CEN A observation at MeV-energies

During a balloon flight with the MPI Compton telescope from Uberaba/Brasil gamma-ray emission from the direction of Cen A was observed at MeV-energies. The observed flux connects to the X-ray spectrum of Cen A beyond 0.7 MeV and has a statistical significance of 4.1. The extension beyond 3 MeV has a significance of 3.8. Possible interpretations of the energy spectrum are discussed

Inequalities for nucleon generalized parton distributions with helicity flip

Several positivity bounds are derived for generalized parton distributions (GPDs) with helicity flip.Comment: 20 page

Identifying Prognostic Indicators for Electrical Treeing in Solid Insulation through PD Analysis

This paper presents early results from an experimental study of electrical treeing on commercially available pre-formed silicone samples. A needle-plane test arrangement was set up using hypodermic needles. Partial discharge (PD) data was captured using both the IEC 60270 electrical method and radio frequency (RF) sensors, and visual observations are made using a digital microscope. Features of the PD plot that corresponded to electrical tree growth were assessed, evaluating the similarities and differences of both PD measurement techniques. Three univariate phase distributions were extracted from the partial discharge phase-resolved (PRPD) plot and the first four statistical moments were determined. The implications for automated lifetime prediction of insulation samples due to electrical tree development are discussed

Exotic hybrid mesons in hard electroproduction

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 $1/Q^2$. This is due to the non-vanishing leading twist distribution amplitude for the hybrid meson, which may be normalized thanks to its relation to the energy momentum tensor and to the QCD sum rules technique. The hard amplitude is considered up to next-to-leading order in $\alpha_{S}$ and we explore the consequences of fixing the renormalization scale ambiguity through the BLM procedure. We study the particular case where the hybrid meson decays through a $\pi\eta$ meson pair. We discuss the $\pi\eta$ generalized distribution amplitude and then calculate the production amplitude for this process. We propose a forward-backward asymmetry in the production of $\pi$ and $\eta$ mesons as a signal for the hybrid meson production. We briefly comment on hybrid electroproduction at very high energy, in the diffractive limit where a QCD Odderon exchange mechanism should dominate. The conclusion of our study is that hard electroproduction is a promissing way to study exotic hybrid mesons, in particular at JLAB, HERA (HERMES) or CERN (Compass)

Model study of generalized parton distributions with helicity flip

Generalized parton distributions with helicity flip are studied in the quark sector, within a simple version of the MIT bag model, assuming an SU(6) wave function for the proton target. In the framework under scrutiny it turns out that only the generalized transversity distribution, H_T^q, is non vanishing. For this quantity, the forward limit is properly recovered and numerical results are found to underestimate recent lattice data for its first moment. Positivity bounds recently proposed are fulfilled by the obtained distribution. The relevance of the analysis for the planning of measurements of the quark generalized transversity is addressed.Comment: 15 pages, 4 figures; shortened version accepted for publication in Phys. Rev.

Exclusive diffractive electroproduction of dijets in collinear factorization

Exclusive electroproduction of hard dijets can be described within the collinear factorization. This process has clear experimental signature and provides one with an interesting alternative venue to test QCD description of hard diffractive processes and extract information on generalized nucleon parton distributions. In this work we present detailed leading-order QCD calculations of the relevant cross sections, including longitudinal momentum fraction distribution of the dijets and their azimuthal angle dependence.Comment: 11 pages, 14 Postscript figures, uses revtex4.st

Dual parameterization of generalized parton distributions and description of DVCS data

We discuss a new leading-order parameterization of generalized parton distributions of the proton, which is based on the idea of duality. In its minimal version, the parameterization is defined by the usual quark singlet parton distributions and the form factors of the energy-momentum tensor. We demonstrate that our parameterization describes very well the absolute value, the Q^2-dependence and the W-dependence of the HERA data on the total DVCS cross section and contains no free parameters in that kinematics. The parameterization suits especially well the low-x_{Bj} region, which allows us to advocate it as a better alternative to the frequently used double distribution parameterization of the GPDs.Comment: 13 pages, 2 figures, LaTeX. Revised version: equation for the DVCS cross section corrected; one reference added; numerical results did not chang