Unraveling the Gluon Sivers Function in Hadronic Collisions at RHIC

Understand

We study the transverse single-spin asymmetries for $p^\uparrow p\to \pi\, X$ and $p^\uparrow p\to \gamma\, X$ within the so-called color gauge invariant generalized parton model (CGI-GPM) which, in addition to spin and transverse momentum effects, includes initial and final state interactions with the polarized proton remnants.

• We compute all relevant contributions, focusing in particular on the process dependence of the gluon Sivers function, which, for these processes, can always be expressed as a linear combination of two independent, universal terms.
• This study extends and completes a previous one, where only quark initiated partonic processes were considered.
• We then perform a combined phenomenological analysis of RHIC data on transverse single-spin asymmetries in $p^\uparrow p\to \pi\, X$ and $p^\uparrow p\to D\, X$, putting the first preliminary constraints on these two gluon Sivers functions.