Perturbative QCD and beyond: azimuthal angle correlations in deuteron-deuteron scattering from Bose-Einstein correlations

TL;DR

This paper explores azimuthal angle correlations in deuteron-deuteron scattering within perturbative QCD, revealing long-range correlations due to Bose-Einstein effects that influence flow coefficients across all harmonic orders.

Contribution

It demonstrates that Bose-Einstein correlations induce azimuthal correlations with multiple length scales, including a perturbative scale related to saturation, extending understanding of particle correlations in high-energy nuclear collisions.

Findings

Correlations are independent of rapidity differences for large rapidities.

Correlations with the saturation scale are perturbative and estimable via CGC.

Long-range correlations contribute to all flow harmonics, not just even ones.

Abstract

In this paper, we found within the framework of perturbative QCD, that in deuteron-deuteron scattering the Bose-Einstein correlations due to two parton showers production, induce azimuthal angle correlations, with three correlation lengths: the size of the deuteron ($R_D$), the proton radius ($R_N$), and the size of the BFKL Pomeron which, is closely related to the saturation momentum ($R_c \sim 1/Q_s$). These correlations are independent of the values of rapidities of the produced gluons (long range rapidity correlations), for large rapidities ($\bas |y_1 - y_2| \geq 1$), and have no symmetry with respect to $\phi \to \pi - \phi$ ($ \vec{p}_{T1} \to - \vec{p}_{T1}$). Therefore, they give rise to $v_n$ for all values of $n$, not only even values. The contributions with the correlation length $R_D$ and $R_N$ crucially depend on the non-perturbative contributions, and to obtain estimates of their values, requiries a lot of modeling, while the correlations with $R_c \sim 1/Q_s$ have a perturbative QCD origin, and can be estimated in the ColorGlass Condensate (CGC) approach.