Correlated pion-proton pair emission off hot and dense QCD matter

TL;DR

This study presents the first detailed multi-differential analysis of correlated pion-proton pairs from high-energy gold-gold collisions, revealing complex resonance behavior and dependencies on isospin, rapidity, and transverse momentum.

Contribution

It provides novel multi-differential measurements of pion-proton correlations in heavy-ion collisions at 2.42 GeV, highlighting deviations from vacuum resonance properties and complex yield dependencies.

Findings

Invariant mass distributions deviate from vacuum Breit-Wigner shapes.

Yield follows a power law with respect to participating nucleons.

Strong dependence of the power law exponent on pair transverse momentum.

Abstract

In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at \sqrt{s_{NN}} = 2.42 GeV collected with HADES. In this energy regime the population of \Delta(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dM{\pi}pdpTdy distributions of correlated {\pi}p pairs have been determined by subtracting the {\pi}p combinatorial background using an iterative method. The invariant-mass distributions in the \Delta(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1 < Minv (GeV/c2) < 1.4, the yield is found to be similar for {\pi}+p and {\pi}-p pairs, and to follow a power law <Apart>^{\alpha}, where <Apart> is the mean number of participating nucleons. The exponent {\alpha} depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is {\alpha} = 1.5 \pm 0.08stat \pm 0.2sys.