| 1. |
- Abelev, B., et al.
(författare)
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Technical Design Report for the Upgrade of the ALICE Inner Tracking System
- 2014
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
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Tidskriftsartikel (refereegranskat)abstract
- LICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. A key element of the ALICE upgrade is the construction of a new, ultra-light, high-resolution Inner Tracking System (ITS) based on monolithic CMOS pixel detectors. The primary focus of the ITS upgrade is on improving the performance for detection of heavy-flavour hadrons, and of thermal photons and low-mass di-electrons emitted by the QGP. With respect to the current detector, the new Inner Tracking System will significantly enhance the determination of the distance of closest approach to the primary vertex, the tracking efficiency at low transverse momenta, and the read-out rate capabilities. This will be obtained by seven concentric detector layers based on a 50 μm thick CMOS pixel sensor with a pixel pitch of about 30×30 μm2. This document, submitted to the LHCC (LHC experiments Committee) in September 2013, presents the design goals, a summary of the R&D activities, with focus on the technical implementation of the main detector components, and the projected detector and physics performance.
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| 2. |
- Abelev, B., et al.
(författare)
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Upgrade of the ALICE Experiment Letter Of Intent
- 2014
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
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Tidskriftsartikel (refereegranskat)abstract
- ALICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. These plans are presented in the ALICE Upgrade Letter of Intent, submitted to the LHCC (LHC experiments Committee) in September 2012. In order to fully exploit the physics reach of the LHC in this field, high-precision measurements of the heavy-flavour production, quarkonia, direct real and virtual photons, and jets are necessary. This will be achieved by an increase of the LHC Pb–Pb instant luminosity up to 6×1027 cm−2s−1 and running the ALICE detector with the continuous readout at the 50 kHz event rate. The physics performance accessible with the upgraded detector, together with the main detector modifications, are presented.
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| 3. |
- Abelev, B., et al.
(författare)
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Azimuthal anisotropy of D-meson production in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:3
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Tidskriftsartikel (refereegranskat)abstract
- The production of the prompt charmed mesonsD(0), D+, andD(*+) relative to the reaction plane was measured in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision of root s(NN) = 2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. D mesons were reconstructed via their hadronic decays at central rapidity in the transverse-momentum (pT) interval 2-16 GeV/c. The azimuthal anisotropy is quantified in terms of the second coefficient v(2) in a Fourier expansion of the D-meson azimuthal distribution and in terms of the nuclear modification factor R-AA, measured in the direction of the reaction plane and orthogonal to it. The v(2) coefficient was measured with three different methods and in three centrality classes in the interval 0%-50%. A positive v(2) is observed in midcentral collisions (30%-50% centrality class), with a mean value of 0.204(-0.036)(+0.099) (tot.unc.) in the interval 2 < pT < 6 GeV/c, which decreases towards more central collisions (10%-30% and 0%-10% classes). The positive v(2) is also reflected in the nuclear modification factor, which shows a stronger suppression in the direction orthogonal to the reaction plane formidcentral collisions. The measurements are compared to theoretical calculations of charm-quark transport and energy loss in high-density strongly interacting matter at high temperature. The models that include substantial elastic interactions with an expanding medium provide a good description of the observed anisotropy. However, they are challenged to simultaneously describe the strong suppression of high-pT yield of D mesons in central collisions and their azimuthal anisotropy in noncentral collisions.
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| 4. |
- Abelev, B., et al.
(författare)
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Beauty production in pp collisions at root s=2.76 TeV measured via semi-electronic decays
- 2014
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 738, s. 97-108
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE Collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity |y| < 0.8 and transverse momentum 1 < p(T)< 10 GeV/c, in pp collisions at root s = 2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD predictions agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, sigma(b -> e) = 3.47 +/- 0.40(stat)(+1.12)(-1.33)(sys) +/- 0.07(norm) mu b, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) calculations to obtain the total b (b) over bar production cross section, sigma(b (b) over bar) = 130 +/- 15.1(stat)(+42.1)(-49.8)(sys)(+3.4)(-3.1)(extr) +/- 2.5(norm) +/- 4.4(BR) mu b. (C) 2014 The Authors. Published by Elsevier B.V.
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| 5. |
- Abelev, B., et al.
(författare)
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Event-by-event mean p(T) fluctuations in pp and Pb-Pb collisions at the LHC
- 2014
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 74:10
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Tidskriftsartikel (refereegranskat)abstract
- Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at root s = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at root S-NN = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb-Pb data exhibit a similar-multiplicity dependence as that observed in pp. In central Pb-Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb-Pb are in qualitative agreement with previous measurements in Au-Au at lower collision energies and with expectations from models that incorporate collective phenomena.
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| 6. |
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| 7. |
- Abelev, B., et al.
(författare)
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Freeze-out radii extracted from three-pion cumulants in pp, p-Pb and Pb-Pb collisions at the LHC
- 2014
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 739, s. 139-151
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Tidskriftsartikel (refereegranskat)abstract
- In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose-Einstein correlations of identical bosons at low relative momentum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e. g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correlations in pp, p-Pb and Pb-Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p-Pb collisions are found to be 5-15% larger than those in pp, while those in Pb-Pb are 35-55% larger than those in p-Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p-Pb as compared to pp collisions at similar multiplicity. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
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| 8. |
- Abelev, B., et al.
(författare)
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J/psi production and nuclear effects in p-Pb collisions at=5.02 TeV
- 2014
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :2
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive J/psi production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < y (cms) < 3.53 and -4.46 < y (cms) < -2.96, down to zero transverse momentum, studying the mu (+) mu (-) decay mode. In this paper, the J/psi production cross section and the nuclear modification factor R (pPb) for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/psi yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results.
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| 9. |
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| 10. |
- Abelev, B., et al.
(författare)
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Measurement of quarkonium production at forward rapidity in collisions at TeV
- 2014
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 74:8
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Tidskriftsartikel (refereegranskat)abstract
- The inclusive production cross sections at forward rapidity of , , (1S) and (2S) are measured in collisions at with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.35 pb. Quarkonia are reconstructed in the dimuon-decay channel and the signal yields are evaluated by fitting the invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum and rapidity , over the ranges GeV/c for , GeV/c for all other resonances and for . The measured cross sections integrated over and , and assuming unpolarized quarkonia, are: b, b, nb and nb, where the first uncertainty is statistical and the second one is systematic. The results are compared to measurements performed by other LHC experiments and to theoretical models.
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