Induced polarization of Lambda(1116) in kaon electroproduction

We have measured. the induced polarization of the Lambda(1116) in the reaction ep - \u3e e\u27 K+ Lambda, detecting the scattered e\u27 and K+ in the final state along with the proton from the decay Lambda - \u3e p pi(-). The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy W (1.6 \u3c = W \u3c = 2.7 GeV) and covered the full range of the kaon production angle at an average momentum transfer Q(2) = 1.90 GeV2. In this experiment a 5.50-GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the W and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially Q(2) independent in our kinematic domain, suggesting that somewhere below the Q(2) covered here there must be a strong Q(2) dependence. Along with previously published photo-and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved s-channel resonances

A Spectacular VHE Gamma-Ray Outburst from PKS 2155-304 in 2006

Since 2002 the VHE (>100 GeV) gamma-ray flux of the high-frequency peaked BL Lac PKS 2155-304 has been monitored with the High Energy Stereoscopic System (HESS). An extreme gamma-ray outburst was detected in the early hours of July 28, 2006 (MJD 53944). The average flux above 200 GeV observed during this outburst is ~7 times the flux observed from the Crab Nebula above the same threshold. Peak fluxes are measured with one-minute time scale resolution at more than twice this average value. Variability is seen up to ~600 s in the Fourier power spectrum, and well-resolved bursts varying on time scales of ~200 seconds are observed. There are no strong indications for spectral variability within the data. Assuming the emission region has a size comparable to the Schwarzschild radius of a ~10^9 solar mass black hole, Doppler factors greater than 100 are required to accommodate the observed variability time scales.Comment: 4 pages, 3 figures; To appear in the Proceedings of the 30th ICRC (Merida, Mexico

Discovery of VHE gamma-rays from RGB J0152+017

The BL Lac object RGB J0152+017 (z = 0.080) was predicted to be a very high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio fluxes. We report recent observations of this source made in late October and November 2007 with the H.E.S.S. array consisting of four imaging atmospheric Cerenkov telescopes. Contemporaneous observations were made in X-rays with the Swift and RXTE satellites, in the optical band with the ATOM telescope, and in the radio band with the Nancay Radio Telescope. As a result, RGB J0152+017 is discovered as a source of VHE gamma-rays by H.E.S.S. A signal of 173 gamma-ray photons corresponding to a statistical significance of 6.6 sigmas was found in the data. The energy spectrum of the source can be described by a powerlaw with a spectral index of = 2.95 +- 0.36stat +- 0.20syst. The integral flux above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source spectral energy distribution (SED) can be described using a two-component (extended jet and blob in jet) non-thermal synchrotron self-Compton (SSC) leptonic model, plus a thermal host galaxy component. The parameters that are found are very close to those found for TeV blazars in similar SSC studies. The location of its synchrotron peak, as derived from the SED in Swift data, allows clear classification as a high-frequency-peaked BL Lac (HBL).Comment: 6 pages, 5 figures; accepted to appear in the proceedings of the Workshop on Blazar Variability across the Electromagnetic Spectrum, 22-25 April 2008, Palaiseau, Franc

Absorption of the ω\omega and ϕ\phi Mesons in Nuclei

Due to their long lifetimes, the $\omega$ and $\phi$ mesons are the ideal candidates for the study of possible modifications of the in-medium meson-nucleon interaction through their absorption inside the nucleus. During the E01-112 experiment at the Thomas Jefferson National Accelerator Facility, the mesons were photoproduced from $^{2}$H, C, Ti, Fe, and Pb targets. This paper reports the first measurement of the ratio of nuclear transparencies for the $e^{+}e^{-}$ channel. The ratios indicate larger in-medium widths compared with what have been reported in other reaction channels.Comment: 6 pages, 4 figure

Electronic Structure of Transition Metals Fe, Ni and Cu in the GW Approximation

The quasiparticle band structures of 3d transition metals, ferromagnetic Fe, Ni and paramagnetic Cu, are calculated by the GW approximation. The width of occupied 3d valence band, which is overestimated in the LSDA, is in good agreement with experimental observation. However the exchange splitting and satellite in spectra are not reproduced and it is required to go beyond the GW approximation. The effects of static screening and dynamical correlation are discussed in detail in comparison with the results of the static COHSEX approximation. The dynamical screening effects are important for band width narrowing.Comment: 4 pages, 3 figure

A comparison of forward and backward pp pair knockout in 3He(e,e'pp)n

Measuring nucleon-nucleon Short Range Correlations (SRC) has been a goal of the nuclear physics community for many years. They are an important part of the nuclear wavefunction, 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 $^3$He$(e,e'pp)n$ reaction, looking at events with high momentum protons ($p_p > 0.35$ GeV/c) and a low momentum neutron ($p_n< 0.2$ 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, $\vec q$). 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.Comment: 8 pages, 9 figures, submitted to Phys Rev C. Version 2 incorporates minor corrections in response to referee comment