Evidence for Q-Dependent Nuclear Transverse-Momentum Redistribution Beyond Broadening from AI-driven analysis of p-Cu Drell-Yan

TL;DR

This study reveals that nuclear transverse-momentum effects in p-Cu Drell-Yan are Q-dependent redistributions rather than simple broadening, identified through AI-driven analysis.

Contribution

It introduces a novel AI-based method to extract Q-dependent nuclear transverse-momentum profiles from experimental data, challenging the universal broadening assumption.

Findings

Nuclear modification shows Q-dependent redistribution, not universal broadening.

Identified a shoulder and probability flow between regions in the transverse momentum distribution.

Analysis covers specific x and Q ranges in p-Cu Drell-Yan data.

Abstract

We extract a target-side Cu transverse-momentum profile from fixed-target $p$--Cu Drell--Yan data by holding a momentum-space proton reference fixed and training only an asymmetric Cu kernel in the small-$q_T$ region. In the supported window, $0.15 \le x_{Cu} \le 0.46$ and $7.5 \le Q_M \le 15.75$ GeV, the nuclear modification is not a universal width increase. It appears as $Q$-dependent redistribution: an $\mathcal{O}(1~{\rm GeV})$ shoulder and compensating probability flow between shoulder and resolved-tail regions, beyond one-parameter broadening.