Rapidity dependence of the proton-to-pion ratio in Au+Au and p+p collisions at sqrt(s_NN) = 62.4 and 200 GeV

TL;DR

This study measures the proton-to-pion ratios in Au+Au and p+p collisions at different energies and pseudorapidities, revealing a strong pseudorapidity dependence and similarities across energies consistent with grand-canonical models.

Contribution

It provides detailed measurements of p/pi ratios across energies, pseudorapidities, and collision systems, highlighting a unique pseudorapidity point where the ratio is system-size independent.

Findings

Strong pseudorapidity dependence of p/pi ratios.

Similarity of ratios at different energies and pseudorapidities.

Identification of a pseudorapidity point with system-size independent ratios.

Abstract

The proton-to-pion ratios measured in the BRAHMS experiment for Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV are presented as a function of transverse momentum and collision centrality at selected pseudorapidities in the range of 0 to 3.8. A strong pseudorapidity dependence of these ratios is observed. We also compare the magnitude and p_T-dependence of the p/pi ratios measured in Au+Au collisions at \rootsnn{200} and $\eta \approx 2.2$ with the same ratio measured at \rootsnn{62.4} and $\eta = 0$. The great similarity found between these ratios throughout the whole p_T range (up to 2.2 GeV/$c$) is consistent with particle ratios in A+A collisions being described with grand-canonical distributions characterized by the baryo-chemical potential \mibn. At the collision energy of 62.4 GeV, we have observed a unique point in pseudorapidity, $\eta = 3.2$, where the p/pi+ ratio is independent of the collision system size in a wide p_T-range of $0.3 \le p_{T} \le 1.8$ GeV/$c$.