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.     

Photoproduction of Mesons off the Deuteron Quasifree and Coherent Processes

Photoproduction of mesons off the deuteron has been investigated at a tagged photon beam of the Bonn ELSA accelerator with the combined Crystal Barrel - TAPS electromagnetic calorimeter for incident photon energies up to 2.5 GeV. The mesons have been detected in coincidence with recoil protons, neutrons and deuterons. This allow the measurement of meson production reactions off the quasifree nucleons bound in the deutron, as well as the coherent production off the deuteron. The comparison of quasifree proton reactions to free proton reactions can confirm or invalidate possible nuclear effects on the extracted cross section reactions. Furthermore the isospin composition of a resonance can be estimated from the comparison of quasifree proton and neutron reactions. The quasifree photoproduction of the η＇ and π°η mesons off nucleons and the coherent photoproduction of π°η--pairs off the deuteron are discussed.     

Investigation of the anomaly in $\eta$-photoproduction off the neutron

Quasi-free photoproduction of wmesons off the neutron and off the proton has been studied using a deuterium target and bremsstrahlung photons produced by MAMI-C with incident energies up to 1.5 GeV. The wmesons were detected in coincidence with the recoil nucleons thus a fully exclusive measurement was performed. Preliminary results show a bump-like structure in the excitation function for the neutron close to W ≈ 1675 MeV which is not seen for the proton. Considering the experimental resolution and using a Breit-Wigner fit the width of this structure was approximated below 50 MeV.     

Photoproduction of ω-Mesons at ELSA and the role of azimuthal asymmetries

Measurements of ω photoproduction of the Crystal-Barrel/TAPS experiment at the ELSA accelerator of Bonn University are presented which used linearly polarized tagged photon beam from threshold to Eγ = 1700MeV. The azimuthal asymmetries ∑and ∑πindicate s-channel resonance contributions on top of the established t-channel exchange processes. These findings are further enhanced by a very first measurement of the G-asymmetry which, in addition to the polarized photon beam, also requires a longitudinally polarized proton target. An intuitive interpretation of the specific sensitivity of the azimuthal asymmetries to the reaction mechanisms involved is given.     

Photoproduction of multi-meson final states — recent results from the Crystal-Barrel/TAPS experiment at ELSA-

Multi-meson final states such as γp →pπ0π0 and γp →pπ0η have been investigated with the Crystal-Barrel/TAPS experiment at ELSA. Baryon cascades via △π and △η and also via higher mass baryon resonances are clearly observed. Based on this data and on data from other reactions a partial wave analysis has been performed from which partial decay widths of various N＊ and △＊ states into the different pπ0π0 and pπ0η decay channels have been determined, leading partly to unexpected results. In addition, polarisation observables have been investigated. The beam asymmetry X has been determined for both reactions and double polarisation data using a longitudinally polarised target and a circularly or linearly polarised photon beam has been taken. Given the angular coverage of the Crystal-Baxrel/TAPS experiment this data covers almost the full angular range and phase space. This data will provide new and important information for the partial wave analyses and bring us one step closer towards a complete experiment.     

Disintegration of the deuteron by linearly polarized photons at low energies

The cross section and the Σ-asymmetry of the reaction d(γ^→,p) were measured in the energy interval E_γ = 5–10 MeV. Cross sections dσ and dσ_⊥ were derived from the measured quantities dσ₀ and Σ-asymmetry. The results are compared with theoretical calculations available for this energy region.     

Precision measurements of strangeness photoproduction at threshold energies with the Crystal Ball at MAMI-C

The photoproduction of K＋ mesons from the nucleon provides important constraints on the nucleon excitation spectrum and at threshold energies challenges effective field theories based on chiral perturbation in the strange quark sector. Preliminary cross-section measurements for γ（P, K＋）A are presented at an unprecedented beam energy resolution. The data was collected at the MAMI-C facility in Mainz using the Crystal Ball Detector. A new method of K＋ detection was used in which the K＋ is tagged from its weak decay products in the detector crystals. This technique has application with other calorimeters at present and future hadron facilities.     

Precision measurements of strangeness photoproduction at threshold energies with the Crystal Ball at MAMI-C

The photoproduction of K~+ mesons from the nucleon provides important constraints on the nucleon excitation spectrum and at threshold energies challenges effective field theories based on chiral perturbation in the strange quark sector. Preliminary cross-section measurements for γ(p, K~+)A are presented at an unprece-dented beam energy resolution. The data was collected at the MAMI-C facility in Mainz using the Crystal Ball Detector. A new method of K~+ detection was used in which the K~+ is tagged from its weak decay products in the detector crystals. This technique has application with other calorimeters at present and future hadron facilities.     

Positive pion production from polarized protons by linearly polarized photons in the energy range 280–420 MeV

The method is described of measuring the polarization observables Σ, P and T for the reaction γp → nπ⁺ in a double polarization experiment (polarized target + polarized beam). The measured angular distribution of these observables are presented for the photon energy range 280–420 MeV at c.m. pion emission angles between 30° and 150°. The obtained experimental data are included in the energy-independent multipole analysis of the reactions γp → Nπ.     

Probing the strange quark condensate by di-electrons from φ-meson decays in heavy-ion collisions at SIS energies

QCD sum rules predict that the change of the strange quark condensate 〈ˉss〉 in hadron matter at finite baryon density causes a shift of the peak position of the di-electron spectra from φ-meson decays. Due to the expansion of hadron matter in heavy-ion collisions, the φ peak suffers a smearing governed by the interval of density in the expanding fireball, which appears as an effective broadening of the di-electron spectrum in the φ region. The emerging broadening is sensitive to the in-medium change of 〈ˉss〉. This allows to probe directly in-medium modifications of 〈ˉss〉 via di-electron spectra in heavy-ion collisions at SIS energies with HADES. Received: 22 November 2002 / Accepted: 30 January 2003 / Published online: 29 April 2003     

Changes in the intensity distribution and polarization of non-uniformly polarized beams focused by a spherically aberrated lens with annular aperture

Based on the generalized Huygens-Fresnel diffraction integral and beam coherence polarization (BCP) matrix formulation, the focusing properties of a type of non-uniformly polarized (NUP) beam through a spherical aberrated lens with annular aperture are studied. The dependence of focal shift, intensity distribution, power in the bucket (PIB) and degree of polarization on the spherical aberration coefficient, obscure ratio and polarization parameters is illustrated numerically. The focusing of NUP beams by a spherically aberrated lens with circular aperture is treated as a special case, where the inner radius of the aperture is equal to zero.     

IR Fourier Spectroscopy in Vivo of Human Skin during Its Ablation on Exposure to YAG:Er Laser Radiation and Polarization of the Light Scattered by the Integument

We consider the possibility of monitoring the process of human skin ablation on exposure to pulsed IR laser radiation with the use of the polarization and IR Fourier spectroscopy of disturbed total internal reflection. The laws of the change in the content of water and proteins in the surface layers of skin as a result of cyclic laser effect have been discovered. The interrelation between the degree of polarization of the backward scattered probe radiation with the wavelength corresponding to the maxima of absorption of an oxygenated form of hemoglobin and the index of erythema occurring due to laser action has been established.