[Prex] Coherent-Nuclear Pion Photoproduction and Neutron Radii

[Jay Benesch]

not directly relevant but possibly of interest

https://arxiv.org/abs/1907.11764

Coherent-Nuclear Pion Photoproduction and Neutron Radii
Gerald A. Miller
(Submitted on 26 Jul 2019)

     { {\bf Background:} Knowing the difference between the neutron and 
proton densities of nuclei is a significant topic because of its 
importance for understanding neutron star structures and cooling 
mechanisms. The coherent-nuclear photoproduction of pions, 
$({\g,\pi^0})$, combined with elastic electron scattering, has been 
suggested to be a very accurate probe of density differences. {\bf 
Purpose:} Study the ${(\g,\pi^0})$ reaction mechanism so as to better 
access the uncertainties involved in extracting the neutron density. 
{\bf Methods:} Include the effects of final-state pion-nucleus 
charge-exchange reactions on the cross section and study the influence 
of the non-zero spatial extent of the proton. {\bf Results:} The effects 
of final-state charge-exchange increase the cross section between 6\% 
and 5\%, generally decreasing as the momentum transfer increases. This 
leads to an increase of the extracted neutron skin distance by about 
50\%. The validity of the previous treatments of the proton size is 
confirmed. {\bf Conclusion:} The model dependence of the theoretically 
computed cross section increases the total systematic uncertainty 
(experiment plus theory) in extracting the neutron skin from the 
${(\g,\pi^0})$ cross section by at least a factor of three. }

Comments: 	9 pages. 5 figures
Subjects: 	Nuclear Theory (nucl-th); High Energy Physics - Phenomenology 
(hep-ph); Nuclear Experiment (nucl-ex)
Report number: 	NY at UW-19-09