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

Long-range angular correlations of π, K and p in p–Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

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 < $p_T$ < 4 GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |$\eta_{lab}$| < 0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of $p_T$ and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, $v_2^p$, is observed to be smaller than that for pions, $v_2^\pi$, up to about $p_T$ = 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 $v_2^p$ is found to be smaller at low $p_T$ and larger at higher $p_T$ than $v_2^\pi$, with a crossing occurring at about 2 GeV. 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.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 $0.3 < p_{\rm T} < 4$ GeV/$c$. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta_{\rm lab}|<0.8$. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of $p_{\rm T}$ and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, $v_2^p$, is observed to be smaller than that for pions, $v_2^\pi$, up to about $p_{\rm T} = 2$ 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 $v_2^p$ is found to be smaller at low $p_{\rm T}$ and larger at higher $p_{\rm T}$ than $v_2^pi$, with a crossing occurring at about 2 GeV. 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.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, v2p , is observed to be smaller than that for pions, v2π , 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 v2p is found to be smaller at low pT and larger at higher pT than v2π , 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

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

Measurement of visible cross sections in proton-lead collisions at sqrt(sNN) = 5.02 TeV in van der Meer scans with the ALICE detector

In 2013, the Large Hadron Collider provided proton-lead and lead-proton collisions at the center-of-mass energy per nucleon pair sqrt(sNN) = 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 < eta< 4.9, -3.3 < eta < -3.0 and 2.8 < eta < 5.1, -3.7 < eta < -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

Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC

The average transverse momentum versus the charged-particle multiplicity $N_{ch}$ was measured in p-Pb collisions at a collision energy per nucleon-nucleon pair $\sqrt{s_{NN}}$ = 5.02 TeV and in pp collisions at collision energies of $\sqrt{s}$ = 0.9, 2.76, and 7 Tev in the kinematic range 0.15 with $N_{ch}$ is observed, which is much stronger than that measured in Pb-Pb collisions. For pp collisions, this could be attributed, within a model of hadronizing strings, to multiple-parton interactions and to a final-state color reconnection mechanism. The data in p-Pb and Pb-Pb collisions cannot be described by an incoherent superposition of nucleon-nucleon collisions and pose a challenge to most of the event generators

Measurement of quarkonium production at forward rapidity in pppp collisions at s=7\sqrt{s} = 7 TeV

The inclusive production cross sections at forward rapidity of J/$\psi$, $\psi$(2S), $\Upsilon$(1S) and $\Upsilon$(2S) are measured in pp collisions at $\sqrt{s}$ = 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 $\mu^+\mu^-$ invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum $p_T$ and rapidity y, over the transverse momentum range 0 < $p_T$ < 20 GeV/c for J/$\psi$ and 0 < $p_T$ < 12 GeV/c for all other resonances and for 2.5 < y < 4. The measured cross sections integrated over $p_T$ and y, and assuming unpolarized quarkonia, are: $\sigma_{J/\psi}$=6.69 $\pm$ 0.04 $\pm$ 0.61 $\mu$ b, $\sigma_{\psi(2S)}$ = 1.13 $\pm$ 0.07 $\pm$ 0.14 $\mu$b, $\sigma_{\Upsilon(1S)}$ = 54.2 $\pm$ 5.0 $\pm$ 6.7 nb and $\sigma_{\Upsilon(2S)}$=18.4 $\pm$ 3.7 $\pm$ 2.2 nb, where the first uncertainty is statistical and the second one is systematic. These cross sections are obtained assuming unpolarized quarkonium production. The results are compared to measurements performed by other LHC experiments and to theoretical models.The inclusive production cross sections at forward rapidity of J/$\psi$, $\psi$(2S), $\Upsilon$(1S) and $\Upsilon$(2S) are measured in pp collisions at $\sqrt{s} = 7$ TeV with the ALICE detector at the LHC. The analysis is based in 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 $\mu^+\mu^-$ invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum $p_{\rm T}$ and rapidity $y$, over the ranges $0 < p_{\rm T} < 20$ GeV/$c$ for J/$\psi$, $0 < p_{\rm T} < 12$ GeV/$c$ for all other resonances and for $2.5 < y < 4$. The measured cross sections integrated over $p_{\rm T}$ and $y$, and assuming unpolarized quarkonia, are: $\sigma_{J/\psi} = 6.69 \pm 0.04 \pm 0.63$ $\mu$b, $\sigma_{\psi^{\prime}} = 1.13 \pm 0.07 \pm 0.14$ $\mu$b, $\sigma_{\Upsilon{\rm(1S)}} = 54.2 \pm 5.0 \pm 6.7$ nb and $\sigma_{\Upsilon{\rm (2S)}} = 18.4 \pm 3.7 \pm 2.2$ 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.The inclusive production cross sections at forward rapidity of ${\mathrm{J}/\psi }$ , ${\psi (\mathrm{2S})}$ , $\Upsilon$ (1S) and $\Upsilon$ (2S) are measured in $\mathrm{pp}$ collisions at $\sqrt{s}=7~\mathrm{TeV}$ 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 $\mu ^+\mu ^-$ invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum ${p_\mathrm{T}}$ and rapidity $y$ , over the ranges $0<{p_\mathrm{T}}<20$  GeV/c for ${\mathrm{J}/\psi }$ , $0<{p_\mathrm{T}}<12$  GeV/c for all other resonances and for $2.5<y<4$ . The measured cross sections integrated over ${p_\mathrm{T}}$ and $y$ , and assuming unpolarized quarkonia, are: $\sigma _\mathrm{{\mathrm{J}/\psi }}=6.69\pm 0.04\pm 0.63$   \upmu b, $\sigma _{\psi (\mathrm{2S})}=1.13\pm 0.07\pm 0.19$   \upmu b, $\sigma _{\Upsilon (\mathrm{1S})}=54.2\,\pm \, 5.0\pm 6.7$  nb and $\sigma _{\Upsilon (\mathrm{2S})}=18.4\,\pm \,3.7\,\pm \, 2.9$  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