标题： Exclusive $ρ^0$ 介子光致生成与HERA中的领先中子 显示英文标题

标题： Exclusive $ρ^0$ Meson Photoproduction with a Leading Neutron at HERA

摘要： 首次测量了在HERA上与领先中子相关的$\rho^0$介子的独占光致生产。 数据是在$2006$年和$2007$年使用H1探测器采集的，在质心系能量为$\sqrt{s}=319$GeV时，对应的积分亮度为$1.16$pb$^{-1}$。 $\rho^0$介子的横向动量为$p_T<1$ GeV，它们通过其衰变为带电π介子进行重建，而携带入射质子动量大部分的领先中子，$x_L>0.35$，在前向中子量热计中被探测到。 测量的相空间由光子虚度$Q^2 < 2$ GeV$^2$、光子-质子系统的总能量$20 < W_{\gamma p} < 100$ GeV 和领先中子的极角$\theta_n < 0.75$ mrad 定义。 反应的截面$\gamma p \to \rho^0 n \pi^+$是作为多个变量的函数进行测量的。 数据被解释为一种双外围过程，涉及在质子顶点的介子交换，随后在虚介子上弹性光生一个$\rho^0$介子。 在单介子交换主导的框架下，光子-介子散射的弹性截面$\sigma^{\rm el}(\gamma\pi^+ \to \rho^0\pi^+)$被提取出来。 该截面的值表明对于独占反应$\gamma p\to\rho^0 n \pi^+$存在显著的吸收修正。 显示英文摘要

摘要： A first measurement is presented of exclusive photoproduction of $\rho^0$ mesons associated with leading neutrons at HERA. The data were taken with the H1 detector in the years $2006$ and $2007$ at a centre-of-mass energy of $\sqrt{s}=319$ GeV and correspond to an integrated luminosity of $1.16$ pb$^{-1}$. The $\rho^0$ mesons with transverse momenta $p_T<1$ GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, $x_L>0.35$, are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality $Q^2 < 2$ GeV$^2$, the total energy of the photon-proton system $20 < W_{\gamma p} < 100$ GeV and the polar angle of the leading neutron $\theta_n < 0.75$ mrad. The cross section of the reaction $\gamma p \to \rho^0 n \pi^+$ is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a $\rho^0$ meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, $\sigma^{\rm el}(\gamma\pi^+ \to \rho^0\pi^+)$, is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction $\gamma p\to\rho^0 n \pi^+$.