Low Energy Studies of the Pion-Nucleon System

[72227]在TRIUMF介子设备上，将对介子-核子物理中的两个主题进行实验研究。首先，我们将对质子捕获负介子后产生的电子-正电子对进行完整的运动学研究。在这个实验的低能量下，由介子捕获产生的虚光子探测核子的轴向电流。通过测量电子动量和正电子动量，确定了虚光子的完全运动学。这使得截面可以分解为纵向、横向和各种介子电产生实验特征的干扰响应函数。然而，在目前的实验中，核子的轴向结构是由测量的响应函数在小的类时动量下唯一确定的。最近声称在低能介子-核子相互作用中违反同位旋对称将被实验研究。在同位旋对称下，弹性介子-核子散射的振幅决定了介子电荷交换截面。我们将对液氢中负介子相互作用后的正角中性介子产率进行新的低能测量。根据测量到的衰变伽马射线能谱，确定了介子产率和角分布，并将在新的高分辨率碘化钠光谱仪上进行测量。

0072227KovashTwo topics in pion-nucleon physics will be experimentally investigated at the TRIUMF meson facility. In one, we will make a complete kinematical study of electron-positron pair production following capture of negative pions by the proton. At the low energies of this experiment, the virtual photon produced by pion capture probes the axial currents of the nucleon. By measuring the electron and positron momenta, the complete kinematics of the virtual photon are determined. This allows the cross section to be decomposed into the longitudinal, transverse, and various interference response functions characteristic of pion electroproduction experiments. In the present experiment, however, the axial structure of the nucleon is uniquely determined at small time-like momenta from the measured response functions. Recent claims of a violation of isospin symmetry in the low energy pion-nucleon interaction will be investigated experimentally. Under isospin symmetry, the amplitude for elastic pion-nucleon scattering determines thepion charge-exchange cross section. We will make new low energy measurements of the forward-angle neutral pion yield following negative pion interactions in liquid hydrogen. The pion yield and angular distribution are determined from the measured decay gamma-ray energy spectrum, which will be measured in a new high resolution sodium-iodide spectrometer.