Abstract
Measurements of charged jet production as a function of centrality are presented for p–Pb collisions recorded at sqrt{s_mathrm {NN}}= 5.02 TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon–nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-k_mathrm {T} algorithm for resolution parameters R = 0.2 and R = 0.4 in the transverse momentum range 20 to 120 GeV/c. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p–Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.
Highlights
The measurement of benchmark processes in proton–nucleus collisions plays a crucial role for the interpretation of nucleus–nucleus collision data, where one expects to create a system with high temperature in which the elementary constituents of hadronic matter, quarks and gluons, are deconfined for a short time: the quark-gluon plasma (QGP) [1]
For the analysis presented in this paper, the main detectors used for event and centrality selection are two scintillator detectors (V0A and V0C), covering the pseudo-rapidity range of 2.8 < ηlab < 5.1 and −3.7 < ηlab < −1.7, respectively [35], and the Zero Degree Calorimeters (ZDCs), composed of two sets of neutron (ZNA and ZNC) and proton calorimeters (ZPA and ZPC) located at a distance ±112.5 m from the interaction point
The scaling behaviour of the p–Pb spectra with respect to the pp reference is quantified by the nuclear modification factor QpPb (Eq 7)
Summary
The measurement of benchmark processes in proton–nucleus collisions plays a crucial role for the interpretation of nucleus–nucleus collision data, where one expects to create a system with high temperature in which the elementary constituents of hadronic matter, quarks and gluons, are deconfined for a short time: the quark-gluon plasma (QGP) [1]. The study of hard parton scatterings and their subsequent fragmentation via reconstructed jets plays a crucial role in the characterisation of the hot and dense medium produced in Pb–Pb collisions while jet measurements in p–Pb and pp collisions provide allow to constrain the impact of cold nuclear matter effects in heavy-ion collisions. Jet production may be influenced, already in p–Pb collisions, by multiple scattering of partons and hadronic re-interaction in the initial and final state [4,5]. In the absence of any modification in the initial state, the partonic scattering rate in nuclear collisions compared to pp collisions is expected to increase linearly with the average number of binary nucleon–nucleon collisions Ncoll.
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