First measurement of the polarization observable E and helicity-dependent cross sections in single π0 photoproduction from quasi-free nucleons
First measurement of the polarization observable E and helicity-dependent cross sections in single π0 photoproduction from quasi-free nucleons
复制标题
DOI：
10.1016/j.physletb.2017.04.079
复制
发表时间：
2017-07-10
影响因子：
4.4
通讯作者：
Zana, L.
中科院分区：
文献类型：
--
作者：
Dieterle, M.;Witthauer, L.;Zana, L.
在德国美因茨的电子加速器设施 MAMI 中，首次测量了束缚在氘核中的质子和中子的单 pi(0) 光产生的双偏振可观测 E 以及与螺旋度相关的截面 sigma(1/2) 和 sigma(3/2)。该实验使用圆偏振光子束和纵向偏振氘化丁醇靶。使用水晶球和 TAPS 电磁量热计检测了来自 pi(0) 介子的反应产物、反冲核子和衰变光子。通过 pi N-0 最终状态的运动学重建消除了核费米运动的影响。与自由质子靶测量的数据的比较表明，横截面的绝对尺寸因核终态相互作用（FSI）效应而显着改变。然而，对不对称性 E 没有显着影响，因为 sigma(1/2) 和 sigma(3/2) 分量似乎以类似的方式受到影响。因此，在中子和质子的 FSI 效应相似的假设下，通过结合用准自由中子测量的不对称性 E 和针对 FSI 效应校正的非极化截面，可以获得自由中子的两个螺旋度相关截面的最佳近似。 (C) 2017 年作者。由 Elsevier B.V. 出版
The double-polarization observable E and the helicity-dependent cross sections sigma(1/2) and sigma(3/2) have been measured for the first time for single pi(0) photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the pi(0) meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the pi N-0 final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry E since the sigma(1/2) and sigma(3/2) components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry E measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons. (C) 2017 The Authors. Published by Elsevier B.V.