First measurements of balance functions (BFs) of all combinations of identified charged hadron (π,K,p) pairs in Pb–Pb collisions at sNN=2.76 TeV recorded by the ALICE detector are presented. The BF ...measurements are carried out as two-dimensional differential correlators versus the relative rapidity (Δy) and azimuthal angle (Δφ) of hadron pairs, and studied as a function of collision centrality. The Δφ dependence of BFs is expected to be sensitive to the light quark diffusivity in the quark–gluon plasma. While the BF azimuthal widths of all pairs substantially decrease from peripheral to central collisions, the longitudinal widths exhibit mixed behaviors: BFs of ππ and cross-species pairs narrow significantly in more central collisions, whereas those of KK and pp are found to be independent of collision centrality. This dichotomy is qualitatively consistent with the presence of strong radial flow effects and the existence of two stages of quark production in relativistic heavy-ion collisions. Finally, the first measurements of the collision centrality evolution of BF integrals are presented, with the observation that charge balancing fractions are nearly independent of collision centrality in Pb–Pb collisions. Overall, the results presented provide new and challenging constraints for theoretical models of hadron production and transport in relativistic heavy-ion collisions.
We report on the measurement of the inclusive ϒ(1S) production in Pb–Pb collisions at sNN=2.76 TeV carried out at forward rapidity (2.5<y<4) and down to zero transverse momentum using its μ+μ− decay ...channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive ϒ(1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon–nucleon 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 ϒ(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.
We report on the production of inclusive ϒ(1S) and ϒ(2S) in p–Pb collisions at sNN=5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (−4.46<ycms<−2.96) and forward ...(2.03<ycms<3.53) rapidity down to zero transverse momentum. The production cross sections of the ϒ(1S) and ϒ(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of ϒ(1S). A suppression of the inclusive ϒ(1S) yield in p–Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon–nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.
On the threshold of LHC data there were intensive test and upgrade of GRID application software for all LHC experiments at the top of the modern LCG middleware (gLite). The update of such software ...for ALICE experiment at LHC, AliEn1 had provided stable and secure operation of sites developing LHC data. The activity of Russian RDIG (Russian Data Intensive GRID) computer federation which is the distributed Tier-2 centre are devoted to simulation and analysis of LHC data in accordance with the ALICE computing model 2. Eight sites of this federation interesting in ALICE activity upgrade their middle ware in accordance with requirements of ALICE computing what ensured success of MC production and end-user analysis activity at all eight sites. The result of occupancy and efficiency of each site in the time of LHC operation will be presented in the report. The outline the results of CPU and disk space usage at RDIG sites for the data simulation and analysis of first LHC data from the exposition of ALICE detector 3 will be presented as well. There will be presented also the information about usage of parallel analysis facility based on PROOF 4.
Charged jet production cross sections in p–Pb collisions at sNN=5.02 TeV measured with the ALICE detector at the LHC are presented. Using the anti-kT algorithm, jets have been reconstructed in the ...central rapidity region from charged particles with resolution parameters R=0.2 and R=0.4. The reconstructed jets have been corrected for detector effects and the underlying event background. To calculate the nuclear modification factor, RpPb, of charged jets in p–Pb collisions, a pp reference was constructed by scaling previously measured charged jet spectra at s=7 TeV. In the transverse momentum range 20≤pT,chjet≤120 GeV/c, RpPb is found to be consistent with unity, indicating the absence of strong nuclear matter effects on jet production. Major modifications to the radial jet structure are probed via the ratio of jet production cross sections reconstructed with the two different resolution parameters. This ratio is found to be similar to the measurement in pp collisions at s=7 TeV and to the expectations from PYTHIA pp simulations and NLO pQCD calculations at sNN=5.02 TeV.
Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5<|η|<4.0) and associated particles in the central range (|η|<1.0) are measured with the ALICE ...detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV. The trigger particles are reconstructed using the muon spectrometer, and the associated particles by the central barrel tracking detectors. In high-multiplicity events, the double-ridge structure, previously discovered in two-particle angular correlations at midrapidity, is found to persist to the pseudorapidity ranges studied in this Letter. The second-order Fourier coefficients for muons in high-multiplicity events are extracted after jet-like correlations from low-multiplicity events have been subtracted. The coefficients are found to have a similar transverse momentum (pT) dependence in p-going (p–Pb) and Pb-going (Pb–p) configurations, with the Pb-going coefficients larger by about 16±6%, rather independent of pT within the uncertainties of the measurement. The data are compared with calculations using the AMPT model, which predicts a different pT and η dependence than observed in the data. The results are sensitive to the parent particle v2 and composition of reconstructed muon tracks, where the contribution from heavy flavour decays is expected to dominate at pT>2 GeV/c.
ϒ production in p–Pb interactions is studied at the centre-of-mass energy per nucleon–nucleon collision sNN=8.16 TeV with the ALICE detector at the CERN LHC. The measurement is performed ...reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals 2.03<ycms<3.53 and −4.46<ycms<−2.96, down to zero transverse momentum. In this work, results on the ϒ(1S) production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the ϒ(1S) yields with respect to pp collisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the ϒ(2S) nuclear modification factor is evaluated, suggesting a suppression similar to that of the ϒ(1S). A first measurement of the ϒ(3S) has also been performed. Finally, results are compared with previous ALICE measurements in p–Pb collisions at sNN=5.02 TeV and with theoretical calculations.
An excess of J/ψ yield at very low transverse momentum (pT<0.3 GeV/c), originating from coherent photoproduction, is observed in peripheral and semicentral hadronic Pb–Pb collisions at a ...center-of-mass energy per nucleon pair of sNN=5.02 TeV. The measurement is performed with the ALICE detector via the dimuon decay channel at forward rapidity (2.5<y<4). The nuclear modification factor at very low pT and the coherent photoproduction cross section are measured as a function of centrality down to the 10% most central collisions. These results extend the previous study at sNN=2.76 TeV, confirming the clear excess over hadronic production in the pT range 0−0.3 GeV/c and the centrality range 70–90%, and establishing an excess with a significance greater than 5σ also in the 50–70% and 30–50% centrality ranges. The results are compared with earlier measurements at sNN=2.76 TeV and with different theoretical predictions aiming at describing how coherent photoproduction occurs in hadronic interactions with nuclear overlap.
A measurement of the production of prompt Λc+ baryons in Pb–Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC is reported. The Λc+ and Λ‾c− were reconstructed at midrapidity (|y|<0.5) ...via the hadronic decay channel Λc+→pKS0 (and charge conjugate) in the transverse momentum and centrality intervals 6<pT<12 GeV/c and 0–80%. The Λc+/D0 ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at s=7 TeV and in p–Pb collisions at sNN=5.02 TeV. In particular, the values in p–Pb and Pb–Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties in the common pT interval covered by the measurements in the two collision systems. The Λc+/D0 ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The Λc+ nuclear modification factor, RAA, is also presented. The measured values of the RAA of Λc+, Ds+ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy (RAAD0<RAADs+<RAAΛc+), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium.
The production of prompt Λc+ baryons at midrapidity (|y|<0.5) was measured in central (0–10%) and mid-central (30–50%) Pb–Pb collisions at the center-of-mass energy per nucleon–nucleon pair sNN=5.02 ...TeV with the ALICE detector. The results are more precise, more differential in centrality, and reach much lower transverse momentum (pT=1 GeV/c) with respect to previous measurements performed by the ALICE, STAR, and CMS Collaborations in nucleus–nucleus collisions, allowing for an extrapolation down to pT=0. The pT-differential Λc+/D0 ratio is enhanced with respect to the pp measurement for 4<pT<8 GeV/c by 3.7 standard deviations (σ), while the pT-integrated ratios are compatible within 1σ. The observed trend is similar to that observed in the strange sector for the Λ/KS0 ratio. Model calculations including coalescence or statistical hadronization for charm-hadron formation are compared with the data.
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