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Title: Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering

Abstract

We present the first measurements of the e(vector sign)p{yields}ep{gamma} cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. The Q{sup 2} dependence (from 1.5 to 2.3 GeV{sup 2}) of the helicity-dependent cross section indicates the twist-2 dominance of DVCS, proving that generalized parton distributions (GPDs) are accessible to experiment at moderate Q{sup 2}. The helicity-independent cross section is also measured at Q{sup 2}=2.3 GeV{sup 2}. We present the first model-independent measurement of linear combinations of GPDs and GPD integrals up to the twist-3 approximation.

Authors:
; ; ; ;  [1]; ; ; ; ; ;  [2]; ; ; ;  [3]; ; ; ; ;  [4]
  1. CEA Saclay, DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France)
  2. Universite Blaise Pascal/CNRS-IN2P3, F-63177 Aubiere (France)
  3. Laboratoire de Physique Subatomique et de Cosmologie, 38026 Grenoble (France)
  4. Old Dominion University, Norfolk, Virginia 23508 (United States) (and others)
Publication Date:
OSTI Identifier:
20861542
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 97; Journal Issue: 26; Other Information: DOI: 10.1103/PhysRevLett.97.262002; (c) 2006 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; APPROXIMATIONS; COMPTON EFFECT; CROSS SECTIONS; DISTRIBUTION; HELICITY; QUARKS

Citation Formats

Camacho, C. Munoz, Beaumel, M., Garcon, M., Guichon, P. A. M., Sabatie, F., Camsonne, A., Ferdi, C., Brossard, M., Fieschi, J.-M., Laveissiere, G., Michel, B., Mazouz, M., Guillon, B., Real, J.-S., Voutier, E., Gavalian, G., Amarian, M., Hayes, D., Hyde-Wright, C. E., and Ibrahim, H. Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering. United States: N. p., 2006. Web. doi:10.1103/PHYSREVLETT.97.262002.
Camacho, C. Munoz, Beaumel, M., Garcon, M., Guichon, P. A. M., Sabatie, F., Camsonne, A., Ferdi, C., Brossard, M., Fieschi, J.-M., Laveissiere, G., Michel, B., Mazouz, M., Guillon, B., Real, J.-S., Voutier, E., Gavalian, G., Amarian, M., Hayes, D., Hyde-Wright, C. E., & Ibrahim, H. Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering. United States. doi:10.1103/PHYSREVLETT.97.262002.
Camacho, C. Munoz, Beaumel, M., Garcon, M., Guichon, P. A. M., Sabatie, F., Camsonne, A., Ferdi, C., Brossard, M., Fieschi, J.-M., Laveissiere, G., Michel, B., Mazouz, M., Guillon, B., Real, J.-S., Voutier, E., Gavalian, G., Amarian, M., Hayes, D., Hyde-Wright, C. E., and Ibrahim, H. Sun . "Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering". United States. doi:10.1103/PHYSREVLETT.97.262002.
@article{osti_20861542,
title = {Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering},
author = {Camacho, C. Munoz and Beaumel, M. and Garcon, M. and Guichon, P. A. M. and Sabatie, F. and Camsonne, A. and Ferdi, C. and Brossard, M. and Fieschi, J.-M. and Laveissiere, G. and Michel, B. and Mazouz, M. and Guillon, B. and Real, J.-S. and Voutier, E. and Gavalian, G. and Amarian, M. and Hayes, D. and Hyde-Wright, C. E. and Ibrahim, H.},
abstractNote = {We present the first measurements of the e(vector sign)p{yields}ep{gamma} cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. The Q{sup 2} dependence (from 1.5 to 2.3 GeV{sup 2}) of the helicity-dependent cross section indicates the twist-2 dominance of DVCS, proving that generalized parton distributions (GPDs) are accessible to experiment at moderate Q{sup 2}. The helicity-independent cross section is also measured at Q{sup 2}=2.3 GeV{sup 2}. We present the first model-independent measurement of linear combinations of GPDs and GPD integrals up to the twist-3 approximation.},
doi = {10.1103/PHYSREVLETT.97.262002},
journal = {Physical Review Letters},
number = 26,
volume = 97,
place = {United States},
year = {Sun Dec 31 00:00:00 EST 2006},
month = {Sun Dec 31 00:00:00 EST 2006}
}
  • We present the first measurements of {rvec e}p {yields} ep{gamma} cross section in the deep virtual Compton scattering (DVCS) regime and the valence quark region (x{sub Bj} = 0.36). From JLab E00-110, we extract the imaginary part of the Bethe-Heitler (BH)--DVCS interference terms, to order twist-3 for Q{sup 2} = 1.5, 1.9, and 2.3 GeV{sup 2}, and the real part of the BH-DVCS interference terms at Q{sup 2}2 = 2.3 GeV{sup 2}. We present the first model-independent measurement of linear combinations of generalized parton distributions (GPDs) and GPD integrals up to twist-3 approximation. The validity of this approximation is stronglymore » supported by the absence of Q{sup 2}-variation of the extracted terms--thereby constraining the size of higher twist contributions to our observables.« less
  • The author outlines a perturbative QCD approach to the analysis of the deeply virtual Compton scattering process {gamma}{sup *}p {r_arrow} {gamma}p{prime} in the limit of vanishing momentum transfer t=(p{prime}{minus}p){sup 2}. The DVCS amplitude in this limit exhibits a scaling behavior described by a two-argument distributions F(x,y) which specify the fractions of the initial momentum p and the momentum transfer r {equivalent_to} p{prime}{minus}p carried by the constituents of the nucleon. The kernel R(x,y;{xi},{eta}) governing the evolution of the non-forward distributions F(x,y) has a remarkable property: it produces the GLAPD evolution kernel P(x/{xi}) when integrated over y and reduces to the Brodsky-Lepagemore » evolution kernel V(y,{eta}) after the x-integration. This property is used to construct the solution of the one-loop evolution equation for the flavor non-singlet part of the non-forward quark distribution.« less
  • We propose precision measurements of the helicity-dependent and helicity independent cross sections for the ep {yields} ep{gamma} reaction in Deeply Virtual Compton Scattering (DVCS) kinematics. DVCS scaling is obtained in the limits Q{sup 2} >> {Lambda}{sub QCD}{sup 2}, x{sub Bj} fixed, and -{Delta}{sup 2} = -(q-q{prime}){sup 2} << Q{sup 2}. We consider the specific kinematic range Q{sup 2} > 2 GeV{sup 2}, W > 2 GeV, and -{Delta}{sup 2} {le} 1 GeV{sup 2}. We will use our successful technique from the 5.75 GeV Hall A DVCS experiment (E00-110). With polarized 6.6, 8.8, and 11 GeV beams incident on the liquidmore » hydrogen target, we will detect the scattered electron in the Hall A HRS-L spectrometer (maximum central momentum 4.3 GeV/c) and the emitted photon in a slightly expanded PbF{sub 2} calorimeter. In general, we will not detect the recoil proton. The H(e,e{prime}{gamma})X missing mass resolution is sufficient to isolate the exclusive channel with 3% systematic precision.« less
  • We develop the minimal model of a new leading order parametrization of generalized parton distributions (GPDs) introduced by Polyakov and Shuvaev. The model for GPDs H and E is formulated in terms of the forward quark distributions, the Gegenbauer moments of the D-term, and the forward limit of the GPD E. The model is designed primarily for small and medium-size values of x{sub B}, x{sub B}{<=}0.2. We examine two different models of the t dependence of the GPDs: the factorized exponential model and the nonfactorized Regge-motivated model. Using our model, we successfully described the deeply virtual Compton scattering (DVCS) crossmore » section measured by H1 and ZEUS, the moments of the beam-spin A{sub LU}{sup sin{phi}}, the beam-charge A{sub C}{sup cos{phi}}, and the transversely polarized target A{sub UT}{sup sin{phi}}{sup cos{phi}} DVCS asymmetries measured by HERMES and A{sub LU}{sup sin{phi}} measured by CLAS. The data on A{sub C}{sup cos{phi}} prefer the Regge-motivated model of the t dependence of the GPDs. The data on A{sub UT}{sup sin{phi}}{sup cos{phi}} indicate that the u and d quarks carry only a small fraction of the proton total angular momentum.« less