Exclusive pion electroproduction off nucleons and nuclei

We present our results for the exclusive electroproduction of pions off nucleons and nuclei at high values of $Q^2$. In electroproduction of nuclei $A(e,e'\pi)$ we consider the Color Transparency (CT) effect recently observed at JLAB. It is shown that the description of $\pi$ production off nucleons is mandatory for the proof of the CT signal at JLAB. We further develop the models for exclusive production of $\pi$ off nucleons at JLAB and HERMES. At first we describe a model based on exclusive-inclusive connection. In the second approach we combine a Regge pole approach with the residual effect of nucleon resonances. The nucleon resonances are described using a dual connection between the exclusive form factors and inclusive deep inelastic structure functions. We present the results for the beam spin azimuthal asymmetries measured at JLAB in exclusive electroproduction of charged and neutral pions.Comment: 15 pages, 10 figures. Invited talk at the NAPP 2010 - 3rd International Conference on Nuclear and Particle Physics with CEBAF, October 3rd to 8th 2010, Dubrovnik, Croati

Deep exclusive electroproduction of π+\pi^+ at HERMES

Deeply virtual electroproduction of pion in exclusive reaction $p(e,e'\pi^+)n$ is studied using a two-component model which includes soft hadronic and hard partonic reaction mechanisms. The results are compared with the experimental data measured at HERMES in the deep inelastic region for values of $Q^2>1$ GeV$^2$ and $W^2 > 10$ GeV$^2$. At forward angles the $\pi^+$ cross section is longitudinal and is dominated by exchange of Regge poles, with $\pi$ the dominant trajectory. The off-forward region with $-t>1$ GeV$^2$ is transverse and shows the dominance of partonic subprocesses. An implication of present results for the future JLAB facilities are briefly discussed.Comment: 10 pages, 4 figure

Deep exclusive charged π\pi electroproduction above the resonance region

A description of exclusive charged pion electroproduction $(e,e'\pi^{\pm})$ off nucleons at high energies is proposed. The model combines a Regge pole approach with residual effect of nucleon resonances. The exchanges of $\pi$(140), vector $\rho(770)$ and axial-vector $a_1(1260)$ and $b_1(1235)$ Regge trajectories are considered. The contribution of nucleon resonances is described using a dual connection between the exclusive hadronic form factors and inclusive deep inelastic structure functions. The model describes the measured longitudinal, transverse and interference cross sections at JLAB and DESY. The scaling behavior of the cross sections is in agreement with JLAB and deeply virtual HERMES data. The results for a polarized beam-spin azimuthal asymmetry in $(\vec{e},e'\pi^{\pm})$ are presented. Model predictions for JLAB at 12 GeV are given.Comment: 29 page

Λ(1520)\Lambda(1520) and Σ(1385)\Sigma(1385) in the nuclear medium

Recent studies of the $\Lambda(1520)$ resonance within chiral unitary theory with coupled channels find the resonance as a dynamically generated state from the interaction of the decuplet of baryons and the octet of mesons, essentially a quasibound state of $\pi \Sigma^*(1385)$ in this case, although the coupling of the $\Lambda(1520)$ to the $\bar{K}N$ and $\pi \Sigma$ makes this picture only approximate. The $\pi \Sigma^*(1385)$ decay channel of the $\Lambda(1520)$ is forbidden in free space for the nominal mass of the $\Sigma^*(1385)$, but the coupling of the $\pi$ to $ph$ components in the nuclear medium opens new decay channels of the $\Lambda(1520)$ in the nucleus and produces a much larger width. Together with medium modifications of the $\bar{K}N$ and $\pi \Sigma$ decay channels, the final width of the $\Lambda(1520)$ at nuclear matter density is more than five times bigger than the free one. We perform the calculations by dressing simultaneously the $\Lambda(1520)$ and the $\Sigma^*(1385)$ resonances, finding moderate changes in the mass but substantial ones in the width of both resonances.Comment: 20 pages, 6 figures; comparison made to data, new references and new (small) decay channel include

Ekskluzivna elektrotvorba piona na nukleonima i jezgrama

We present our results for the exclusive electroproduction of pions off nucleons and nuclei at high values of Q2 . In electroproduction of nuclei A(e, e′π) we consider the color transparency (CT) effect recently observed at JLAB. It is shown that the description of π production off nucleons is mandatory for the proof of the CT signal at JLAB. We further develop the models for exclusive production of π off nucleons at JLAB and HERMES. We first describe a model based on exclusive-inclusive connection. In the second approach, we combine a Regge pole approach with the residual effect of nucleon resonances. The nucleon resonances are described using a dual connection between the exclusive form factors and inclusive deep inelastic structure functions. We present the results for the beam spin azimuthal asymmetries measured at JLAB in exclusive electroproduction of charged and neutral pions.Izlažemo ishode svojih računa za ekskluzivnu elektrotvorbu piona na nukleonima i jezgrama za visoke vrijednosti Q2 . Razmatramo pojavu prozirnosti (CT) za boje koju su opazili nedavno u JLabu u elektrotvorbi A(e, e′π) na jezgrama. Pokazujemo da je opis tvorbe π obvezatan za dokaz CT podatka iz JLaba. Zatim razvijamo model za ekskluzivnu tvorbu π na nukleonima u JLabu i HERMESu. Prvo opisujemo model zasnovan na spoju ekskluzivno-inkluzivno. U drugom pristupu spajamo metodu Reggeovih polova s učinkom dalekih nukleonskih rezonancija. Nukleonske rezonancije opisujemo rabeći dvojni spoj ekskluzivnih faktora oblika i strukturnih funkcija duboko neelastičnih inkluzivnih procesa. Opisujemo i ishode mjerenja azimutalnih asimetrija spina snopa iz JLaba u ekskluzivnoj elektrotvorbi nabijenih i neutralnih piona

Primakoff production of π0\pi^0, η\eta and η′\eta' in the Coulomb field of a nucleus

Photoproduction of neutral pseudoscalar mesons $\pi^0,\eta(547)$ and $\eta'(958)$ in the Coulomb field of an atomic nucleus is studied using a model which describes the Primakoff and nuclear parts of the production amplitude. At high energies the nuclear background is dominated by the exchange of $C$-parity odd Regge trajectories. In the coherent production the isospin filtering makes the $\omega(782)$ a dominant trajectory. The calculations are in agreement with $\pi^0$ data from JLAB provided the photon shadowing and final state interactions of mesons are taken into account. The kinematic conditions which allow to study the Primakoff effect in $\eta$ and $\eta'$ photoproduction off nuclei are further discussed. We also give predictions for the higher energies available at the JLAB upgrade.Comment: 15 pages, 14 figures, discussion added, final version to be published in Phys. Rev.

Beam spin asymmetry in deeply virtual π\pi production

An interpretation of the beam spin azimuthal asymmetries measured at JLAB in deep exclusive electroproduction of charged and neutral pions is presented. The model combines a Regge pole approach with the effect of nucleon resonances. The $s$- and $u$-channel contributions are described using a dual Bloom-Gilman connection between the exclusive form factors and inclusive deep inelastic structure functions. The results are in agreement with data provided the excitations of nucleon resonances are taken into account.Comment: 5 pages, 3 figures. Talk at the 19th International Spin Physics Symposium (SPIN2010), Sept.27-Oct.2, 2010, Juelich, German