First LHC results on coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV

The first LHC measurement on ultra-peripheral heavy-ion collisions was carried out with the ALICE experiment. In this paper, ALICE results on exclusive J/psi studies in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV, in the rapidity region -3.6 < y < -2.6, are given. The coherent J/psi cross section was found to be dsigma/dy_coh_J/\psi = 1.00 +/- 0.18 (stat) +0.24 -0.26 (syst) mb. These studies favour theoretical models that include strong modifications to the nuclear gluon density, also known as nuclear gluon shadowing.Comment: Presented at DIFFRACTION 2012: International Workshop on Diffraction in High-Energy Physics. Puerto del Carmen, Canary Islands, 10-15 September 201

Prospects for ϕ\phi meson production in pp collisions at the ALICE experiment

The ALICE experiment at the CERN Large Hadron Collider (LHC) will allow the study of resonance production in nucleus-nucleus and proton-proton collisions. This paper presents results based on physics performance studies to discuss prospects in ALICE for $\phi$(1020) meson production in pp interactions during the LHC startup.Comment: To appear in the proceedings of International Conference on Strangeness in Quark Matter (SQM 2007), Levoca, Slovakia, 24-29 Jun 2007. Submitted to J.Phys.

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

Quantum tomography for collider physics: Illustrations with lepton pair production

Quantum tomography is a method to experimentally extract all that is observable about a quantum mechanical system. We introduce quantum tomography to collider physics with the illustration of the angular distribution of lepton pairs. The tomographic method bypasses much of the field-theoretic formalism to concentrate on what can be observed with experimental data, and how to characterize the data. We provide a practical, experimentally-driven guide to model-independent analysis using density matrices at every step. Comparison with traditional methods of analyzing angular correlations of inclusive reactions finds many advantages in the tomographic method, which include manifest Lorentz covariance, direct incorporation of positivity constraints, exhaustively complete polarization information, and new invariants free from frame conventions. For example, experimental data can determine the $entanglement$ $entropy$ of the production process, which is a model-independent invariant that measures the degree of coherence of the subprocess. We give reproducible numerical examples and provide a supplemental standalone computer code that implements the procedure. We also highlight a property of $complex$ $positivity$ that guarantees in a least-squares type fit that a local minimum of a $\chi^{2}$ statistic will be a global minimum: There are no isolated local minima. This property with an automated implementation of positivity promises to mitigate issues relating to multiple minima and convention-dependence that have been problematic in previous work on angular distributions.Comment: 25 pages, 3 figure

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