Proton Compton effect in the ?(1232) energy region

Abstract

The proton Compton effect 7 +P--+ 7 +P in the A (1232) energy region has been thoroughly studied. At the Bonn 500 MeV synchrotron differential cross sections were measured covering a large range of the CM scattering angle (50~ 130 ~ and an energy range from 240 to 440 MeV (LAB energy of the primary photon). A contribution to the counting rate from the competing process of rc ~ photoproduction was strongly suppressed by detecting both particles in the final state and by a proper choice of the endpoint energy of the gamma ray beam. The remaining contribution was monitored experimentally. The measured data were complemented by cross sections at 0 ~ which were computed from the total y p cross sections with an input from a multipole analysis of single pion photoproduction. Preliminary results of this experiment have been published in Lett. Nuovo Cimento. In the meantime the experimental data were reanalyzed. The final data presented here are larger than the preliminary ones by about 15 %.

Cross Sections for the ReactionHe4(γ,γ)HeEj1, Booth2, D3 et al. 1988Phys. Rev. Lett.21080View full textAdd to dashboardCite

“…Our data gave results of 33 ±4 and 0.16 ±0.03 ^b/sr at an average incident laboratory photon energy of 313 MeV, compared to published measured values of 30 ±2 and 0.17 ±0.02 jub/sr for /r° and /, respectively. 4 ' 12 Our final cross sections are compared with the calcula- We conclude that our measurements of the coherent photon-scattering cross section for 4 He at an average laboratory energy of 320 MeV show good agreement with the Koch-Moniz-Ohtsuka isobar-hole calculation. Taken together with the good fit made by the model to the elastic pion scattering from 4 He, they indicate substantial support for the theoretical approach, at least close to the peak of the resonance.…”

“…Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 8 August 1988) We have measured the differential cross sections for coherent Compton photon scattering in the reaction 4 He(/,y) 4 He at laboratory angles of 24°, 30°, 45°, and 60° with an average laboratory photon energy of 320 MeV, at 22° with 358 MeV, and at 30° with 260 MeV. These measurements are the first unambiguous test of the A-hole formalism for this reaction near the peak of the cross section for the A resonance.…”

“…The amount of incoherent scattering is consistent with the estimates calculated by Arenhovel. 6 4 He, where for the first time the coherent scattering was resolved from background in a complex nucleus. 7 The present experiment was performed in the C line of the MIT-Bates Linear Accelerator Center.…”

“…Our energy calibra- tions were accurate to about ±0.5% during the 10-d period of data acquisition. Figure 3 shows the detected scattered-photon spectrum for 4 He at an average laboratory scattering angle of 30° with an electron end-point energy of 330 MeV. Because of nuclear recoil, the maximum scattered photon energy is 326.2 MeV and the maximum decay photon energy from K 0 decay is 311.7 MeV.…”

Nucleon Compton scattering in the nonrelativistic quark model

“…The d a t a from Ref. [14] at 320 MeV and our calculation for intermediate sets made up of the nucleon and A(1232), these plus P waves, and all of the states up to N=2 are plotted in Fig. 12.…”