Measurement of quarkonium production at forward rapidity in pp collisions at √s=7 TeV

The inclusive production cross sections at forward rapidity of J/ψ , ψ(2S) , Υ (1S) and Υ (2S) are measured in pp collisions at s√=7 TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.35 pb‾¹ . Quarkonia are reconstructed in the dimuon-decay channel and the signal yields are evaluated by fitting the μ+μ− invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum pT and rapidity y , over the ranges 0<pT<20 GeV/c for J/ψ , 0<pT<12 GeV/c for all other resonances and for \(2.5 . The measured cross sections integrated over pT and y , and assuming unpolarized quarkonia, are: σJ/ψ=6.69±0.04±0.63 μ b, σψ(2S)=1.13±0.07±0.19 μ b, σΥ(1S)=54.2±5.0±6.7 nb and σΥ(2S)=18.4±3.7±2.9 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

Event-by-event mean pT fluctuations in pp and Pb–Pb collisions at the LHC

Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at TeX TeX 0.9, 2.76 and 7 TeV, and Pb–Pb collisions at TeX TeX 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb–Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb–Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb–Pb are in qualitative agreement with previous measurements in Au–Au at lower collision energies and with expectations from models that incorporate collective phenomena

Suppression of ψ(2S) production in p-Pb collisions at √sNN=5.02 TeV .

The ALICE Collaboration has studied the inclusive production of the charmonium state ψ(2S) in proton-lead (p-Pb) collisions at the nucleon-nucleon centre of mass energy √sNN = 5.02TeV at the CERN LHC. The measurement was performed at forward (2.03 < ycms < 3.53) and backward (−4.46 < ycms < −2.96) centre of mass rapidities, studying the decays into muon pairs. In this paper, we present the inclusive production cross sections σ (2S), both integrated and as a function of the transverse momentum pT, for the two ycms domains. The results are compared to those obtained for the 1S vector state (J/ψ), by showing the ratios between the production cross sections, as well as the double ratios [σ (2S)/σJ/ ]pPb/[σ (2S)/σJ/ ]pp between p-Pb and proton-proton collisions. Finally, the nuclear modification factor for inclusive ψ(2S) is evaluated and compared to the measurement of the same quantity for J/ψ and to theoretical models including parton shadowing and coherent energy loss mechanisms. The results show a significantly larger suppression of the ψ(2S) compared to that measured for J/ψ and to models. These observations represent a clear indication for sizeable final state effects on ψ(2S) production

Production of charged pions, kaons and protons at large transverse momenta in pp and Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

Transverse momentum spectra of $\pi^{\pm}, K^{\pm}$ and $p(\bar{p})$ up to $p_T$ = 20 GeV/c at mid-rapidity, |y| $\le$ 0.8, in pp and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV have been measured using the ALICE detector at the LHC. At intermediate $p_T$ (2-8 GeV/c) an enhancement of the proton-to-proton ratio, (p + \bar{p})/(\pi^+ + \pi^-\(), with respect to pp collisions is observed and the ratio reaches 0.80 in central Pb-Pb collisions. The measurement of the nuclear modification factors for \(\pi^{\pm}, K^{\pm} and $p(\bar{p})$ indicates that within the systematic and statistical uncertainties they are the same at high $p_T$ (> 10 GeV/c), suggesting that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets.publishedVersio

Transverse momentum dependence of inclusive primary charged-particle production in p–Pb collisions at √sNN=5.02 TeV

The transverse momentum ( pT ) distribution of primary charged particles is measured at midrapidity in minimum-bias p–Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector at the LHC in the range \(0.15 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 sNN−−−√=2.76 TeV