Abstract
Inclusive J/$\psi$ production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy $\sqrt{s_{\rm NN}}$ = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains $2.03<y_{\rm cms}<3.53$ and $-4.46<y_{\rm cms}<-2.96$, down to zero transverse momentum, studying the $\mu^+\mu^-$ decay mode. In this paper, the J/$\psi$ production cross section and the nuclear modification factor $R_{\rm pPb}$ for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/$\psi$ 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.
Highlights
The production of charmonia, bound states of c and c quarks, is the object of intense theoretical and experimental investigations [1]
In the NRQCD approach [2], charmonium production is seen as a two-step process which includes the creation of the cc pair in a hard scattering, described perturbatively, and the subsequent evolution of the pair towards a bound state with specific quantum numbers, which is modeled in a non-perturbative way
The evolving cc pair can be in a color-singlet (CS) as well as in a color-octet (CO) state, with the strength of the CO amplitude contributions being controlled by non-perturbative factors, extracted by fits to experimental data
Summary
F σpJp/ψ Partially correlated σpMPBb σpJp/ψ Correlated B.R. TpPb σpJp/ψ σpJP/ψb, RpPb σPJ/bψp, RPbp. Results from a calculation in the CGC framework [58], combined with a CEM production model, are shown Within our uncertainties, both the model based on shadowing only and the coherent energy loss approach are able to describe the data, while the CGC-based prediction overestimates the observed suppression. No strong variation of the nuclear modification factors is observed, in particular at backward rapidity, where models including coherent energy loss suggest a steeper behaviour Both σpJp/ψ and TpPb cancel out when forming the ratio RFB of the nuclear modification factors for a rapidity range symmetric with respect to ycms = 0. A fair agreement is seen with predictions based on a pure nuclear shadowing scenario [55, 56, 61], parameterized using the EPS09 approach, as well as with models including a contribution from coherent partonic energy loss [13]. The results presented in this paper provide an important baseline for the interpretation of heavy-ion collision results and are in agreement with those presented by the LHCb Collaboration [64]
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