Freiburg 1999 – scientific programme
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HK: Physik der Hadronen und Kerne
HK 44: Elektromagnetische und hadronische Proben VII
HK 44.7: Group Report
Wednesday, March 24, 1999, 17:30–18:00, E
Deeply-virtual electroproduction of photons and mesons on the nucleon — •M. Vanderhaeghen1, P.A.M. Guichon2, and M. Guidal3 — 1Institut f"ur Kernphysik, Universit"at Mainz — 2CEA-Saclay, DAPNIA/SPhN, F-91191 Gif-sur-Yvette, France — 3IPN Orsay, F-91406 Orsay, France
The deeply virtual Compton scattering (DVCS) and the exclusive electroproduction of vector mesons (ρ0, ρ±, ω, Φ) and pseudoscalar mesons (π0, π±, η) in the Bjorken regime are sensitive to the recently introduced off-forward or skewed parton distributions [1][2]. These distributions constitute a generalization of the unpolarized and polarized parton distributions measured in deeply inelastic scattering. Model independent sum rules relate these distributions to the nucleon elastic form factors and the total spin of the nucleon carried by the quarks. We performed calculations [3][4] using different models for these off-forward parton distributions, for experiments at JLab, HERMES and COMPASS. Both predictions for the leading order perturbative QCD amplitude and higher twist corrections to the leading order amplitude will be presented. A recently approved experiment a JLab [5] that we proposed to test the predicted scaling behavior of the leading order longitudinal ρ0 electroproduction amplitude will also be presented and prospects will be discussed to measure these generalized parton distributions in the near future.
[1] X. Ji, Phys.Rev.Lett. 78, 610 (1997); Phys.Rev.D 55, 7114 (1997)
[2] A.V. Radyushkin, Phys.Lett.B 380, 417 (1996)
[3] M. Vanderhaeghen, P.A.M. Guichon and M. Guidal, Phys.Rev.Lett. 80, 5064 (1998)
[4] P.A.M. Guichon and M. Vanderhaeghen, Prog.Part.Nucl.Phys. 41, 125 - 190 (1998)
[5] JLab experiment E98-107, spokespersons M. Guidal, C. Marchand and E. Smith