标题： HERA中直接和resolved光子产生中的二喷注角分布 显示英文标题

标题： Dijet Angular Distributions in Direct and Resolved Photoproduction at HERA

摘要： 喷气光子产生，其中两个最高横向能量（$\ETJ$）喷流的$\ETJ$大于 6 GeV，并且喷流-喷流不变质量大于 23 GeV，在 HERA $ep$对撞机上的 ZEUS 探测器中进行了研究。分辨和直接光子产生样本被分离出来。对于这两个样本，测量了双喷流质心系中喷流-喷流轴与束流方向之间夹角的截面。所测得的角度分布彼此显著不同。它们与 QCD 计算预测一致，其中不同的角度分布反映了硬子过程中交换的夸克和胶子的不同自旋。 显示英文摘要

摘要： Jet photoproduction, where the two highest transverse energy ($\ETJ$) jets have $\ETJ$ above 6 GeV and a jet-jet invariant mass above 23~GeV, has been studied with the ZEUS detector at the HERA $ep$ collider. Resolved and direct photoproduction samples have been separated. The cross section as a function of the angle between the jet-jet axis and the beam direction in the dijet rest frame has been measured for the two samples. The measured angular distributions differ markedly from each other. They agree with the predictions of QCD calculations, where the different angular distributions reflect the different spins of the quark and gluon exchanged in the hard subprocess.