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Title: Polarization Transfer in Proton Compton Scattering at High Momentum Transfer

Abstract

Compton scattering from the proton was investigated at s=6.9 GeV{sup 2} and t=-4.0 GeV{sup 2} via polarization transfer from circularly polarized incident photons. The longitudinal and transverse components of the recoil proton polarization were measured. The results are in disagreement with a prediction of perturbative QCD based on a two-gluon exchange mechanism, but agree well with a prediction based on a reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton.

Authors:
;  [1];  [2];  [3]; ;  [4]; ; ;  [5];  [6]; ;  [7];  [8]; ; ;  [9]; ; ; ;  [10] more »;  [11] « less
  1. University of Glasgow, Glasgow G12 8QQ (United Kingdom)
  2. Yerevan Physics Institute, Yerevan 375036 (Armenia)
  3. (United States)
  4. California State University Los Angeles, Los Angeles, California 90032 (United States)
  5. Universite Blaise Pascal/IN2P3, F-63177 Aubiere (France)
  6. IPN, Orsay B.P. no. 1 F-91406, Orsay (France)
  7. University of Massachusetts, Amherst, Massachusetts 01003 (United States)
  8. University of New Hampshire, Durham, New Hampshire 03824 (United States)
  9. University of Maryland, College Park, Maryland 20742 (United States)
  10. University of Illinois, Urbana-Champaign, Illinois 61801 (United States)
  11. Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States) [and others
Publication Date:
OSTI Identifier:
20696397
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 94; Journal Issue: 24; Other Information: DOI: 10.1103/PhysRevLett.94.242001; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; COMPTON EFFECT; GLUONS; MOMENTUM TRANSFER; PHOTONS; POLARIZATION; PROTONS; QUANTUM CHROMODYNAMICS; QUARKS; REACTION KINETICS; SPIN

Citation Formats

Hamilton, D.J., Annand, J.R.M., Mamyan, V.H., Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, Aniol, K.A., Margaziotis, D.J., Bertin, P.Y., Camsonne, A., Laveissiere, G., Bimbot, L., Bosted, P., Paschke, K., Calarco, J.R., Chang, G.C., Horn, T., Savvinov, N., Chang, T.-H., Danagoulian, A., Nathan, A.M., Roedelbronn, M., and Chen, J.-P.. Polarization Transfer in Proton Compton Scattering at High Momentum Transfer. United States: N. p., 2005. Web. doi:10.1103/PhysRevLett.94.242001.
Hamilton, D.J., Annand, J.R.M., Mamyan, V.H., Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, Aniol, K.A., Margaziotis, D.J., Bertin, P.Y., Camsonne, A., Laveissiere, G., Bimbot, L., Bosted, P., Paschke, K., Calarco, J.R., Chang, G.C., Horn, T., Savvinov, N., Chang, T.-H., Danagoulian, A., Nathan, A.M., Roedelbronn, M., & Chen, J.-P.. Polarization Transfer in Proton Compton Scattering at High Momentum Transfer. United States. doi:10.1103/PhysRevLett.94.242001.
Hamilton, D.J., Annand, J.R.M., Mamyan, V.H., Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, Aniol, K.A., Margaziotis, D.J., Bertin, P.Y., Camsonne, A., Laveissiere, G., Bimbot, L., Bosted, P., Paschke, K., Calarco, J.R., Chang, G.C., Horn, T., Savvinov, N., Chang, T.-H., Danagoulian, A., Nathan, A.M., Roedelbronn, M., and Chen, J.-P.. Fri . "Polarization Transfer in Proton Compton Scattering at High Momentum Transfer". United States. doi:10.1103/PhysRevLett.94.242001.
@article{osti_20696397,
title = {Polarization Transfer in Proton Compton Scattering at High Momentum Transfer},
author = {Hamilton, D.J. and Annand, J.R.M. and Mamyan, V.H. and Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 and Aniol, K.A. and Margaziotis, D.J. and Bertin, P.Y. and Camsonne, A. and Laveissiere, G. and Bimbot, L. and Bosted, P. and Paschke, K. and Calarco, J.R. and Chang, G.C. and Horn, T. and Savvinov, N. and Chang, T.-H. and Danagoulian, A. and Nathan, A.M. and Roedelbronn, M. and Chen, J.-P.},
abstractNote = {Compton scattering from the proton was investigated at s=6.9 GeV{sup 2} and t=-4.0 GeV{sup 2} via polarization transfer from circularly polarized incident photons. The longitudinal and transverse components of the recoil proton polarization were measured. The results are in disagreement with a prediction of perturbative QCD based on a two-gluon exchange mechanism, but agree well with a prediction based on a reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton.},
doi = {10.1103/PhysRevLett.94.242001},
journal = {Physical Review Letters},
number = 24,
volume = 94,
place = {United States},
year = {Fri Jun 24 00:00:00 EDT 2005},
month = {Fri Jun 24 00:00:00 EDT 2005}
}
  • Compton scattering from the proton was investigated at s = 6.9 GeV{sup 2} and t = -4.0 TeV{sup 2} via polarization transfer from circularly polarized incident photons. The longitudinal and transverse components of the recoil proton polarization were measured. The results are in excellent agreement with a prediction based on a reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton and in disagreement with a prediction of pQCD based on a two-gluon exchange mechanism.
  • Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and -t = 2-7 GeV2 with statistical accuracy of a few percent. The scaling power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0 +/- 0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.
  • Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s=5-11 and -t=2-7 GeV{sup 2} with a statistical accuracy of a few percent. The scaling power for the s dependence of the cross section at fixed center-of-mass angle was found to be 8.0{+-}0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.
  • Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7 GeV at a proton scattering angle of theta(p)(cm) cm = 70 degrees. The longitudinal transfer K-LL, measured to be 0.645 +/- 0.059 +/- 0.048, where the first error is statistical and the second is systematic, has the same sign as predicted for the reaction mechanism in which the photon interacts with a single quark carrying themore » spin of the proton. However, the observed value is similar to 3 times larger than predicted by the generalized-parton-distribution-based calculations, which indicates a significant unknown contribution to the scattering amplitude.« less