Abstract
Double-spin asymmetries in exclusive electroproduction of real photons from a transversely polarized hydrogen target are measured with respect to the product of target polarization with beam helicity and beam charge, and with respect to the product of target polarization with beam helicity alone. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe–Heitler process. They are related to the real part of the same combination of Compton form factors as that determining the previously published transverse target single-spin asymmetries through the imaginary part. The results for the double-spin asymmetries are found to be compatible with zero within the uncertainties of the measurement, and are not incompatible with the predictions of the only available GPD-based calculation.
Highlights
Generalized Parton Distributions (GPDs) provide a framework for describing the multidimensional structure of the nucleon [1, 2, 3]
The resulting systematic uncertainty is defined as the root-mean-square average of the five differences between the asymmetry amplitude extracted from the Monte Carlo data based on five GPD model variants [38] and the corresponding model predictions calculated analytically at the mean kinematic values of that bin
The results for the Fourier amplitudes of the beam-chargedifference and charge-averaged double-spin asymmetries AILT and ALBTH+DVCS defined in Eqs. 26 and 27 are presented in Figs. 2 and 3 respectively, as a function of −t, xB, or Q2, while integrating over the other variables. (In the HERMES acceptance, xB and Q2 are highly correlated.) These values are given in Tables 2 and 3
Summary
Generalized Parton Distributions (GPDs) provide a framework for describing the multidimensional structure of the nucleon [1, 2, 3]. HERMES obtained results on transverse-target asymmetries [24], which can constrain GPD E Knowledge on both H and E opens access towards the determination of the total u and dquark angular momentum through the Ji sum rule [3]. This paper reports the first measurement of azimuthal asymmetries with respect to target polarization combined with beam helicity and beam charge, and with respect to target polarization combined with beam helicity alone, for exclusive electroproduction of real photons from a transversely polarized hydrogen target. One of these new asymmetries has the potential in principle to constrain GPD E
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