Searching for TMD-factorization breaking in p+p and p+A collisions: Color interactions in QCD

TL;DR

This study measures dihadron and photon-hadron correlations in proton-proton and proton-nucleus collisions to explore potential TMD-factorization breaking effects caused by color exchanges in QCD, focusing on nonperturbative transverse momentum effects.

Contribution

It provides experimental measurements of transverse momentum correlations sensitive to factorization breaking, offering data to test QCD predictions about color interactions.

Findings

Measured nonperturbative momentum widths in p+p and p+A collisions.

Identified azimuthal correlations sensitive to TMD evolution.

Set the stage for future theoretical comparisons on factorization breaking.

Abstract

Dihadron and isolated direct photon-hadron angular correlations have been measured in $p$+$p$ and $p$+A collisions to investigate possible effects from transverse-momentum-dependent factorization breaking due to color exchange between partons involved in the hard scattering and the proton remnants. The correlations are sensitive to nonperturbative initial-state and final-state transverse momentum $k_T$ and $j_T$ in the azimuthal nearly back-to-back region $\Delta \phi \sim \pi$. In this region, transverse-momentum-dependent evolution can be studied when several different hard scales are measured. To have sensitivity to small transverse momentum scales, nonperturbative momentum widths of \pout, the out-of-plane transverse momentum component perpendicular to the trigger particle, are measured. To quantify the magnitude of any transverse-momentum-dependent factorization breaking effects, calculations will need to be performed for comparison.