8301422
Beam-helicity asymmetries in double-pion photoproduction off the proton.
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels gamma[over -->]p-->pi(+)pi(0)n, gamma[over -->]p-->pi(0)pi(0)p, and gamma[over -->]p-->pi(+)pi(-)p. The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of pi(0) mesons were detected in a 4pi electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction dynamics.
118682194
First measurement of the circular beam asymmetry in the gamma p -->pi0 eta p reaction
The circular photon asymmetry for πη photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the ∆(1700)D33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D33 amplitude.
119923608
Helicity dependence of the total inclusive cross section on the deuteron
Abstract A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200 E γ 800 MeV . The experiment used a 4 π detection system, a circularly polarized tagged photon beam and a frozen spin target which provided longitudinally polarized deuterons. These new results are a significant improvement on the existing data and allow a detailed comparison with state-of-the-art calculations.
118792397
Search for the charge-conjugation-forbidden decay omega ->eta pi(0)
A new upper limit of 2.3x10(-4) on the branching ratio of the decay omega -<eta pi(0) has been obtained using the Crystal Ball multiphoton spectrometer at the Mainz Microtron MAMI. This decay is forbidden by charge-conjugation invariance of the strong and electromagnetic interactions. We have also obtained the upper limit of 2.3x10(-4) for the forbidden decay omega -< 3 pi(0) and the upper limit of 2.4x10(-4) for omega -< 2 pi(0).
118530051
Measurement of 3pi^0 photoproduction on the proton from threshold to 1.4 GeV
A. Starostin, ∗ I. M. Suarez, † B. M. K. Nefkens, J. Ahrens, J. R. M. Annand, H. J. Arends, K. Bantawa, P.A. Bartolome, R. Beck, V. Bekrenev, A. Braghieri, D. Branford, W. J. Briscoe, J. Brudvik, S. Cherepnya, B.T. Demisse, M. Dieterle, E. J. Downie, 3 L. V. Fil’kov, D. I. Glazier, R. Gregor, E. Heid, D. Hornidge, I. Jaegle, O. Jahn, T. C. Jude, V. L. Kashevarov, I. Keshelashvili, R. Kondratiev, M. Korolija, A. Koulbardis, S. Kruglov, B. Krusche, V. Lisin, K. Livingston, I. J. D. MacGregor, D. M. Manley, M. Martinez, J. C. McGeorge, E. F. McNicoll, D. Mekterovic, V. Metag, A. Mushkarenkov, M. Oberle, M. Ostrick, P. Pedroni, A. Polonski, S. Prakhov, J. Robinson, G. Rosner, T. Rostomyan, S. Schumann, 5 M. H. Sikora, D. Sober, I. Supek, M. Thiel, A. Thomas, M. Unverzagt, 5 D. P. Watts, D. Wertmueller, and L. Witthauer
120615302
Measurement of the helicity dependence for the gamma p -> n pi(+) channel in the second resonance region
The helicity dependence of the γp→nπ + reaction has been measured for the first time in the photon energy range from 450 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. Although these polarized data are mainly sensitive to mechanisms involving the D 13 (1520) resonance, a cusp structure at the η production threshold can be clearly observed. These data are significantly different from the predictions of the existing multipole analyses and are used to determine the helicity amplitudes of the D 13 (1520) and S 11 (1535) resonances with improved accuracy.
17022554
Symmetries of discontinuous flows and the dual Rankine–Hugoniot conditions in fluid dynamics
Abstract It has recently been shown that the maximal kinematical invariance group of polytropic fluids, for smooth subsonic flows, is the semidirect product of SL  (2,  R ) and the static Galilei group G . This result purports to offer a theoretical explanation for an intriguing similarity, that was recently observed, between a supernova explosion and a plasma implosion. In this paper we extend this result to discuss the symmetries of discontinuous flows, which further validates the explanation by taking into account shock waves, which are the driving force behind both the explosion and implosion. This is accomplished by constructing a new set of Rankine–Hugoniot conditions, which follow from Noether’s conservation laws. The new set is dual to the standard Rankine–Hugoniot conditions and is related to them through the SL  (2,  R ) transformations. The entropy condition, that the shock needs to satisfy for physical reasons, is also seen to remain invariant under the transformations.
15784128
Vortex free energies in SO(3) and SU(2) lattice gauge theory
Abstract Lattice gauge theories with gauge groups SO(3) and SU(2) are compared. The free energy of electric twist, an order parameter for the confinement- deconfinement transition which does not rely on centre-symmetry breaking, is measured in both theories. The results are used to calibrate the scale in SO(3).
16812415
More evidence of localization in the low-lying Dirac spectrum
We have extended our computation of the inverse participation ratio of low-lying (asqtad) Dirac eigenvectors in quenched SU(3). The scaling dimension of the confining manifold is clearer and very near 3. We have also computed the 2-point correlator which further characterizes the localization.
11272883
Instantons and monopoles in general Abelian gauges
A relation between the total instanton number and the quantum numbers of magnetic monopoles that arise in general Abelian gauges in SU (2) Yang-Mills theory is established. The instanton number is expressed as the sum of the `twists' of all monopoles, where the twist is related to a generalized Hopf invariant. The origin of a stronger relation between instantons and monopoles in the Polyakov gauge is discussed.
8580765
Comparison of SO(3) and SU(2) Lattice Gauge Theory
Abstract The Villain form of SO (3) lattice gauge theory is studied and compared to Wilson's SU (2) theory. The topological invariants in SO (3) which correspond to twisted boundary conditions in SU (2) are discussed and lattice observables are introduced for them. An apparent SO (3) phase with negative adjoint Polyakov loop is explained in terms of these observables. The electric twist free energy, an order parameter for the confinement–deconfinement transition, is measured in both theories to calibrate the temperature. The results indicate that lattices with about 700 4 sites or larger will be needed to study the SO (3) confined phase. Alternative actions are discussed and an analytic path connecting SO (3) and SU (2) lattice gauge theory at weak coupling is exhibited. The relevance for confinement of the centre of the gauge group is discussed.