| 31. |
- Abelev, B., et al.
(author)
-
Production of charged pions, kaons and protons at large transverse momenta in pp and Pb-Pb collisions at root s(NN)=2.76 TeV
- 2014
-
In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 736, s. 196-207
-
Journal article (peer-reviewed)abstract
- Transverse momentum spectra of pi(+/-), K-+/- and p((p) over bar) up to p(T) = 20 GeV/c at mid-rapidity in pp, peripheral (60-80%) and central (0-5%) Pb-Pb collisions at v root s(NN) = 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pionratios both show a distinct peak at p(T) approximate to 3 GeV/c in central Pb-Pb collisions. Below the peak, p(T) < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For p(T) > 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for pi(+/-), K-+/- and p((p) over bar) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
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| 32. |
- Abelev, B., et al.
(author)
-
Production of K*(892)(0) and phi(1020) in pp collisions at root s=7 TeV
- 2012
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 72:10
-
Journal article (peer-reviewed)abstract
- The production of K*(892)(0) and phi(1020) in pp collisions at root s = 7 TeV was measured by the ALICE experiment at the LHC. The yields and the transverse momentum spectra d(2)N/dydp(T) at midrapidity vertical bar y vertical bar < 0.5 in the range 0 < p(T) < 6 GeV/c for K*(892)(0) and 0.4 < p(T) < 6 GeV/c for phi(1020) are reported and compared to model predictions. Using the yield of pions, kaons, and Omega baryons measured previously by ALICE at root s = 7 TeV, the ratios K*/K-, phi/K*, phi/ K-, phi/pi(-), and (Omega + <(Omega)over bar>)/phi are presented. The values of the K*/K-, phi/K* and phi/K- ratios are similar to those found at lower centre-of-mass energies. In contrast, the phi/pi(-) ratio, which has been observed to increase with energy, seems to saturate above 200 GeV. The (Omega + (Omega) over bar)/phi ratio in the p(T) range 1-5 GeV/ c is found to be in good agreement with the prediction of the HIJING/B (B) over bar v2.0model with a strong colour field.
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| 33. |
- Abelev, B., et al.
(author)
-
Suppression of Upsilon(1S) at forward rapidity in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2014
-
In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 738, s. 361-372
-
Journal article (peer-reviewed)abstract
- We report on the measurement of the inclusive Upsilon(1S) production in Pb-Pb collisions at root s(NN) = 2.76 TeV carried out at forward rapidity (2.5 < y < 4) and down to zero transverse momentum using its mu(+)mu(-) decay channel with the ALICE detector at the Large Hadron Collider. Astrong suppression of the inclusive Upsilon(1S) yield is observed with respect to pp collisions scaled by the number of independent nucleo-nnucleon collisions. The nuclear modification factor, for events in the 0-90% centrality range, amounts to 0.30 +/- 0.05(stat) +/- 0.04(syst). The observed Upsilon(1S) suppression tends to increase with the centrality of the collision and seems more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence. (C) 2014 The Authors. Published by Elsevier B. V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP(3).
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| 34. |
- Abelev, B., et al.
(author)
-
Technical Design Report for the Upgrade of the ALICE Inner Tracking System
- 2014
-
In: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
-
Journal article (peer-reviewed)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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| 35. |
- Abelev, B., et al.
(author)
-
Transverse momentum dependence of inclusive primary charged-particle production in p-Pb collisions at root S-NN=5.02 TeV
- 2014
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 74:9
-
Journal article (peer-reviewed)abstract
- The transverse momentum (pT) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at root S-NN = 5.02 TeV with the ALICE detector at the LHC in the range 0.15 < pT < 50 GeV/c. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for pT larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for pT around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb-Pb collisions at root S-NN = 2.76 TeV.
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| 36. |
- Abelev, B., et al.
(author)
-
Two- and three-pion quantum statistics correlations in Pb-Pb collisions at root S-NN=2.76 TeV at the CERN Large Hadron Collider
- 2014
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:2
-
Journal article (peer-reviewed)abstract
- Correlations induced by quantum statistics are sensitive to the spatiotemporal extent as well as dynamics of particle-emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two- and three-pion correlations of same and mixed charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at root S-NN = 2.76 TeV at the CERN Large Hadron Collider with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission. The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged-pion emission of 23% +/- 8%.
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| 37. |
- Abelev, B., et al.
(author)
-
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
-
In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 720:1-3, s. 52-62
-
Journal article (peer-reviewed)abstract
- The inclusive transverse momentum (p(T)) distributions of primary charged particles are measured in the pseudo-rapidity range vertical bar eta vertical bar <0.8 as a function of event centrality in Pb-Pb collisions at root S-NN = 2.76 TeV with ALICE at the LHC. The data are presented in the p(T) range 0.15 < p(T) <50 GeV/c for nine centrality intervals from 70-80% to 0-5%. The results in Pb-Pb are presented in terms of the nuclear modification factor R-AA using a pp reference spectrum measured at the same collision energy. We observe that the suppression of high-p(T) particles strongly depends on event centrality. The yield is most suppressed in central collisions (0-5%) with R-AA approximate to 0.13 at p(T) = 6-7 GeV/c. Above p(T) = 7 GeV/c, there is a significant rise in the nuclear modification factor, which reaches R-AA approximate to 0.4 for p(T) > 30 GeV/c. In peripheral collisions (70-80%), only moderate suppression (R-AA approximate to 0.6-0.7) and a weak p(T) dependence is observed. The measured nuclear modification factors are compared to other measurements and model calculations. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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| 38. |
- Abelev, B., et al.
(author)
-
Centrality determination of Pb-Pb collisions at root s(NN)=2.76 TeV with ALICE
- 2013
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:4
-
Journal article (peer-reviewed)abstract
- This publication describes the methods used to measure the centrality of inelastic Pb-Pb collisions at a center-of-mass energy of 2.76 TeV per colliding nucleon pair with ALICE. The centrality is a key parameter in the study of the properties of QCD matter at extreme temperature and energy density, because it is directly related to the initial overlap region of the colliding nuclei. Geometrical properties of the collision, such as the number of participating nucleons and the number of binary nucleon-nucleon collisions, are deduced from a Glauber model with a sharp impact parameter selection and shown to be consistent with those extracted from the data. The centrality determination provides a tool to compare ALICE measurements with those of other experiments and with theoretical calculations.
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| 39. |
- Abelev, B., et al.
(author)
-
Charge correlations using the balance function in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
-
In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 723:4-5, s. 267-279
-
Journal article (peer-reviewed)abstract
- In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a probe to gain insight into the charge creation mechanisms. In this Letter, we report the first results of such studies using the electric charge balance function in the relative pseudorapidity (Delta eta) and azimuthal angle (Delta phi) in Pb-Pb collisions at root s(NN) = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The width of the balance function decreases with growing centrality (i.e. for more central collisions) in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured correlations in Delta phi but fails to describe the correlations in Delta eta. A thermal blast-wave model incorporating local charge conservation and tuned to describe the p(T) spectra and v(2) measurements reported by ALICE, is used to fit the centrality dependence of the width of the balance function and to extract the average separation of balancing charges at freeze-out. The comparison of our results with measurements at lower energies reveals an ordering with root s(NN): the balance functions become narrower with increasing energy for all centralities. This is consistent with the effect of larger radial flow at the LHC energies but also with the late stage creation scenario of balancing charges. However, the relative decrease of the balance function widths in Delta eta and Delta phi, with centrality from the highest SPS to the LHC energy exhibits only small differences. This observation cannot be interpreted solely within the framework where the majority of the charge is produced at a later stage in the evolution of the heavy-ion collision. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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| 40. |
- Abelev, B., et al.
(author)
-
Charge separation relative to the reaction plane in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
-
In: Physical Review Letters. - 1079-7114. ; 110:1
-
Journal article (peer-reviewed)abstract
- Measurements of charge-dependent azimuthal correlations with the ALICE detector at the LHC are reported for Pb-Pb collisions at root s(NN) = 2.76 TeV. Two- and three-particle charge-dependent azimuthal correlations in the pseudorapidity range vertical bar eta vertical bar < 0.8 are presented as a function of the collision centrality, particle separation in pseudorapidity, and transverse momentum. A clear signal compatible with a charge-dependent separation relative to the reaction plane is observed, which shows little or no collision energy dependence when compared to measurements at RHIC energies. This provides a new insight for understanding the nature of the charge-dependent azimuthal correlations observed at RHIC and LHC energies. DOI: 10.1103/PhysRevLett.110.012301
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