Two-nucleon emission with polarised photons

MacGregor, I.J.D. (2001) Two-nucleon emission with polarised photons. In: 5th International Workshop on Electromagnetically Induced 2-Hadron Emission, Lund, Sweden, 13-16 Jun 2001, pp. 314-324.

Abstract

The 12C(gamma,pp) and 12C(gamma,pn) reactions have recently been measured in the Delta-resonance region using linearly polarised tagged photons. The experiments used the Glasgow tagged-photon spectrometer[1] at the Mainz 855 MeV electron microtron MAMI [2]. Data corresponding to the direct emission of nucleon pairs form (1p)2 and (1p)(1s) orbits were selected using missing energy and angular cuts. The experiments investigated the photon energy, missing energy, recoil momentum and angular dependences of the photon asymmetry Sigma and the cross sections sigma_parallel (sigma_perpendicular) for events emitted parallel (perpendicular) to the plane of polarisation of the incident photons. The data are compared with state-of-the-art calculations of direct two-nucleon emission using the model developed by the Gent theory group [3]. The experimental data reveal important features which were not accessible to previous experiments with unpolarised photons. In particular the 12C(gamma,pp) reaction shows a strong (negative) peak in Sigma at missing energies just above the reaction threshold., which is interpreted as new evidence of a direct photoproduction process for this reaction channel. The theoretical calculations reproduce some of the general trends of the measured data, but do not agree in detail with the experimental spectra. At high missing energies, for Egamma> 250 MeV, where two-step processes dominate, Sigma has a substantial negative value for both reaction channels. This is attributed to a strong asymmetry in the initial photon absorption process.

• Item Type: Conference Proceedings
• Additional Information: ISBN:916311612X
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: MacGregor, Professor Douglas
• Authors: MacGregor, I.J.D.
• Subjects: Q Science > QC Physics
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Research Group: Nuclear Physics
• Copyright Holders: Copyright © 2001 The Author
• Publisher Policy: Reproduced with the permission of the publisher