Quasi-free Compton scattering and the polarizabilities of the neutron

Abstract

Differential cross-sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been measured using the Glasgow/Mainz photon tagging spectrometer at. the Mainz MAMI accelerator together with the Mainz 48 cm empty set x 64 cm NaI(Tl) photon detector and the Gottingen SENECA recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV at theta(gamma)(LAB) = 136.2degrees. Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron detection efficiency of the SENECA detector was measured via the reaction p(gamma, pi(+)n). The "free" proton Compton scattering cross-sections extracted from the bound proton data are in reasonable agreement with those for the free proton which gives confidence in the method to extract the differential cross-section for free scattering from quasi-free data. Differential cross-sections on the free neutron have been extracted and the difference of the electromagnetic polarizabilities of the neutron has been determined to be alpha(n) - beta(n) = 9.8 +/- 3.6(stat)(-1.1)(+2.1)(syst) +/- 2.2(model) in units of 10(-4) fm(3). In combination with the polarizability sum alpha(n) + beta(n) = 15.2 +/- 0.5 deduced from photoabsorption data, the neutron electric and magnetic polarizabilities, alpha(n) = 12.5 +/- 1.8(stat)(-0.6)(+1.1)(syst) +/- 1.1(model) and beta(n) = 2.7 -/+ 1.8(stat)(-1.1)(+0.6)(syst) -/+ 1.1(model) are obtained. The backward spin polarizability of the neutron was determined to be gamma(pi)((n)) = (58.6 +/- 4.0) x 10(-4)fm(4).