Related papers: Nucleon Tensor Charge from Exclusive $\pi^o$ Elect…
We have studied in perturbative QCD all independent helicity amplitudes describing the photoproduction of light vector mesons at large $t$. We found a new hard production mechanism which is related to the possibility for a real photon to…
We estimate the sizeable cross section for deep exclusive electroproduction of an exotic $J^{PC}=1^{-+}$ hybrid meson in the Bjorken regime. The production amplitude scales like the one for usual meson electroproduction, i.e. as $1/Q^2$.…
The data were accumulated with the HERMES forward spectrometer using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. Exclusive electroproduction of $\omega$ mesons on unpolarized hydrogen and deuterium targets is…
Spin and transverse momentum dependent parton distributions - Generalized Parton Distributions (GPDs) - are at the interface between the QCD structure of the hadrons and observable quantities. The GPDs are linear superpositions within…
We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of $x_B$ (0.36, 0.48 and 0.60) and $Q^2$ (3.1 to 8.4 GeV$^2$) obtained from Jefferson Lab Hall A experiment E12-06-014. The…
We show that in hard exclusive electroproduction, ep-->eVp, the leading-twist hard-scattering coefficient for the production of a transversely polarized vector meson V vanishes to all orders of perturbation theory. This implies that this…
We describe a new way to access the chiral odd transversity parton distribution in the proton through the photoproduction of lepton pairs. The basic ingredient is the interference of the usual Bethe Heitler or Drell-Yan amplitudes with the…
We present a study of the central exclusive $\pi^{+} \pi^{-}$ production via the photoproduction mechanism in nucleon-nucleon collisions. The photon-pomeron/reggeon and pomeron/reggeon-photon exchanges both for the $\rho^{0}$ resonance…
Hard exclusive pi+ electroproduction is investigated within the handbag approach. The prominent role of the pion-pole contribution is demonstrated. It is also shown that the experimental data require a twist-3 effect which ensues from the…
We report on a measurement of hard exclusive $\pi^0$ muoproduction on the proton by COMPASS using 160 GeV/$c$ polarised $\mu^+$ and $\mu^-$ beams of the CERN SPS impinging on a liquid hydrogen target. From the average of the measured…
Exclusive diffractive processes on the nucleon are investigated within a model in which the quark-nucleon interaction is mediated by Pomeron exchange and the quark substructure of mesons is described within a framework based on the…
Exclusive $\pi^0$ electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in $Q^2$, $x_B$, $t$, and $\phi_\pi$,…
Using a physically motivated parameterization based on the reggeized diquark model we perform a flavor separation of the chiral-odd generalized parton distributions obtained from both $\pi^0$ and $\eta$ exclusive electroproduction. In our…
The tensor charges of the nucleon are calculated in the framework of the SU(3) chiral quark soliton model. The rotational $1/N_c$ and strange quark mass corrections are taken into account up to linear order. We obtain the following…
Transversity distribution, together with the unpolarized and the helicity distributions, represents a basic piece of information on the internal structure of nucleons. Its peculiar property of being a chiral-odd quantity implies that it can…
Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, $Q^2$, and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon…
A sizeable difference in the differential production cross section of top and antitop quarks, respectively, is predicted for hadronically produced heavy quarks. It is of order $\alpha_s$ and arises from the interference between charge odd…
Due to multiple possible polarizations hard exclusive production of tensor mesons by virtual photons or in heavy meson decays offers interesting possibilities to study the helicity structure of the underlying short-distance process.…
We discuss the production of hadrons in polarized lepton nucleon interactions and in the current jet fragmentation region; using the QCD hard scattering formalism we compute the helicity density matrix of the hadron and show how its…
The natural interpretation of deep inelastic scattering is in terms of hard scattering on QCD constituents of the target. We examine the relation between amplitudes measured in exclusive lepto-production and the quark content of the…