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Doubly virtual Compton scattering and the beam normal spin asymmetry

Gorchtein, Mikhail (2006) Doubly virtual Compton scattering and the beam normal spin asymmetry. Physical Review C, 73 (3). Art. No. 035213. ISSN 0556-2813. doi:10.1103/PhysRevC.73.035213.

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We construct an invariant basis for Compton scattering with two virtual photons (VVCS). The basis tensors are chosen to be gauge invariant and orthogonal to each other. The properties of the corresponding 18 invariant amplitudes are studied in detail. We consider the special case of elastic VVCS with the virtualities of the initial and final photons equal. The invariant basis for VVCS in this orthogonal form does not exist in the literature. We furthermore use this VVCS tensor for a calculation of the beam normal spin asymmetry in the forward kinematics. For this, we relate the invariant amplitudes to the helicity amplitudes of the VVCS reaction. The imaginary parts of the latter are related to the inclusive cross section by means of the optical theorem. We use the phenomenological value of the transverse cross section sigmaT~0.1 mb and the Callan-Gross relation which relates the longitudinal cross section sigmaL to the transverse one. The result of the calculation agrees with an existing calculation, and predicts negative values of the asymmetry Bn of order of 5 ppm in the energy range from 3 to 45 GeV and for very forward angles.

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Additional Information:©2006 The American Physical Society (Received 7 December 2005; published 27 March 2006) The author is grateful to Dr. Nicole F. Bell for useful comments on the manuscript. This work was supported by the US Department of Energy contract DOE-FG02-05ER 41361.
Subject Keywords:Compton effect; helicity (elementary particles); photon-nucleon scattering; elementary particle interaction models; elementary particle inclusive interactions
Issue or Number:3
Record Number:CaltechAUTHORS:GORprc06a
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3847
Deposited By: Archive Administrator
Deposited On:17 Jul 2006
Last Modified:08 Nov 2021 20:12

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