Upsilon production in p(d)A collisions at RHIC and the LHC

Abstract

We study the effect of nuclear matter in Upsilon production in dAu collisions at RHIC and pPb collisions at the LHC. We find that the nuclear modification factor, R^Upsilon_dAu, measured at RHIC is not satisfactorily reproduced by the conventional effects used in the literature, namely the modification of the gluon distribution in bound nucleons and an --effective-- survival probability for a bound state to escape the nucleus. In particular, we argue that this probability should be close to 1 as opposed to the J/psi case. We note that, at backward rapidities, the unexpected suppression of R^Upsilon_dAu observed by PHENIX hints at the presence of a gluon EMC effect, analogous to the quark EMC effect -- but likely stronger. Further nuclear matter effects, such as saturation and fractional energy loss, are discussed, but none of them fit in a more global picture of quarkonium production. Predictions for Upsilon(nS) for the forthcoming pPb run at 5 TeV at the LHC are also presented.

16 pages, 7 figures, LaTeX. v4: good agreement with the final PHENIX data with a strong gluon EMC effect; EPS09 uncertainty band added as well as predictions for a forward-backward asymmetry in pPb collisions at the LHC which does not require any pp references