Abstract
Neutral pion and eta meson invariant differential yields were measured in non-single diffractive p–Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of pi ^{0} and eta meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of 0.3< p_{mathrm{T}} < 20 hbox { GeV}/c and 0.7< p_{mathrm{T}} < 20hbox { GeV}/c, respectively. The measured eta /pi ^{0} ratio increases with p_{mathrm{T}} and saturates for p_{mathrm{T}} > 4 hbox {GeV}/c at 0.483 pm 0.015_{mathrm{stat}} pm 0.015_{mathrm{sys}}. A deviation from m_{mathrm{T}} scaling is observed for p_{mathrm{T}}< 2 hbox {GeV}/c. The measured eta /pi ^{0} ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full p_{mathrm{T}} range. The measured eta /pi ^{0} ratio at high p_{mathrm{T}} also agrees within uncertainties with measurements from nucleus–nucleus collisions. The pi ^{0} and eta yields in p–Pb relative to the scaled pp interpolated reference, R_{{mathrm{pPb}}}, are presented for 0.3 < p_{mathrm{T}}< 20 hbox {GeV}/c and 0.7 < p_{mathrm{T}}< 20 hbox {GeV}/c, respectively. The results are compared with theoretical model calculations. The values of R_{{mathrm{pPb}}} are consistent with unity for transverse momenta above 2 hbox {GeV}/c. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb–Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.
Highlights
Proton-nucleus collisions are an important tool for the study of strongly interacting matter and the Quark–Gluon Plasma (QGP), complementing and extending measurements carried out with high energy collisions of heavy nuclei [1]
Within the framework of collinearly-factorized perturbative QCD, effects of the nuclear environment are parameterized using nuclear-modified parton distribution functions [5–10], which have been determined from global fits at next-to-leading order (NLO) to data from deep inelastic scattering (DIS), Drell–Yan, and π 0 production
This paper presents the measurement of π 0 and η pT differential invariant yields, together with the η√/π 0 ratio in nonsingle diffractive (NSD) p–Pb collisions at sNN = 5.02 TeV
Summary
Proton-nucleus (pA) collisions are an important tool for the study of strongly interacting matter and the Quark–Gluon Plasma (QGP), complementing and extending measurements carried out with high energy collisions of heavy nuclei [1]. CGC-based calculations successfully describe measurements of particle multiplicities and inclusive hadron production at high pT in pp, d−Au and p–Pb collisions at RHIC and at the LHC [17–19]. Additional measurements of inclusive hadron production at the LHC will provide new constraints on CGC calculations, and help to refine this theoretical approach. The EPOS3 model [26] requires the inclusion of collective radial flow in p–Pb collisions to successfully describe the pT spectrum of charged pions, kaons, protons, and baryons [27,28] Tests of this model with neutral pions and η mesons will provide additional constraints to this approach. Strong suppression of inclusive hadron yields at high pT has been observed in heavy-ion collisions at RHIC [39–44] and the LHC [45–49] This suppression arises from partonic energy loss in the QGP [50–53].
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