1. |
- 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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2. |
- Abbas, E., et al.
(author)
-
Centrality dependence of the pseudorapidity density distribution for charged particles 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. ; 726:4-5, s. 610-622
-
Journal article (peer-reviewed)abstract
- We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0-5%, 5-10%, 10-20%, and 20-30% most central events) in Pb-Pb collisions at root s(NN) = 2.76 TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, -5.0 < eta < 5.5, and employing a special analysis technique based on collisions arising from LHC 'satellite' bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles (N-ch = 17165 +/- 772 for the 0-5% most central collisions). From the measured dN(ch)/d eta distribution we derive the rapidity density distribution, dN(ch)/dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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3. |
- Abbas, E., et al.
(author)
-
Mid-rapidity anti-baryon to baryon ratios in pp collisions at root s=0.9, 2.76 and 7 TeV measured by ALICE
- 2013
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:7
-
Journal article (peer-reviewed)abstract
- The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for (p) over bar /p, (Lambda) over bar/Lambda, (Xi) over bar (+)/(Xi) over bar (-) and (Omega) over bar (+)/(Omega) over bar (-) in pp collisions at root s = 0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of (p) over bar /p, (Lambda) over bar/(Lambda) over bar, (Xi) over bar (+)/(Xi) over bar (-) and (Omega) over bar (+)/(Omega) over bar (-), reaching values compatible with unity for root s = 7 TeV, complement the earlier (p) over bar /p measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of alpha(J) approximate to 0.5, which are suppressed with increasing rapidity interval Delta y. Any significant contribution of an exchange not suppressed at large Delta y (reached at LHC energies) is disfavoured.
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4. |
- Abelev, B., et al.
(author)
-
Centrality dependence of pi, K, and p production in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:4
-
Journal article (peer-reviewed)abstract
- In this paper measurements are presented of pi(+/-), K-+/-, p, and (p) over bar production at midrapidity (vertical bar y vertical bar < 0.5), in Pb-Pb collisions at root s(NN) = 2.76 TeV as a function of centrality. The measurement covers the transverse-momentum (p(T)) range from 100, 200, and 300 MeV/c up to 3, 3, and 4.6 GeV/c for pi, K, and p, respectively. The measured p(T) distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the p(T) distributions are not well reproduced by hydrodynamic models. Ratios of integrated particle yields are found to be nearly independent of centrality. The yield of protons normalized to pions is a factor similar to 1.5 lower than the expectation from thermal models.
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5. |
- 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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6. |
- Abelev, B., et al.
(author)
-
Centrality, rapidity and transverse momentum dependence of J/Psi suppression in Pb-Pb collisions at root(NN)-N-S=2.76TeV
- 2014
-
In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 734, s. 314-327
-
Journal article (peer-reviewed)abstract
- The inclusive J/.nuclear modification factor (R-AA) in Pb-Pb collisions at root(NN)-N-S = 2.76TeVhas been measured by ALICE as a function of centrality in the e+ e-decay channel at mid-rapidity (| y| < 0.8) and as a function of centrality, transverse momentum and rapidity in the + -decay channel at forward-rapidity (2.5 < y < 4). The J/.yields measured in Pb-Pb are suppressed compared to those in ppcollisions scaled by the number of binary collisions. The RAAintegrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is 0.72 - 0.06(stat.) - 0.10(syst.) at mid-rapidity and 0.58 - 0.01(stat.) - 0.09(syst.) at forward-rapidity. At low transverse momentum, significantly larger values of RAAare measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the J/.yield originates from charm quark (re) combination in the deconfined partonic medium. (C) 2014 The Authors. Published by Elsevier B. V.
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7. |
- 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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8. |
- Abelev, B., et al.
(author)
-
Charged kaon femtoscopic correlations in pp collisions at root s=7 TeV
- 2013
-
In: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 87:5
-
Journal article (peer-reviewed)abstract
- Correlations of two charged identical kaons (KchKch) are measured in pp collisions at root s = 7 TeV by the ALICE experiment at the Large Hadron Collider (LHC). One-dimensional (KKch)-K-ch correlation functions are constructed in three multiplicity and four transverse momentum ranges. The (KKch)-K-ch femtoscopic source parameters R and lambda are extracted. The (KKch)-K-ch correlations show a slight increase of femtoscopic radii with increasing multiplicity and a slight decrease of radii with increasing transverse momentum. These trends are similar to the ones observed for pi pi and K-s(0) K-s(0) correlations in pp and heavy-ion collisions. However at high multiplicities, there is an indication that the one-dimensional correlation radii for charged kaons are larger than those for pions in contrast to what was observed in heavy-ion collisions at the Relativistic Heavy-Ion Collider. DOI:10.1103/PhysRevD.87.052016
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9. |
- Abelev, B., et al.
(author)
-
J/psi production and nuclear effects in p-Pb collisions at=5.02 TeV
- 2014
-
In: Journal of High Energy Physics. - 1029-8479. ; :2
-
Journal article (peer-reviewed)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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10. |
- 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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11. |
- Abelev, B., et al.
(author)
-
Pseudorapidity Density of Charged Particles in p plus Pb Collisions at root s(NN)=5.02 TeV
- 2013
-
In: Physical Review Letters. - 1079-7114. ; 110:3
-
Journal article (peer-reviewed)abstract
- The charged-particle pseudorapidity density measured over four units of pseudorapidity in nonsingle-diffractive p + Pb collisions at a center-of-mass energy per nucleon pair root s(NN) = 5.02 TeV is presented. The average value at midrapidity is measured to be 16.81 +/- 0.71 (syst), which corresponds to 2.14 +/- 0.17 (syst) per participating nucleon, calculated with the Glauber model. This is 16% lower than in nonsingle-diffractive pp collisions interpolated to the same collision energy and 84% higher than in d + Au collisions at root s(NN) = 0.2 TeV. The measured pseudorapidity density in p + Pb collisions is compared to model predictions and provides new constraints on the description of particle production in high-energy nuclear collisions. DOI: 10.1103/PhysRevLett.110.032301
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12. |
- Abelev, B., et al.
(author)
-
Transverse Momentum Distribution and Nuclear Modification Factor of Charged Particles in p plus Pb Collisions at root(NN)-N-s=5.02 TeV
- 2013
-
In: Physical Review Letters. - 1079-7114. ; 110:8
-
Journal article (peer-reviewed)abstract
- The transverse momentum (pT) distribution of primary charged particles is measured in minimum bias (non-single-diffractive) p + Pb collisions at root(NN)-N-s = 5.02 TeV with the ALICE detector at the LHC. The pT spectra measured near central rapidity in the range 0.5< p(T) < 20 GeV/c exhibit a weak pseudorapidity dependence. The nuclear modification factor R-pPb is consistent with unity for p(T) above 2 GeV/c. This measurement indicates that the strong suppression of hadron production at high p(T) observed in Pb + Pb collisions at the LHC is not due to an initial-state effect. The measurement is compared to theoretical calculations. DOI: 10.1103/PhysRevLett.110.082302
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13. |
- 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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14. |
- Abelev, B., et al.
(author)
-
Upgrade of the ALICE Experiment Letter Of Intent
- 2014
-
In: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
-
Journal article (peer-reviewed)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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15. |
- Abbas, E., et al.
(author)
-
Charmonium and e(+)e(-) pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:11
-
Journal article (peer-reviewed)abstract
- The ALICE Collaboration at the LHC has measured the J/psi and psi' photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at root s(NN) = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 mu b(-1). The cross section for coherent and incoherent J/psi production in the rapidity interval -0.9 < y < 0.9, are d sigma(coh)(J/psi)/dy = 2.38(-0.24)(+0.34)(sta + sys) mb and d sigma(inc)(J/psi)/dy = 0.98(-0.17)(+0.19)(sta + sys) mb and , respectively. The results are compared to theoretical models for J/psi production and the coherent cross section is found to be in good agreement with those models incorporating moderate nuclear gluon shadowing at Bjorken-x around 10(-3), such as EPS09 parametrization. In addition the cross section for the process gamma gamma -> e(+)e(-) has been measured and found to be in agreement with models implementing QED at leading order.
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16. |
- Abbas, E., et al.
(author)
-
Performance of the ALICE VZERO system
- 2013
-
In: Journal of Instrumentation. - 1748-0221. ; 8
-
Journal article (peer-reviewed)abstract
- ALICE is an LHC experiment devoted to the study of strongly interacting matter in proton-proton, proton-nucleus and nucleus-nucleus collisions at ultra-relativistic energies. The ALICE VZERO system, made of two scintillator arrays at asymmetric positions, one on each side of the interaction point, plays a central role in ALICE. In addition to its core function as a trigger source, the VZERO system is used to monitor LHC beam conditions, to reject beam-induced backgrounds and to measure basic physics quantities such as luminosity, particle multiplicity, centrality and event plane direction in nucleus-nucleus collisions. After describing the VZERO system, this publication presents its performance over more than four years of operation at the LHC.
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17. |
- Abelev, B., et al.
(author)
-
D Meson Elliptic Flow in Noncentral Pb-Pb Collisions at root(S)(NN)=2.76 TeV
- 2013
-
In: Physical Review Letters. - 1079-7114. ; 111:10
-
Journal article (peer-reviewed)abstract
- Azimuthally anisotropic distributions of D-0, D+, and D*+ mesons were studied in the central rapidity region (vertical bar y vertical bar < 0.8) in Pb-Pb collisions at a center-of-mass energy root(S)(NN) = 2.76 TeV per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient upsilon(2) (commonly denoted elliptic flow) was measured in the centrality class 30%-50% as a function of the D meson transverse momentum p(T), in the range 2-16 GeV/c. The measured upsilon(2) of D mesons is comparable in magnitude to that of light-flavor hadrons. It is positive in the range 2 < p(T) < 6 GeV/c with 5.7 sigma significance, based on the combination of statistical and systematic uncertainties.
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18. |
- Abelev, B, et al.
(author)
-
Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
- 2013
-
In: Physical Review Letters. - 1079-7114. ; 111:23
-
Journal article (peer-reviewed)abstract
- The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta p_{T} between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even p_{T} shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.
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19. |
- Abelev, B., et al.
(author)
-
Energy dependence of the transverse momentum distributions of charged particles in pp collisions measured by ALICE
- 2013
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:12
-
Journal article (peer-reviewed)abstract
- Differential cross sections of charged particles in inelastic pp collisions as a function of pT have been measured at root s = 0.9, 2.76 and 7 TeV at the LHC. The pT spectra are compared to NLO-pQCD calculations. Though the differential cross section for an individual root s cannot be described by NLO-pQCD, the relative increase of cross section with root s is in agreement with NLO-pQCD. Based on these measurements and observations, procedures are discussed to construct pp reference spectra at root s = 2.76 and 5.02 TeV up to pT = 50 GeV/c as required for the calculation of the nuclear modification factor in nucleus-nucleus and proton-nucleus collisions.
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20. |
- Abelev, B, et al.
(author)
-
K_{S}^{0} and Λ Production in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
- 2013
-
In: Physical Review Letters. - 1079-7114. ; 111:22
-
Journal article (peer-reviewed)abstract
- The ALICE measurement of K_{S}^{0} and Λ production at midrapidity in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV is presented. The transverse momentum (p_{T}) spectra are shown for several collision centrality intervals and in the p_{T} range from 0.4 GeV/c (0.6 GeV/c for Λ) to 12 GeV/c. The p_{T} dependence of the Λ/K_{S}^{0} ratios exhibits maxima in the vicinity of 3 GeV/c, and the positions of the maxima shift towards higher p_{T} with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate p_{T} is not observed in pp interactions at sqrt[s]=0.9 TeV and at sqrt[s]=7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured p_{T} spectra above 2 GeV/c progressively decouple from hydrodynamical-model calculations. For higher values of p_{T}, models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the p_{T} dependence of the Λ/K_{S}^{0} ratio.
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21. |
- Abelev, B., et al.
(author)
-
Long-range angular correlations of pi, K and p in p-Pb collisions at root s(NN)=5.02 TeV
- 2013
-
In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 726:1-3, s. 164-177
-
Journal article (peer-reviewed)abstract
- Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3 < p(T) < 4 GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range vertical bar n(lab)vertical bar < 0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of p(T) and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, 4, is observed to be smaller than that for pions, v(2)(pi), up to about p(T) = 2 GeV/c. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The v(2)(p) is found to be smaller at low P-T and larger at higher p(T) than v(2)(pi), with a crossing occurring at about 2 GeV/c. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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22. |
- Abelev, B., et al.
(author)
-
Measurement of quarkonium production at forward rapidity in collisions at TeV
- 2014
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 74:8
-
Journal article (peer-reviewed)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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23. |
- Abelev, B., et al.
(author)
-
Multi-strange baryon production at mid-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. ; 728, s. 216-227
-
Journal article (peer-reviewed)abstract
- The production of Xi(-) and Omega(-) baryons and their anti-particles in Pb-Pb collisions root s(NN) = 2.76 TeV has been measured using the ALICE detector. The transverse momentum spectra at mid-rapidity (vertical bar y vertical bar < 0.5) for charged Xi and Omega hyperons have been studied in the range 0.6 < P-T < 8.0 GeV/c and 1.2 < p(T) < 7.0 GeV/c, respectively, and in several centrality intervals (from the most central 0-.10% to the most peripheral 60-80% collisions). These spectra have been compared with the predictions of recent hydrodynamic models. In particular, the Krakow and EPOS models give a satisfactory description of the data, with the latter covering a wider P-T range. Mid-rapidity yields, integrated over p(T), have been determined. The hyperon-to-pion ratios are similar to those at RHIC: they rise smoothly with centrality up to < N-part > similar to 150 and saturate thereafter. The enhancements (yields per participant nucleon relative to those in pp collisions) increase both with the strangeness content of the baryon and with centrality, but are less pronounced than at lower energies. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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24. |
- Abelev, B., et al.
(author)
-
Multiplicity dependence of pion, kaon, proton and lambda production in p-Pb collisions at root s(NN)=5.02 TeV
- 2014
-
In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 728, s. 25-38
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Journal article (peer-reviewed)abstract
- In this Letter, comprehensive results on pi(+/-), K-+/-, K-S(0), p((p) over bar) and A((A) over bar) production at mid-rapidity (0 < y(CMS) < 0.5) in p-Pb collisions at root s(NN) = 5.02 TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb-Pb collisions at the LHC. The measured pr distributions are compared to d-Au, Au-Au and Pb-Pb results at lower energy and with predictions based on QCD-inspired and hydrodynamic models. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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25. |
- Abelev, B., et al.
(author)
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Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC
- 2013
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 727:4-5, s. 371-380
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Journal article (peer-reviewed)abstract
- The average transverse momentum (p(T)) versus the charged-particle multiplicity N-ch was measured in p-Pb collisions at a collision energy per nucleon-nucleon root S-NN = 5.02 TeV and in pp collisions at collision energies of root s = 0.9, 2.76, and 7 TeV in the kinematic range 0.15 < p(T) < 10.0 GeV/c and vertical bar eta vertical bar < 0.3 with the ALICE apparatus at the LHC. These data are compared to results in Pb-Pb collisions at root S-NN = 2.76 TeV at similar charged-particle multiplicities. In pp and p-Pb collisions, a strong increase of (p(T)) with N-ch is observed, which is much stronger than that measured in Pb-Pb collisions. For pp collisions, this could be attributed, within a model of hadronizing strings, to multiple-parton interactions and to a final-state color reconnection mechanism. The data in p-Pb and Pb-Pb collisions cannot be described by an incoherent superposition of nucleon-nucleon collisions and pose a challenge to most of the event generators. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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