Centrality dependence of proton and antiproton spectra in Pb+Pb collisions at 40A GeV and 158A GeV measured at the CERN SPS

TL;DR

This study measures proton and antiproton spectra in Pb+Pb collisions at 40A and 158A GeV, analyzing how their distributions depend on collision centrality and comparing results with transport model predictions.

Contribution

It provides detailed measurements of (anti-)proton yields and spectra at two energies, revealing centrality effects and testing transport models against experimental data.

Findings

Average transverse mass shows modest centrality dependence.

Midrapidity yields normalized to wounded nucleons are relatively stable.

Rapidity distribution shapes vary significantly with centrality, especially at 40A GeV.

Abstract

The yields of (anti-)protons were measured by the NA49 Collaboration in centrality selected Pb+Pb collisions at 40A GeV and 158A GeV. Particle identification was obtained in the laboratory momentum range from 5 to 63 GeV/c by the measurement of the energy loss dE/dx in the TPC detector gas. The corresponding rapidity coverage extends 1.6 units from mid-rapidity into the forward hemisphere. Transverse mass spectra, the rapidity dependences of the average transverse mass, and rapidity density distributions were studied as a function of collision centrality. The values of the average transverse mass as well as the midrapidity yields of protons when normalized to the number of wounded nucleons show only modest centrality dependences. In contrast, the shape of the rapidity distribution changes significantly with collision centrality, especially at 40A GeV. The experimental results are compared to calculations of the HSD and UrQMD transport models.