Inclusive J/psi production has been studied with the ALICE detector in
p-Pb collisions at the nucleon-nucleon center of mass energy = 5.02 TeV
at the CERN LHC. The measurement is performed in the center of mass
rapidity domains 2.03 < y (cms) < 3.53 and -4.46 < y (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 (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