Measurement of Transverse Single-Spin Asymmetries for Di-Jet Production in Proton-Proton Collisions at $\sqrt{s} = 200$ GeV

TL;DR

This study measures the angular distribution between jet pairs in polarized proton collisions to investigate spin-momentum correlations, finding asymmetries consistent with zero and smaller than those observed in SIDIS, challenging existing theories.

Contribution

First measurement of di-jet opening angle distributions in polarized proton collisions, providing new insights into Sivers functions across different parton regions.

Findings

All measured asymmetries are consistent with zero.

Asymmetries are smaller than those observed in SIDIS.

Results challenge current theoretical models.

Abstract

We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity ($-1 \leq \eta \leq +2$) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in SIDIS and forward hadron production in pp collisions.