chip (ALPIDE), based on the Monolithic Active Pixel Sensors (MAPS) technology, has been developed for this upgrade. The new ITS will improve dramatically the resolution of the detector and its ability to reconstruct the particle trajectories and identify secondary vertices.

    2
    Inner half-layers of the upgraded ITS. [Credit: Antoine Junique]

    A novel Muon Forward Tracker (MFT), implementing the same custom ALPIDE chip, will also be installed in the forward region of the detector. Thanks to its excellent spatial resolution, not only will ALICE be more sensitive to several measurements, but also it will be able to access new ones that are currently beyond reach. A new Fast Interaction Trigger (FIT) detector will also replace three current forward detectors, with the aim of providing the minimum-bias trigger and excellent time resolution for identifying decay vertices.

    The increased collision rate also requires a major upgrade of the ALICE TPC. The current detector is limited by its read-out chambers, which are based on multi-wire proportional chamber (MWPC) technology. Thus, they will be replaced with multi-stage gas electron multiplier (GEM) chambers, the development of which has required intense R&D activities. The TPC upgrade will increase the read-out rate of the detector by about two orders of magnitude, while preserving its excellent tracking and particle identification capabilities.

    The readout of the TPC and muon-chambers will be performed by the newly designed SAMPA chip, which is a 32-channel front-end analogue-to-digital converter with integrated digital signal processor.

    The new common online-offline (O2) system will transfer data from the detector directly to computers either continuously or with minimal trigger requirements. A new computing facility for the O2system is being installed at the experimental site.

    Whereas the machine will sleep, this long shut down period will be nothing but quiet for all the engineers and physicists who will work on a tight schedule to make the ALICE experiment ready for the next challenges.

    3
    Assembly of one of the gas electron multiplier chambers of the upgraded TPC detector in cleanroom. [Credit: CERN]

    See the full article here .


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    Meet CERN in a variety of places:


    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE

    CERN/ALICE Detector

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

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  • richardmitnick 1:44 pm on October 5, 2018 Permalink | Reply
    Tags: “We have developed new and powerful tools to investigate the properties of the small droplet of QGP (early universe) that we create in the experiments”, , CERN ALICE, , , , The state of the Early Universe: The beginning was fluid, The transport properties of the Quark-Gluon Plasma will determine the final shape of the cloud of produced particles after the collision so this is our way of approaching the moment of QGP creation it, We want to know what happened in the beginning of the collision and first few moments afterwards, Working with the LHC replacing the lead-ions usually used for collisions with Xenon-ions   

    From Niels Bohr Institute: “The state of the Early Universe: The beginning was fluid” 

    University of Copenhagen

    Niels Bohr Institute bloc

    From Niels Bohr Institute

    04 October 2018

    You Zhou, Postdoc
    Experimental Particle Physics
    Niels Bohr Institute, University of Copenhagen
    Email: you.zhou@nbi.ku.dk
    Phone: +45 35 33 12 82

    Scientists from the Niels Bohr Institute, University of Copenhagen, and their colleagues from the international ALICE collaboration recently collided Xenon nuclei, in order to gain new insights into the properties of the Quark-Gluon Plasma (the QGP) – the matter that the universe consisted of up to a microsecond after the Big Bang.

    The QGP, as the name suggests, is a special state consisting of the fundamental particles, the quarks, and the particles that bind the quarks together, the gluons. The result was obtained using the ALICE experiment at the 27 km long superconducting Large Hadron Collider (LHC) at CERN. The result is now published in Physics Letters B.

    1
    Fig. 1 [Left] An event from the first Xenon-Xenon collision at the Large Hadron Collider at the top energy of the Large Hadron Collider (5.44 TeV ) registered by ALICE [credit: ALICE]. Every colored track (The blue lines) corresponds to the trajectory of a charged particle produced in a single collision; [Right] formation of anisotropic flow in relativistic heavy-ion collisions due to the geometry of the hot and dense overlap zone (shown in red color).

    The beginning was a liquid state of affairs

    The particle physicists at the Niels Bohr Institute have obtained new results, working with the LHC, replacing the lead-ions, usually used for collisions, with Xenon-ions. Xenon is a “smaller” atom with fewer nucleons in its nucleus. When colliding ions, the scientists create a fireball that recreates the initial conditions of the universe at temperatures in excess of several thousand billion degrees. In contrast to the Universe, the lifetime of the droplets of QGP produced in the laboratory is ultra short, a fraction of a second (In technical terms, only about 10-22 seconds). Under these conditions the density of quarks and gluons is very large and a special state of matter is formed in which quarks and gluons are quasi-free (dubbed the strongly interacting QGP). The experiments reveal that the primordial matter, the instant before atoms formed, behaves like a liquid that can be described in terms of hydrodynamics.

    How to approach “the moment of creation”

    “One of the challenges we are facing is that, in heavy ion collisions, only the information of the final state of the many particles which are detected by the experiments are directly available – but we want to know what happened in the beginning of the collision and first few moments afterwards”, You Zhou, Postdoc in the research group Experimental Subatomic Physics at the Niels Bohr Institute, explains. “We have developed new and powerful tools to investigate the properties of the small droplet of QGP (early universe) that we create in the experiments”. They rely on studying the spatial distribution of the many thousands of particles that emerge from the collisions when the quarks and gluons have been trapped into the particles that the Universe consists of today. This reflects not only the initial geometry of the collision, but is sensitive to the properties of the QGP. It can be viewed as a hydrodynamical flow.” The transport properties of the Quark-Gluon Plasma will determine the final shape of the cloud of produced particles, after the collision, so this is our way of approaching the moment of QGP creation itself”, You Zhou says.

    Two main ingredients in the soup: Geometry and viscosity

    The degree of anisotropic particle distribution – the fact that there are more particles in certain directions – reflects three main pieces of information: The first is, as mentioned, the initial geometry of the collision. The second is the conditions prevailing inside the colliding nucleons. The third is the shear viscosity of the Quark-Gluon Plasma itself. Shear viscosity expresses the liquid’s resistance to flow, a key physical property of the matter created. “It is one of the most important parameters to define the properties of the Quark-Gluon Plasma”, You Zhou explains, “ because it tells us how strongly the gluons bind the quarks together “.

    The Xenon experiments yield vital information to challenge theories and models

    “With the new Xenon collisions, we have put very tight constraints on the theoretical models that describe the outcome. No matter the initial conditions, Lead or Xenon, the theory must be able to describe them simultaneously. If certain properties of the viscosity of the quark gluon plasma are claimed, the model has to describe both sets of data at the same time, says You Zhou. The possibilities of gaining more insight into the actual properties of the “primordial soup” are thus enhanced significantly with the new experiments. The team plans to collide other nuclear systems to further constrain the physics, but this will require significant development of new LHC beams.

    Science is not a lonesome affair, far from it

    “This is a collaborative effort within the large international ALICE Collaboration, consisting of more than 1800 researchers from 41 countries and 178 institutes”. You Zhou emphasised.

    See the full article here .


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    Niels Bohr Institute Campus

    The Niels Bohr Institute (Danish: Niels Bohr Institutet) is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.

    The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr’s birth – October 7, 1965 – the Institute officially became The Niels Bohr Institute.[1] Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.[2]

    During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe (and sometimes further abroad) often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.

    On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute.

    The University of Copenhagen (UCPH) (Danish: Københavns Universitet) is the oldest university and research institution in Denmark. Founded in 1479 as a studium generale, it is the second oldest institution for higher education in Scandinavia after Uppsala University (1477). The university has 23,473 undergraduate students, 17,398 postgraduate students, 2,968 doctoral students and over 9,000 employees. The university has four campuses located in and around Copenhagen, with the headquarters located in central Copenhagen. Most courses are taught in Danish; however, many courses are also offered in English and a few in German. The university has several thousands of foreign students, about half of whom come from Nordic countries.

    The university is a member of the International Alliance of Research Universities (IARU), along with University of Cambridge, Yale University, The Australian National University, and UC Berkeley, amongst others. The 2016 Academic Ranking of World Universities ranks the University of Copenhagen as the best university in Scandinavia and 30th in the world, the 2016-2017 Times Higher Education World University Rankings as 120th in the world, and the 2016-2017 QS World University Rankings as 68th in the world. The university has had 9 alumni become Nobel laureates and has produced one Turing Award recipient

     
  • richardmitnick 2:32 pm on September 25, 2018 Permalink | Reply
    Tags: , CERN ALICE, , , , , , ,   

    From ALICE at CERN: “What the LHC upgrade brings to CERN” 

    CERN
    CERN New Masthead

    From From ALICE at CERN

    25 September 2018
    Rashmi Raniwala
    Sudhir Raniwala

    Six years after discovery, Higgs boson validates a prediction. Soon, an upgrade to Large Hadron Collider will allow CERN scientists to produce more of these particles for testing Standard Model of physics.

    FNAL magnets such as this one, which is mounted on a test stand at Fermilab, for the High-Luminosity LHC Photo Reidar Hahn

    Six years after the Higgs boson was discovered at the CERN Large Hadron Collider (LHC), particle physicists announced last week that they have observed how the elusive particle decays.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    The finding, presented by ATLAS and CMS collaborations, observed the Higgs boson decaying to fundamental particles known as bottom quarks.

    In 2012, the Nobel-winning discovery of the Higgs boson validated the Standard Model of physics, which also predicts that about 60% of the time a Higgs boson will decay to a pair of bottom quarks.

    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.


    Standard Model of Particle Physics from Symmetry Magazine

    According to CERN, “testing this prediction is crucial because the result will either lend support to the Standard Model — which is built upon the idea that the Higgs field endows quarks and other fundamental particles with mass — or rock its foundations and point to new physics”.

    The Higgs boson was detected by studying collisions of particles at different energies. But they last only for one zeptosecond, which is 0.000000000000000000001 seconds, so detecting and studying their properties requires an incredible amount of energy and advanced detectors. CERN announced earlier this year that it is getting a massive upgrade, which will be completed by 2026.

    Why study particles?

    Particle physics probes nature at extreme scales, to understand the fundamental constituents of matter. Just like grammar and vocabulary guide (and constrain) our communication, particles communicate with each other in accordance with certain rules which are embedded in what are known as the ‘four fundamental interactions’. The particles and three of these interactions are successfully described by a unified approach known as the Standard Model. The SM is a framework that required the existence of a particle called the Higgs boson, and one of the major aims of the LHC was to search for the Higgs boson.

    How are such tiny particles studied?

    Protons are collected in bunches, accelerated to nearly the speed of light and made to collide. Many particles emerge from such a collision, termed as an event. The emergent particles exhibit an apparently random pattern but follow underlying laws that govern part of their behaviour. Studying the patterns in the emission of these particles help us understand the properties and structure of particles.

    Initially, the LHC provided collisions at unprecedented energies allowing us to focus on studying new territories. But, it is now time to increase the discovery potential of the LHC by recording a larger number of events.

    3
    No image credit or caption

    So, what will an upgrade mean?

    After discovering the Higgs boson, it is imperative to study the properties of the newly discovered particle and its effect on all other particles. This requires a large number of Higgs bosons. The SM has its shortcomings, and there are alternative models that fill these gaps. The validity of these and other models that provide an alternative to SM can be tested by experimenting to check their predictions. Some of these predictions, including signals for “dark matter”, “supersymmetric particles” and other deep mysteries of nature are very rare, and hence difficult to observe, further necessitating the need of a High Luminosity LHC (HL-LHC).

    Imagine trying to find a rare variety of diamond amongst a very large number of apparently similar looking pieces. The time taken to find the coveted diamond will depend on the number of pieces provided per unit time for inspection, and the time taken in inspection. To complete this task faster, we need to increase the number of pieces provided and inspect faster. In the process, some new pieces of diamond, hitherto unobserved and unknown, may be discovered, changing our perspective about rare varieties of diamonds.

    Once upgraded, the rate of collisions will increase and so will the probability of most rare events. In addition, discerning the properties of the Higgs boson will require their copious supply. After the upgrade, the total number of Higgs bosons produced in one year may be about 5 times the number produced currently; and in the same duration, the total data recorded may be more than 20 times.

    With the proposed luminosity (a measure of the number of protons crossing per unit area per unit time) of the HL-LHC, the experiments will be able to record about 25 times more data in the same period as for LHC running. The beam in the LHC has about 2,800 bunches, each of which contains about 115 billion protons. The HL- LHC will have about 170 billion protons in each bunch, contributing to an increase in luminosity by a factor of 1.5.

    How will it be upgraded?

    The protons are kept together in the bunch using strong magnetic fields of special kinds, formed using quadrupole magnets. Focusing the bunch into a smaller size requires stronger fields, and therefore greater currents, necessitating the use of superconducting cables. Newer technologies and new material (Niobium-tin) will be used to produce the required strong magnetic fields that are 1.5 times the present fields (8-12 tesla).

    The creation of long coils for such fields is being tested. New equipment will be installed over 1.2 km of the 27-km LHC ring close to the two major experiments (ATLAS and CMS), for focusing and squeezing the bunches just before they cross.

    CERN crab cavities that will be used in the HL-LHC


    FNAL Crab cavities for the HL-LHC

    Hundred-metre cables of superconducting material (superconducting links) with the capacity to carry up to 100,000 amperes will be used to connect the power converters to the accelerator. The LHC gets the protons from an accelerator chain, which will also need to be upgraded to meet the requirements of the high luminosity.

    Since the length of each bunch is a few cm, to increase the number of collisions a slight tilt is being produced in the bunches just before the collisions to increase the effective area of overlap. This is being done using ‘crab cavities’.

    The experimental particle physics community in India has actively participated in the experiments ALICE and CMS. The HL-LHC will require an upgrade of these too. Both the design and the fabrication of the new detectors, and the ensuing data analysis will have a significant contribution from the Indian scientists.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

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    Meet CERN in a variety of places:


    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

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  • richardmitnick 1:09 pm on June 11, 2018 Permalink | Reply
    Tags: A wealth of ALICE results at Quark Matter 2018, , , CERN ALICE, , , ,   

    From ALICE at CERN: “A wealth of ALICE results at Quark Matter 2018” 

    CERN

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    From ALICE at CERN

    Contributing 35 talks and almost 100 posters, the ALICE Collaboration has had a strong participation in QM2018, which took place in Venice from 13 to 19 May, where an ample set of new results was presented.

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    The 27th edition of the Quark Matter conference took place in Venice in the week 13-19 May. In ALICE, preparations for the conference started months ago, with new analyses in all the Physics Working Groups. More than 70 new preliminary results were reviewed and approved for the conference and 16 new papers were made available on the preprint server right before the start of the conference.

    In the opening session, Alexander Kalweit presented the ALICE highlights talk, which covered many of the new results, and provided pointers to the 35 contributed talks and almost 100 posters that ALICE presented in the following days. The new results from ALICE covered a broad set of topics, including particle production in pp, p-Pb, and Pb-Pb collisions, and for the first time also Xe-Xe collisions, which were produced by the LHC in a short test run in October 2017. In the following, we will highlight a few of the new results that were presented by ALICE at Quark Matter.

    3
    Alexander Kalweit giving his talk on the ALICE highlights.

    For the small system collisions, pp and p-Pb, we reported on recent measurements on production of resonances and (anti-)nuclei as a function of the total charged particle multiplicity. These results show an intriguing dependence of the production of high-momentum particles on the overall multiplicity, which is likely due to the occurrence of multiple semi-hard scatterings in a single proton-proton collision. The goal of these measurements is to study the onset of effects such as strangeness enhancement and radial and elliptic flow, which are typically associated with Quark-Gluon Plasma formation.

    New results on heavy flavour production in p-Pb collisions show that the charmed baryon production rate is much larger than was expected from electron-positron collisions, and the baryon-to-meson ratio is characterized by a maximum at intermediate pT, which is also seen for light flavor baryon-to-meson ratios. This suggests that there is a common production mechanism for light flavor baryons like the protons and Λ baryon and for the charmed Λc baryon. A first result of Λc baryon production in Pb-Pb collisions was presented, which also shows a large baryon/meson ratio. Improving the precision of these measurements is one of the goals of the detector upgrade programme, which was discussed in another session.

    New results on production of the quarkonia J/Ψ and Ψ(2s) in p-Pb collision at √sNN = 8.2 TeV provide more precise information on the density distributions of quarks and gluons in the nucleus. The production of Ψ(2s) is significantly suppressed with respect to expectations from proton-proton collisions, even in the proton-going direction where no suppression is seen for the lower-mass J/Ψ. This suppression is not fully understood yet, but may be coming from final state interactions with light particles at similar momenta.

    In October last year, the LHC collided Xe nuclei for a few hours and ALICE recorded about 2M collisions, which allow studying the dependence of particle production and QGP effects on the size of the colliding nuclei: the isotope of Xe that was used has 129 nucleons, whereas Pb has 208 nucleons. The total multiplicity (number of produced particles) in Xe-Xe collisions is found to be similar to that in Pb-Pb with the same number of participating nucleons, except for very central Xe-Xe collisions, where an increase of particle production per participant pair is found. The elliptic and triangular flow in Xe-Xe and Pb-Pb collisions are very similar when comparing analogous centralities, as expected, because of the similarity of the initial shape of the system. The smaller number of nucleons in Xe leads to larger fluctuations of the initial geometry, which in turn lead to a larger flow signal in central events; the measured values agree with model calculations. The relative abundances of light flavour hadrons in the new Xe-Xe data confirms the previously-established picture that particle chemistry depends mostly on final state particle multiplicity at LHC energies. Finally, for high-momentum particle production, we observe a similar nuclear modification factor in Xe and Pb when comparing collisions with the same multiplicity. This is qualitatively in line with expectations, since parton energy loss depends on the density and the volume of the system, but more detailed model comparisons are being pursued.

    A dedicated study of the nuclear modification factor of peripheral Pb-Pb collisions shows that, while the suppression of high-momentum particle production that is associated with parton energy loss initially decreases when the collisions become less central, it increases again for very peripheral collisions. This non-monotonic behavior suggests that there is a different mechanism that suppresses high-momentum particle production in very peripheral collisions; one possible explanation is that the individual nucleon-nucleon collisions in the nuclear collision have larger impact parameters and that this reduces the number of parton scatterings, and thus the particle production at high transverse momentum. It is also relevant for the interpretation of collisions of small systems, where the observed azimuthal anisotropy suggests that final state interactions are important, but no suppression of final state particle production is found.

    ALICE also presented a first attempt to measure azimuthal anisotropy of direct photons at the LHC, which probes the time evolution of the temperature and pressure in the Quark Gluon Plasma. The measured signal is large, suggesting the importance of late emission of photons. However, the uncertainties are still sizeable and further improvements are needed to firmly establish this conclusion.

    The Quark Gluon Plasma is also studied using high momentum particles that traverse the plasma and interact with it. At the conference, ALICE presented new results on the nuclear modification factor for jets, as well as studies of the substructure of jets, which aim to be directly sensitive to the radiation of gluons by fast partons as they go through the plasma. A suppression of large-angle symmetric splittings is found, which suggests that partons in a parton shower interact independently with the Quark Gluon Plasma if the angle between them is large enough.

    All in all, the Quark Matter conference was a very interesting meeting, with an unprecedented number of new results from ALICE and the other experiments, as well as discussions of new ideas from theorist colleagues. The topics represented above are only a small selection of what was shown at the conference. The release of a large number of new results at the conference has sparked a lot of new discussions, which are being followed up in several places and we are looking forward to the new insights in strongly interaction matter that this will bring.

    See the full article here .


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  • richardmitnick 12:52 pm on May 14, 2018 Permalink | Reply
    Tags: , CERN ALICE, , , , , The 2018 ALICE data-taking has finally started   

    From ALICE at CERN: “The 2018 ALICE data-taking has finally started” 

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    From ALICE at CERN

    11 May 2018
    Virginia Greco

    1
    A proton-proton collision event at a centre-of-mass energy of 13 TeV, recorded by ALICE on 30 April 2018, one of the first with proton beams containing 1200 bunches. Particle tracks (multiple colours) and energy deposits (yellow and orange blocks) can be seen in the event. The large number of tracks is due to many simultaneous collisions taking place from the same crossing of two bunches of protons; the many vertices, corresponding to the various simultaneous collisions, can be seen in the right-hand-bottom image [Credit: ALICE/CERN].

    On 17 April, the LHC operators declared stable beams for the first time in 2018 and ALICE, as the other experiments, started taking data. The conditions of running, though, were far from being the nominal ones, since there were only three proton bunches per beam and the luminosity was low. In the following days, the number of bunches was stepwise increased and on 28 April, 13 days ahead of schedule, 1200 bunches of protons per beam were successfully injected and collided. This was a crucial step in the intensity ramp up of the LHC towards the optimal running configuration – which foresees 2556 bunches per beam – because it formally marked the beginning of the 2018 physics season.

    Over the last month, ALICE carried out a few tests, starting from the timing calibration of some of the subdetectors. The first days of stable beams were particularly suitable for this, since the few bunches injected (first 3 and then 12) were well separated in time.

    When the number of bunches increased, some days were dedicated to stability studies of one of the subdetectors, the Time-Projection Chamber (TPC), which, during the end-of-year shutdown, had undergone some interventions to minimize the risk of current leakage in its field cage at high luminosity. In particular, it had been cleaned up of some dust deposited in the inside [see previous article – add link] and the gas mixture had been changed by replacing neon with argon and by adding water, because this composition appeared to reduce the risk of overcurrent.

    The objective of these tests was to measure the maximum luminosity that the TPC can handle with the present configuration, in anticipation of the Pb-Pb run scheduled for the end of 2018 and of the future Run 3, which will take place after the second long shutdown (2019-2020). In ALICE, the proton beams are normally off-centred in order to reduce the luminosity with respect to that made available by the LHC, thus it is sufficient to slightly move and overlap more the beams to get a higher luminosity. The study was performed increasing the luminosity in following steps, starting from 15 Hz/ubarn – which corresponds to 10 kHz/ubarn in Pb-Pb collisions – up to 20 and 30 Hz/ubarn. The TPC ran stably up to 20 Hz/ubarn, over which some leakage current development was observed. This is a satisfactory result, which shows that the interventions produced positive effects. Nevertheless, the TPC team will plan further tests to push the detector towards its limits.

    A voltage scan was also performed on the TPC to test it for spatial distortions, which could increase because of the use of argon. Charged particles passing through the chamber ionize the gas and this creates distortion in the electromagnetic field. Static distortions are not problematic because, once measured and mapped, can be compensated for when data are analyzed. On the contrary, dynamic distortions might create troubles. These can be mitigated, though, by applying alternating potential to the cover electrodes of the readout chamber, so it is important to find the best configuration. The data taken during this test are now being analyzed. The results will give indications on the most convenient running conditions to adopt.

    Once these studies were concluded, a special physics run was put in place using a low magnetic field. The ALICE solenoid normally generates a field of 0.5 T, but the latter was lowered to 0.2 T to satisfy a request coming from one of the physics groups. 500 million minimum bias events were taken over 10 days with low B-field, which will be used for measuring the electron-positron pair production in the low invariant mass region.

    Once the quantity of events requested for this purpose had been reached, and even overcome, the magnetic field was increased back to the nominal value. In the meanwhile, the LHC operators continued the intensity ramp-up and, on 7 May, reached the nominal running conditions with 2556 bunches per beam.

    Currently, in ALICE data are being taken with a set of triggers and special setups, as requested by some subdetector groups: in particular, the Electromagnetic calorimeter (EMCal) and the Di-Jet Calorimeter (DCal).

    A few more special setups will be used in the following weeks, before starting a long data taking period with a fixed trigger configuration, which will hopefully last for some months.

    See the full article here .

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  • richardmitnick 10:12 am on April 16, 2018 Permalink | Reply
    Tags: , , CERN ALICE, , , , , Ready- Set- Go   

    From CERN ALICE: “Ready, Set, Go” 

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    16 April 2018
    Virginia Greco

    During the recent weeks, test, calibration and configuration activities were carried on to prepare the ALICE detector for the imminent restart of beam. In advance with respect to the original plan, the LHC is expected to deliver collisions with stable beams on 17 April.

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    The LHC is getting ready for injecting physics beam. The first collisions with stable beams of 2018 will be delivered between 16 and 17 of April.

    Thanks to the excellent performance exhibited by the LHC during the latest weeks, the schedule of the accelerator restarting has been compressed and collisions with stable beams will be delivered beforehand. As a consequence, the ALICE experiment has sped up its commissioning as well to be ready to take data as soon as possible.

    The operations in the experimental cavern, which included some minor repairing and interventions on the muon arm and the TPC, are concluded. Technical runs were started at the beginning of March. During them, the various detectors and systems were left working for many hours in a row – without beams in the accelerator – to check their correct functioning and their stability over time. In the first two weeks, these tests were performed only between 7 am and 11 pm and then the detector switched off, so that no crew was required to stay in the control room at night. Following this, full shifts (24 hours a day) were started and tests continued. Dry runs like these are key to the preparation for data taking, since they allow the experts to identify possible issues and glitches and to fix them in time for the restart.

    The detectors were gradually included in these common coordinated runs but only after successfully completing a reintegration procedure of their detector control system (DCS), necessary to ensure proper transitioning of detectors from normal to beam-safe running conditions.

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    The TPC and the TRD also went through an energy calibration (called “krypton calibration”) performed using a solid rubidium source, which decays into a gaseous excited state of krypton that mixes with the gas volumes of the detectors. This excited state returns to its ground state inside the detector with a known energy spectrum.

    The Data Acquisition System (DAQ) together with the Central Trigger Processor (CTP) and the High-Level Trigger (HLT), in turn, worked to get prepared for the Pb-Pb collisions that will be delivered at the end of the year, from November on. In particular, various tests have been carried out – and will be continued throughout the year whenever possible – to check, tune and improve how the full chain (from the detector signals to the final data storage) behaves when pushed to the limit of its capacity. Specifically, ‘fake’ events, carrying no meaningful information but having rates and sizes similar to those of the events expected in the future Pb-Pb collisions, were generated to put a significant load on the data channels and – partially – on the processing stages.

    After completion of two weeks of dry runs, the ALICE magnet was switched on and data from cosmic ray interactions were taken with many of the detectors until the accelerator team was ready to start test injection in the beam pipe.

    During this beam operation time, when the experts of the machine put in place their commissioning procedure, the ALICE detector has been put in a beam-safe state. In practice, only the systems that have minimal risk of being damaged when hit by the beam when switched on can actually run. The others have to stay in standby mode or run in a non-standard configuration (for example, no high voltage is applied to the detectors that normally require it).

    Collisions with unstable beams were delivered on April 12 and stable beams will be declared at some point between 16 and 17 of April. The ALICE experiment is all set and ready to start its 2018 race.

    See the full article here .

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  • richardmitnick 4:20 pm on October 27, 2017 Permalink | Reply
    Tags: , , CERN ALICE, , , , ,   

    From ALICE at CERN: “Probing the QGP with heavy flavours: recent results” 

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    16 October 2017
    Elena Bruna

    Heavy quarks, like charm and beauty, are unique probes of the Quark-Gluon Plasma (QGP) created in Pb-Pb collisions at LHC energies. Their production occurs via high-Q2 processes, and therefore it is possible to test pQCD calculations for charm and beauty production at LHC energies. In addition, their large masses imply a short formation time, and therefore a longer exposure to the full system evolution. Measurements of D mesons, as well as electrons and muons from heavy-flavour hadron decays from ALICE during LHC Run 1 have proved strong quenching and collectivity of charm quarks in the QGP.

    There are still some open key questions towards a more quantitative understanding of the processes behind energy loss and collective effects, in particular: are heavy quarks affected by initial state effects? What is the role of recombination of charm quarks with lighter quarks in the hadronization process? Are heavy quarks affected by the collective expansion of the medium, and how is this related to the bulk expansion? The recent ALICE results from LHC Run 2 on both p-Pb and Pb-Pb collisions improve the precision of Run 1 results, opening new avenues to characterize the QGP and initial state effects.

    The p-Pb collisions at √sNN = 5.02 TeV recorded by ALICE in 2016 allowed studies of the nuclear modification factor of D mesons with high precision selecting the events on the basis of their centrality. To avoid the uncertainty on the pp reference, we performed the ratio (QCP) of the D0 pT distributions in central over peripheral p-Pb collisions, considering the different number of binary collisions. The D0 QCP, reported in Fig. 1, shows an enhancement from 1 in the pT range 3-8 GeV/c with a 1.7 level (considering statistical and systematic uncertainty including the one on normalization). The current precision of the measurement is still preventing us from drawing conclusions on the role of the different Cold Nuclear Matter effects and on possible presence of additional hot-medium effects, however it poses an interesting question on what are the mechanisms at play in small systems, and to what extent heavy quarks are influenced by them

    1
    Figure 1: D0 central (0-10%)-to-peripheral (60-100%) nuclear modification factor (QCP) as a function of pT in p-Pb collisions at √sNN = 5.02 TeV (ALICE-PUBLIC-2017-008).

    Moving to heavy-ion collisions, ALICE has measured the nuclear modification factor RAA in Pb-Pb at √sNN = 5.02 TeV. Figure 2 shows the RAA for the average of D0, D+, D*+ mesons as a function of pT, together with that of Ds+ for the 0-10% centrality class.

    The larger statistics from Run 2 data allows for more precise measurements and higher pT reach. The central RAA values are higher for Ds+ mesons w.r.t. non-strange D mesons, but the two measurements are compatible within uncertainties. It is interesting to notice that the TAMU (Phys. Lett. B735 (2014) 445) and PHSD (PRC 93 (2016) 034906) models, which include recombination of charm quarks with the enhanced strange quarks in the QGP, predict a large increase of the Ds+ RAA.

    2
    Figure 2: Average of of D0, D+, D*+ (black) and Ds+ (orange) RAA as a function of pT for 0-10% Pb-Pb collisions at √sNN = 5.02 TeV (ALICE-PUBLIC-2017-003).

    3
    Figure 3: D0, D+ average v2 in 30–50% Pb–Pb collisions at √sNN = 5.02 TeV for events with largest q2 (blue), smallest q2 (red) and using the full sample (grey).

    The observable used to characterize the azimuthal anisotropy of the produced particles is the elliptic flow v2, which quantifies, at low pT, the degree of collectivity of the system. The recent ALICE paper on the D-meson v2 in 30-50% Pb-Pb collisions at √sNN = 5.02 TeV (arXiv:1707.01005) shows a positive v2 at low-intermediate pT, suggesting that charm quarks interact with the medium constituents and are sensitive to the collective expansion of the medium. A step forward in this direction is to measure the D-meson v2 in events with different eccentricity, defined by the second-harmonic flow vector q2, obtained from the azimuthal angles of all the tracks in the event. The average of D0 and D+ v2 was measured for the 60% of events with the smallest q2 and for 20% of the events with the largest q2. The result, shown in Fig.3, shows a significant separation between D-meson v2 in events with large and small q2, suggesting that charm quarks are influenced by the light-hadron bulk collectivity and by event-by-event initial fluctuations. These event engineering techniques are becoming a new testing ground for models to understand the relation between heavy and light quark collectivity.

    The LHC Run 2 has so far provided ALICE with large data samples in different collision systems to start setting constraints on models for heavy-flavour production, energy loss and collectivity. The remaining part of Run 2, together with Run 3 and Run 4, will allow for further improvements of the measurements and new differential observables to pose crucial constraints to theory models.

    See the full article here .

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