Performance of the ALICE Experiment at the CERN LHC

ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables

Production of inclusive ϒ(1S) and ϒ(2S) in p–Pb collisions at sNN=5.02\sqrt{s_{\rm NN}} = 5.02 TeV

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

Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at sNN\sqrt{s_NN} = 5.02 TeV with ALICE at LHC

Two-particle angular correlations between unidentified 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. The transverse-momentum range 0.7 < $p_{T,assoc} < p_{T,trig}$ < 5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |η| < 0.9. The near-side long-range pseudorapidity correlations observed in high-multiplicity p–Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non- jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton–parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p–Pb collisions. Further, the number scales in the intermediate multiplicity region with the number of binary nucleon–nucleon collisions estimated with a Glauber Monte-Carlo simulation.Two-particle angular correlations between unidentified 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. The transverse-momentum range 0.7<pT,assoc<pT,trig<5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |η|<0.9 . The near-side long-range pseudorapidity correlations observed in high-multiplicity p–Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton–parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p–Pb collisions. Further, the number scales only in the intermediate multiplicity region with the number of binary nucleon–nucleon collisions estimated with a Glauber Monte-Carlo simulation.Two-particle angular correlations between unidentified 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. The transverse-momentum range 0.7 $< p_{\rm{T}, assoc} < p_{\rm{T}, trig} <$ 5.0 GeV/$c$ is examined, to include correlations induced by jets originating from low momen\-tum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta|<0.9$. The near-side long-range pseudorapidity correlations observed in high-multiplicity p-Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton--parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p-Pb collisions. Further, the number scales in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation

Elliptic flow of identified hadrons in Pb-Pb collisions at sNN\sqrt{s_{\rm{NN}}} = 2.76 TeV

The elliptic flow coefficient ($v_{2}$) of identified particles in Pb--Pb collisions at $\sqrt{s_\mathrm{{NN}}} = 2.76$ TeV was measured with the ALICE detector at the LHC. The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of $|\Delta\eta| > 0.9$ between the identified hadron under study and the reference particles. The $v_2$ is reported for $\pi^{\pm}$, $\mathrm{K}^{\pm}$, $\mathrm{K}^0_\mathrm{S}$, p+$\overline{\mathrm{p}}$, $\mathrm{\phi}$, $\Lambda$+$\overline{\mathrm{\Lambda}}$, $\Xi^-$+$\overline{\Xi}^+$ and $\Omega^-$+$\overline{\Omega}^+$ in several collision centralities. In the low transverse momentum ($p_{\mathrm{T}}$) region, $p_{\mathrm{T}} 3$GeV/$c$.The elliptic flow coefficient (v$_{2}$) of identified particles in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ 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 |Δη| > 0.9 between the identified hadron under study and the reference particles. The v$_{2}$ is reported for π$^{±}$, K$^{±}$, K$_{S}^{0}$ , $\mathrm{p}+\overline{\mathrm{p}}$ , ϕ, $\Lambda +\overline{\Lambda}$ , ${\Xi}^{-}+{\overline{\Xi}}^{+}$ and ${\Omega}^{-}+{\overline{\Omega}}^{+}$ in several collision centralities. In the low transverse momentum (p$_{T}$) region, p$_{T}$ 3 GeV/c.The elliptic flow coefficient ($v_{2}$) of identified particles in Pb-Pb collisions at $\sqrt{s_\mathrm{{NN}}} = 2.76$ TeV was measured with the ALICE detector at the LHC. The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of $|\Delta\eta| > 0.9$ between the identified hadron under study and the reference particles. The $v_2$ is reported for $\pi^{\pm}$, $\mathrm{K}^{\pm}$, $\mathrm{K}^0_\mathrm{S}$, p+$\overline{\mathrm{p}}$, $\mathrm{\phi}$, $\Lambda$+$\overline{\mathrm{\Lambda}}$, $\Xi^-$+$\overline{\Xi}^+$ and $\Omega^-$+$\overline{\Omega}^+$ in several collision centralities. In the low transverse momentum ($p_{\mathrm{T}}$) region, $p_{\mathrm{T}} 3$GeV/$c$

Inclusive photon production at forward rapidities in proton-proton collisions at s\sqrt{s} = 0.9, 2.76 and 7 TeV

The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities ($2.3 < \eta < 3.9$) in proton-proton collisions at three center-of-mass energies, $\sqrt{s}=0.9$, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2% $\pm$ 0.3% (stat) $\pm$ 8.8% (sys) and 61.2% $\pm$ 0.3% (stat) $\pm$ 7.6% (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities ( $2.3 < \eta < 3.9$ ) in proton–proton collisions at three center-of-mass energies, $\sqrt{s}$   $=$ 0.9, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 $\pm$ 0.3 % (stat) $\pm$ 8.8 % (sys) and 61.2 $\pm$ 0.3 % (stat) $\pm$ 7.6 % (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities ($2.3 < \eta < 3.9$) in proton-proton collisions at three center-of-mass energies, $\sqrt{s}=0.9$, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2% $\pm$ 0.3% (stat) $\pm$ 8.8% (sys) and 61.2% $\pm$ 0.3% (stat) $\pm$ 7.6% (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range

Production of inclusive ϒ(1S) and ϒ(2S) in p–Pb collisions at √sNN = 5.02 TeV

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

Exclusive J/ψ\mathrm{J/}\psi photoproduction off protons in ultra-peripheral p-Pb collisions at sNN=5.02\sqrt{s_{\rm NN}}=5.02 TeV

We present the first measurement at the LHC of exclusive J/$\psi$ photoproduction off protons, in ultra-peripheral proton-lead collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, 2.5We present the first measurement at the LHC of exclusive J/ψ photoproduction off protons, in ultraperipheral proton-lead collisions at sNN=5.02  TeV. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, 2.5<y<4 (p-Pb) or -3.6<y<-2.6 (Pb-p), and no other particles observed in the ALICE acceptance. The measured cross sections σ(γ+p→J/ψ+p) are 33.2±2.2(stat)±3.2(syst)±0.7(theor)  nb in p-Pb and 284±36(stat)-32+27(syst)±26(theor)  nb in Pb-p collisions. We measure this process up to about 700 GeV in the γp center of mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the J/ψ photoproduction cross section in γp energies from about 20 to 700 GeV, or equivalently, from Bjorken x scaling variable between ∼2×10-2 and ∼2×10-5, thus indicating no significant change in the gluon density behavior of the proton between HERA and LHC energies.We present the first measurement at the LHC of exclusive J/\psi$photoproduction off protons, in ultra-peripheral proton-lead collisions at$\sqrt{s_{\rm NN}}=5.02$TeV. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame,$2.5<y<4$(p-Pb) or$-3.6<y<-2.6$(Pb--p), and no other particles observed in the ALICE acceptance. The measured cross sections$\sigma (\gamma + {\rm p} \rightarrow J/\psi + {\rm p})$are 33.2$\pm$2.2 (stat)$\pm$3.1 (syst)$\pm$0.7 (theo) nb in p-Pb and 284$\pm$36 (stat)$^{+27}_{-32}$(syst)$\pm$26 (theo) nb in Pb-p collisions. We measure this process up to about 700 GeV in the$\gamma {\rm p}$centre-of-mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the$J/\psi$photoproduction cross section in$\gamma {\rm p}$energies from about 20 to 700 GeV, or equivalently, from Bjorken-$x$between$\sim 2\times 10^{-2}$to$\sim 2\times 10^{-5}$, thus indicating no significant change in the gluon density behaviour of the proton between HERA and LHC energies

K*(892)^0 and PHI(1020) production in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV

The yields of the K*(892) and PHI(1020) resonances are measured in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV through their hadronic decays using the ALICE detector. The measurements are performed in multiple centrality intervals at mid-rapidity (|y|<0.5) in the transverse-momentum ranges 0.3<pt<5 GeV/c for the K*(892)^0 and 0.5<pt<5 GeV/c for the PHI(1020). The yields of K*(892)^0 are suppressed in central Pb-Pb collisions with respect to pp and peripheral Pb-Pb collisions. This suppression is discussed in a scenario in which the K*(892)^0 decays during the evolution of the fireball and the decay products scatter, thus escaping detection through invariant-mass reconstruction. In contrast, the PHI(1020) meson, due to its long lifetime, decays outside the fireball. These particles are also used as probes to study the mechanisms of particle production. The shape of the pt distribution of the PHI(1020) meson, but not its yield, is reproduced fairly well by hydrodynamical models for central Pb-Pb collisions. In central Pb-Pb collisions at low and intermediate pt, the p/PHI(1020) ratio is flat in pt, while the p/pi and PHI(1020)/pi ratios show a pronounced increase and have similar shapes to each other. These results indicate that the shapes of the pt distributions of these particles in central Pb-Pb collisions are determined predominantly by the particle masses and radial flow. Finally, PHI(1020) production in Pb-Pb collisions is enhanced, with respect to the yield in pp collisions and the yield of charged pions, by an amount similar to the Lambda and Xi

Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at √s = 2.76 TeV

The pT-differential production cross section of electrons from semileptonic decays of heavy-flavor hadrons has been measured at mid-rapidity in proton-proton collisions at s√=2.76 TeV in the transverse momentum range 0.5 < pT < 12 GeV/c with the ALICE detector at the LHC. The analysis was performed using minimum bias events and events triggered by the electromagnetic calorimeter. Predictions from perturbative QCD calculations agree with the data within the theoretical and experimental uncertainties