A study of photon-nucleus collisions at high transverse energy

[摘要] We have measured, for the first time, the atomic number dependence of photon-nucleus collisions at high transverse energy. The measurements were made at FNAL by using a large acceptance calorimeter with 50-400 GeV photons incident on LH$sb2,$ LD$sb2,$ Be, C, Al, Cu, Sn and Pb targets. The cross section is parameterized as $sigmasb{gamma A} = sigmasb{gamma p}Aspalpha,$ where $alpha$ is found to increase from 0.9 to 1.1 when the total transverse energy $Esb{T}$ is increased from roughly 6 GeV to 12 GeV; $alpha$ is also found to increase with the photon energy at fixed $xsb{T}equiv Esb{T}/sqrt{s},$ but depends only weakly on the photon energy at fixed $Esb{T}.$ The increase of $alpha$ with total transverse energy is qualitatively consistent with previous measurements from the hadron-nucleus collisions, but our $alpha$ values are somewhat lower. At high transverse energy, photon induced collisions are found to be more jet-like than pion induced collisions, revealing the point-like nature of the photons at high $Esb{T}.$ The mean planarity in $gamma A$ collisions is independent of A in the kinematic range covered by this experiment.

[发布机构] Rice University

[效力级别] physics