Abstract
The first study of ϕ-meson production in p–Pb collisions at forward and backward rapidity, at a nucleon–nucleon centre-of-mass energy sNN=5.02 TeV, has been performed with the ALICE apparatus at the LHC. The ϕ-mesons have been identified in the dimuon decay channel in the transverse momentum (pT) range 1<pT<7 GeV/c, both in the p-going (2.03<y<3.53) and the Pb-going (−4.46<y<−2.96) directions — where y stands for the rapidity in the nucleon–nucleon centre-of-mass — the integrated luminosity amounting to 5.01±0.19 nb−1 and 5.81±0.20 nb−1, respectively, for the two data samples. Differential cross sections as a function of transverse momentum and rapidity are presented. The forward–backward ratio for ϕ-meson production is measured for 2.96<|y|<3.53, resulting in a ratio ∼0.5 with no significant pT dependence within the uncertainties. The pT dependence of the ϕ nuclear modification factor RpPb exhibits an enhancement up to a factor 1.6 at pT=3–4 GeV/c in the Pb-going direction. The pT dependence of the ϕ-meson cross section in pp collisions at s=2.76 TeV, which is used to determine a reference for the p–Pb results, is also presented here for 1<pT<5 GeV/c and 2.5<y<4, for a 78±3 nb−1 integrated luminosity sample.
Highlights
Proton–nucleus (p–A) collisions are of special interest in the context of high-energy nuclear physics for two reasons
We first present the measurement of the production√cross sections, starting with its pT-dependence in pp collisions at s = 2.76 TeV, followed by p–Pb collision results as a function of pT and rapidity
The values are obtained as the ratio between the number of dimuons at the output of the reconstruction chain — including the effect of the event selection pT-differential production cross section for the φ-meson in pp collisions at s =
Summary
Proton–nucleus (p–A) collisions are of special interest in the context of high-energy nuclear physics for two reasons. A precise characterisation of particle production processes in p–A collisions is needed as a reference for nucleus–nucleus data This allows in-medium effects — linked to the formation of a deconfined phase of the QCD matter, the quark–gluon plasma (QGP) [1,2,3] — to be disentangled from the effects already present in cold nuclear matter. The smallest x values contributing to the wave function of the colliding nucleus can be probed by looking at particle production at large rapidities, in the p-going direction. Such a measurement can extend towards lower x-values the results of the lowerenergy measurements by the PHOBOS and BRAHMS experiments at RHIC [7,8]. Measurements of identified particle production may, in particular, provide useful constraints for forthcoming theoretical studies of the saturation mechanism at small x
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