Recent results on ultra-peripheral Pb-Pb and p-Pb collisions at the ALICE experiment

In this paper, we will discuss results on coherent and incoherent J/ψ photoproduction in ultra-peripheral Pb-Pb collisions at = 2.76, as well as preliminary results on exclusive J/ψ and two-photon production in ultra-peripheral p-Pb collisions at = 5.02 TeV. Results on four-pion production in ultra-peripheral Pb-Pb collisions will also be given. Finally, the prospects for other UPC measurements in ALICE will be briefly mentioned

Recent results on ultra-peripheral Pb-Pb and p-Pb collisions at the ALICE experiment

In this paper, we will discuss results on coherent and incoherent J/ψ photoproduction in ultra-peripheral Pb-Pb collisions at = 2.76, as well as preliminary results on exclusive J/ψ and two-photon production in ultra-peripheral p-Pb collisions at = 5.02 TeV. Results on four-pion production in ultra-peripheral Pb-Pb collisions will also be given. Finally, the prospects for other UPC measurements in ALICE will be briefly mentioned

J/ψ production and nuclear effects in p-Pb collisions at sNN−−−√ = 5.02 TeV

This is the published version.Inclusive J/ψ production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy sNN−−−√ = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < y cms < 3.53 and −4.46 < y cms < −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 R pPb 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

Neutral pion production at midrapidity in pp and Pb–Pb collisions at √sNN=2.76TeV

This is the published version.Invariant yields of neutral pions at midrapidity in the transverse momentum range 0.6<pT<12GeV/c measured in Pb–Pb collisions at sNN−−−√=2.76 TeV are presented for six centrality classes. The pp reference spectrum was measured in the range 0.4<pT<10GeV/c at the same center-of-mass energy. The nuclear modification factor, RAA, shows a suppression of neutral pions in central Pb–Pb collisions by a factor of up to about 8−10 for 5≲pT≲7GeV/c. The presented measurements are compared with results at lower center-of-mass energies and with theoretical calculations

Multiplicity dependence of jet-like two-particle correlation structures in p–Pb collisions at √sNN=5.02TeV

Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p–Pbcollisions at a nucleon–nucleon centre-of-mass energy of 5.02TeV. The transverse-momentum range 0.7 <pT,assoc<pT,trig<5.0GeV/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–Pbcollisions 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–Pbcollisions. 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.Funded by SCOAP

Transverse momentum dependence of inclusive primary charged-particle production in p–Pb collisions at √sNN=5.02 TeV

This is the published version.The transverse momentum (pT) distribution of primary charged particles is measured at midrapidity in minimum-bias p–Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector at the LHC in the range 0.15<pT<50 GeV/c. 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 pT larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for pT around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb–Pb collisions at sNN−−−√=2.76 TeV

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

We report on the production of inclusive Υ(1S) and Υ(2S) in p–Pb collisions at √sNN=5.02TeVat 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

K∗(892)0 and φ(1020) production in Pb-Pb collisions at √ sNN = 2.76 TeV

The yields of the K∗(892)0 and ϕ(1020) resonances are measured in Pb-Pb collisions at 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 ϕ(1020). The yields of K∗(892)0 are suppressed in central Pb-Pb collisions with respect to pp and peripheral Pb-Pb collisions (perhaps due to rescattering of its decay products in the hadronic medium), while the longer-lived ϕ(1020) meson is not suppressed. These particles are also used as probes to study the mechanisms of particle production. The shape of the pT distribution of the ϕ(1020) meson, but not its yield, is reproduced fairly well by hydrodynamic models for central Pb-Pb collisions. In central Pb-Pb collisions at low and intermediate pT, the p/ϕ(1020) ratio is flat in pT, while the p/π and ϕ(1020)/π 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, ϕ(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 Λ and Ξ

Production of Σ(1385)± and Ξ(1530)0 in proton–proton collisions at s√= 7 TeV

The production of the strange and double-strange baryon resonances (Σ(1385)±, Ξ(1530)0) has been measured at mid-rapidity (|y|<0.5) in proton–proton collisions at s√ = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the ϕ(1860) pentaquark, decaying in the Ξπ channel, has been carried out but no evidence is seen.Funded by SCOAP

Suppression of ψ(2S) production in p-Pb collisions at sNN−−−√ = 5.02 TeV

This is the published version. Open Access, Copyright CERN, for the benefit of the ALICE Collaboration. Article funded by SCOAP3.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 sNN−−−√ = 5.02 TeV at the CERN LHC. The measurement was performed at forward (2.03 < y cms < 3.53) and backward (−4.46 < y cms < −2.96) centre of mass rapidities, studying the decays into muon pairs. In this paper, we present the inclusive production cross sections σ ψ(2S), both integrated and as a function of the transverse momentum p T, for the two y cms 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 ψ(2S) /σ J/ψ ]pPb /[σ ψ(2S) /σ J/ψ ]pp 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