Glauber gluons in pion-induced Drell-Yan processes

TL;DR

This paper proposes that Glauber gluons explain the violation of the Lam-Tung relation in pion-induced Drell-Yan processes, highlighting a unique effect in pions and suggesting experimental tests at GSI and J-PARC.

Contribution

It introduces Glauber gluons as a key factor in explaining the anomalous angular distribution in pion-induced Drell-Yan processes, a novel insight in the field.

Findings

Glauber gluons can account for the Lam-Tung relation violation.

The effect is significant in pions due to their dual role as Nambu-Goldstone bosons and bound states.

Proposes experimental discrimination of mechanisms via p p̄ Drell-Yan measurements.

Abstract

We point out that the existence of Glauber gluons in the $k_T$ factorization theorem can account for the violation of the Lam-Tung relation, namely, the anomalous lepton angular distribution, observed in pion-induced Drell-Yan processes. Radiations, that balance the lepton-pair transverse momentum, cause the responsible spin-transverse-momentum correlation in the Glauber-gluon background. It is argued that the Glauber effect is significant in the pion due to its unique role of being a Nambu-Goldstone boson and a $q\bar q$ bound state simultaneously. This mechanism is compared to other resolutions in the literature by means of vacuum effects and Boer-Mulders functions. We propose to discriminate the above resolutions by measuring the $p\bar p$ Drell-Yan process at GSI and J-PARC.