Upper limits on η and η′ production in central S-Au collisions at 200 GeV/nucleon

Inclusive photon measurements from heavy ion experiments at the CERN SPS limit the ratio η/η^o in central S-induced collisions at mid rapidity to less than 0.15 which excludes an η yield larger than 1.5 times the value measured in p-p collisions. In addition, the photon data show that the η production cross section cannot increase by more than 25% going from peripheral to central S-Au collision. The same data also limits the η′/η ratio to less than 0.75. These results exclude an enhanced η or η′ production as a major contribution to the recently discovered strong low mass dilepton excess in heavy ion collisions at the CERN SPS.