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— The time and energy resolutions were measured for four prototypes of the PHOS electromagnetic calorimeter for the ALICE experiment at the Large Hadron Collider at CERN. Each prototype was made up of nine identical detection elements assembled as a 3 × 3 array. The detection element was based on a lead tungstate (PbWO 4 ) scintillating crystal with a length of 180 mm and a cross section of 22 × 22 mm 2 , which was viewed from its end face by a photodetector. Avalanche photodiodes and silicon photomultipliers with different active areas (Hamamatsu, Japan) were used as photodetectors. The measurements were made with the electron component of secondary particle beams of the PS proton synchrotron at CERN in the momentum range of 1−10 GeV/ c at a temperature of 17.5°C.

A bstract The cross section for coherent photonuclear production of J/ ψ is presented as a function of the electromagnetic dissociation (EMD) of Pb. The measurement is performed with the ALICE detector in ultra-peripheral Pb-Pb collisions at a centre-of-mass energy per nucleon pair of s NN = 5.02 TeV. Cross sections are presented in five different J/ ψ rapidity ranges within | y | < 4, with the J/ ψ reconstructed via its dilepton decay channels. In some events the J/ ψ is not accompanied by EMD, while other events do produce neutrons from EMD at beam rapidities either in one or the other beam direction, or in both. The cross sections in a given rapidity range and for different configurations of neutrons from EMD allow for the extraction of the energy dependence of this process in the range 17 < W γ Pb , n < 920 GeV, where W γ Pb , n is the centre-of-mass energy per nucleon of the γ Pb system. This range corresponds to a Bjorken- x interval spanning about three orders of magnitude: 1.1 × 10 − 5 < x < 3.3 × 10 − 2 . In addition to the ultra-peripheral and photonuclear cross sections, the nuclear suppression factor is obtained. These measurements point to a strong depletion of the gluon distribution in Pb nuclei over a broad, previously unexplored, energy range. These results, together with previous ALICE measurements, provide unprecedented information to probe quantum chromodynamics at high energies.

A bstract Measurements of anisotropic flow coefficients with two- and multi-particle cumulants for inclusive charged particles in Pb-Pb collisions at s N N = 5.02 and 2.76 TeV are reported in the pseudorapidity range | η | < 0.8 and transverse momentum 0.2 < p T < 50 GeV/ c . The full data sample collected by the ALICE detector in 2015 (2010), corresponding to an integrated luminosity of 12.7 (2.0) μ b −1 in the centrality range 0-80%, is analysed. Flow coefficients up to the sixth flow harmonic ( v 6 ) are reported and a detailed comparison among results at the two energies is carried out. The p T dependence of anisotropic flow coefficients and its evolution with respect to centrality and harmonic number n are investigated. An approximate power-law scaling of the form v n ( p T ) ∼  p T n /3 is observed for all flow harmonics at low p T (0.2 < p T < 3 GeV/ c ). At the same time, the ratios v n / v m n / m are observed to be essentially independent of p T for most centralities up to about p T = 10 GeV/ c . Analysing the differences among higher-order cumulants of elliptic flow ( v 2 ), which have different sensitivities to flow fluctuations, a measurement of the standardised skewness of the event-by-event v 2 distribution P ( v 2 ) is reported and constraints on its higher moments are provided. The Elliptic Power distribution is used to parametrise P ( v 2 ), extracting its parameters from fits to cumulants. The measurements are compared to different model predictions in order to discriminate among initial-state models and to constrain the temperature dependence of the shear viscosity to entropy-density ratio.

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.

The elliptic (v2), triangular (v3), and quadrangular (v4) flow coefficients of π±, K±, p+p¯¯¯,Λ+Λ¯¯¯¯,K0S, and the ϕ-meson are measured in Pb-Pb collisions at √sNN=5.02 TeV. Results obtained with the scalar product method are reported for the rapidity range |y| < 0.5 as a function of transverse momentum, pT, at different collision centrality intervals between 0–70%, including ultra-central (0–1%) collisions for π±, K±, and p+p¯¯¯. For pT < 3 GeV/c, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta (3 < pT < 8–10 GeV/c), particles show an approximate grouping according to their type (i.e., mesons and baryons). The ϕ-meson v2, which tests both particle mass dependence and type scaling, follows p+p¯¯¯ v2 at low pT and π± v2 at intermediate pT. The evolution of the shape of vn(pT) as a function of centrality and harmonic number n is studied for the various particle species. Flow coefficients of π±, K±, and p+p¯¯¯ for pT < 3 GeV/c are compared to iEBE-VISHNU and MUSIC hydrodynamical calculations coupled to a hadronic cascade model (UrQMD). The iEBE-VISHNU calculations describe the results fairly well for pT < 2.5 GeV/c, while MUSIC calculations reproduce the measurements for pT < 1 GeV/c. A comparison to vn coefficients measured in Pb-Pb collisions at √sNN=2.76 TeV is also provided.

The pT-differential production cross section of prompt Λ c + charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at s√=7 TeV and in p-Pb collisions at sNN−−−√=5.02 TeV at midrapidity. The Λ c + and Λ¯¯¯¯c¯¯¯ were reconstructed in the hadronic decay modes Λ c +  → pK−π+, Λ c +  → pK S 0 and in the semileptonic channel Λ c +  → e+νeΛ (and charge conjugates). The measured values of the Λ c + /D0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and pT intervals, where the Λ c + production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ c + nuclear modification factor, RpPb, is also presented. The RpPb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium.

The measurement of primary π ± , K ± , p and p ¯ production at mid-rapidity ( | y | < 0.5) in proton–proton collisions at s = 7 TeV performed with a large ion collider experiment at the large hadron collider (LHC) is reported. Particle identification is performed using the specific ionisation energy-loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/ c for pions, from 0.2 up to 6 GeV/ c for kaons and from 0.3 up to 6 GeV/ c for protons. The measured spectra and particle ratios are compared with quantum chromodynamics-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Furthermore, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies.

A bstract The elliptic flow coefficient ( v 2 ) of identified particles in Pb-Pb collisions at s N N = 2.76 TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of |Δ η | > 0 . 9 between the identified hadron under study and the reference particles. The v 2 is reported for π ± , K ± , K S 0 , p + p ¯ , ϕ , Λ + Λ ¯ , Ξ − + Ξ ¯ + and Ω − + Ω ¯ + in several collision centralities. In the low transverse momentum ( p T ) region, p T < 3 GeV/ c , v 2 ( p T ) exhibits a particle mass dependence consistent with elliptic flow accompanied by the transverse radial expansion of the system with a common velocity field. The experimental data for π ± and the combined K ± and K S 0 results, are described fairly well by hydrodynamic calculations coupled to a hadronic cascade model (VISHNU) for central collisions. However, the same calculations fail to reproduce the v 2 ( p T ) for p + p ¯ , ϕ , Λ + Λ ¯ and Ξ − + Ξ ¯ + . For transverse momentum values larger than about 3 GeV/ c , particles tend to group according to their type, i.e. mesons and baryons. The present measurements exhibit deviations from the number of constituent quark (NCQ) scaling at the level of ±20% for p T > 3 GeV/ c .

The transverse momentum ( p T ) spectra and elliptic flow coefficient ( v 2 ) of deuterons and anti-deuterons at mid-rapidity ( | y | < 0.5 ) are measured with the ALICE detector at the LHC in Pb–Pb collisions at s NN = 2.76 TeV. The measurement of the p T spectra of (anti-)deuterons is done up to 8 GeV / c in 0–10% centrality class and up to 6 GeV / c in 10–20% and 20–40% centrality classes. The v 2 is measured in the 0.8 <  p T   < 5 GeV / c interval and in six different centrality intervals (0–5, 5–10, 10–20, 20–30, 30–40 and 40–50%) using the scalar product technique. Measured π ± , K ± and p+ p ¯ transverse-momentum spectra and v 2 are used to predict the deuteron p T spectra and v 2 within the Blast-Wave model. The predictions are able to reproduce the v 2 coefficient in the measured p T range and the transverse-momentum spectra for p T  > 1.8 GeV / c within the experimental uncertainties. The measurement of the coalescence parameter B 2 is performed, showing a p T dependence in contrast with the simplest coalescence model, which fails to reproduce also the measured v 2 coefficient. In addition, the coalescence parameter B 2 and the elliptic flow coefficient in the 20–40% centrality interval are compared with the AMPT model which is able, in its version without string melting, to reproduce the measured v 2 ( p T ) and the B 2 ( p T ) trend.

A bstract We report the measurement of a new observable of jet quenching in central Pb-Pb collisions at s N N = 2.76 TeV, based on the semi-inclusive rate of charged jets recoiling from a high transverse momentum (high- p 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 T,jet ch  < 100 GeV. Reference distributions for pp collisions at s = 2.76 TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at s = 7 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.