Measurement of Transparency Ratios for Protons from Short-Range Correlated Pairs

Nuclear transparency, Tp(A), is a measure of the average probability for a struck proton to escape the nucleus without significant re-interaction. Previously, nuclear transparencies were extracted for quasi-elastic A(e,e′p) knockout of protons with momentum below the Fermi momentum, where the spectral functions are well known. In this Letter we extract a novel observable, the transparency ratio, Tp(A)/Tp(12C), for knockout of high-missing-momentum protons from the breakup of short-range correlated pairs (2N-SRC) in Al, Fe and Pb nuclei relative to C. The ratios were measured at momentum transfer Q2 ⩾1.5(GeV/c)2 and xB⩾1.2 where the reaction is expected to be dominated by electron scattering from 2N-SRC. The transparency ratios of the knocked-out protons coming from 2N-SRC breakup are 20–30% lower than those of previous results for low missing momentum. They agree with Glauber calculations and agree with renormalization of the previously published transparencies as proposed by recent theoretical investigations. The new transparencies scale as A−1/3, which is consistent with dominance of scattering from nucleons at the nuclear surface

Luminescence and radiation defects in irradiated ruby

The excitations of luminescence in irradiated and non-irradiated ruby crystals are investigated by means of highly polarized synchrotron radiation. In the VUV luminescence spectra the existence of quick and slow emission was observed in irradiated and nonirradiated crystals. The luminescence bands with maximum at 3.8 eV are produced by F+ centers. A new type of quick luminescence was established for the band at 4.6 eV. It is called cross-luminescence and is connected with the recombination of valence band electrons with holes in low-lying core levels. It is shown that the band at 3.0 eV is not due to anionic centers (F-centers), but is determined by a short lifetime emission center

Comparative modeling of infrared fiber lasers

The modeling and design of fiber lasers facilitate the process of their practical realization. Of particular interest during the last few years is the development of lanthanide ion-doped fiber lasers that operate at wavelengths exceeding 2000 nm. There are two main host glass materials considered for this purpose, namely fluoride and chalcogenide glasses. Therefore, this study concerned comparative modeling of fiber lasers operating within the infrared wavelength region beyond 2000 nm. In particular, the convergence properties of selected algorithms, implemented within various software environments, were studied with a specific focus on the central processing unit (CPU) time and calculation residual. Two representative fiber laser cavities were considered: One was based on a chalcogenide-selenide glass step-index fiber doped with trivalent dysprosium ions, whereas the other was a fluoride step-index fiber doped with trivalent erbium ions. The practical calculation accuracy was also assessed by comparing directly the results obtained from the different models

Transverse Polarization of Σ+ (1189) in Photoproduction on a Hydrogen Target in CLAS

Experimental results on the Σ+(1189) hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson Laboratory are presented. The Σ+(1189) was reconstructed in the exclusive reaction γ+p→K0S+Σ+(1189) via the Σ+→pπ0 decay mode. The K0S was reconstructed in the invariant mass of two oppositely charged pions with the π0 identified in the missing mass of the detected pπ+π− final state. Experimental data were collected in the photon energy range Eγ=1.0 –3.5 GeV (√s range 1.66–2.73 GeV). We observe a large negative polarization of up to 95% . As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances

Comparison of Forward and Backward \u3ci\u3epp\u3c/i\u3e Pair Knockout in \u3csup\u3e3\u3c/sup\u3eHe(e,e\u27pp)n

Measuring nucleon-nucleon short range correlations (SRCs) has been a goal of the nuclear physics community for many years. They are an important part of the nuclear wave function, accounting for almost all of the high-momentum strength. They are closely related to the EMC effect. While their overall probability has been measured, measuring their momentum distributions is more difficult. In order to determine the best configuration for studying SRC momentum distributions, we measured the 3He(e,e\u27pp)n reaction, looking at events with high-momentum protons (pp \u3e 0.35 GeV/c) and a low-momentum neutron (pn \u3c 0.2 GeV/c). We examined two angular configurations: either both protons emitted forward or one proton emitted forward and one backward (with respect to the momentum transfer, q). The measured relative momentum distribution of the events with one forward and one backward proton was much closer to the calculated initial-state pp relative momentum distribution, indicating that this is the preferred configuration for measuring SRC. ©2012 American Physical Societ

Precise Measurements of Beam Spin Asymmetries in Semi-inclusive π\u3csup\u3e0\u3c/sup\u3e Production

We present studies of single-spin asymmetries for neutral pion electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV polarized electrons from an unpolarized hydrogen target, using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. A substantial sin phi(h) amplitude has been measured in the distribution of the cross section asymmetry as a function of the azimuthal angle φh of the produced neutral pion. The dependence of this amplitude on Bjorken x and on the pion transverse momentum is extracted with significantly higher precision than previous data and is compared to model calculations. (C) 2011 Elsevier B.V

Polarization transfer in wide-angle Compton scattering and single-pion photoproduction from the proton

Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7 GeV at a proton scattering angle of θpcm=70°. The longitudinal transfer KLL, measured to be 0.645±0.059±0.048, where the first error is statistical and the second is systematic, has the same sign as predicted for the reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton. However, the observed value is ∼3 times larger than predicted by the generalized-parton-distribution-based calculations, which indicates a significant unknown contribution to the scattering amplitude

Measurement of the Neutron F2 Structure Function Via Spectator Tagging with CLAS

We report on the first measurement of the F2 structure function of the neutron from the semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to ≲ 100MeV/c and their angles to ≳ 100° relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The Fn2 data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 \u3c Q2 \u3c 4.52 GeV2, with uncertainties from nuclear corrections estimated to be less than a few percent. These measurements provide the first determination of the neutron to proton structure function ratio Fn2/Fp2 at ≲ 0.2 ≲ x ≲ 0.8 with little uncertainty due to nuclear effects. 2012 American Physical Society

Evidence for the Onset of Color Transparency in ρ0 Electroproduction off Nuclei

We have measured the nuclear transparency of the incoherent diffractive A( e , e ′ ρ0 ) process in 12C and 56Fe targets relative to 2H using a 5 GeV electron beam. The nuclear transparency, the ratio of the produced ρ0 ʼs on a nucleus relative to deuterium, which is sensitive to ρA interaction, was studied as function of the coherence length (lc), a lifetime of the hadronic fluctuation of the virtual photon, and the four-momentum transfer squared (Q2). While the transparency for both 12C and 56Fe showed no lc dependence, a significant Q2 dependence was measured, which is consistent with calculations that included the color transparency effects

Tensor Correlations Measured in 3He(e,e\u27 pp)n

We have measured the 3He(e,e\u27 pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum ptot. For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low ptot and rises to approximately 0.5 at large ptot. This shows the dominance of tensor over central correlations at this relative momentum