We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0–5%, 5–10%, 10–20%, and 20–30% most central events) in Pb–Pb collisions at View the MathML source at the LHC. The measurement is performed using the full coverage of the ALICE detectors, −5.0<η<5.5 , and employing a special analysis technique based on collisions arising from LHC ‘satellite’ bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles (View the MathML source for the 0–5% most central collisions). From the measured dNch/dη distribution we derive the rapidity density distribution, dNch/dy , under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models.

The ALICE Collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity |y|<0.8 and transverse momentum 1<pT<10 GeV/c, in pp collisions at s=2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD predictions agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, σb→e=3.47±0.40(stat)-1.33+1.12(sys)±0.07(norm) μb, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) calculations to obtain the total bb production cross section, σbb=130±15.1(stat)-49.8+42.1(sys)-3.1+3.4(extr)±2.5(norm)±4.4(BR) μb. © 2014.

The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at √s_NN=2.76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%–80%) to central (0%–5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.

In this paper measurements are presented of π±, K±, p, and p⎯⎯⎯ production at midrapidity (∣∣y∣∣<0.5), in Pb-Pb collisions at sNN‾‾‾‾√=2.76 TeV as a function of centrality. The measurement covers the transverse-momentum (pT) range from 100, 200, and 300 MeV/c up to 3, 3, and 4.6 GeV/c for π, K, and p, respectively. The measured pT distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the pT distributions are not well reproduced by hydrodynamic models. Ratios of integrated particle yields are found to be nearly independent of centrality. The yield of protons normalized to pions is a factor ∼1.5 lower than the expectation from thermal models.

This publication describes the methods used to measure the centrality of inelastic Pb-Pb collisions at a center-of-mass energy of 2.76 TeV per colliding nucleon pair with ALICE. The centrality is a key parameter in the study of the properties of QCD matter at extreme temperature and energy density, because it is directly related to the initial overlap region of the colliding nuclei. Geometrical properties of the collision, such as the number of participating nucleons and the number of binary nucleon-nucleon collisions, are deduced from a Glauber model with a sharp impact parameter selection and shown to be consistent with those extracted from the data. The centrality determination provides a tool to compare ALICE measurements with those of other experiments and with theoretical calculations.

The inclusive J/ψ nuclear modification factor (RAA) in Pb-Pb collisions at √sNN=2.76TeV has been measured by ALICE as a function of centrality in the e +e - decay channel at mid-rapidity (|y| < 0.8) and as a function of centrality, transverse momentum and rapidity in the μ +μ - decay channel at forward-rapidity (2.5 < y < 4). The J/ψ yields measured in Pb-Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions. The RAA integrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is 0.72 ± 0.06(stat.) ± 0.10(syst.) at mid-rapidity and 0.58 ± 0.01(stat.) ± 0.09(syst.) at forward-rapidity. At low transverse momentum, significantly larger values of RAA are measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the J/ψ yield originates from charm quark (re)combination in the deconfined partonic medium. © 2014 The Authors.

The ALICE Collaboration at the LHC has measured the J/ψ and ψ photoproduction at mid-rapidity in ultra-peripheral Pb–Pb collisions at √ sNN = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 μb−1. The cross section for coherent and incoherent J/ψ production in the rapidity interval −0.9 < y < 0.9, are dσcoh J/ψ/dy = 2.38+0.34 −0.24(sta +sys) mb and dσinc J/ψ/dy = 0.98+0.19 −0.17(sta + sys) mb, respectively. The results are compared to theoretical models for J/ψ production and the coherent cross section is found to be in good agreement with those models incorporating moderate nuclear gluon shadowing at Bjorkenx around 10−3, such as EPS09 parametrization. In addition the cross section for the process γγ →e + e − has been measured and found to be in agreement with models implementing QED at leading order.

In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a probe to gain insight into the charge creation mechanisms. In this Letter, we report the first results of such studies using the electric charge balance function in the relative pseudorapidity (Δη) and azimuthal angle (Δφ) in Pb–Pb collisions at with the ALICE detector at the Large Hadron Collider. The width of the balance function decreases with growing centrality (i.e. for more central collisions) in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured correlations in Δφ but fails to describe the correlations in Δη. A thermal blast-wave model incorporating local charge conservation and tuned to describe the pT spectra and v2 measurements reported by ALICE, is used to fit the centrality dependence of the width of the balance function and to extract the average separation of balancing charges at freeze-out. The comparison of our results with measurements at lower energies reveals an ordering with : the balance functions become narrower with increasing energy for all centralities. This is consistent with the effect of larger radial flow at the LHC energies but also with the late stage creation scenario of balancing charges. However, the relative decrease of the balance function widths in Δη and Δφ with centrality from the highest SPS to the LHC energy exhibits only small differences. This observation cannot be interpreted solely within the framework where the majority of the charge is produced at a later stage in the evolution of the heavy-ion collision.

Azimuthally anisotropic distributions of D0, D+, and D*+ mesons were studied in the central rapidity region (|y|<0.8) in Pb-Pb collisions at a center-of-mass energy sNN‾‾‾‾√=2.76  TeV per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient v2 (commonly denoted elliptic flow) was measured in the centrality class 30%–50% as a function of the D meson transverse momentum pT, in the range 2–16  GeV/c. The measured v2 of D mesons is comparable in magnitude to that of light-flavor hadrons. It is positive in the range 2<pT<6  GeV/c with 5.7σ significance, based on the combination of statistical and systematic uncertainties.

The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at ffiffiffiffiffiffiffiffi sNN p ¼ 2:76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta pT between 1.2 and 1:7 GeV=c. Combined with the observation of a vanishing rapidity-even pT shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.

The results on open heavy flavour and charmonium production in pp collisions at the LHC with the ALICE experiment are presented, based on data collected in 2010 at √s =7 TeV. In particular charm production at central rapidity is measured in a number of exclusive decay channels into charged hadrons, e.g. D0 → K−π+, D+ → K−π+π+ and D∗+ → D0π+. Beauty and charm pro- duction can be studied at central and forward rapidity through the inclusive channels decaying in single electron and muon, respectively; J/ψ production at central and forward rapidities has been measured in the dielectron and dimuon channels, respectively. Finally, perspectives on heavy flavour measurements in Pb–Pb collisions are discussed.

A golden age for heavy-quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau-Charm factories, JLab, the ILC, and beyond. The list of newly found conventional states expanded to include h(c)(1P), chi(c2)(2P), B-c(+), and eta(b)(1S). In addition, the unexpected and still-fascinating X(3872) has been joined by more than a dozen other charmonium- and bottomonium-like "XYZ" states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c (c) over bar, b (b) over bar, and b (c) over bar bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrial-strength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.

We report on the first measurement of the triangular v3, quadrangular v4, and pentagonal v5 charged particle flow in Pb-Pb collisions at √s_NN=2.76  TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show that the triangular flow can be described in terms of the initial spatial anisotropy and its fluctuations, which provides strong constraints on its origin. In the most central events, where the elliptic flow v2 and v3 have similar magnitude, a double peaked structure in the two-particle azimuthal correlations is observed, which is often interpreted as a Mach cone response to fast partons. We show that this structure can be naturally explained from the measured anisotropic flow Fourier coefficients.

We report on the first measurement of inclusive J/ψ elliptic flow v2 in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at sNN‾‾‾‾√=2.76  TeV in the rapidity range 2.5<y<4.0. The dependence of the J/ψ v2 on the collision centrality and on the J/ψ transverse momentum is studied in the range 0≤pT<10  GeV/c. For semicentral Pb-Pb collisions at sNN‾‾‾‾√=2.76  TeV, an indication of nonzero v2 is observed with a largest measured value of v2=0.116±0.046(stat)±0.029(syst) for J/ψ in the transverse momentum range 2≤pT<4  GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/ψ nuclear modification factor and favors the scenario of a significant fraction of J/ψ production from charm quarks in a deconfined partonic phase.

The ALICE Collaboration has studied J/ψ production in pp collisions at √s=7  TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/ψ polarization parameters λθ and λϕ were obtained. The study was performed in the kinematic region 2.5<y<4, 2<pt<8  GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.

The ALICE experiment has measured the inclusive J/ψ production in Pb-Pb collisions at √sNN=2.76  TeV down to zero transverse momentum in the rapidity range 2.5<y<4. A suppression of the inclusive J/ψ yield in Pb-Pb is observed with respect to the one measured in pp collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0%–80% most central collisions, is 0.545±0.032(stat)±0.083(syst) and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including J/ψ production from charm quarks in a deconfined partonic phase can describe our data.

The ALICE Collaboration reports the measurement of the relative J/ψ yield as a function of charged particle pseudorapidity density dNch/dη in pp collisions at at the LHC. J/ψ particles are detected for pt>0, in the rapidity interval |y|<0.9 via decay into e+e−, and in the interval 2.5<y<4.0 via decay into μ+μ− pairs. An approximately linear increase of the J/ψ yields normalized to their event average (dNJ/ψ/dy)/〈dNJ/ψ/dy〉 with (dNch/dη)/〈dNch/dη〉 is observed in both rapidity ranges, where dNch/dη is measured within |η|<1 and pt>0. In the highest multiplicity interval with 〈dNch/dη(bin)〉=24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/ψ yield by a factor of about 5 at 2.5<y<4 (8 at |y|<0.9) is observed.

The ALICE measurement of K0S and production at midrapidity in Pb-Pb collisions at ffiffiffiffiffiffiffiffi sNN p ¼ 2:76 TeV is presented. The transverse momentum (pT) spectra are shown for several collision centrality intervals and in the pT range from 0:4 GeV=c (0:6 GeV=c for ) to 12 GeV=c. The pT dependence of the =K0S ratios exhibits maxima in the vicinity of 3 GeV=c, and the positions of the maxima shift towards higher pT with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate pT is not observed in pp interactions at ffiffiffis p ¼ 0:9 TeV and at ffiffiffis p ¼ 7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured pT spectra above 2 GeV=c progressively decouple from hydrodynamical-model calculations. For higher values of pT, models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the pT dependence of the K0S ratio.

The ALICE experiment has measured low-mass dimuon production in pp collisions at √s = 7 TeV in the dimuon rapidity region 2.5 < y < 4. The observed dimuon mass spectrum is described as a superposition of resonance decays (η,ρ,ω,η,φ) into muons and semi-leptonic decays of charmed mesons. The measuredproduction cross sections for ω and φ are σω(1 < pt <5 GeV/c, 2.5 < y < 4) = 5.28±0.54(stat)±0.49(syst) mb and σφ(1 < pt <5 GeV/c, 2.5 < y < 4) = 0.940 ± 0.084(stat) ± 0.076(syst) mb. The differential cross sections d2σ/dy dpt are extracted as a function of pt for ω and φ. The ratio between the ρ and ω cross section is obtained. Results for the φ are compared with other measurements at the same energy and with predictions by models.

Identical neutral kaon pair correlations are measured in √s = 7 TeV pp collisions in the ALICE experiment. One-dimensional K0sK0s correlation functions in terms of the invariant momentum difference of kaon pairs are formed in two multiplicity and two transverse momentum ranges. The femtoscopic parameters for the radius and correlation strength of the kaon source are extracted. The fit includes quantum statistics and final-state interactions of the a0/f0 resonance. K0sK0s correlations show an increase in radius for increasing multiplicity and a slight decrease in radius for increasing transverse mass, mT, as seen in ππ correlations in pp collisions and in heavy-ion collisions. Transverse mass scaling is observed between the K0sK0s and ππ radii. Also, the first observation is made of the decay of the f2(1525) meson into the K0sK0s channel in pp collisions.

We report on the high statistics two-pion correlation functions from pp collisions at √s=0.9  TeV and √s=7  TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant nonfemtoscopic correlations are observed, and are argued to be the consequence of “mini-jet”-like structures extending to low pt. They are well reproduced by the Monte-Carlo generators and seen also in π+π- correlations.

Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < pT,assoc < pT,trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and pT bins, and the widths show no significant evolution with event multiplicity or pT. These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge.

Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3<pT<4 GeV/c . The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |ηlab|<0.8 . Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of pT and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, View the MathML source , is observed to be smaller than that for pions, View the MathML source , up to about pT=2 GeV/c . To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The View the MathML source is found to be smaller at low pT and larger at higher pT than View the MathML source , with a crossing occurring at about 2 GeV/c . This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system.

Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at 0.9, 2.76 and 7 TeV, and Pb–Pb collisions at 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. © 2014, The Author(s).

The production of the prompt charmed mesons D0, D+, and D∗+ relative to the reaction plane was measured in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision of sNN=2.76TeV with the ALICE detector at the CERN Large Hadron Collider. D mesons were reconstructed via their hadronic decays at central rapidity in the transverse-momentum (pT) interval 2-16 GeV/c. The azimuthal anisotropy is quantified in terms of the second coefficient v2 in a Fourier expansion of the D-meson azimuthal distribution and in terms of the nuclear modification factor RAA, measured in the direction of the reaction plane and orthogonal to it. The v2 coefficient was measured with three different methods and in three centrality classes in the interval 0%-50%. A positive v2 is observed in midcentral collisions (30%-50% centrality class), with a mean value of 0.204-0.036+0.099 (tot. unc.) in the interval 2<pT<6GeV/c, which decreases towards more central collisions (10%-30% and 0%-10% classes). The positive v2 is also reflected in the nuclear modification factor, which shows a stronger suppression in the direction orthogonal to the reaction plane for midcentral collisions. The measurements are compared to theoretical calculations of charm-quark transport and energy loss in high-density strongly interacting matter at high temperature. The models that include substantial elastic interactions with an expanding medium provide a good description of the observed anisotropy. However, they are challenged to simultaneously describe the strong suppression of high-pT yield of D mesons in central collisions and their azimuthal anisotropy in noncentral collisions. © 2014 CERN, for the ALICE Collaboration.

A measurement of the transverse momentum spectra of jets in Pb–Pb collisions at √sNN = 2.76TeV is reported. Jets are reconstructed from charged particles using the anti-kT jet algorithm with jet resolution parameters R of 0.2 and 0.3 in pseudorapidity || < 0.5. The transverse momentum pT of charged particles is measured down to 0.15GeV/c which gives access to the low pT fragments of the jet. Jets found in heavy-ion collisions are corrected event-by-event for average background density and on an inclusive basis (via unfolding) for residual background fluctuations and detector effects. A strong suppression of jet production in central events with respect to peripheral events is observed. The suppression is found to be similar to the suppression of charged hadrons, which suggests that substantial energy is radiated at angles larger than the jet resolution parameter R = 0.3 considered in the analysis. The fragmentation bias introduced by selecting jets with a high pT leading particle, which rejects jets with a soft fragmentation pattern, has a similar effect on the jet yield for central and peripheral events. The ratio of jet spectra with R = 0.2 and R = 0.3 is found to be similar in Pb–Pb and simulated PYTHIA pp events, indicating no strong broadening of the radial jet structure in the reconstructed jets with R < 0.3.

The pt-differential inclusive production cross sections of the prompt charmed mesons D0, D+, and D∗+ in the rapidity range |y| < 0.5 were measured in proton-proton collisions at √s = 7 TeV at the LHC using the ALICE detector. Reconstructing the decays D0 → K−π+, D+ → K−π+π+, D∗+ → D0π+, and their charge conjugates, about 8,400 D0, 2,900 D+, and 2,600 D∗+ mesons with 1 < pt < 24 GeV/c were counted, after selection cuts, in a data sample of 3.14×108 events collected with a minimum-bias trigger (integrated luminosity Lint = 5 nb−1). The results are described within uncertainties by predictions based on perturbative QCD.

The ALICE Collaboration has measured inclusive J/ψ production in pp collisions at a center-of-mass energy at the LHC. The results presented in this Letter refer to the rapidity ranges |y|<0.9 and 2.5<y<4 and have been obtained by measuring the electron and muon pair decay channels, respectively. The integrated luminosities for the two channels are and , and the corresponding signal statistics are and . We present dσJ/ψ/dy for the two rapidity regions under study and, for the forward-y range, in the transverse momentum domain 0<pt<8 GeV/c. The results are compared with previously published results at and with theoretical calculations.

The p T-differential inclusive production cross section of the prompt charm-strange meson D s + in the rapidity range | y | < 0.5 was measured in proton-proton collisions at sqrt(s) = 7 TeV at the LHC using the ALICE detector. The analysis was performed on a data sample of 2.98 × 10 8 events collected with a minimum-bias trigger. The corresponding integrated luminosity is L int = 4.8 nb - 1. Reconstructing the decay D s + → φ{symbol} π +, with φ{symbol} → K - K +, and its charge conjugate, about 480 D s ± mesons were counted, after selection cuts, in the transverse momentum range 2 < p T < 12 GeV / c. The results are compared with predictions from models based on perturbative QCD. The ratios of the cross sections of four D meson species (namely D 0, D +, D * + and D s +) were determined both as a function of p T and integrated over p T after extrapolating to full p T range, together with the strangeness suppression factor in charm fragmentation. The obtained values are found to be compatible within uncertainties with those measured by other experiments in e + e -, ep and pp interactions at various centre-of-mass energies

Inclusive J/ψ production has been studied with the ALICE detector in p-Pb collisions at the nucleon–nucleon center of mass energy √sNN = 5.02TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96, down to zero transverse momentum, studying the μ+μ− decay mode. In this paper, the J/ψ production cross section and the nuclear modification factor RpPb for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/ψ yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results.

Angular correlations between unidentified charged trigger (t) and associated (a) particles are measured by the ALICE experiment in Pb–Pb collisions at √sNN = 2.76 TeV for transverse momenta 0.25 < pt,aT < 15 GeV/c, where ptT > paT . The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval |η| < 1.0. Distributions in relative azimuth φ ≡ φt − φa are analyzed for |η| ≡ |ηt − ηa| > 0.8, and are referred to as “long-range correlations”. Fourier components Vn ≡ cos(nφ) are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, then the pair anisotropy Vn(ptT , paT ) is fully described in terms of single-particle anisotropies vn(pT ) as Vn(ptT , paT ) = vn(ptT )vn(paT ). This expectation is tested for 1 n 5 by applying a global fit of all Vn(ptT , paT ) to obtain the best values vn{GF}(pT ). It is found that for 2n5, the fit agrees well with data up to paT∼ 3–4 GeV/c, with a trend of increasing deviation as ptT and paT are increased or as collisions become more peripheral. This suggests that no pair correlation harmonic can be described over the full 0.25 < pT < 15 GeV/c range using a single vn(pT ) curve; such a description is however approximately possible for 2 n 5 when paT <4 GeV/c. For the n = 1 harmonic, however, a single v1(pT ) curve is not obtained even within the reduced range paT <4 GeV/c.

The pT-differential production cross sections of the prompt charmed mesons D0, D+, D∗+, and Ds+ and their charge conjugate in the rapidity interval -0.96<ycms<0.04 were measured in p-Pb collisions at a center-of-mass energy sNN=5.02TeV with the ALICE detector at the LHC. The nuclear modification factor RpPb, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%-20% uncertainties with unity in the transverse momentum interval 1<pT<24GeV/c. No significant difference among the RpPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter. © 2014 CERN, for the ALICE Collaboration.

The ALICE experiment at the LHC has studied J/ψ production at midrapidity in pp collisions at √s = 7TeV through its electron pair decay on a data sample corresponding to an integrated luminosity Lint = 5.6 nb−1. The fraction of J/ψ from the decay of long-lived beauty hadrons was determined for J/ψ candidates with transverse momentum pt > 1.3GeV/c and rapidity |y| < 0.9. The cross section for prompt J/ψ mesons, i.e. directly produced J/ψ and prompt decays of heavier charmonium states such as the ψ(2S) and χc resonances, is σprompt J/ψ (pt > 1.3 GeV/c, |y| < 0.9) = 8.3±0.8 (stat.) ± 1.1 (syst.) +1.5−1.4 (syst. pol.) μb. The cross section for the production of b-hadrons decaying to J/ψ with pt > 1.3GeV/c and |y| < 0.9 is σJ/ψ←hB (pt > 1.3 GeV/c, |y| < 0.9) = 1.46 ± 0.38 (stat.) +0.26−0.32 (syst.) μb. The results are compared to QCD model predictions. The shape of the pt and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the bb pair total cross section and dσ/dy at mid-rapidity.

The first measurement of neutron emission in electromagnetic dissociation of 208^Pb nuclei at the LHC is presented. The measurement is performed using the neutron zero degree calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at √s_NN=2.76 TeV with neutron emission are sigma_singleEMD=187.4 +-0.2 (stat) +13.2-11-2 (syst) b and sigma_mutualEMD= 5.7 +-0.1 (stat) +-0.4 (syst) b, respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.

he ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for p⎯⎯/p, Λ⎯⎯⎯/Λ, Ξ⎯⎯⎯+/Ξ− and Ω⎯⎯⎯+/Ω− in pp collisions at s√=0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of p⎯⎯/p, Λ⎯⎯⎯/Λ, Ξ⎯⎯⎯+/Ξ− and Ω⎯⎯⎯+/Ω−, reaching values compatible with unity for s√=7 TeV, complement the earlier p⎯⎯/p measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of αJ≈0.5, which are suppressed with increasing rapidity interval Δy. Any significant contribution of an exchange not suppressed at large Δy (reached at LHC energies) is disfavoured.

The first measurements of the invariant differential cross sections of inclusive π0 and η meson production at mid-rapidity in proton–proton collisions at √s=0.9 TeV and √s=7 TeV are reported. The π0 measurement covers the ranges 0.4<pT<7 GeV/c and 0.3<pT<25 GeV/c for these two energies, respectively. The production of η mesons was measured at √s=7 TeV in the range 0.4<pT<15 GeV/c. Next-to-Leading Order perturbative QCD calculations, which are consistent with the π0 spectrum at √s=0.9 TeV, overestimate those of π0 and η mesons at √s=7 TeV, but agree with the measured η/π0 ratio 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 p T and rapidity y, over the ranges 0<p T <20 GeV/c for J/ψ, 0<p T <12 GeV/c for all other resonances and for (2.5) . The measured cross sections integrated over p T and y, and assuming unpolarized quarkonia, are: σ J/ψ =6.69±0.04±0.63 μ b, σ ψ(2S) =1.13±0.07±0.19 μ b, σ Υ(1S) =54.2±5.0±6.7 nb and σ Υ(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. © 2014, The Author(s).

The differential production cross section of electrons from semileptonic heavy-flavor hadron decays has been measured at midrapidity (jyj < 0:5) in proton-proton collisions at ffisffiffi p ¼ 7 TeV with ALICE at the LHC. Electrons were measured in the transverse momentum range 0:5<pt < 8 GeV=c. Predictions from a fixed-order perturbative QCD calculation with next-to-leading-log resummation agree with the data within the theoretical and experimental uncertainties.

A measurement of the multi-strange Ξ− and Ω− baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for inelastic proton–proton collisions at a centre-of-mass energy of 7 TeV. The transverse momentum (pT) distributions were studied at mid-rapidity (|y|<0.5) in the range of 0.6<pT<8.5 GeV/c for Ξ− and baryons, and in the range of 0.8<pT<5 GeV/c for Ω− and . Baryons and antibaryons were measured as separate particles and we find that the baryon to antibaryon ratio of both particle species is consistent with unity over the entire range of the measurement. The statistical precision of the current data has allowed us to measure a difference between the mean pT of Ξ− () and Ω− (). Particle yields, mean pT, and the spectra in the intermediate pT range are not well described by the PYTHIA Perugia 2011 tune Monte Carlo event generator, which has been tuned to reproduce the early LHC data. The discrepancy is largest for Ω− (). This PYTHIA tune approaches the pT spectra of Ξ− and baryons below pT<0.85 GeV/c and describes the Ξ− and spectra above pT>6.0 GeV/c. We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of as a function of transverse mass.

The yield of charged particles associated with high-pt trigger particles (8<pt<15  GeV/c) is measured with the ALICE detector in Pb-Pb collisions at √sNN=2.76  TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jetlike correlation peaks in azimuthal dihadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta pt>3  GeV/c on the away side drops to about 60% of that observed in pp collisions, while on the near side a moderate enhancement of 20%–30% is found.

The ALICE Zero Degree Calorimeter system (ZDC) is composed of two identical sets of calorimeters, placed at opposite sides with respect to the interaction point, 114 meters away from it, complemented by two small forward electromagnetic calorimeters (ZEM). Each set of detectors consists of a neutron (ZN) and a proton (ZP) ZDC. They are placed at zero degrees with respect to the LHC axis and allow to detect particles emitted close to beam direction, in particular neutrons and protons emerging from hadronic heavy-ion collisions (spectator nucleons) and those emitted from electromagnetic processes. For neutrons emitted by these two processes, the ZN calorimeters have nearly 100% acceptance. During the √ sNN = 2.76 TeV Pb-Pb data-taking, the ALICE Collaboration studied forward neutron emission with a dedicated trigger, requiring a minimum energy deposition in at least one of the two ZN. By exploiting also the information of the two ZEM calorimeters it has been possible to separate the contributions of electromagnetic and hadronic processes and to study single neutron vs. multiple neutron emission. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at √ s NN = 2.76 TeV, with neutron emission, are σ single EMD = 187:4 ± 0.2 (stat.)-11.2 +13.2 (syst.) b and σmutual EMD = 5.7 ± 0.1 (stat.) ±0.4 (syst.) b, respectively [1]. This is the first measurement of electromagnetic dissociation of 208Pb nuclei at the LHC energies, allowing a test of electromagnetic dissociation theory in a new energy regime. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model. © Owned by the authors, published by EDP Sciences, 2014.

In 2013, the Large Hadron Collider provided proton-lead and lead-proton collisions at the center-of-mass energy per nucleon pair s NN=5.02 TeV . Van der Meer scans were performed for both configurations of colliding beams, and the cross section was measured for two reference processes, based on particle detection by the T0 and V0 detectors, with pseudo-rapidity coverage 4.6 < η < 4.9, -3.3 < η < -3.0 and 2.8 < η < 5.1, -3.7 < η < -1.7, respectively. Given the asymmetric detector acceptance, the cross section was measured separately for the two configurations. The measured visible cross sections are used to calculate the integrated luminosity of the proton-lead and lead-proton data samples, and to indirectly measure the cross section for a third, configuration-independent, reference process, based on neutron detection by the Zero Degree Calorimeters. © CERN 2014 for the benefit of the Alice collaboration.

Invariant yields of neutral pions at midrapidity in the transverse momentum range (Formula presented.)c measured in Pb–Pb collisions at (Formula presented.) TeV are presented for six centrality classes. The pp reference spectrum was measured in the range (Formula presented.)c at the same center-of-mass energy. The nuclear modification factor, (Formula presented.), shows a suppression of neutral pions in central Pb–Pb collisions by a factor of up to about (Formula presented.) for (Formula presented.) ≲(Formula presented.)c. The presented measurements are compared with results at lower center-of-mass energies and with theoretical calculations. © 2014, The Author(s).

The effect of event background fluctuations on charged particle jet reconstruc- tion in Pb-Pb collisions at √sNN = 2.76 TeV has been measured with the ALICE experi- ment. The main sources of non-statistical fluctuations are characterized based purely on experimental data with an unbiased method, as well as by using single high pt particles and simulated jets embedded into real Pb-Pb events and reconstructed with the anti-kt jet finder. The influence of a low transverse momentum cut-off on particles used in the jet reconstruction is quantified by varying the minimum track pt between 0.15 GeV/c and 2 GeV/c. For embedded jets reconstructed from charged particles with pt > 0.15 GeV/c, the uncertainty in the reconstructed jet transverse momentum due to the heavy-ion back- ground is measured to be 11.3GeV/c (standard deviation) for the 10% most central Pb- Pb collisions, slightly larger than the value of 11.0GeV/c measured using the unbiased method. For a higher particle transverse momentum threshold of 2 GeV/c, which will gen- erate a stronger bias towards hard fragmentation in the jet finding process, the standard deviation of the fluctuations in the reconstructed jet transverse momentum is reduced to 4.8-5.0GeV/c for the 10% most central events. A non-Gaussian tail of the momentum uncertainty is observed and its impact on the reconstructed jet spectrum is evaluated for varying particle momentum thresholds, by folding the measured fluctuations with steeply falling spectra.

In this Letter we report the first results on π±, K±, p, and p̅ production at midrapidity (|y|&lt;0.5) in central Pb-Pb collisions at √sNN=2.76  TeV, measured by the ALICE experiment at the LHC. The pT distributions and yields are compared to previous results at √sNN=200  GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with √sNN, which in hydrodynamic models is expected as a consequence of the increasing particle density. While the K/π ratio is in line with predictions from the thermal model, the p/π ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.

The production of K∗(892)0 and ϕ(1020) in pp collisions at $sqrt{s}=7~mathrm{TeV}$ was measured by the ALICE experiment at the LHC. The yields and the transverse momentum spectra d2 N/dydp T at midrapidity |y|<0.5 in the range 0<p T<6 GeV/c for K∗(892)0 and 0.4<p T<6 GeV/c for ϕ(1020) are reported and compared to model predictions. Using the yield of pions, kaons, and Ω baryons measured previously by ALICE at $sqrt{s}=7 mathrm{TeV}$ , the ratios K∗/K−, ϕ/K∗, ϕ/K−, ϕ/π −, and $(Omega + overline{Omega })/phi$ are presented. The values of the K∗/K−, ϕ/K∗ and ϕ/K− ratios are similar to those found at lower centre-of-mass energies. In contrast, the ϕ/π − ratio, which has been observed to increase with energy, seems to saturate above 200 GeV. The $(Omega + overline {Omega })/phi$ ratio in the p T range 1–5 GeV/c is found to be in good agreement with the prediction of the $mathrm{HIJING}/mathrm{B}overline{mathrm{B}}$ v2.0 model with a strong colour field.

The production of Ξ− and Ω− baryons and their anti-particles in Pb–Pb collisions at View the MathML source has been measured using the ALICE detector. The transverse momentum spectra at mid-rapidity (|y|<0.5 ) for charged Ξ and Ω hyperons have been studied in the range 0.6<pT<8.0 GeV/c and 1.2<pT<7.0 GeV/c , respectively, and in several centrality intervals (from the most central 0–10% to the most peripheral 60–80% collisions). These spectra have been compared with the predictions of recent hydrodynamic models. In particular, the Kraków and EPOS models give a satisfactory description of the data, with the latter covering a wider pT range. Mid-rapidity yields, integrated over pT , have been determined. The hyperon-to-pion ratios are similar to those at RHIC: they rise smoothly with centrality up to 〈Npart〉∼150 and saturate thereafter. The enhancements (yields per participant nucleon relative to those in pp collisions) increase both with the strangeness content of the baryon and with centrality, but are less pronounced than at lower energies.

The ALICE experiment at the LHC has studied inclusive J/psi production at central and forward rapidities in pp collisions at root s = 7 TeV. In this Letter, we report on the first results obtained detecting the J/psi through the dilepton decay into e(+)e(-) and mu(+)mu(-) pairs in the rapidity ranges vertical bar y vertical bar < 0.9 and 2.5 < y < 4, respectively, and with acceptance down to zero PT. In the dielectron channel the analysis was carried Out on a data sample corresponding to an integrated luminosity L(int) = 5.6 nb(-1) and the number of signal events is N(J/psi) = 352 +/- 32 (stat.) +/- 28 (syst.): the corresponding figures in the dimuon channel are L(int) = 15.6 nb(-1) and N(J/psi) = 1924 +/- 77 (stat.) +/- 144 (syst.). The measured production cross sections are sigma(J/psi) (vertical bar y vertical bar < 0.9) = 10.7 +/- 1.0 (stat.) +/- 1.6 (syst.)(-2.3)(+1.6) (syst.pol.) mu b and sigma(J/psi) (2.5 < y < 4) = 6.31 +/- 0.25 (stat.) +/- 0.76 (syst.)(-1.96)(+0.95) (syst.pol.) mu b. The differential cross sections, in transverse momentum and rapidity, of the J/psi were also measured.

The production of π +, π −, K+, K−, p, and p at mid-rapidity has been measured in proton-proton collisions at √ s = 900 GeV with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum (pt) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from pt = 100 MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean pt are compared with previous measurements, and the trends as a function of collision energy are discussed.

Inclusive transverse momentum spectra of primary charged particles in Pb-Pb collisions at root s(NN) = 2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented for central and peripheral collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross section. The measured charged particle spectra in |eta| < 0.8 and 0.3 < p(T) < 20 GeV/c are compared to the expectation in pp collisions at the same root s(NN), scaled by the number of underlying nucleon-nucleon collisions. The comparison is expressed in terms of the nuclear modification factor R-AA. The result indicates only weak medium effects (R-AA approximate to 0.7) in peripheral collisions. In central collisions, R-AA reaches a minimum of about 0.14 at p(T) = 6-7 GeV/c and increases significantly at larger p(T). The measured suppression of high-p(T) particles is stronger than that observed at lower collision energies, indicating that a very dense medium is formed in central Pb-Pb collisions at the LHC.

Transverse momentum spectra of π ±, K ± and p(p-) up to pT = 20 GeV/c at mid-rapidity in pp, peripheral (60-80%) and central (0-5%) Pb-Pb collisions at √sNN=2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT ≈ 3 GeV/c in central Pb-Pb collisions. Below the peak, pT < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For pT > 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for π ±, K ± and p(p-) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets. © 2014 The Authors.

In this Letter, comprehensive results on π±, K±, Ko<inf>S</inf>, p(p) and A(A) production at mid-rapidity (0 < yCMS < 0.5) in p-Pb collisions at √S<inf>NN</inf> = 5.02 TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb-Pb collisions at the LHC. The measured pT distributions are compared to d-Au, Au-Au and Pb-Pb results at lower energy and with predictions based on QCD-inspired and hydrodynamic models. © 2013 The Authors. Published by Elsevier B.V.

The production of the prompt charm mesons D0, D+, D∗+, and their an- tiparticles, was measured with the ALICE detector in Pb-Pb collisions at the LHC, at a centre-of-mass energy √sNN = 2.76 TeV per nucleon-nucleon collision. The pt-differential production yields in the range 2 < pt < 16 GeV/c at central rapidity, |y| < 0.5, were used to calculate the nuclear modification factor RAA with respect to a proton-proton reference obtained from the cross section measured at √s = 7 TeV and scaled to √s = 2.76 TeV. For the three meson species, RAA shows a suppression by a factor 3–4, for transverse momenta larger than 5 GeV/c in the 20% most central collisions. The suppression is reduced for peripheral collisions.

Measurements of the sphericity of primary charged particles in minimum bias proton–proton collisions at s√=0.9, 2.76 and 7 TeV with the ALICE detector at the LHC are presented. The observable is measured in the plane perpendicular to the beam direction using primary charged tracks with p T>0.5 GeV/c in |η|<0.8. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity (N ch) is reported for events with different p T scales (“soft” and “hard”) defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity is presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low N ch, whereas the event generators show an opposite tendency. The combined study of the sphericity and the mean p T with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.

Correlations induced by quantum statistics are sensitive to the spatiotemporal extent as well as dynamics of particle-emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two- and three-pion correlations of same andmixed charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at √ sNN = 2.76 TeV at the CERN Large Hadron Collider with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission. The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged-pion emission of 23% ± 8%.

We present measurements of Underlying Event observables in pp collisions at √s = 0:9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum pT;LT in the event. Dierent regions are dened with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three dierent pT thresholds: 0.15, 0.5 and 1.0 GeV=c. In the Transverse region we observe an increase in the multiplicity of a factor 2{3 between the lower and higher collision energies, depending on the track pT threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed pT in the Transverse region by about 10{30%.

The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at root(NN)-N-S = 2.76 TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.

Abstract: 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 (formula presented.) = 5.02 TeV at the CERN LHC. The measurement was performed at forward (2.03 < y<inf>cms</inf>< 3.53) and backward (−4.46 < y<inf>cms</inf>< −2.96) centre of mass rapidities, studying the decays into muon pairs. In this paper, we present the inclusive production cross sections σ<inf>ψ(2S)</inf>, both integrated and as a function of the transverse momentum p<inf>T</inf>, for the two y<inf>cms</inf> 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<inf>ψ(2S)</inf>/σ<inf>J/ψ</inf> ]<inf>pPb</inf>/[σ<inf>ψ(2S)</inf>/σ<inf>J/ψ</inf>]<inf>pp</inf> 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.[Figure not available: see fulltext. © 2014, The Author(s).

We report on the measurement of the inclusive ϒhooked(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 ϒhooked(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 ϒhooked(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. © 2014 The Authors.

The transverse momentum (Formula presented.) distribution of primary charged particles is measured at midrapidity in minimum-bias p–Pb collisions at (Formula presented.)NN = 5.02(Formula presented.) TeV with the ALICE detector at the LHC in the range. 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 (Formula presented.) larger than 2 GeV/(Formula presented.)(Formula presented.) around 4 (Formula presented.). The measurement is compared to theoretical calculations and to data in Pb–Pb collisions at (Formula presented.) TeV. © 2014, The Author(s).

ALICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark-Gluon Plasma (QGP), using proton-proton, proton-nucleus and nucleus-nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018-2019. These plans are presented in the ALICE Upgrade Letter of Intent, submitted to the LHCC (LHC experiments Committee) in September 2012. In order to fully exploit the physics reach of the LHC in this field, high-precision measurements of the heavy-flavour production, quarkonia, direct real and virtual photons, and jets are necessary. This will be achieved by an increase of the LHC Pb-Pb instant luminosity up to 6×1027 cm-2s-1 and running the ALICE detector with the continuous readout at the 50 kHz event rate. The physics performance accessible with the upgraded detector, together with the main detector modifications, are presented. © 2014 CERN on behalf of The ALICE Collaboration.