Lattice QCD Study of the Pentaquark Baryons

We study the spin $\frac12$ hadronic state in quenched lattice QCD to search for a possible $S=+1$ pentaquark resonance. Simulations are carried out on $8^3\times 24$, $10^3\times 24$, $12^3\times 24$ and $16^3\times 24$ lattices at $\beta$=5.7 at the quenched level with the standard plaquette gauge action and Wilson quark action. We adopt two independent operators with I=0 and $J^P=\frac12$ to construct a $2\times 2$ correlation matrix. After the diagonalization of the correlation matrix, we successfully obtain the energies of the ground-state and the 1st excited-state in this channel. The volume dependence of the energies suggests the existence of a possible resonance state slightly above the NK threshold in I=0 and $J^P=\frac12^-$ channel.Comment: Talk given at the International Workshop on PENTAQUARK04, SPring-8, Japan, 20-23 July 2004; 7 pages, 3 figure

Precision study of B^* B\pi coupling for the static heavy-light meson

We compute the B^*B\pi coupling \hat{g}_{\infty} for static heavy-light meson using all-to-all propagators. It is shown that low-mode averaging with 100 low-lying eigenmodes indeed improves the signal for the 2-point and 3-point functions for heavy-light meson significantly. Our study suggests that the all-to-all propagator will be a very efficient method for high precision computation of the B^*B\pi coupling especially in unquenched QCD where the number of configurations is limited.Comment: 30 pages, 25 figures, typos correcte

Constraints on a New Light Spin-One Particle from Rare b -> s Transitions

The anomalously large like-sign dimuon charge asymmetry in semileptonic b-hadron decays recently measured by the D0 Collaboration may be hinting at the presence of CP-violating new physics in the mixing of B_s mesons. It has been suggested that the effect of a nonstandard spin-1 particle lighter than the b quark with flavor-changing couplings to b and s quarks can reproduce the D0 result within its one-sigma range. Here we explore the possibility that the new particle also couples to charged leptons l=e,mu and thus contributes to rare b -> s processes involving the leptons. We consider in particular constraints on its couplings from existing experimental data on the inclusive B -> X_s l^+ l^- and exclusive B -> K^{(*)} l^+ l^- decays, as well as the anomalous magnetic moments of the leptons. We find that there is parameter space of the particle that is allowed by the current data. Future measurements of these B transitions and rare decays of the B_s meson, such as B_s -> (phi,eta,eta') l^+ l^- and B_s -> l^+ l^-, at LHCb and next-generation B factories can probe its presence or couplings more stringently.Comment: 19 pages, 5 figure