Production of direct photons and neutral mesons at large transverse momenta byπ−andpbeams at 500 GeV/c
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Abstract
We present results from the initial run of Fermilab experiment E706. The data include incident ${\ensuremath{\pi}}^{\ensuremath{-}}$ and $p$ beams at 500 GeV/c on Be and Cu targets, and span the kinematic ranges of transverse momentum and rapidity of $3.5\ensuremath{\le}{p}_{T}\ensuremath{\le}10$ GeV/c and $\ensuremath{-}0.7\ensuremath{\le}{y}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\le}0.7$, respectively. We have measured cross sections for ${\ensuremath{\pi}}^{0}$ and direct-photon production, as well as the $\frac{\ensuremath{\eta}}{{\ensuremath{\pi}}^{0}}$ production ratio. From the data on Be and Cu, we have extracted the nuclear dependence of ${\ensuremath{\pi}}^{0}$ production, parametrized as ${A}^{\ensuremath{\alpha}}$. 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.