Photo- and Electro-excitation of Bound Neutrons and Protons

TL;DR

This paper investigates whether final state interactions and kinematical cuts contaminate neutron-target data extracted from deuteron-target experiments, revealing persistent effects that influence cross sections and polarization asymmetries.

Contribution

It provides a theoretical analysis showing that FSI effects remain in neutron data even after applying standard kinematical cuts, challenging the assumption of clean quasi-free neutron measurements.

Findings

FSI effects persist in unpolarized cross sections after cuts

FSI influences differ between neutron and proton channels

Kinematical cuts do not fully eliminate FSI contamination

Abstract

Data for pion photo-productions off the neutron ($\gamma n\to \pi N$) have been primarily extracted from deuteron-target data ($\gamma d\to \pi NN$) by applying kinematical cuts thereby isolating the quasi-free samples. We critically examine if the neutron-target data obtained through this conventional procedure can be contaminated by final state interactions (FSI) and/or the kinematical cuts. The analysis is conducted with a theoretical model for $\gamma d\to \pi NN$ that takes account of the impulse mechanisms supplemented by the $NN$ and $\pi N$ rescattering mechanisms. We show that the FSI effects still visibly remain in the extracted $\gamma$`$n$'$\to\pi N$ unpolarized cross sections and polarization asymmetries $E$ even after the kinematical cuts are applied. We also find the FSI effects on $\gamma$`$n$'$\to\pi^0n$ can be somewhat different from those on $\gamma$`$p$'$\to\pi^0p$.