Measurement of Sivers Asymmetries for Di-jets in \sqrt{s}=200 GeV pp Collisions at STAR

TL;DR

This study measures the Sivers asymmetries in di-jet production in proton-proton collisions at 200 GeV, finding results consistent with zero and smaller than theoretical predictions based on SIDIS data, suggesting small gluon Sivers effects.

Contribution

First measurement of Sivers asymmetries for di-jets in pp collisions at STAR, providing new insights into parton transverse momentum correlations.

Findings

Analyzing power is consistent with zero across a broad pseudorapidity range.

Measured asymmetries are smaller than predictions based on SIDIS data.

Results suggest gluon Sivers asymmetries are also small.

Abstract

Measurement of the transverse spin dependence of the di-jet opening angle in pp collisions at sqrt{s}=200 GeV has been performed by the STAR collaboration. An analyzing power consistent with zero has been observed over a broad range in pseudorapidity sum of the two jets with respect to the polarized beam direction. A non-zero (Sivers) correlation between transverse momentum direction of partons in the initial state and transverse spin orientation of the parent proton has been previously observed in semi-inclusive deep inelastic scattering (SIDIS). The present measurements are much smaller than deduced from predictions made for STAR di-jets based on non-zero quark Sivers functions deduced from SIDIS, and furthermore indicate that gluon Sivers asymmetries are comparably small.