Proceedings of The XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007), 2008
We analyze the spectral properties of the quark propagator above the critical temperature for the... more We analyze the spectral properties of the quark propagator above the critical temperature for the deconfinement phase transition in quenched lattice QCD using clover improved Wilson fermions. The bare quark mass dependence of the quark spectral function is analyzed by varying the hopping parameter κ in Landau gauge. We assume a two-pole structure for the quark spectral function, which is numerically found to work quite well for any value of κ. It is shown that in the chiral limit the quark spectral function has two collective modes that correspond to the normal and plasmino excitations, while it is dominated by a single-pole structure when the bare quark mass becomes large.
The European Physical Journal A - Hadrons and Nuclei, 1998
The angular distribution of nucleons emitted in the 12 C(γ,pn) reaction has been measured using t... more The angular distribution of nucleons emitted in the 12 C(γ,pn) reaction has been measured using tagged photons at the Mainz microtron MAMI. The variation of the reaction strength with the polar angles of the two emitted nucleons is reported for Eγ = 120 − 150 MeV. The proton angular distribution peaks at more backward angles than the 2 H(γ,p) differential cross section indicating a departure from the simple quasi-deuteron model of 2N photo-emission. The distribution shape is in reasonable agreement with microscopic theoretical models which include both πand ρ-exchange.
A multi-cell He gas-scintillator active target, designed for the measurement of photoreaction cro... more A multi-cell He gas-scintillator active target, designed for the measurement of photoreaction cross sections, is described. The target has four main chambers, giving an overall thickness of 0.103 g/cm^2 at an operating pressure of 2 MPa. Scintillations are read out by photomultiplier tubes and the addition of small amounts of N_2 to the He, to shift the scintillation emission from UV to visible, is discussed. First results of measurements at the MAX IV Laboratory tagged-photon facility show that the target has good timing resolution and can cope well with a high-flux photon beam. The determination of reaction cross sections from target yields relies on a Monte Carlo simulation, which considers scintillation light transport, photodisintegration processes in ^4He, background photon interactions in target windows and interactions of the reaction-product particles in the gas and target container. The predictions of this simulation are compared to the measured target response.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
The characteristics of the Solid-state Neutron Detector, under development for neutron-scattering... more The characteristics of the Solid-state Neutron Detector, under development for neutron-scattering measurements at the European Spallation Source, have been simulated with a Geant4-based computer code. The code models the interactions of thermal neutrons and ionising radiation in the 6 Li-doped scintillating glass of the detector, the production of scintillation light and the transport of optical, scintillation photons through the the scintillator, en route to the photocathode of the attached multi-anode photomultiplier. Factors which affect the optical-photon transport, such as surface finish, pixelation of the glass sheet, provision of a front reflector and optical coupling media are compared. Predictions of the detector response are compared with measurements made with neutron and gamma-ray sources, a collimated alpha source and finely collimated beams of 2.5 MeV protons and deuterons.
The first data on target and beam-target asymmetries for the γp → π 0 ηp reaction at photon energ... more The first data on target and beam-target asymmetries for the γp → π 0 ηp reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the ∆3/2 − amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves.
The helicity dependence of the γ p → pπ 0 reaction has been measured for the first time in the ph... more The helicity dependence of the γ p → pπ 0 reaction has been measured for the first time in the photon energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its parameters.
Total photoabsorption cross sections for H1, H2, and He3 from 200 to 800 MeV
Physical Review C, 1996
The total photoabsorption cross sections for 1H, 2H, and 3He have been measured for incident phot... more The total photoabsorption cross sections for 1H, 2H, and 3He have been measured for incident photon energies ranging from 200 to 800 MeV. The 3He data are the first for this nucleus. By using the large acceptance detector DAPHNE in conjunction with the tagged photon beam facility of the MAMI accelerator in Mainz, cross sections of high precision have been
Determination of the E2/M1 ratio in the γN→Δ(1232) transition from a simultaneous measurement of p(γ→,p)π0 and p(γ→,π+)n
Physical Review C, 2000
A fast module for pulse shape analysis
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1987
ABSTRACT
Helicity dependence of the $\gamma p\rightarrow N \pi$ channels and multipole analysis in the $\Delta$ region
The European Physical Journal A, 2004
ABSTRACT
Elastic Compton Scattering from Deuterium at 40-110 MeV
maxlab.lu.se
... The Mount Allison University, Sackville, New Brunswick, Canada Contact: David Hornidge, dhorn... more ... The Mount Allison University, Sackville, New Brunswick, Canada Contact: David Hornidge, [email protected] The University of Saskatchewan, Saskatoon, Saskatchewan, Canada Contact: Rob Pywell, [email protected] ...
We report the first measurement of the double-spin asymmetry A LT for charged pion electroproduct... more We report the first measurement of the double-spin asymmetry A LT for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized 3 He target. The kinematics focused on the valence quark region, 0:16 < x < 0:35 with 1:4 < Q 2 < 2:7 GeV 2 . The corresponding neutron A LT asymmetries were extracted from the measured 3 He asymmetries and proton over 3 He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g q 1T and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for À production on 3 He and the neutron, while our þ asymmetries are consistent with zero.
New possibilities of hypernuclear studies at modern electron accelerators based on recently devel... more New possibilities of hypernuclear studies at modern electron accelerators based on recently developed radio frequency photomultiplier tubes are discussed.
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Papers by John Annand