Production of Eta-Mesons in 200 AGeV/c S+S and S+Au Reactions

TL;DR

This study measures eta-meson production cross sections in S+Au and S+S collisions at 200 AGeV/c, revealing similar spectral shapes to pi0 mesons and providing ratios of eta to pi0 yields across different collision systems.

Contribution

First measurement of eta-meson production cross sections in S+Au and S+S collisions at CERN SPS using gamma-gamma decay reconstruction.

Findings

Spectral shapes of eta and pi0 mesons are identical when plotted against transverse mass.

The eta to pi0 transverse mass spectrum ratio is approximately 0.5.

Integrated eta to pi0 cross section ratios are around 0.12 to 0.15 for the studied collisions.

Abstract

Minimum Bias production cross sections of $\eta$ mesons have been measured in 200 AGeV/c S+Au and S+S collisions at the CERN SPS by reconstructing the $\eta \to \gamma\gamma$ decay. The measurements have been made over the rapidity range $2.1 \leq y \leq 2.9$ using the leadglass spectrometer of WA80. Within the statistical and systematical uncertainties the spectral shapes of $\pi^0$ and $\eta$ mesons yields are identical when their invariant differential cross section is plotted as a function of the transverse mass. The relative normalization of the $\eta$ to $\pi^0$ transverse mass spectra is found to be $0.53 \pm 0.07$ for S+Au and $0.43 \pm 0.15$ for S+S reactions. Extrapolation to full phase space leads to an integrated cross section ratio of $\eta$ to $\pi^0$ mesons of $0.147 \pm 0.017 {\rm (stat.)} \pm 0.015 {\rm (syst.)}$, and $0.120 \pm 0.034 {\rm (stat.)} \pm 0.022 {\rm (syst.)}$ for S+Au and S+S collisions, respectively.