Single spin asymmetry in forwardpAcollisions

Abstract

We compute the transverse single spin asymmetry in light hadron production p ↑ p → hX and p ↑ A → hX including the gluon saturation effect in the unpolarized nucleon/nucleus. In the forward (large-xF ) region, the dominant contribution comes from the so-called derivative term associated with the soft gluonic pole. This leads to the cancellation of nuclear effects in AN which can be tested at RHIC. We also show that the soft fermionic pole disappears in the saturation environment.

Nuclear Dependence of the Transverse Single-Spin Asymmetry in the Production of Charged Hadrons at Forward Rapidity in Polarized p+p , p+Al , and Aidala1, Akiba2, Alfred3 et al. 2019Phys. Rev. Lett.

“…The dynamics of gluons in the small-x regime, where the gluon density is predicted to increase drastically, can be described by the color-glass condensate (CGC) formalism [39] at the saturation scale Q s , where Q 2 sA ∝ A 1/3 for the target nucleus [40,41]. In recent years, substantial attention has been given to an interplay between small-x physics and spin physics by studying TSSAs in transversely-polarized proton and ion collisions (p ↑ +A) and gluon saturation effects in a nucleus are taken into account for various calculations of TSSAs in p ↑ +A collisions [40][41][42][43][44][45][46][47][48][49][50][51]. An A-dependence of TSSAs can arise from the A-dependence of Q s when the probe is at or below Q s , while TSSAs are expected to be A-independent at higher scales [42,43,[49][50][51].…”

Exact relations for twist-3 gluon distribution and fragmentation functions from operator identities

“…We can also derive another relation from (44). Following a similar step from (19) to (20), we obtain the following relation.…”

Single spin asymmetries in forward p−p/A collisions revisited: The role of color entanglement

“…[36], and the Wilson line structure in the rest two terms are also organized in different ways as compared to that in Ref. [36]. Before computing the twist-3 piece, as a consistency check, let us first have a look at the twist-2 part of the derived amplitude by setting p ⊥ = 0.…”

“…5 which describes the interaction between the collinear gluon from the projectile and color source inside the target is missing in Ref. [36], and the Wilson line structure in the rest two terms are also organized in different ways as compared to that in Ref. [36].…”

“…To include saturation effect, the authors of Ref. [36] derived the Wilson line structure using some heuristic argument, which, however differs from that we directly derived in the hybrid approach for the Sivers type contribution. To be more explicit, the Wilson line structure we obtained can be cast into the combination G DP − N 2 c G 4 where G DP is the normal dipole type gluon distribution, and G 4 is the gluon distribution that arises from color entanglement effect.…”