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  • richardmitnick 5:45 pm on August 8, 2014 Permalink | Reply
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    Fromk ALICE at CERN: “Inauguration of the new ALICE Run Control Centre” 

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    12 July 2014
    Federico Ronchetti

    The new ALICE Run Control Centre was inaugurated on the occasion of the collaboration dinner organized at Point 2 during the recent ALICE week. Eight months of restructuring works have reshaped the internal space arrangement of the working areas and fully refurbished all the services such as air conditioning and networking. Almost one hundred collaborators participating to the ALICE week dinner had the chance to enter the ARC for the first time and to get a live experience of the new environment.

    center
    The new ALICE Run Control Centre was inaugurated during the collaboration dinner organized at Point 2.

    In fact the ARC is already being used by several detector groups to carry on the first standalone tests since all the ALICE online systems underwent major improvements in terms of hardware and software requiring now a very intense phase of integration and commissioning. At the same time the ARC was recently used to manage one of the LHC dry runs, in which the machine activity is simulated in order to verify that all the interface systems with the experiment do respond correctly.

    room
    All the ALICE online systems underwent major improvements and the new ARC is getting ready for the second run of the LHC.

    I was personally very happy that our collaborators who signed up for the ALICE dinner could experience the ARC already in an operational phase in addition to appreciating the new ergonomic and neat style. I was also very happy that all the celebration preparation was somewhat kept hidden from me and during a short toast I was “given” as a gift a nice wall handler to hold the beam line technical drawings and that a very stylish and colourful banner with the “Alice Run Control Center” stamp on it appeared from nowhere.

    folks

    I really would like to thank all my colleagues who have helped me in the design of the ARC – Roberto Divià , Gilda Scioli and Ombretta Pinazza and those who followed all the construction and installation phases as Arturo Tauro and once again Roberto Divià. We and the collaboration wanted the ARC so that each of us could contribute to the data taking in the best way, having an efficient and comfortable environment in which for sure we will all spend many hours for the years to come.

    entry
    The entrance to the new ARC; where the journey of discovery begins.

    See the full article here.

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  • richardmitnick 3:44 am on June 12, 2014 Permalink | Reply
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    From CERN/ALICE: “New PMTs for the ALICE V0-C detector” 

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    27 May 2014
    Panos Charitos

    During the 2011 proton-proton run it was observed that the efficiency of the PMTs used in the V0 detectors had started to deteriorate. Gerardo Corral says: “At that time time we still had to take data and we could make no intervention but we continued monitoring the performance of the PMTs. Based on a series of measurements, it was clear in 2012 that the effect was probably due to radiation and ageing effects. Our colleagues from the University of Lyon had the chance to remove a number of PMTs from the C side of the V0 detector and make some more detailed testing and measurements.” He continues: “They took out 6 PMTs out of the 32 that are used in the C side and confirmed that their performance was reduced. We knew that we had to deal with this problem and the LS1 was the perfect opportunity”. For the A side of V0 things were more difficult as this side of the detector lies closer to the region of the beam pipe and one had to be very careful to avoid damaging the pipe.”

    The new PMTs arrived near the end of 2013 and were calibrated to be ready for installation. Gerardo explains that this is not just a replacement but also an upgrade as the new PMTs can operate at lower voltage. Reducing the high voltage means that one is also reducing the after-pulse signal which was one of the problems that V0 faced from the first runs. With the replacement of the PMTs the team is able to tackle these two issues: “We have PMTs with better gain that also work with lower voltage and thus reduce the after-pulse effect”.

    team
    Installing the new ALICE PMTs: Solangel Rojas Torres, Ildefonso Leon Monzon, Gerardo Herrera Corral, Arturo Tauro, Werner Riegler, Pieter Ijzermans and Elisa Laudi.

    The installation of the new PMTs took place during the second week of April. All the PMTs on the A side have been replaced and soon the team will start working on replacing the PMTs on the C side of V0. Gerardo explains: “The A side is much more complicated, though it lies 3.3 m from the IP it is still in the beam-pipe. We had to move the V0-A 30 cm away on the region where a very delicate beryllium pipe sits. It was a very slow process during which we took a lot of precautions”. Gerardo Herrera Corral with Ildefonso Leon Monzon and a PhD student Solangel Rojas Torres worked closely with members of the ALICE Technical Management team, namely Werner Riegler, Arturo Tauro, Corrado Gargiulo, Pieter Ijzermans and Elisa Laudi.

    The installation has been very successful since we had no accidents or other causes of delay. The PMTs have now been tested and a very good signal has been measured in all of them.
    PMTs in V0

    The V0 detector is a disk with 42 cm diameter and 2.5 cm thick. It is segmented in 32 cells with each cell linked to readout with optical fibres. When a charged particle crosses the plastic light is produced by scintillation. The fibres take out the light and shift the wavelength from blue to the green part of the spectrum. So green light arrives to the PMTs since their photocathode is more sensitive to these wavelengths. Through photoelectric effect electrons are emitted from the photo-cathode and travel through an elecromagnetic field; they hit a series of dynodes, amplifying the number of electrons and in that way the signal is strengthened.

    team 2

    V0 is very important for ALICE as it provides level – zero triggering. The new PMTs will give better efficiency but also allow reducing the after-pulsing signal. When you hit the window you have a pulse of electrons coming from the dynodes and a few nanoseconds later you have a second pulse that is not authentic but is created in the PMTs due to the ionization of the gas. The vacuum in the PMTs is not perfect; the gas atoms are ionized by the electrons and go to the opposite direction as they have positive charge, they hit again producing more electrons and give a second pulse. This is very bad for triggering as these signals are fake triggers that we have to suppress. With the new PMTs the after-pulse probability is ten times lower and V0 will be better equipped to play its triggering role in the forthcoming run in 2015.

    See the full article here.

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  • richardmitnick 8:56 am on May 22, 2014 Permalink | Reply
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    From CERN ALICE: “ALICE in Quark Matter 2014″ 

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    ALICE

    29 April 2014
    Panos Charitos

    The Quark Matter 2014 conference is the twenty-fourth edition of the most prestigious series of international meetings in the field of ultrarelativistic heavy-ion collisions. The meetings bring together theorists and experimentalists committed to understanding the fundamental properties of strongly interacting matter at extreme energy densities. The conditions reached in head-on nuclear collisions at the highest currently available energies correspond to those in primordial matter a few tens of microseconds after the Big Bang. Thus, this type of laboratory research improves our understanding of the early phase of the Universe.

    The first Quark Matter conference took place in 1980 in Darmstadt. Since then, the meetings of this series have been organized approximately every 1.5 years. The recent instances were in Jaipur, India (2008), Knoxville, USA (2009), Annecy, France (2011), and Washington DC, USA (2012). The current meeting brings the conference to Darmstadt again, a place with a long-standing tradition of heavy-ion research and is jointly organized by GSI Helmholtzzentrum für Schwerionenforschung GmbH, Technische Universität Darmstadt, and Universität Heidelberg.

    The scientific programme of Quark Matter 2014 includes numerous topics such as QCD at high temperature and densities, Jets, Open Heavy Flavour and Quarkonia and Electromagnetic Probes. Moreover, the collective dynamics appearing in QGP system and the relations with other strongly coupled systems will be covered along with issues related to correlations and fluctuations and the hadron chemistry. Last but not least, the newest theoretical developments will be discussed during the conference as well as the plans for future experimental facilities and developments in the instrumentation.

    ALICE presents a wealth of scientific results in the upcoming conference with 31 parallel talks and one plenary talk. In addition, in the special poster session ALICE participates with 90 posters reflecting the experiment’s rich scientific programme. The efficient operation of the ALICE detector and the hard work of the ALICE physics working groups were essential ingredients in getting all these results. In the last few weeks, physicists have been very busy with a series of preview and approval sessions during which all the results are scrutinized and the experiment’s last findings are discussed. Last but not least it is worth mentioning that more than one third of the participants in QM2014 are members of the ALICE Collaboration echoing the importance of ALICE studies in the field of ultrarelativistic heavy-ion collisions.

    darm
    Quark Matter 2014 will be hosted in Darmstadium convention center, named in honor of the chemical element with atomic number 110 that was discovered in Darmstadt in 1994.

    The organizers also welcome students’ active participation, which they think is essential for a good conference. Financial support will be provided for a limited number of applicants while a series of introductory lectures will be offered during the Student Day on Sunday, May 18, 2014. More than 300 students have already registered for the event that will be held in GSI and ALICE juniors are encouraged to participate.

    We are looking forward to Quark Matter 2014 and finding out more about the latest developments in our field as the LHC is preparing for the next run at 13 TeV.

    See the full article here.

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  • richardmitnick 1:30 pm on May 8, 2014 Permalink | Reply
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    From ALICE Matters at CERN: “ALICE T0 detector” 

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    ALICE

    29 April 2014
    Tatyana Karavicheva [tatiana@inr.ru]

    The T0 detector was designed and built and is operated by a Finnish-Russian team. The members come from two institutes in Finland (University of Jyväskylä and Helsinki Institute of Physics) and three in Russia (Institute for Nuclear Research RAS, Moscow Engineering Physics Institute, Russian Research Centre Kurchatov Institute).

    The current T0 detector consists of two arrays of Cherenkov counters (T0C and T0A) positioned at the opposite sides of the Interaction Point at distances of -70 cm and 370 cm. Each array has 12 cylindrical counters equipped with a quartz radiator and a photomultiplier tube.

    to
    Since its installation during Easter of 2007 T0-C remains inaccessible, hidden under the layers of FMD and ITS detectors and services. Standing from left to right: A.Bogdanov, A.Reshetin, A.Kurepin, and F.Guber.

    Small but important

    T0 is primarily a trigger and timing detector but it also played a crucial role during the high luminosity part of Run 1. Being the first of the ALICE detectors to be turned on, T0 provided a direct feedback to the LHC team enabling them to tune and monitor the collision rate at Point 2. This valuable service allowed the first beams for ALICE to be delivered on time.

    array
    T0-A array after installation in January 2008.

    The fastest got even faster

    During Run 1 T0 was delivering the trigger signals to the CTP just 625 ns after the collision time; being one the fastest of the ALICE detectors. Trigger consolidation for Run 2 requires reduction of that latency to below 425 ns. To achieve such a drastic cut T0 had to relocate the entire electronics from the racks O18-19 to the racks close to the CTP (C33-34) and reroute and shorten the cables. This Herculean task has already been completed and the T0 team is now recommissioning the detector.

    three
    Smiling faces next to the relocated T0 electronics. From left to right: D.Serebryakov, A.Reshetin, T.Karavicheva, and W.H.Trzaska.

    FIT for the future

    The ALICE upgrade for Run 3 is a challenge for all the system. To face that challenge T0, V0 and FMD teams have joined forces and resources to design, build and operate Fast Interaction Trigger (FIT). FIT will provide the functionality of both the T0 and V0 maintaining excellent timing and trigger properties together with the desired centrality and event plane resolution. It will consist of the Cherenkov radiators (T0+) and scintillators (V0+). Both will use common fast electronics, digitization, and readout as outlined in the Chapter 10 of the Readout & Trigger System TDR:

    http://cds.cern.ch/record/1603472

    integ
    Proposed integration of FIT and FMT. T0+ units are shown as rectangular boxes around the beam tube. (Drawing by Corrado Gargiulo.)

    See the full article here.

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  • richardmitnick 12:17 pm on April 22, 2014 Permalink | Reply
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    From ALICE at CERN: “LHC: the world’s largest photon collider” 

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    28 March 2014
    Joakim Nystrand and Daniel Tapia Takaki

    The CERN Large Hadron Collider (LHC) has worked fantastically well in the past few years, going beyond all expectations. It started its physics programme in 2009 colliding protons at 900 GeV, and then reaching into the Tera electron-volt range supplanting the Fermilab Tevatron accelerator as the most powerful hadron-hadron collider. The LHC was also designed to collide heavy-ions, with the idea of exploring a new energy domain beyond that of RHIC at the Brookhaven National Laboratory. In 2010 this task was completed when the LHC collided lead (Pb) beams at 2.76 TeV, an energy which is more than an order of magnitude larger than that at RHIC.

    lhc

    Although the LHC was not primarily designed to study photon-hadron and photon-photon collisions, they occur in both pp and heavy-ion collisions. The beam energies at the LHC are high enough to make the LHC the most energetic photon source ever built. The protons and ions which are accelerated by the LHC themselves carry an electromagnetic field, which can be viewed as a source of photons. That is, a photon generated by one of these hadrons can interact with another photon (or with a hadron) producing all kinds of particles. Such physics processes are called photon-induced reactions, as they are driven by the interacting photon.

    The appearance of these events stands in sharp contrast to central heavy-ion collisions, where the overlap between the incoming ions is the largest, and thousands of particles are produced. The relevant collisions typically occur at impact parameters of several tens (or even hundreds) of femtometres – cases when the incoming ions barely overlap, and well beyond the range of the strong force.

    jj
    J/ψ candidate in an ultra-peripheral Pb-Pb collision. A dimuon pair in otherwise an empty detector.

    It is worth pointing out that photon-induced processes have by far the largest cross sections in Pb-Pb collisions at the LHC. The total cross section for breaking up one of the nuclei through a photonuclear process is over 200 barns. In most of these reactions the nucleus just breaks up without any particle production. However, the cross section for having at least one photoproduced charged particle inside the main ALICE tracker device (the Time Projection Chamber) acceptance is still substantial, about 4 b. But both these numbers are dwarfed by the total cross section for producing an e+e- pair from an interaction between two photons. This cross section is about 3 million times larger than that for normal hadronic pp collisions.

    A photonuclear interaction that has attracted a lot of interest is exclusive vector meson production. That is, a reaction where only a vector meson is produced in the final state, and nothing else. The large cross section of this process is understood from what is known as Vector Meson Dominance. This means that the photon may fluctuate into a quark-anti-quark pair and, since the photon has spin 1 and negative parity, the fluctuation will most likely be to a Vector Meson. The J/ψ vector meson is one of the particles that is particularly interesting for the heavy-ion community.

    Previously, the HERA experiments at DESY, namely, H1 and ZEUS, studied systematically the photo-production of J/ψ and were able to reach 300 GeV in the centre-of-mass of the photon-proton collision. The proton contains a large number of gluons each carrying a very small fraction of the proton momentum.

    The interaction between hadrons and gluons is governed by the theory of strong interactions called Quantum Chromo-Dynamics (QCD), although there is not yet any known method to predict the gluon density inside a nucleon or a nucleus. Having a good understanding of the proton gluon density is essential for many physics analysis processes sensitive to the strong interaction that governs the interaction between hadrons and gluons.

    There are some theoretical and phenomenological constraints on how the gluon density should behave at high energy but there is not an overall agreement as to what happens when we reach very high energies such as those produced at the LHC. There are several theoretical ideas that can describe what could happen at the LHC photon-hadron energies. Gluon saturation is one of these ideas. J/ψ photoproduction is thought to be sensitive to this in a way that this effect can be easily factorized from other possible mechanics. Nobody knows at what energy gluon saturation phenomena might start to show up in a way that we can distinguish it, but certainly the 1 TeV energy scale is worth studying.

    So far, ALICE has studied photon-photon, photon-lead and photon-proton interactions. At the LHC we are not only reaching the highest energies when colliding photons, but also exploring new kinematic regions that have never been explored before. Some of these photons are indeed very energetic, allowing us to produce collisions at 1 Teraelectronvolt for the first time.

    The ALICE collaboration has recently taken advantage of this effect in a study of coherent photoproduction of J/ψ mesons in Pb-Pb interactions. The J/ψ is detected through its dimuon decay in the muon arm of the ALICE detector [1,2], which also provides the trigger for these events, or in its dielectron or dimuon decay in the central barrel [3]. At the rapidities (y around 3) studied in the muon arm, J/ψ photoproduction is sensitive mainly to the gluon distribution at values of Bjorken-x of about 10–2, whereas at mid-rapidity on probes x ≈ 10 -3. The result from ALICE is that the data favour models that include strong modifications to the nuclear gluon distribution, known as nuclear shadowing.

    During the first running period of the LHC there have been quite a few results on photon-induced collisions. Results with heavy-ion beams have so far come only from ALICE. LHCb has, however, accumulated an impressive statistics of about 100,000 exclusively produced J/ψs in p-p collisions, and CMS have published papers on two-photon interactions in p-p collisions, including a study of W+W- production. In the future, one can expect higher luminosities and thereby probe rarer final states. There are in addition to exclusive vector meson production several things one can look for. These include two-photon production of rare final states, for example γγ→ K0K0, light-by-light scattering, γγ →γγ, and various inclusive photonuclear processes, for example γ +A → jet +X.

    See the full article here.

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  • richardmitnick 6:27 am on April 1, 2014 Permalink | Reply
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    From ALICE Matters at CERN- “LHC: the world’s largest photon collider” 

    CERN New Masthead

    CERN ALICE MATTERS

    CERN ALICE Icon HUGE

    28 March 2014
    Joakim Nystrand and Daniel Tapia Takaki

    The CERN Large Hadron Collider (LHC) has worked fantastically well in the past few years, going beyond all expectations. It started its physics programme in 2009 colliding protons at 900 GeV, and then reaching into the Tera electron-volt range supplanting the Fermilab Tevatron accelerator as the most powerful hadron-hadron collider. The LHC was also designed to collide heavy-ions, with the idea of exploring a new energy domain beyond that of RHIC at the Brookhaven National Laboratory . In 2010 this task was completed when the LHC collided lead (Pb) beams at 2.76 TeV, an energy which is more than an order of magnitude larger than that at RHIC.

    Fermilab Tevatron
    Tevatron at Fermilab

    Brookhaven RHIC
    RHIC at Brookhaven

    LHC Grand Tunnel
    Grand Tunnel of the LHC at CERN

    CERN ALICE Detector
    ALICE

    Although the LHC was not primarily designed to study photon-hadron and photon-photon collisions, they occur in both pp and heavy-ion collisions. The beam energies at the LHC are high enough to make the LHC the most energetic photon source ever built. The protons and ions which are accelerated by the LHC themselves carry an electromagnetic field, which can be viewed as a source of photons. That is, a photon generated by one of these hadrons can interact with another photon (or with a hadron) producing all kinds of particles. Such physics processes are called photon-induced reactions, as they are driven by the interacting photon.

    The appearance of these events stands in sharp contrast to central heavy-ion collisions, where the overlap between the incoming ions is the largest, and thousands of particles are produced. The relevant collisions typically occur at impact parameters of several tens (or even hundreds) of femtometres – cases when the incoming ions barely overlap, and well beyond the range of the strong force.

    pair
    J/ψ candidate in an ultra-peripheral Pb-Pb collision. A dimuon pair in otherwise an empty detector.

    It is worth pointing out that photon-induced processes have by far the largest cross sections in Pb-Pb collisions at the LHC. The total cross section for breaking up one of the nuclei through a photonuclear process is over 200 barns. In most of these reactions the nucleus just breaks up without any particle production. However, the cross section for having at least one photoproduced charged particle inside the main ALICE tracker device (the Time Projection Chamber) acceptance is still substantial, about 4 b. But both these numbers are dwarfed by the total cross section for producing an e+e- pair from an interaction between two photons. This cross section is about 3 million times larger than that for normal hadronic pp collisions.

    A photonuclear interaction that has attracted a lot of interest is exclusive vector meson production. That is, a reaction where only a vector meson is produced in the final state, and nothing else. The large cross section of this process is understood from what is known as Vector Meson Dominance. This means that the photon may fluctuate into a quark-anti-quark pair and, since the photon has spin 1 and negative parity, the fluctuation will most likely be to a Vector Meson. The J/ψ vector meson is one of the particles that is particularly interesting for the heavy-ion community.

    Previously, the HERA experiments at DESY, namely, H1 and ZEUS, studied systematically the photo-production of J/ψ and were able to reach 300 GeV in the centre-of-mass of the photon-proton collision. The proton contains a large number of gluons each carrying a very small fraction of the proton momentum.

    The interaction between hadrons and gluons is governed by the theory of strong interactions called Quantum Chromo-Dynamics (QCD), although there is not yet any known method to predict the gluon density inside a nucleon or a nucleus. Having a good understanding of the proton gluon density is essential for many physics analysis processes sensitive to the strong interaction that governs the interaction between hadrons and gluons.

    There are some theoretical and phenomenological constraints on how the gluon density should behave at high energy but there is not an overall agreement as to what happens when we reach very high energies such as those produced at the LHC. There are several theoretical ideas that can describe what could happen at the LHC photon-hadron energies. Gluon saturation is one of these ideas. J/ψ photoproduction is thought to be sensitive to this in a way that this effect can be easily factorized from other possible mechanics. Nobody knows at what energy gluon saturation phenomena might start to show up in a way that we can distinguish it, but certainly the 1 TeV energy scale is worth studying.

    So far, ALICE has studied photon-photon, photon-lead and photon-proton interactions. At the LHC we are not only reaching the highest energies when colliding photons, but also exploring new kinematic regions that have never been explored before. Some of these photons are indeed very energetic, allowing us to produce collisions at 1 Teraelectronvolt for the first time.

    The ALICE collaboration has recently taken advantage of this effect in a study of coherent photoproduction of J/ψ mesons in Pb-Pb interactions. The J/ψ is detected through its dimuon decay in the muon arm of the ALICE detector, which also provides the trigger for these events, or in its dielectron or dimuon decay in the central barrel. At the rapidities (y around 3) studied in the muon arm, J/ψ photoproduction is sensitive mainly to the gluon distribution at values of Bjorken-x of about 10–2, whereas at mid-rapidity on probes x ≈ 10 -3. The result from ALICE is that the data favour models that include strong modifications to the nuclear gluon distribution, known as nuclear shadowing.

    During the first running period of the LHC there have been quite a few results on photon-induced collisions. Results with heavy-ion beams have so far come only from ALICE. LHCb has, however, accumulated an impressive statistics of about 100,000 exclusively produced J/ψs in p-p collisions, and CMS have published papers on two-photon interactions in p-p collisions, including a study of W+W- production. In the future, one can expect higher luminosities and thereby probe rarer final states. There are in addition to exclusive vector meson production several things one can look for. These include two-photon production of rare final states, for example gg→ K0K0, light-by-light scattering, gg →gg, and various inclusive photonuclear processes, for example g +A → jet +X.

    See the full article, with notes, here.
    See ALICE MATTERS here.

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  • richardmitnick 7:20 am on August 10, 2013 Permalink | Reply
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    From CERN: “The amazing world of smashed protons and lead ions” 

    CERN New Masthead

    In the CERN Bulletin
    Issue No. 33-35/2013 – Monday 12 August 2013
    Antonella Del Rosso

    alice

    “When a single proton (p) is smashed against a lead ion (Pb), unexpected events may occur: in the most violent p-Pb collisions, correlations of particles exhibit similar features as in lead-lead collisions where quark-gluon plasma is formed. This and other amazing results were presented by the ALICE experiment at the SQM2013 conference held in Birmingham from 21 to 27 July.

    event
    Event display from the proton-lead run, in January 2013. This event was generated by the High Level Trigger (HLT) of the ALICE experiment.

    Jet quenching is one of the most powerful signatures of quark-gluon plasma (QGP) formed in high-energy lead-lead collisions. QGP is expected to exist only in specific conditions involving extremely hot temperatures and a very high particle concentration. These conditions are not expected to apply in the case of less ‘dense’ particle collisions such as proton-lead collisions. ‘When we observe the results of these collisions in ALICE, we do not see a strong particle-jet suppression; however, when studying the most violent p-Pb collisions we observe signatures in particle production characteristic of a hydrodynamic nature,’ explains Mateusz Ploskon from the ALICE collaboration. ‘Indeed, some of the properties of the correlations of particles produced in proton-lead collisions resemble those associated with the formation of QGP in lead-lead collisions.’

    More data is needed to resolve the conundrum but in the meantime the physics community is excited as the phenomena observed in proton-lead collisions could have strong implications for our understanding of the QCD – the theory that describes the interactions of strongly interacting subatomic particles. ‘The p-lead data already provide an extremely useful baseline for the collisions of heavy ions; however, we need more time and more data to understand the intriguing observations from proton-lead collisions – it remains to be seen whether we learn something new about hadronic and nuclear collisions at high energies, and whether these observations have any unexpected implications for our understanding of QGP based on lead-lead collisions,’ says Mateusz.”

    See the full article here.

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  • richardmitnick 10:29 am on July 31, 2013 Permalink | Reply
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    From CERN: “ALICE through a gamma-ray looking glass” 

    CERN New Masthead

    31 July 2013
    Christine Sutton

    “The ALICE experiment at CERN specializes in heavy-ion collisions at the LHC, which can produce thousands of particles. In analysing this maelstrom, the researchers need to know exactly how material is distributed in the detector – and it turns out that the LHC’s simpler proton–proton collisions can help.

    layers
    A gamma-ray view of the layers of the ALICE detector. (Image: ALICE)

    Gamma-rays produced in the proton–proton collisions, mainly from the decays of neutral pions, convert into pairs of electrons and positrons as they fly through matter in the detector. The origin of these pairs can be accurately detected, providing a precise 3D image that includes even the inaccessible innermost parts of the experiment. The process is almost exactly the same as in 1895 when Wilhelm Röntgen produced an X-ray image of his wife’s hand – the inner parts of the body could be seen for the first time without surgery. The main difference lies in the energy of the radiation – ten times greater for the gamma rays in ALICE than for Röntgen’s X-rays. Importantly for the ALICE experiment, it allows the team to check crucial simulations.”

    See the full article here.

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  • richardmitnick 7:36 am on July 25, 2013 Permalink | Reply
    Tags: , , CERN ALICE, , , , , ,   

    From CERN: “Standard Model held strong at EPS conference” 

    CERN New Masthead

    25 July 2013
    Ashley Jeanne Wennersherron

    “This year’s European Physical Society High-Energy Physics conference, which came to an end yesterday, was packed with results from the Large Hadron Collider.

    The most recent results on new boson discovered last year were presented by ATLAS and CMS – all of which indicate that the particle is a Higgs boson of the kind predicted by the Standard Model. Further studies are needed to pin down all of the boson’s properties.

    std
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column and the Higgs boson in the fifth.

    The CMS and LHCb collaborations both presented the most recent analyses of a Bs (pronounced B-sub-s) particle decaying into two muons. The two experiments measured this decay at more than 4 sigma, meaning that there is very little chance that this is a statistical fluctuation. These measurements are also in good agreement with the Standard Model. If the measurements deviated even slightly from the predictions, it would be a clear sign of new physics.

    Out of the wealth of results on the physics of the top quark presented by ATLAS and CMS, the CMS collaboration announced the first observation of a rare process: the associated production of a single top quark and a W boson. Both ATLAS and CMS had previously seen evidence for this process but not to this significance of more than 5 sigma. The observation confirms the Standard Model prediction.

    All four of the large LHC experiments, ALICE, ATLAS, CMS and LHCb, presented results from the first proton-lead run at the accelerator. Earlier runs with collisions between two beams of lead nuclei (each nucleus containing a total of 208 protons and neutrons) indicated that a hot, dense medium results. In this material, quarks and gluons float unbound. First results now suggest that a similar system is created in proton-lead collisions, despite there being far fewer neutrons and protons. Further analysis is needed to understand these unexpected features.

    During the conference, the EPS recognized several collaborations and individual scientists for the work done to further the field of physics. In particular, the High-Energy Physics prize honoured the work of ATLAS and CMS for their discovery of a Higgs boson.”

    See the full article here.

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  • richardmitnick 2:04 pm on March 21, 2013 Permalink | Reply
    Tags: , , , CERN ALICE, , , ,   

    From ALICE at CERN: “ALICE 20th Anniversary” 

    CERN New Masthead

    THERE IS A TON OF UNEXPLAINED JARGON IN THIS ARTICLE. IT IS REALLY WRITTEN EXPECTING SPECIALISTS TO BE THE READERS. BUT I OFFER IT FOR ANYONE WHO MIGHT KNOW WHAT IS GOING ON OR WHO MIGHT WISH A STARTING POINT TO DIG IN AND FIND OUT.

    21 March 2013
    Panos Charitos

    20 years ago ALICE started its amazing adventure in the wonderland of strong interactions and the study of extraordinary forms of matter like the Quark Gluon Plasma.

    CERN’s ion programme has a long history and was initiated in 1986 with the acceleration of oxygen ions at 60 and 200 GeV/nucleon, and continued with sulphur ions at 200 GeV/nucleon up to 1993. The first Lead-ion beams at 160 GeV/nucleon became available in 1994. The accelerating chain for 16O and 32S consisted of an ion source of the electron–cyclotron resonance (ECR) type, a radio-frequency quadrupole (RFQ) pre-accelerator, the linear accelerator injector (LINAC I), the PSBooster , the PSand the SPS. For the acceleration of lead ions, a new ECR source, a new RFQ and a new LINAC had to be constructed. The results of the light-ion programme strongly supported its continuation with heavier-ion beams. In particular, the energy densities reached during the collisions appeared to be high enough to be interesting, and many of the suggested signatures for the onset of a quark–gluon plasma phase turned out to be experimentally accessible. The experience gained was instrumental in assessing the feasibility of experiments with lead ions and for indicating the necessary detector modifications. Seven experiments participated in the lead-age adventure.

    Following the previous successes of the heavy-ion physics programme at CERN the idea of a heavy-ion dedicated experiment that would study lead-lead collisions at the new energy scale of the LHC was discussed. During the previous years, the experience gained was instrumental in assessing the feasibility of experiments with lead ions and for indicating the necessary detector modifications that were needed to move with the lead-age adventure at the new scale of the LHC.

    The first appearance of ALICE was in the Evian meeting back in 1992. Jurgen Schukraft recalls that: “We had to do enormous extrapolations because the LHC was a factor of 300 higher in centre-of-mass energy and a factor of 7 in beam mass compared with the light-ion programme, which started in 1986 at both the CERN SPS and the Brookhaven AGS.” A Letter of Intent for a new experiment at the LHC was submitted on 1 March 1993 to the LHC Committee that was formed shortly after the Evian meeting. It marks the first official use of the name ALICE and it was signed by 230 people coming from 42 institutes around the world. It was clearly describing the proposal of the ALICE Collaboration for building a dedicated heavy-ion detector to exploit the unique physics potential of nucleus-nucleus interaction at LHC energies and where the formation of a new phase of matter, the quark gluon plasma is expected. The submission of the letter of intent was followed by a detailed technical proposal that was submitted two years later in 1995 and shortly endorsed by the LHCC and the CERN management.

    early

    mega

    ALICE studies strong interactions by using particles – created inside the hot volume of the Quark Gluon Plasma as it expands and cools down – that live long enough to reach the sensitive detector layers located around the interaction region. The physics programme at ALICE relies on being able to identify all of them – i.e. to determine if they are electrons, photons, pions, etc – and to determine their charge. This involves making the most of the different ways that particles interact with matter. Over twenty years, ALICE has developed a wide range of R&D activities, confronted many challenges in designing and building new detectors that could cope with the physical challenges at the new energy scales. One should also refer to the big data challenge as heavy-ion collisions produce petabytes of data that need to be stored and later analysed in order to get new physics results.

    event

    Following the first run, ALICE successfully reported on the formation of QGP and offered a new insight on the nature of strong interacting matter at extreme densities. The existence of such a phase and its properties are a key issue in QCD for the understanding of confinement and of chiral-symmetry restoration. Wherever you look, from the energy loss of fast quarks to quarkonia, from the details of the dynamical evolution of the system to the very first study of charmed hadrons and the loss of energy, the interplay between , to name just a few, the ALICE results stand out for their quality and relevance. Following the recent proton-lead run that opens new horizons for the heavy-ion community at CERN, ALICE is now looking forward to a series of upgrades during the LS1.

    Paolo Giubellino notes: ‘This has been the result of many years of work and dedication of all of us, and we can all be proud of now sharing this remarkable harvest. It has been an enormous effort, but we can now say it was really worth it, and all share the happiness for this wealth of results. We all contributed to this accomplishment, and we should all draw from it even more motivation to go forward for the next many years to come!'”

    See the full article here.

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries


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