Sea quark effects in B_K from N_f=2 clover-improved Wilson fermions

We report calculations of the parameter B_K appearing in the Delta S=2 neutral kaon mixing matrix element, whose uncertainty limits the power of unitarity triangle constraints for testing the standard model or looking for new physics. We use two flavours of dynamical clover-improved Wilson lattice fermions and look for dependence on the dynamical quark mass at fixed lattice spacing. We see some evidence for dynamical quark effects and in particular B_K decreases as the sea quark masses are reduced towards the up/down quark mass.Comment: 17 pages, 4 figures, uses JHEP3.cls, added comments and reference

An exploratory study of B(K) from N(f) = 2 clover-improved Wilson fermions

We report calculations of Bk using two flavours of dynamical clover-improved Wilson lattice fermions and look for dependence on the dynamical quark mass at fixed lattice spacing. We see some evidence for dynamical quark effects. In particular Bk decreases as the sea quark masses are reduced towards the up/down quark mass. Our meson masses are quite heavy and a firm prediction of the Bk value is a task for future simulations

Investigation of inelastic \mth{\alpha}-scattering on \chem{^{24}Mg} and \chem{^{28}Si}

Effects of three different $\alpha$-nucleus potentials, the normal Woods-Saxon (WS), the squared WS and the molecular, have been studied using the differential cross-section data of inelastically scattered $\alpha$-particles on \chem{^{24}Mg} and \chem{^{28}Si} at 54 and 26 MeV incident energies, respectively. The angular distributions of inelastic scattering to the first $2^+$ and $4^+$ states of the two nuclei have been analyzed in terms of a coupled-channel formalism. The macroscopic rotational model using both the squared WS and the molecular potentials can produce satisfactorily a simultaneous description of the elastic data and the inelastic-scattering data of the $2^+$ and $4^+$ states for both the targets. The normal WS potential fails to describe the elastic and inelastic data, simultaneously. The effects of second-order deformed potential are also investigated. Microscopic coupled-channel calculations, using the $0^+$-$2^+$ coupling and the Gaussian $\alpha$-nucleon interaction in the form-factor, have also been performed for the \chem{^{28}Si} target using both the squared WS and molecular potentials, the latter one giving a reasonable description of the data

Investigation of \mth{\alpha}-nucleus interaction in the \chem{^{27}Al(\alpha,\alpha)^{27}Al} scattering and \chem{^{27}Al(\alpha,d)^{29}Si} reaction

Full finite-range macroscopic calculations in the distorted-wave Born approximation have been performed using the molecular and Michel $\alpha$-nucleus potentials to analyze the angular distributions of cross-sections of the $^{27}$Al($\alpha,d$)$^{29}$Si reaction, at 26.5 and 27.2 MeV incident energies, leading to seven transitions up to the excitation energy $E_{\rm X} = 4.08$ MeV of the final nucleus. The parameters of the two types of the $\alpha$-nucleus potentials are determined from the elastic-scattering data. Both the molecular and Michel potentials, without any adjustment to the parameters needed to fit the elastic-scattering data, are able in most cases to reproduce, simultaneously, the absolute cross-sections particularly at large angles, where the previous calculations failed to reproduce by orders of magnitude, and the gross pattern of angular distributions of the reaction. The deuteron-cluster spectroscopic factors for most of the seven transitions, deduced using the two $\alpha$-$^{27}$Al potentials, differ from those obtained in earlier works. The spectroscopic factor for the ground-state transition, deduced in the present work for the 25.8 MeV data, agrees well with the shell model prediction

Sea quark effects in B(K) from N(f)=2 clover-improved Wilson fermions

We report calculations of BK using two flavours of dynamical clover-improved Wilson lattice fermions and look for dependence on the dynamical quark mass at fixed lattice spacing. We see some evidence for dynamical quark effects. In particular BK decreases as the sea quark masses are reduced towards the up/down quark mass. Our meson masses are quite heavy and a firm prediction of BK is a task for future simulations