Measurement of dijet kT in p-Pb collisions at √sNN=5.02 TeV

A measurement of dijet correlations in p–Pb collisions at √ sNN = 5.02 TeV with the ALICE detector is presented. Jets are reconstructed from charged particles measured in the central tracking detectors and neutral energy deposited in the electromagnetic calorimeter. The transverse momentum of the full jet (clustered from charged and neutral constituents) and charged jet (clustered from charged particles only) is corrected event-by-event for the contribution of the underlying event, while corrections for underlying event fluctuations and finite detector resolution are applied on an inclusive basis. A projection of the dijet transverse momentum, kTy = p ch+ne T,jet sin(∆ϕdijet) with ∆ϕdijet the azimuthal angle between a full and charged jet and p ch+ne T,jet the transverse momentum of the full jet, is used to study nuclear matter effects in p–Pb collisions. This observable is sensitive to the acoplanarity of dijet production and its potential modification in p–Pb collisions with respect to pp collisions. Measurements of the dijet kTy as a function of the transverse momentum of the full and recoil charged jet, and the event multiplicity are presented. No significant modification of kTy due to nuclear matter effects in p–Pb collisions with respect to the event multiplicity or a PYTHIA8 reference is observed

Measurement of electrons from heavy-flavour hadron decays in p-Pb collisions at √sNN=5.02TeV

The production of electrons from heavy-flavour hadron decays was measured as a function of transverse momentum (p(T)) in minimum-bias p-Pb collisions at root s(NN) = 5.02 TeV using the ALICE detector at the LHC. The measurement covers the p(T) interval 0.5 < p(T) < 12 GeV/c and the rapidity range -1.065 < y(cms) < 0.135 in the centre-of-mass reference frame. The contribution of electrons from background sources was subtracted using an invariant mass approach. The nuclear modification factor R-pPb was calculated by comparing the p(T)-differential invariant cross section in p-Pb collisions to a pp reference at the same centre-of-mass energy, which was obtained by interpolating measurements at root s = 2.76 TeV and root s= 7 TeV. The R-pPb is consistent with unity within uncertainties of about 25%, which become larger for p(T) below 1 GeV/c. The measurement shows that heavy-flavour production is consistent with binary scaling, so that a suppression in the high-p(T) yield in Pb-Pb collisions has to be attributed to effects induced by the hot medium produced in the final state. The data in p-Pb collisions are described by recent model calculations that include cold nuclear matter effects. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V

Measurement of jet suppression in central Pb–Pb collisions at √sNN=2.76 TeV

The transverse momentum (pT) spectrum and nuclear modification factor (RAA) of recon- structed jets in 0–10% and 10–30% central Pb–Pb collisions at √sNN = 2.76 TeV were mea- sured. Jets were reconstructed using the anti-kT jet algorithm with a resolution parameter of R = 0.2 from charged and neutral particles, utilizing the ALICE tracking detectors and Elec- tromagnetic Calorimeter (EMCal). The jet pT spectra are reported in the pseudorapidity in- terval of |ηjet| 5 GeV/c to suppress jets constructed from the combinatorial background in Pb–Pb collisions. The leading charged particle requirement applied to jet spectra both in pp and Pb–Pb collisions had a negligible effect on the RAA. The nuclear modification factor RAA was found to be 0.28 ± 0.04 in 0–10% and 0.35 ± 0.04 in 10–30% collisions, indepen- dent of pT, jet within the uncertainties of the measurement. The observed suppression is in fair agreement with expectations from two model calculations with different approaches to jet quenching

Centrality dependence of inclusive J/ψ production in p-Pb collisions at √sNN =5.02 TeV

We present a measurement of inclusive J/ ψ production in p–Pb collisions at √sNN = 5.02 TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, pT, in the backward (−4.46 < ycms < −2.96) and forward (2.03 < ycms < 3.53) rapidity intervals in the dimuon decay channel and in the mid-rapidity region (−1.37 < ycms < 0.43) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The pT-differential J/ ψ production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average pT and p2 T values. The nuclear modification factor is presented as a function of centrality for the three rapidity intervals, and as a function of pT for several centrality classes at backward and forward rapidity. At mid- and forward rapidity, the J/ ψ yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p–Pb collisions at forward rapidity, and with decreasing pT of the J/ ψ. At backward rapidity, the nuclear modification factor is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p–Pb collisions