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).

title: Measurement of 3pi^0 photoproduction on the proton from threshold to 1.4 GeV
abstract: 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

title: STATUS OF THE GDH EXPERIMENT ON THE DEUTERON AT MAMI

title: Quasi-free Compton scattering and the polarizabilities of the neutron
abstract: Differential cross-sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been measured using the Glasgow/Mainz photon tagging spectrometer at the Mainz MAMI accelerator together with the Mainz [48]cm ;SPMOslash; × [64]cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. The data cover photon energies ranging from [200]MeV to [400]MeV at θLABγ = 136.2°. Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron detection efficiency of the SENECA detector was measured via the reaction p(γ,π+n). The “free” proton Compton scattering cross-sections extracted from the bound proton data are in reasonable agreement with those for the free proton which gives confidence in the method to extract the differential cross-section for free scattering from quasi-free data. Differential cross-sections on the free neutron have been extracted and the difference of the electromagnetic polarizabilities of the neutron has been determined to be αn - βn = 9.8±3.6(stat)+2.1-1.1(syst)±2.2(model) in units of [10-4]fm3. In combination with the polarizability sum αn + βn = 15.2±0.5 deduced from photoabsorption data, the neutron electric and magnetic polarizabilities, αn = 12.5±1.8(stat)+1.1-0.6(syst)±1.1(model) and βn = 2.7±1.8(stat)+0.6-1.1(syst)±1.1(model) are obtained. The backward spin polarizability of the neutron was determined to be γ(n)π = (58.6±4.0)×10-4fm4.

title: Compton scattering from the free and bound proton above π-threshold
abstract: The differential cross sections for Compton scattering from the proton have been measured at MAMI with three different detector setups. There is a good agreement among all the results. The theoretical calculation based on dispersion relations shows that there is no drastic change necessary in the parameters of this approach.

title: Helicity dependence of the gamma p -> N pi channels and multipole analysis in the Delta region
abstract: A high-quality double-polarization data set for the helicity dependence of the total and differential cross-sections for both gammap --> Npi channels in the Delta region has been obtained in the framework of the GDH experiment. The experiment, performed at the Mainz microtron MAMI, used a 4pi detection system, a circularly polarized photon beam, and a longitudinally polarized frozen-spin target. These data are included in the database to perform a multipole analysis to determine the properties of the Delta(1232)-resonance. For the resonant Delta(1232) multipoles we find a very good agreement with previous analyses, while the nonresonant ones show significant deviations.

title: The Quark Structure of Pentaquarks
abstract: Motivated by the possible observation of the $\Theta^+(1530)$, we study the quark structure of pentaquark states in quenched lattice QCD. The complete set of 19 local sources that have the proper symmetry for positive or negative parity isoscalar pentaquarks is constructed, as well as a nonlocal source composed of two displaced ``good'' diquarks. Quantitative structure information is determined from diagonalizing the 19-dimensional correlation matrix and from calculating the overlaps of sources with the lattice eigenstates. The volume dependence of the overlap is studied to differentiate between scattering and localized resonant states. The positive parity state has a small component of two ``good'' diquarks, and its energy is too much higher than the negative parity state to be a candidate for the $\Theta^+(1530)$.

title: The maximal invariance group of Newton’s equations for a free point particle
abstract: The maximal invariance group of Newton’s equations for a free nonrelativistic point particle is shown to be larger than the Galilei group. It is a semidirect product of the static (nine-parameter) Galilei group and an SL(2,R) group containing time translations, dilations, and a one-parameter group of time-dependent scalings called expansions. This group was first discovered by Niederer in the context of the free Schrodinger equation. We also provide a road map from the free nonrelativistic point particle to the equations of fluid mechanics to which the symmetry carries over. The hitherto unnoticed SL(2,R) part of the symmetry group for fluid mechanics gives a theoretical explanation for an observed similarity between numerical simulations of supernova explosions and numerical simulations of experiments involving laser-induced implosions in inertial confinement plasmas. We also give examples of interacting many-body systems of point particles which have this symmetry group.

title: Monte Carlo Overrelaxation for SU(N) Gauge Theories
abstract: The standard approach to Monte Carlo simulations of SU(N) Yang-Mills theories updates successive SU(2) subgroups of each SU(N) link. We follow up on an old proposal of Creutz, to perform overrelaxation in the full SU(N) group instead, and show that it is more efficient.

title: The ground state of three quarks
abstract: We measure the static three-quark potential in SU(3) lattice gauge theory with improved accuracy, by using all available technical refinements, including Luscher-Weisz exponential variance reduction. Together with insight gained from 3-state Potts model simulations, our results allow us to sort out the merits of the Delta- and Y-ansaetze.

title: 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).