Backward electroproduction of π+ mesons in the second and third nucleon resonance region

The reactionep→enπ ⁺ has been studied in the invariant mass range of 1.44≦W≦1.83 GeV. The outgoing pion was detected in the backward direction (cosλ _π ^* ≦-0.94) with respect to the virtual photon at four-momentum transfers of 0.4≦q ²≦0.7 (GeV/c)². The values of the helicity-1/2-partial wave amplitudesA _2?(D ₁₃(1520)) andA _3?(F ₁₅(1688)) were determined by a phenomenological analysis and compared with single quark transition models (S.Q.T.M.).     

Measurement of the cross-section asymmetry of deuteron photodisintegration process by linearly polarized photons in the energy range E γ = 0.8–1.6 GeV

The first measurements of the cross-section asymmetry for the deuteron photodisintegration process at a cm angle of 90° up to 1.6 GeV were performed at Yerevan Electron Synchrotron. These results are in reasonable agreement with previous measurements at lower energy. Our data show agreement with the asymptotic meson exchange model predictions in the energy range 0.8-1.6 GeV. Received: 3 April 2000 / Accepted: 25 May 2000     

φ-meson photoproduction off the protons by using linearly polarized photons in the mid- to higher-t regimes at threshold energies

Observables from vector meson photoproduction by linearly-polarized photons can be expressed in term of bllinear combinations of helicity amplitudes parameterized by the Spin Density Matrix Elements (SDMEs). These SDMEs give straightforward relations for understanding the nature of the parity exchange at threshold energies, as well as for extracting signatures of the Okubo-Zweig-Iizuka violation. This paper will show preliminary measurements of SDMEs for (γ)p→φp in the photon energy range of 1.7 to 1.9 GeV (momentum transfer squared t range of -1.2 to -0.25 GeV~2) and 1.9 to 2.1 GeV (t range of -1.4 to -0.25 GeV~2) from the g8b experimental data collected in the summer of 2005 in the Hall B of Jefferson Lab.     

Angular distribution of gamma quanta in the capture of polarized μ−-mesons by atomic nuclei

The capture of a polarized ^–-meson from theK-orbit of a mesic atom is investigated for the case when the nucleus after ^–-capture is in an excited state and emits a -quantum of multipolarityL (any type). The angular distribution of circular polarized -quanta with respect to the direction of the polarization of the ^–-meson on theK-orbit is obtained for the case of allowed transitions (according to the Morita-Fujii classification).

---

- ^–-

^–- K- ^–- - L ( ). - ^–- K- ( -).

     

$\phi$-Meson Photoproduction off the protons by using linearly polarized photons in the mid- to higher-$t$ regimes at threshold energies

Observables from vector meson photoproduction by linearly-polarized photons can be expressed in term of bilinear combinations of helicity amplitudes parameterized by the Spin Density Matrix Elements （SDMEs）. These SDMEs give straightforward relations for understanding the nature of the parity exchange at threshold energies, as well as for extracting signatures of the Okubo-Zweig-Iizuka violation. This paper will show preliminary measurements of SDMEs for γp →φp in the photon energy range of 1.7 to 1.9 GeV （momentum transfer squared t range of -1.2 to -0.25 GeV2） and 1.9 to 2.1 CeV （t range of -1.4 to -0.25 GeV2） from the g8b experimental data collected in the summer of 2005 in the Hall B of Jefferson Lab.     

The first π*←π transition of the benzene single crystal in polarized light

The first π*←π transition in the benzene single crystal is investigated at 82 K. Intensities and polarization ratios for both true and false origins in crystal planes (100) and (010) have been measured and rationalized in terms of crystal field perturbation. At liquid nitrogen temperature the origin of the transition is located at 37865 cm^-1 (b), 37817 cm^-1 (c) and 37807 cm^-1(a).     

Medium effects in the production and π0γ decay of ω-mesons in pA collisions in the GeV region

The ω resonance production and its π⁰γ decay in pA reactions close to threshold is considered within the Intranuclear Cascade (INC) model. The π⁰γ invariant-mass distribution shows two components which correspond to the ω decay “inside” and “outside” the nucleus, respectively. The “inside” component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the ω-meson and its decaying pion. The relative contribution of the “inside” component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the π⁰ and γ momenta allows to separate events related to the “inside”ω decay from different sources of background when uncorrelated π⁰'s and γ's are produced. Received: 2 April 2001 / Accepted: 5 June 2001     

Single π~0 electro-production in the resonance region with CLAS

We report the analysis status of single π~0 electroproduction in the resonance region to study the electromagnetic excitation of the nucleon resonances. The study is aimed at understanding of the internal structure and dynamics of the nucleon. The experiment was performed using an unpolarized cryogenic hydrogen target and 2.0 and 5.8 GeV polarized electron beam during the e1e and e1-6 run periods with CLAS at Jefferson Lab. The new measurements will produce a data base with high statistics and large kinematic coverage for the hadronic invariant mass (W) up to 2.0 GeV in the momentum transfer (Q~2) range of 0.3-6.0 GeV~2. Preliminary results will be presented and compared with the various model calculations.     

Single π0electro-production in the resonance region with CLAS＊

We report the analysis status of single π0electroproduction in the resonance region to study the electromagnetic excitation of the nucleon resonances. The study is aimed at understanding of the internal structure and dynamics of the nucleon. The experiment was performed using an unpolarized cryogenic hydrogen target and 2.0 and 5.8 GeV polarized electron beam during the ele and e1-6 run periods with CLAS at Jefferson Lab. The new measurements will produce a data base with high statistics and large kinematic coverage for the hadronic invariant mass （W） up to 2.0 CeV in the momentum transfer （Q2） range of 0.3--6.0 GeV2. Preliminary results will be presented and compared with the various model calculations.     

Asymmetry measurement of the polarized Σ+p elastic scattering and the hyperon-nucleon spin-orbit interaction

In order to study the hyperon-nucleon spin-orbit interaction, asymmetries of the polarized Σ⁺ elastic scattering on protons have been measured. The polarized hyperons were produced through the p(π⁺, K⁺) Σ⁺ reaction in a liquid-scintillator active target, and tracks of Σ⁺p scattering events were recorded with a newly developed track detector named SCITIC (scintillating track image camera). Although analyses of 10 times more data with more sophisticated data-taking systems and more elaborated analyzing tools are under way, data from an early stage of this experiment indicate a large Σ⁺p spin-orbit interaction in contrast to the case of the small ΛN spin-orbit interaction. Received: 27 May 2002 / Accepted: 23 July 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: nakai@post.kek.jp Communicated by Th. Walcher     

Fluorescence spectra of uranium induced by a linearly polarized laser light in a magnetic field

In this paper we reported the fluorescence spectra of U~(238) induced by a linearly polarized laser field in a magnetic field and offered a theoretical analysis. The consistence between the theoretical prediction and experimental results was satisfactory.     

Radiative capture of π−-mesons by light nuclei in a current algebra model

The probabilities of capture of ^–-mesons by nuclei³He,⁶Li,⁶C, and¹⁴N from 1s- and 2p-shells of mesic atoms are calculated by a hard-pion current algebra.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 45–50, November, 1986.     

Cross-section asymmetry for the reactions γd →pn, γd → π0 d by linearly polarized photons in the energy rangeE γ = 0·4 – 0·8 GeV

The beam asymmetryB has been measured for the reactiond pn in the energy rangeE = 0·4 ÷ 0·8 GeV and angles _p ^cm = 45 ÷ 95° and ford ⁰d at energiesE =0·5, 0·6, 0·7 GeV and angle ^cm = 130°. The results obtained are compared to existing theoretical predictions which take into account the possible contribution of dibaryon resonances.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Photoproduction of pion-nucleon pairs on nuclei in the Δ(1232)-resonance region

Data from three experiments performed at the linear accelerator in Saclay, the Tomsk synchrotron, and the MAMI accelerator in Mainz and devoted to studying single pion photoproduction on light nuclei that is accompanied by nucleon emission are analyzed. The behavior of respective experimental cross sections, which is inexplicable in the impulse approximation, is interpreted within a model where the formation of an intermediate quasibound isobar-nucleus state is followed by its decay to a final state involving a pion and a nucleon.     

Phase-shift analysis of π+ p-scattering in the energy region from 194 to 600 MeV

An energy-independent phase-shift analysis ofπ ⁺ p-scattering has been carried out at 16 energies in the region 194–600 MeV. The new data on elastic polarization, obtained in LNPI up to 1983, were included.     

Possible generation of π-condensation in a free space by collisions between photons and protons

A sharply peaked structure is found in the angular distribution of emitted π~+ mesons from photon–proton collisions.This offers a possible way to generate a π~+-condensation in free space. To make the stimulated emission of π~+-mesons efficient, a ring resonator is designed.     

On applicability of the Glauber model for pion elastic scattering by helium in the δ33 resonance region

Elastic scattering of pions by³He and⁴He in the region of the first pion-nucleon resonance is calculated within the Glauber theory. The spin-flip and charge-exchange effects are fully taken into account. Calculated results are compared with experiment and with predictions obtained using the optical model. Some conclusions are drawn concerning the validity of approximations used in deriving the two models. The calculations make clearer some of the limitations of using the Glauber model for very low energies.On leave fromInstitute of Nuclear Physics, e — Prague, Czechoslovakia.     

Production of a0 +-mesons in the reaction pp↦da0 +

We investigate the reaction pp↦da ₀ ⁺ at COSY and SIS energies together with accompanying background reactions and inclusive particle yields. The a ₀ ⁺ is considered as a usual u quark model state with two decay channels a ₀ ⁺↦K ⁺ and a ₀ ⁺↦π⁺η. Calculated cross-sections for a ₀ ⁺ production as well as for the corresponding non-resonant channels pp↦dK ⁺ and pp↦dπ⁺η are compared. Especially, in case of the final channel dπ⁺η, high statistics measurements are necessary to extract the a ₀ ⁺ signal from the high non-resonant background. Received: 20 December 2000 / Accepted: 7 May 2001     

Modulational instability of ultra-intense linearly polarized laser pulse in electron–positron plasmas

Based on the wave equation of ultra-intense linearly polarized laser pulse propagating in electron–positron plasmas, the modulational instability is investigated. The nonlinear dispersion relation and the growth rate of instability are derived. The effects of plasmas number density, temperature, and laser intensity on the growth rate are analyzed. Results show that in an electron–positron plasma with certain background density, the intensity of the modulation instability is mainly determined by the competition between the nonlinearity in the interaction and the relativistic light ponderomotive driven density responses.     

Cross sections and asymmetries for elastic π3He scattering in the energy region around the Δ resonance

For a polarized target, π³He interaction is studied in the fixed-center approximation with all rescatterings included. Only the P ₃₃ wave is taken for the πN interaction. The nuclear wave function is taken either as a sum of Gaussian functions or as a Faddeev wave function in the s-wave approximation. The differential cross sections and asymmetries for elastic π⁺³He scattering at the laboratory energies of T _π, 180, and 256 MeV are calculated. The results are compared with experimental data.