Study of the nucleon using polarized photon beams and polarized targets

本研究利用偏振光光束和偏振光靶通过产生介子和核子共振来研究核子的性质。激光电子伽马源（LEGS）提供能量高达470 MeV的光子偏振光束，这些光子是由储存在国家同步加速器光源中的2.8 GeV电子的偏振激光后向散射获得的。随着冷冻极化HD靶SPHICE的成功研制，该靶SPHICE可以实现质子和氘核的独立极化，以及SASY（自旋不对称）探测器的成功运行，本研究将对质子和中子进行详细的双极化测量。将SPHICE和SASY与LEGS的高质量偏振光子束相结合，实验程序将测量中性和带电介子产生的微分截面。光子作为电磁场的量子，既可以与核子中电荷的分布相互作用，也可以与核子中产生磁场的带电夸克电流相互作用。由于光子的偏振是由激光束的偏振决定的，所以可以使用线偏振和圆偏振。由于核子有一个磁矩，可以通过操纵核子的自旋来定向，因此自旋相关的光产生量可以确定到前所未有的精度。

This research uses photonuclear reactions to investigate the properties of the nucleon through the production of mesons and nucleon resonances using polarized photon beams and polarized targets. The Laser Electron Gamma Source (LEGS) provides a polarized beam with photons havingenergies up to 470 MeV obtained by the backscattering of polarized laser light from 2.8 GeV electrons stored in the National Synchrotron Light Source. With the successful development of the frozen, polarized HD target SPHICE which allows independent polarization of the proton and the deuteron and with the successful operation of the SASY (Spin ASYmmetry) detector, this research will perform detailed double polarization measurements on both the proton and the neutron.Combining SPHICE and SASY with the high quality polarized photon beam at LEGS, the experimental program will measure the differential cross sections for both neutral and charged pion production. The photon, being the quantum of the electromagnetic field, can interact with both thedistribution of electric charges in the nucleon as well as the magnetic-field-producing charged quark currents within the nucleon. Because the polarization of the photon is determined by the polarization of the laser beam, linear and circular polarizations can be used. Since the nucleon has a magnetic moment that can be oriented by manipulating the spin of the nucleon, spin-dependent photoproduction quantities can determined to accuracies never before possible.