Symmetric cumulants as a probe of the proton substructure at LHC energies

TL;DR

This study investigates how spatial correlations between gluonic hot spots inside protons affect symmetric cumulants in high-energy proton-proton collisions, revealing significant impacts on initial state properties and observable correlations.

Contribution

It demonstrates that including spatial correlations between proton constituents can explain anti-correlations in ultra-central collisions, a feature not possible without such correlations.

Findings

Correlations decrease NSC(2,3) and NSC(2,4) in mid-to-ultra central collisions.

Correlations enable negative NSC(2,3) in ultra-central collisions, matching experimental data.

Hot spot radius and repulsive core distance influence the impact of correlations.

Abstract

We present a systematic study of the normalized symmetric cumulants, NSC(n,m), at the eccentricity level in proton-proton interactions at $\sqrt s\!=\! 13$ TeV within a wounded hot spot approach. We focus our attention on the influence of spatial correlations between the proton constituents, in our case gluonic hot spots, on this observable. We notice that the presence of short-range repulsive correlations between the hot spots systematically decreases the values of NSC(2,3) and NSC(2,4) in mid-to-ultra central collisions while increases them in peripheral interactions. In the case of NSC(2,3) we find that, as suggested by data, an anti-correlation of $\varepsilon_2$ and $\varepsilon_3$ in ultra-central collisions, i.e. NSC(2,3)$<0$, is possible within the correlated scenario while it never occurs without correlations. We attribute this fact to the decisive role of correlations on enlarging the probability of interaction topologies that reduce the value of NSC(2,3) and, eventually, make it negative. Further, we explore the dependence of our conclusions on the values of the hot spot radius and the repulsive core distance. Our results add evidence to the idea that considering spatial correlations between the subnucleonic degrees of freedom of the proton may have a strong impact on the initial state properties of proton-proton interactions [1].