Neutral Meson Photoproduction from Complex Nuclei

Abstract

The angular distributions of neutral mesons produced by 170-MeV bremsstrahlung on carbon, aluminum, copper, cadmium, and lead have been obtained through the coincident detection of the decay photons by a scintillation counter system. The experimental data have been analyzed by means of a Monte Carlo prediction based on an impulse-approximation elastic coherent production model. The nuclear density distributions which were used in the synthesis of those predictions which were in best agreement with the experimental data from this experiment have been compared to the charge density distributions inferred from electron scattering experiments. The values of the rms radii of nuclear matter obtained in this experiment are, within the limits of error of the experiment (about 2X10~1 4 cm), consistent with the values of charge distribution radii obtained in electron scattering.The spin-independent part of the neutral meson photoproduction cross section used in the synthesized predictions is obtained using the dispersion theory of Chew, Low, Goldberger, and Nambu. The dependence of the cross section on the meson-nucleon phase shifts used is investigated and a set of phase shifts is presented that results in a correct prediction of the absolute cross sections observed in this experiment; however, this particular set of phase shifts is not unique. 3 E. L. Goldwasser, L.

Nuclear mass form factors from coherent photoproduction of πmesons

“…In this sense it is the ideal reaction to test the matter distribution in the bulk of a nucleus. A first attempt to determine nuclear mass radii with this method was made by Schrack, Leiss and Penner in 1962 [12]. However, at that time the achievable experimental precision was very limited and much inferior to the results from hadron induced reactions which profit from the large cross sections characteristic for the strong interaction.…”

Neutron skins from Coherent Pion Photoproduction

“…Previous (γ, π 0 ) measurements for 208 Pb [39,40] either did not use isotopically pure targets or did not achieve the precision needed to study the neutron skin, mainly because they used π 0 detection systems with limited angular coverage resulting in a small detection efficiency with too large a dependence on pion energy and angle to give definitive results.…”

Coherent? 0 photoproduction on12C,13C and16O in the? (1232) resonance region

“…This becomes clear if one looks at the momenta transferred to the nucleus: three momentum transfer q and four-momentum transfer t are related by q2=(t/2M)2-t (4) where M is the target mass. t is approximately* given by t~ --m~/4k 2-(k. 0) 2 (5) Under our kinematical conditions one has q2 ~ _ t (6) and…”

“…Also in the 4He (v, 7z~ reaction it has been possible to separate in a clear way the coherent process from competing incoherent channels by detecting the outgoing nucleus [3]. For heavier nuclei however the dominance of the coherent process in the measured data had to be shown by other means [4,5].…”