| 1. |
- Aad, G, et al.
(author)
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- 2015
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| 2. |
- Tabiri, S, et al.
(author)
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- 2021
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swepub:Mat__t
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| 3. |
- Bravo, L, et al.
(author)
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- 2021
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swepub:Mat__t
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| 4. |
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Abelev, B., et al.
(author)
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Upgrade of the ALICE Experiment Letter Of Intent
- 2014
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In: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
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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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| 9. |
- Abelev, B., et al.
(author)
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D Meson Elliptic Flow in Noncentral Pb-Pb Collisions at root(S)(NN)=2.76 TeV
- 2013
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In: Physical Review Letters. - 1079-7114. ; 111:10
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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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| 10. |
- Abelev, B, et al.
(author)
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Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
- 2013
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In: Physical Review Letters. - 1079-7114. ; 111:23
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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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| 11. |
- Abelev, B., et al.
(author)
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Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at root s=7 TeV
- 2012
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In: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 86:11
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Journal article (peer-reviewed)abstract
- The differential production cross section of electrons from semileptonic heavy-flavor hadron decays has been measured at midrapidity (\y\ < 0.5) in proton-proton collisions at root s = 7 TeV with ALICE at the LHC. Electrons were measured in the transverse momentum range 0.5 < p(t) < 8 GeV/c. Predictions from a fixed-order perturbative QCD calculation with next-to-leading-log resummation agree with the data within the theoretical and experimental uncertainties. DOI: 10.1103/PhysRevD.86.112007
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| 12. |
- Abelev, B., et al.
(author)
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Multiplicity dependence of two-particle azimuthal correlations in pp collisions at the LHC
- 2013
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In: Journal of High Energy Physics. - 1029-8479. ; :9
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Journal article (peer-reviewed)abstract
- We present the measurements of particle pair yields per trigger particle obtained from di-hadron azimuthal correlations in pp collisions at root s = 0.9, 2.76, and 7TeV recorded with the ALICE detector. The yields are studied as a function of the charged particle multiplicity. Taken together with the single particle yields the pair yields provide information about parton fragmentation at low transverse momenta, as well as on the contribution of multiple parton interactions to particle production. Data are compared to calculations using the PYTHIA6, PYTHIA8, and PHOJET event generators.
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| 13. |
- Abelev, B., et al.
(author)
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Net-Charge Fluctuations in Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2013
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In: Physical Review Letters. - 1079-7114. ; 110:15
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Journal article (peer-reviewed)abstract
- We report the first measurement of the net-charge fluctuations in Pb-Pb collisions at root s(NN) = 2.76 TeV, measured with the ALICE detector at the CERN Large Hadron Collider. The dynamical fluctuations per unit entropy are observed to decrease when going from peripheral to central collisions. An additional reduction in the amount of fluctuations is seen in comparison to the results from lower energies. We examine the dependence of fluctuations on the pseudorapidity interval, which may account for the dilution of fluctuations during the evolution of the system. We find that the fluctuations at the LHC are smaller compared to the measurements at the BNL Relativistic Heavy Ion Collider, and as such, closer to what has been theoretically predicted for the formation of a quark-gluon plasma. DOI: 10.1103/PhysRevLett.110.152301
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| 14. |
- Abelev, B., et al.
(author)
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Production of Muons from Heavy Flavor Decays at Forward Rapidity in pp and Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2012
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In: Physical Review Letters. - 1079-7114. ; 109:11
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Journal article (peer-reviewed)abstract
- The ALICE Collaboration has measured the inclusive production of muons from heavy-flavor decays at forward rapidity, 2.5 < y < 4, in pp and Pb-Pb collisions at root s(NN) = 2.76 TeV. The p(t)-differential inclusive cross section of muons from heavy-flavor decays in pp collisions is compared to perturbative QCD calculations. The nuclear modification factor is studied as a function of p(t) and collision centrality. A weak suppression is measured in peripheral collisions. In the most central collisions, a suppression of a factor of about 3-4 is observed in 6 < p(t) < 10 GeV/c. The suppression shows no significant p(t) dependence.
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| 15. |
- Abelev, B., et al.
(author)
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Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at root s=0.9, 2.76 and 7 TeV
- 2012
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 72:9
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Journal article (peer-reviewed)abstract
- Measurements of the sphericity of primary charged particles in minimum bias proton-proton collisions at root s = 0.9, 2.76 and 7 TeV with the ALICE detector at the LHC are presented. The observable is measured in the plane perpendicular to the beam direction using primary charged tracks with p(T) > 0.5 GeV/c in vertical bar eta vertical bar < 0.8. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity (N-ch) is reported for events with different p(T) scales ("soft" and "hard") defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity is presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low N-ch, whereas the event generators show an opposite tendency. The combined study of the sphericity and the mean p(T) with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.
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| 16. |
- Abelev, B., et al.
(author)
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Charge separation relative to the reaction plane in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
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In: Physical Review Letters. - 1079-7114. ; 110:1
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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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| 17. |
- Abelev, B., et al.
(author)
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Multi-strange baryon production in pp collisions at root s=7 TeV with ALICE
- 2012
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 712:4-5, s. 309-318
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Journal article (peer-reviewed)abstract
- A measurement of the multi-strange Xi(-) and Omega(-) baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for inelastic proton-proton collisions at a centre-of-mass energy of 7 TeV. The transverse momentum (p(T)) distributions were studied at mid-rapidity (vertical bar y vertical bar < 0.5) in the range of 0.6 < p(T) < 8.5 GeV/c Xi(-) for and Xi(+) baryons, and in the range of 0.8 < P-T < 5 GeV/c for Omega(-) and<(Omega)over bar>(+). Baryons and antibaryons were measured as separate particles and we find that the baryon to antibaryon ratio of both particle species is consistent with unity over the entire range of the measurement. The statistical precision of the current data has allowed us to measure a difference between the mean p(T) of Xi(-) ((Xi) over bar)(+) and Omega(-) ((Omega) over bar (+)). Particle yields, mean pi, and the spectra in the intermediate pi range are not well described by the PYTHIA Perugia 2011 tune Monte Carlo event generator, which has been tuned to reproduce the early LHC data. The discrepancy is largest for Omega(-)((Omega) over bar (+)). This PYTHIA tune approaches the pi spectra of Xi(-) and Xi(+) baryons below p(T) <0.85 GeV/c and describes the Xi(-) and Xi(+) spectra above p(T) > 6.0 GeV/c. We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of (Omega(-) +(Omega) over bar (+))/(Xi(-) + Xi(+)) as a function of transverse mass. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 18. |
- Abelev, B., et al.
(author)
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Pion, Kaon, and Proton Production in Central Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2012
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In: Physical Review Letters. - 1079-7114. ; 109:25
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Journal article (peer-reviewed)abstract
- In this Letter we report the first results on pi(+/-), K-+/-, p, and (p) over bar production at midrapidity (vertical bar y vertical bar < 0.5) in central Pb-Pb collisions at root s(NN) = 2.76 TeV, measured by the ALICE experiment at the LHC. The p(T) distributions and yields are compared to previous results at root s(NN) = 200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with root s(NN), which in hydrodynamic models is expected as a consequence of the increasing particle density. While the K/pi ratio is in line with predictions from the thermal model, the p/pi ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.
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| 19. |
- Abelev, B., et al.
(author)
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Technical Design Report for the Upgrade of the ALICE Inner Tracking System
- 2014
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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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| 20. |
- Abbas, E., et al.
(author)
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Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
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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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| 21. |
- Abbas, E., et al.
(author)
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Charmonium and e(+)e(-) pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV
- 2013
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:11
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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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| 22. |
- Abbas, E., et al.
(author)
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J/psi Elliptic Flow in Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2013
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In: Physical Review Letters. - 1079-7114. ; 111:16
-
Journal article (peer-reviewed)abstract
- We report on the first measurement of inclusive J/psi elliptic flow v(2) in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at root s(NN) = 2.76 TeV in the rapidity range 2.5 < y < 4.0. The dependence of the J/psi v(2) on the collision centrality and on the J/psi transverse momentum is studied in the range 0 <= p(T) < 10 GeV/c. For semicentral Pb-Pb collisions at root s(NN) = 2.76 TeV, an indication of nonzero v(2) is observed with a largest measured value of v(2) = 0.116 +/-0.046(stat) +/- 0.029(syst) for J/psi in the transverse momentum range 2 <= p(T) < 4 GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/psi nuclear modification factor and favors the scenario of a significant fraction of J/psi production from charm quarks in a deconfined partonic phase.
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| 23. |
- Abbas, E., et al.
(author)
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Performance of the ALICE VZERO system
- 2013
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In: Journal of Instrumentation. - 1748-0221. ; 8
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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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| 24. |
- Abelev, B., et al.
(author)
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J/psi Suppression at Forward Rapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2012
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In: Physical Review Letters. - 1079-7114. ; 109:7
-
Journal article (peer-reviewed)abstract
- The ALICE experiment has measured the inclusive J/psi production in Pb-Pb collisions at root s(NN) = 2.76 TeV down to zero transverse momentum in the rapidity range 2.5 < y < 4. A suppression of the inclusive J/psi yield in Pb-Pb is observed with respect to the one measured in pp collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0%-80% most central collisions, is 0.545 +/- 0.032(stat) +/- 0.083dsyst_ and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including J/psi production from charm quarks in a deconfined partonic phase can describe our data.
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| 25. |
- Abelev, B., et al.
(author)
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Measurement of inelastic, single- and double-diffraction cross sections in proton-proton collisions at the LHC with ALICE
- 2013
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:6
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Journal article (peer-reviewed)abstract
- Measurements of cross sections of inelastic and diffractive processes in proton-proton collisions at LHC energies were carried out with the ALICE detector. The fractions of diffractive processes in inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions: for single diffraction (diffractive mass M-X < 200 GeV/c(2)) sigma(SD)/sigma(INEL) = 0.21 +/- 0.03, 0.20(-0.08)(+0.07,) and 0.20(-0.07)(+0.04), respectively at centre-of-mass energies root s = 0.9, 2.76, and 7 TeV; for double diffraction (for a pseudorapidity gap Delta eta > 3) sigma(DD)/sigma(INEL) = 0.11 +/- 0.03, 0.12 +/- 0.05, and 0.12(-0.04)(+0.05), respectively at root s = 0.9, 2.76, and 7 TeV. To measure the inelastic cross section, beam properties were determined with van der Meer scans, and, using a simulation of diffraction adjusted to data, the following values were obtained: sigma(INEL) = 62.8(-4.0)(+2.4)(model) +/- 1.2(lumi) mb at root s = 2.76 TeV and 73.2(-4.6)(+2.0)(model) +/- 2.6(lumi) mb at root s = 7 TeV. The single- and double-diffractive cross sections were calculated combining relative rates of diffraction with inelastic cross sections. The results are compared to previous measurements at proton-antiproton and proton-proton colliders at lower energies, to measurements by other experiments at the LHC, and to theoretical models.
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