Neutral meson production in p-Be and p-Au collisions at 450 GeV beam energy

In a joint experiment the TAPS and CERES collaborations have studied the production of the neutral mesons $\pi^\circ,\eta$ and $\omega$ in 450 GeV p-Be and p-Au collisions at the CERN SPS. The mesons were identified by their $\pi^\circ\rightarrow\gamma\gamma$ , $\eta\rightarrow\gamma\gamma$ , and $\omega\rightarrow\pi^\circ\gamma$ decay modes. The cross sections were measured down to very low $p_T$ ( $\geq$ 20 MeV/c) near mid-rapidity ( $3.0 < y < 4.0$ ). The $\eta$ and $\omega$ cross sections are smaller than expected from extrapolations of earlier data to low $p_T$ . Integrated over all $p_T$ , the ratios $\eta/\pi^\circ$ and $\omega$ / $\pi^\circ$ are lower by about 25% compared to previously published values. The reduction may be attributed to the large number of low $p_T$ pions from decays of heavier mesons. In addition, we have studied the dependence of neutral meson production on the mass of the nuclear target and find it in good agreement with previous measurements of charged mesons.