Search

We investigate the possibility of acquiring information on the generalized parton distribution E and, through a model for E, also on the u-quark total angular momentum Ju by studying deeply virtual Compton scattering and hard exclusive ρ0 electroproduction on a transversely polarized hydrogen target at HERMES. It is found that a change in Ju from zero to 0.4 corresponds to a 4σ (2σ) difference in the calculated transverse target-spin asymmetry in deeply virtual Compton scattering (ρ0 electroproduction), where σ is the total experimental uncertainty. [ABSTRACT FROM AUTHOR]

A recoil detector will be installed surrounding the internal gas target of the HERMES experiment at DESY. The recoil detector will improve the selection of exclusive events by a direct measurement of the momentum and track direction of the recoiling particle. The innermost layer of this recoil detector is a new silicon strip detector (SSD). Since Monte Carlo simulations predict proton momenta as low as 100 MeV/c, the SSD will be placed inside the HERA vacuum. A new setup of the electronics enables a dynamic range from below 4 fC at a signal-to-noise ratio of 6.8 up to 270 fC. In this paper, the assembly of the first module and the final setup within the HERMES experiment will be presented. Results from charge-injection tests of a prototype module are given. [ABSTRACT FROM AUTHOR]

Prospects for future measurements of deeply virtual Compton scattering are studied in leading order using different simple models for the parameterizations of generalized parton distributions (GPDs). Measurements of the lepton charge and lepton beam helicity asymmetry will yield important input for theoretical models towards the future extraction of GPDs. The kinematics of the HERMES experiment, complemented with a recoil detector, was adopted to arrive at realistic projected statistical uncertainties. [ABSTRACT FROM AUTHOR]

A method is discussed to determine the hitherto unknown u-quark transversity distribution $\delta u(x)$ from a planned HERMES measurement of a single target-spin asymmetry in semi-inclusive pion electroproduction off a transversely polarized target. Assuming u-quark dominance, the measurement yields the shapes of the transversity distribution $\delta u(x)$ and of the ratio $H_1^{\perp (1)u}(z)/D_1^u(z)$, of polarized and unpolarized u-quark fragmentation functions. The unknown relative normalization can be obtained by identifying the transversity distribution with the well-known helicity distribution at large x and small $Q^2$. The systematic uncertainty of the method is dominated by the assumption of u-quark dominance. [ABSTRACT FROM AUTHOR]