Midrapidity production of π ± , K ± , and (p)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √ s NN = 5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (p T) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0-90%. The comparison of the p T-integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at √ s NN = 2.76 TeV show no significant energy dependence. Blast-wave fits of the p T spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π , K/π) as a function of p T show pronounced maxima at p T ≈ 3 GeV/c in central Pb-Pb collisions. At high p T , particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at √ s NN = 2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high p T and compatible with measurements at √ s NN = 2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.

We report the measured transverse momentum (p T) spectra of primary charged particles from pp, p-Pb and Pb-Pb collisions at a center-of-mass energy √ s NN = 5.02 TeV in the kinematic range of 0.15 < p T < 50 GeV/c and |η| < 0.8. A significant improvement of systematic uncertainties motivated the reanalysis of data in pp and Pb-Pb collisions at √ s NN = 2.76 TeV, as well as in p-Pb collisions at √ s NN = 5.02 TeV, which is also presented. Spectra from Pb-Pb collisions are presented in nine centrality intervals and are compared to a reference spectrum from pp collisions scaled by the number of binary nucleon-nucleon collisions. For central collisions, the p T spectra are suppressed by more than a factor of 7 around 6-7 GeV/c with a significant reduction in suppression towards higher momenta up to 30 GeV/c. The nuclear modification factor R pPb , constructed from the pp and p-Pb spectra measured at the same collision energy, is consistent with unity above 8 GeV/c. While the spectra in both pp and Pb-Pb collisions are substantially harder at √ s NN = 5.02 TeV compared to 2.76 TeV, the nuclear modification factors show no significant collision energy dependence. The obtained results should provide further constraints on the parton energy loss calculations to determine the transport properties of the hot and dense QCD matter.

A detailed study of pseudorapidity densities and multiplicity distributions of primary charged particles produced in proton-proton collisions, at √ s = 0.9, 2.36, 2.76, 7 and 8 TeV, in the pseudorapidity range |η| < 2, was carried out using the ALICE detector. Measurements were obtained for three event classes: inelastic, non-single diffractive and events with at least one charged particle in the pseudorapidity interval |η| < 1. The use of an improved track-counting algorithm combined with ALICE's measurements of diffractive processes allows a higher precision compared to our previous publications. A KNO scaling study was performed in the pseudorapidity intervals |η| < 0.5, 1.0 and 1.5. The data are compared to other experimental results and to models as implemented in Monte Carlo event generators PHOJET and recent tunes of PYTHIA6, PYTHIA8 and EPOS.

We discovered two errors that do not affect the conclusions of the Letter, but do slightly affect the figures and parameters presented. The STAR spectrum data [1] was used assuming the tabulated independent variable was p T , when actually it was m T ÿ m . Also, in fitting the measured spectrum, we incorrectly included the effects of ''resonance'' pions, produced far outside the source region, that do not contribute to the Bose-Einstein enhancement. To address both of these issues, we modified the measured spectrum by removing the 12% weak decay correction [1] and then multiplying by p T p as determined by a linear fit to the measured Hanbury Brown-Twiss (HBT) values of , see Figs. 1 and 2. 10 20 30 40 50 60 70 10 20 30 40 50 60 FIG. 1 (color online). HBT radii R s , R o , R l , and the ratio R o =R s . Data [2]: 5 (green) ) ; 4 (red) ) ÿ ÿ . Solid line (black) ) full calculation; dotted line (green) ) f 0 (no flow); dashed line (red) ) ReU 0 (no refraction); dot-dashed line (blue) ) U 0 (no potential); double-dot-dashed line (magenta) ) substituting Boltzmann for Bose-Einstein thermal distribution. Insets show predictions of low-K T resonance behavior in R o and R s .

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The production of K(892) and (1020) mesons has been measured in p–Pb collisions at 5.02 TeV. K and are reconstructed via their decay into charged hadrons with the ALICE detector in the rapidity range . The transverse momentum spectra, measured as a function of the multiplicity, have a p range from 0 to 15 GeV/c for K and from 0.3 to 21 GeV/c for . Integrated yields, mean transverse momenta and particle ratios are reported and compared with results in pp collisions at 7 TeV and Pb–Pb collisions at 2.76 TeV. In Pb–Pb and p–Pb collisions, K and probe the hadronic phase of the system and contribute to the study of particle formation mechanisms by comparison with other identified hadrons. For this purpose, the mean transverse momenta and the differential proton-to- ratio are discussed as a function of the multiplicity of the event. The short-lived K is measured to investigate re-scattering effects, believed to be related to the size of the system and to the lifetime of the hadronic phase.

The first evidence of spin alignment of vector mesons (K Ã0 and ϕ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ 00 is measured at midrapidity (jyj < 0.5) in Pb-Pb collisions at a center-of-mass energy (ffiffiffiffiffiffiffi ffi s NN p) of 2.76 TeV with the ALICE detector. ρ 00 values are found to be less than 1=3 (1=3 implies no spin alignment) at low transverse momentum (p T < 2 GeV=c) for K Ã0 and ϕ at a level of 3σ and 2σ, respectively. No significant spin alignment is observed for the K 0 S meson (spin ¼ 0) in Pb-Pb collisions and for the vector mesons in pp collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.

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