arXiv subjects

M. Osipenko

Publications and source records attributed to M. Osipenko.

95 records · Page 6Linked to original sources

arXiv2002

Proton and neutron polarized structure functions from low to high Q**2

Phenomenological parameterizations of proton and neutron polarized structure functions, g1p and g1n, are developed for x > 0.02 using deep inelastic data up to ~ 50 (GeV/c)**2 as well as available experimental results on photo- and electro-production of nucleon resonances. The generalized Drell-Hearn-Gerasimov sum rules are predicted from low to high values of Q**2 and compared with proton and neutron data. Furthermore, the main results of the power correction analysis carried out on the Q**2-behavior of the polarized proton Nachtmann moments, evaluated using our parameterization of g1p, are briefly summarized.

nucl-th↗

arXiv2002

Photoproduction of the $ω$ meson on the proton at large momentum transfer

The differential cross section, $dσ/dt$ for $ω$ meson exclusive photoproduction on the proton above the resonance region ($2.6<W<2.9$ GeV) was measured up to a momentum transfer $-t = 5$ GeV$^2$ using the CLAS detector at Jefferson Laboratory. The $ω$ channel was identified by detecting a proton and $π^+$ in the final state and using the missing mass technique. While the low momentum transfer region shows the typical diffractive pattern expected from Pomeron and Reggeon exchange, at large $-t$ the differential cross section has a flat behavior. This feature can be explained by introducing quark interchange processes in addition to the QCD-inspired two-gluon exchange.

hep-ex↗

arXiv2002

Leading and higher twists in the proton polarised structure function g1p at large Bjorken-x

Power corrections to the Q**2 behavior of the Nachtmann moments of the proton polarized structure function g1p are investigated at large Bjorken-x by developing a phenomenological fit of both the resonance (including the photon point) and deep inelastic data up to Q**2 ~ 50 (GeV/c)**2. The leading twist is treated at NLO in the strong coupling constant and the effects of higher orders of the perturbative series are estimated using soft-gluon resummation techniques. In case of the first moment higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and the singlet axial charge is determined to be a0[10 (GeV/c)**2] = 0.16 +/- 0.09. In case of higher order moments, which are sensitive to the large-x region, higher-twist effects are significantly reduced by the introduction of soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2 at variance with the case of the unpolarized transverse structure function of the proton. This finding suggests that spin-dependent correlations among partons may have more impact than spin-independent ones. It is also shown that the parton-hadron local duality is violated in the region of polarized electroproduction of the Delta(1232) resonance.

hep-ph↗

arXiv2001

Leading and higher twists in the proton polarized structure function at large Bjorken x

A phenomenological parameterization of the proton polarized structure function has been developed for x > 0.02 using deep inelastic data up to ~ 50 (GeV/c)**2 as well as available experimental results on both photo- and electro-production of proton resonances. According to the new parameterization the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a zero-crossing point at Q**2 = 0.16 +/- 0.04 (GeV/c)**2. Then, low-order polarized Nachtmann moments have been estimated and their Q**2-behavior has been investigated in terms of leading and higher twists for Q**2 > 1 (GeV/c)**2. The leading twist has been treated at NLO in the strong coupling constant and the effects of higher orders of the perturbative series have been estimated using soft-gluon resummation techniques. In case of the first moment higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and the singlet axial charge has been determined to be a0[10 (GeV/c)**2] = 0.16 +/- 0.09. In case of higher order moments, which are sensitive to the large-x region, higher-twist effects are significantly reduced by the introduction of soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2 at variance with the case of the unpolarized transverse structure function of the proton. Our finding suggests that spin-dependent correlations among partons may have more impact than spin-independent ones. As a byproduct, it is also shown that the Bloom-Gilman local duality is strongly violated in the region of polarized electroproduction of the Delta(1232) resonance.

hep-ph↗

arXiv2000

A Phenomenological Description of (π^{-}Δ^{++}) Photo- and Electroproduction in Nucleon Resonance Region

The (π^{-}Δ^{++}) production on the nucleon by real and virtual photons is discussed as initial step in a simple model approach for the two pion photo- and electroproduction on the nucleon, with emphasis on nucleon resonance excitation which is of interest for new facilities like TJNAF. A calculation for (π^{-}Δ^{++}) channel in resonance excitation region is presented and compared to existing experimental data along with a discussion of physical effects that we find to be of relevance. The calculation is proposed as a starting basis for the investigation of (N^{*}) electromagnetic form factors using experimental data about two pion production by real and virtual photons.

hep-ph↗