M. Vänttinen

NLO corrections to deeply virtual Compton scattering

Abstract We have calculated the NLO corrections to the twist-2 part of the deeply-virtual Compton scattering amplitude. Our results for the transverse and antisymmetric parts agree with recent calculations by Ji and Osborne and by Belitsky and Muller. In addition we present NLO results for the longitudinal part of the amplitude.

Nuclear quark and gluon distributions in coordinate space

Abstract. In coordinate space, quark and gluon distributions of the nucleon are defined as correlation functions involving two field operators separated by a light-cone distance y+= 2l. We study the nuclear modifications of these distributions. The largest effect is a strong depletion of parton distributions (shadowing) at large longitudinal distances, which starts for all parton species at l=2 fm, i.e. at the average nucleon-nucleon separation in nuclei. On the other hand, the nuclear radius does not play a significant role. At l ≲ 1 fm, nuclear modifications of parton distributions are small. The intrinsic structure of individual nucleons is evidently not very much affected by nuclear binding. In particular, there is no evidence for a significant increase of the quark or gluon correlation length in bound nucleons.

Hard exclusive J/ψ leptoproduction on polarized targets

We consider the exclusive production of

Exclusive J/ψ photoproduction and gluon polarization

J/\psi

Nuclear shadowing and the optics of hadronic fluctuations

mesons in polarized virtual-photon--proton collisions. We derive helicity amplitudes for the dominant subprocess

Hard exclusive J/ψ leptoproduction on polarized targets1

\gamma^* g \to J/\psi g

Nuclear shadowing and the optics of hadronic fluctuations ? ? Work supported in part by BMBF.

and show that polarization asymmetries vanish in the case of collinear scattering. Thus, contrary to what has been suggested earlier, this process is not a good probe of the polarized gluon distribution

Nuclear parton distributions in coordinate space

\Delta g(x,Q^2)

NLO corrections to deeply-virtual Compton scattering 1 Work supported in part by BMBF. 1

of the proton.We consider the exclusive production of J/ψ mesons in polarized virtual-photon–proton collisions. We derive helicity amplitudes for the dominant subprocess γ∗g→J/ψg and show that polarization asymmetries vanish in the case of collinear scattering. Thus, contrary to what has been suggested earlier, this process is not a good probe of the polarized gluon distribution Δg(x,Q2) of the proton.

Exclusive J/ ? photoproduction and gluon polarization 1 Work supported in part by BMBF. 1

Abstract In exclusive J/ψ production by polarized photons incident on polarized protons, a finite polarization asymmetry arises because of c c Fermi-motion and binding-energy effects. The asymmetry depends on the polarized nonforward gluon distribution of the proton and thus gives information on gluon polarization in the proton. The analyzing power, however, is rather small.