Production of direct photons and neutral mesons at large transverse momenta byπ−andpbeams at 500 GeV/c

Abstract

We present results from the initial run of Fermilab experiment E706. The data include incident ${\pi }^{-}$ and $p$ beams at 500 GeV/c on Be and Cu targets, and span the kinematic ranges of transverse momentum and rapidity of $3.5\le p_T\le 10$ GeV/c and $-0.7\mathrm{}\le y_{\mathrm{c}.\mathrm{m}.\mathrm{}}\le 0.7$, respectively. We have measured cross sections for ${\pi }^0$ and direct-photon production, as well as the $\frac{\eta }{{\pi }^0}$ production ratio. From the data on Be and Cu, we have extracted the nuclear dependence of ${\pi }^0$ production, parametrized as $A^{\alpha }$. The cross sections are compared with next-to-leading-log QCD predictions for different choices of the QCD momentum scales and several sets of parton distribution functions.