paper

First measurement of the polarization observable $E$ and helicity-dependent cross sections in single $I ¨ ^{0}$ photoproduction from quasi-free nucleons

arXiv:1705.07342 · doi:10.1016/j.physletb.2017.04.079

Abstract

The double-polarization observable $E$ and the helicity-dependent cross sections $I ¨ _{1/2}$ and $I ¨ _{3/2}$ have been measured for the first time for single $I ¨ ^{0}$ 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 $I ¨ ^{0}$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $I ¨ ^{0} N$ 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 $I ¨ _{1/2}$ and $I ¨ _{3/2}$ 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.

accepted for publication in Phys. Lett. B

First measurement of the polarization observable E and helicity-dependent cross sections in single I¨0 photoproduction from quasi-free nucleons

Abstract

First measurement of the polarization observable $E$ and helicity-dependent cross sections in single $I ¨ ^{0}$ photoproduction from quasi-free nucleons