The ALICE Collaboration has measured inclusive J/psi production in pp collisions at a center of mass energy sqrt(s)=2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ...ranges |y|<0.9 and 2.5
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity (|y| < 0.7) is measured in Pb-Pb collisions ...at ... TeV with ALICE at the LHC. The particle azimuthal distribution with respect to the reaction plane can be parametrized with a Fourier expansion, where the second coefficient (v sub(2)) represents the elliptic flow. The v sub(2) coefficient of inclusive electrons is measured in three centrality classes (0-10%, 10-20% and 20-40%) with the event plane and the scalar product methods in the transverse momentum (p sub(T)) intervals 0.5-13 GeV/c and 0.5-8 GeV/c, respectively. After subtracting the background, mainly from photon conversions and Dalitz decays of neutral mesons, a positive v sub(2) of electrons from heavy-flavour hadron decays is observed in all centrality classes, with a maximum significance of 5.9 sigma in the interval 2 < p sub(T) < 2.5 GeV/c in semi-central collisions (20-40%). The value of v sub(2) decreases towards more central collisions at low and intermediate p sub(T) (0.5 < p sub(T) < 3 GeV/c). The v sub(2) of electrons from heavy-flavour hadron decays at mid-rapidity is found to be similar to the one of muons from heavy-flavour hadron decays at forward rapidity (2.5 < y < 4). The results are described within uncertainties by model calculations including substantial elastic interactions of heavy quarks with an expanding strongly-interacting medium. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The elliptic, triangular, quadrangular and pentagonal anisotropic flow coefficients for pi super( plus or minus ), K super( ...plus or minus ) and ... in Pb-Pb collisions at ... TeV were measured with the ALICE detector at the Large Hadron Collider. The results were obtained with the Scalar Product method, correlating the identified hadrons with reference particles from a different pseudorapidity region. Effects not related to the common event symmetry planes (non-flow) were estimated using correlations in pp collisions and were subtracted from the measurement. The obtained flow coefficients exhibit a clear mass ordering for transverse momentum (p sub(T)) values below approximately 3 GeV/c. In the intermediate p sub(T) region (3 < p sub(T) < 6 GeV/c), particles group at an approximate level according to the number of constituent quarks, suggesting that coalescence might be the relevant particle production mechanism in this region. The results for p sub(T) < 3 GeV/c are described fairly well by a hydrodynamical model (iEBE-VISHNU) that uses initial conditions generated by A Multi-Phase Transport model (AMPT) and describes the expansion of the fireball using a value of 0.08 for the ratio of shear viscosity to entropy density ( eta /s), coupled to a hadronic cascade model (UrQMD). Finally, expectations from AMPT alone fail to quantitatively describe the measurements for all harmonics throughout the measured transverse momentum region. However, the comparison to the AMPT model highlights the importance of the late hadronic rescattering stage to the development of the observed mass ordering at low values of p sub(T) and of coalescence as a particle production mechanism for the particle type grouping at intermediate values of p sub(T) for all harmonics. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The measurement of prompt D-meson production as a function of multiplicity in p-Pb collisions at ... TeV with the ALICE ...detector at the LHC is reported. D super(0), D super(+) and D super(+) mesons are reconstructed via their hadronic decay channels in the centre-of-mass rapidity range -0.96 < y sub(cms) < 0.04 and transverse momentum interval 1<p sub(T) <24 GeV/c. The multiplicity dependence of D-meson production is examined by either comparing yields in p-Pb collisions in different event classes, selected based on the multiplicity of produced particles or zero-degree energy, with those in pp collisions, scaled by the number of binary nucleon-nucleon collisions (nuclear modification factor); as well as by evaluating the per-event yields in p-Pb collisions in different multiplicity intervals normalised to the multiplicity-integrated ones (relative yields). The nuclear modification factors for D super(0), D super(+) and D super(+) are consistent with one another. The D-meson nuclear modification factors as a function of the zero-degree energy are consistent with unity within uncertainties in the measured p sub(T) regions and event classes. The relative D-meson yields, calculated in various p sub(T) intervals, increase as a function of the charged-particle multiplicity. The results are compared with the equivalent pp measurements at ... TeV as well as with EPOS 3 calculations. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The inclusive production of the psi (2S) charmonium state was studied as a function of centrality in p-Pb collisions at the ...nucleon-nucleon center of mass energy ... TeV at the CERN LHC. The measurement was performed with the ALICE detector in the center of mass rapidity ranges -4.46 < y sub(cms) < -2.96 and 2.03 < y sub(cms) < 3.53, down to zero transverse momentum, by reconstructing the psi (2S) decay to a muon pair. The psi (2S) production cross section sigma sub( ) psi 2S)is presented as a function of the collision centrality, which is estimated through the energy deposited in forward rapidity calorimeters. The relative strength of nuclear effects on the psi (2S) and on the corresponding 1S charmonium state J/ psi is then studied by means of the double ratio of cross sections sigma sub( ) psi 2S)/ sigma sub(J/) psi sub(pPb) / sigma sub( ) psi 2S)/ sigma sub(J/) psi sub(pp) between p-Pb and pp collisions, and by the values of the nuclear modification factors for the two charmonium states. The results show a large suppression of psi (2S) production relative to the J/ psi at backward (negative) rapidity, corresponding to the flight direction of the Pb-nucleus, while at forward (positive) rapidity the suppressions of the two states are comparable. Finally, comparisons to results from lower energy experiments and to available theoretical models are presented. Figure not available: see fulltext.
The production of J/ psi and psi (2S) was studied with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity (2.5 < y < 4) down to zero transverse ...momentum (p sub( t )) in the dimuon decay channel. Inclusive J/ psi yields were extracted in different centrality classes and the centrality dependence of the average p sub( t ) is presented. The J/ psi suppression, quantified with the nuclear modification factor (R sub(AA)), was measured as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/ psi production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the psi (2S) suppression are provided via the ratio of psi (2S) over J/ psi measured in pp and Pb-Pb collisions. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The production of prompt charmed mesons D super(0), D super(+) and D super(+), and their antiparticles, was measured with ...the ALICE detector in Pb-Pb collisions at the centre-of-mass energy per nucleon pair, ..., of 2.76 TeV. The production yields for rapidity |y| < 0.5 are presented as a function of transverse momentum, p sub(T), in the interval 1-36 GeV/c for the centrality class 0-10% and in the interval 1-16 GeV/c for the centrality class 30-50%. The nuclear modification factor R sub(AA) was computed using a proton-proton reference at ... TeV, based on measurements at ... TeV and on theoretical calculations. A maximum suppression by a factor of 5-6 with respect to binary-scaled pp yields is observed for the most central collisions at p sub(T) of about 10 GeV/c. A suppression by a factor of about 2-3 persists at the highest p sub(T) covered by the measurements. At low p sub(T) (1-3 GeV/c), the R sub(AA) has large uncertainties that span the range 0.35 (factor of about 3 suppression) to 1 (no suppression). In all p sub(T) intervals, the R sub(AA) is larger in the 30-50% centrality class compared to central collisions. The D-meson R sub(AA) is also compared with that of charged pions and, at large p sub(T), charged hadrons, and with model calculations. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The production of prompt D sub(s) super(+) mesons was measured for the first time in collisions of heavy nuclei with the ...ALICE detector at the LHC. The analysis was performed on a data sample of Pb-Pb collisions at a centre-of-mass energy per nucleon pair, ... sub(,) of 2.76 TeV in two different centrality classes, namely 0-10% and 20-50%. D sub(s) super(+) mesons and their antiparticles were reconstructed at mid-rapidity from their hadronic decay channel D sub(s) super(+) arrow right pi super(+), with arrow right K super(-)K super(+), in the transverse momentum intervals 4 < p sub(T) < 12GeV/c and 6 < p sub(T) < 12 GeV/c for the 0-10% and 20-50% centrality classes, respectively. The nuclear modification factor R sub(AA) was computed by comparing the p sub(T)-differential production yields in Pb-Pb collisions to those in proton-proton (pp) collisions at the same energy. This pp reference was obtained using the cross section measured at ... TeV and scaled to ... TeV. The R sub(AA) of D sub(s) super(+) mesons was compared to that of non-strange D mesons in the 10% most central Pb-Pb collisions. At high p sub(T) (8 < p sub(T) < 12 GeV/c) a suppression of the D sub(s) super(+)-meson yield by a factor of about three, compatible within uncertainties with that of non-strange D mesons, is observed. At lower p sub(T) (4 < p sub(T) < 8 GeV/c) the values of the D sub(s) super(+)-meson R sub(AA) are larger than those of non-strange D mesons, although compatible within uncertainties. The production ratios D sub(s) super(+)/D super(0) and D sub(s) super(+)/D super(+) were also measured in Pb-Pb collisions and compared to their values in proton-proton collisions. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The nuclear modification factor, R sub(AA), of the prompt charmed mesons D super(0), D super(+) and D super(+), and their ...antiparticles, was measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass energy ... TeV in two transverse momentum intervals, 5 < p sub(T) < 8 GeV/c and 8 < p sub(T) < 16 GeV/c, and in six collision centrality classes. The R sub(AA) shows a maximum suppression of a factor of 5-6 in the 10% most central collisions. The suppression and its centrality dependence are compatible within uncertainties with those of charged pions. A comparison with the R sub(AA) of non-prompt J/ psi from B meson decays, measured by the CMS Collaboration, hints at a larger suppression of D mesons in the most central collisions. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).We report the measurement of a new observable of jet quenching in central Pb-Pb collisions at ... TeV, based on the ...semi-inclusive rate of charged jets recoiling from a high transverse momentum (high-p sub(T)) charged hadron trigger. Jets are measured using collinear-safe jet reconstruction with infrared cutoff for jet constituents of 0.15 GeV, for jet resolution parameters R = 0.2, 0.4 and 0.5. Underlying event background is corrected at the event-ensemble level, without imposing bias on the jet population. Recoil jet spectra are reported in the range 20<p sub(T,jet) super(ch)<100GeV. Reference distributions for pp collisions at ... TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at ... TeV. The recoil jet yield in central Pb-Pb collisions is found to be suppressed relative to that in pp collisions. No significant medium-induced broadening of the intra-jet energy profile is observed within 0.5 radians relative to the recoil jet axis. The angular distribution of the recoil jet yield relative to the trigger axis is found to be similar in central Pb-Pb and pp collisions, with no significant medium-induced acoplanarity observed. Large-angle jet deflection, which may provide a direct probe of the nature of the quasi-particles in hot QCD matter, is explored. Figure not available: see fulltext.
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