Bs−B¯smixing constraints on FCNC and a nonuniversalZ′

Abstract

${B}_{s}\ensuremath{-}{\overline{B}}_{s}$ mixing has been measured recently by D0 and CDF. The range predicted in the standard model is consistent with data. However, the standard model central values for $\ensuremath{\Delta}{M}_{{B}_{s}}$ and also $\ensuremath{\Delta}{M}_{{B}_{d}}$ are away from the data which may be indications of new physics. Using the observed values of $\ensuremath{\Delta}{M}_{{B}_{s}}$ and $\ensuremath{\Delta}{M}_{{B}_{d}}$ we study general constraints on flavor changing ${Z}^{\ensuremath{'}}$ interactions. In models with nonuniversal ${Z}^{\ensuremath{'}}$ couplings we find that significant enhancements over the standard model are still possible in the rare decay modes $B\ensuremath{\rightarrow}{X}_{s}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$, $B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ and ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$. Tree-level ${Z}^{\ensuremath{'}}$ contributions to $K\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ are now constrained to be very small, but one-loop effects can still enhance the standard model rate by a factor of 2.