PRODUCTION OF ETA-MESONS IN 200 A GEV C S+S AND S+AU REACTIONS/

Minimum Bias production cross sections of eta mesons have been measure d in 200 A GeV/c S+Au and S+S collisions at the CERN SPS by reconstruc ting the eta --> gamma gamma decay. The measurements have been made ov er the rapidity range 2.1 less than or equal to gamma less than or equ al to 2.9 using the leadglass spectrometer of WA80. Within the statist ical and systematical uncertainties the spectral shapes of pi(0) and e ta 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 +/- 0.07 for S+Au and 0.43 +/- 0.15 for S+S reactions. Extrap olation to full phase space leads to an integrated cross section ratio of eta to pi(0) mesons of 0.147 +/- 0.017(stat.) +/- 0.015(syst.), an d 0.120 +/- 0.034(stat.) +/- 0.022(syst.) for S+Au and S+S collisions, respectively.