Cold Nuclear Matter effects in Upsilon production in dAu collisions at RHIC

TL;DR

This paper investigates Cold Nuclear Matter effects on Upsilon production at RHIC in dAu collisions, highlighting potential gluon EMC effects, anti-shadowing, and energy loss mechanisms, despite large experimental uncertainties.

Contribution

It provides the first experimental insights into nuclear modification factors for Upsilon, suggesting possible gluon EMC effects and energy loss mechanisms in cold nuclear matter.

Findings

Hints of gluon EMC effect at backward rapidities

Indications of gluon anti-shadowing at mid rapidity

Possible fractional energy loss at forward rapidities

Abstract

We report on our recent study of Cold Nuclear Matter effects on the Upsilon production at RHIC in dAu collisions. The first experimental results available on the nuclear modification factor R_dAu have rather large uncertainties. They nevertheless allow to bring qualitative information on the nature of the nuclear effects at play on top of the usual nuclear absorption, since the latter is expected to lie in a quite small range around a value close to ten times smaller as for charmonia. At backward rapidities, the behavior of R_dAu hints at the presence of a gluon EMC effect, analogous to the quark EMC effect -- but possibly stronger. Mid rapidity measurements with a better precision are highly desirable to pin down the gluon anti-shadowing, still under debate. At forward rapidities, the data leave some room for an additional fractional energy loss mechanism, recently revived in the literature.