Semileptonic B decay as a test of CKM unitarity

Abstract

I point out that $B\to X_q{ł}^{+}{ł}^{-}$ decays $(q=s,d)$ are sensitive probes of possible violation of CKM unitarity. I compute the decay rates and asymmetries in a minimal extension of the Standard Model containing an additional isosinglet charge (-1/3) quark, which leads to a deviation from CKM unitarity. It is shown that even for small mixing ratios $|z_{qb}/(V_{tq}^{\ast }{V}_{tb})|\sim O({10}^{-2})$, the contribution of the tree-level $Z-$FCNC appearing in the model should change the rates and asymmetries significantly. Especially the CP asymmetry, $A_{CP}(B\to X_s{ł}^{+}{ł}^{-})$, can be enhanced to be few percents, while in the standard model the size is less than $O({10}^{-3})$. On the other hand, $A_{CP}(B\to X_d{ł}^{+}{ł}^{-})$ is not altered so much. Constraints for the mixing ratios are extracted from the experiments of $B\to X_s\gamma$ for $q=s$ and $B_d^0-{\bar{B}}_d^0$ mixing for $q=d$ under a natural assumption that the couplings of the tree-level $Zf\bar{f}$ are almost unity, i.e. $z_{\alpha \alpha }\sim 1$.

11 pages, Latex with eepic.sty and epic.sty, revised for publication

Cited by in corpus (6)

• Direct CP Violation in B -> X_s gamma Decays as a Signature of New Physics
• A Systematic Analysis of the Lepton Polarization Asymmetries in the Rare B Decay, B -> X_sτ^+τ^-
• Lepton Polarization and Forward-Backward Asymmetries in b -> s tau+ tau-
• Constraints on the Mass and Mixing of the 4th Generation Quark From Direct CP Violation${\epsilon }^{\prime }/\epsilon$ and Rare K Decays
• Direct CP Asymmetry of B -> X_d,s γin a model with Vector quarks
• CP Asymmetry of $B\to X_s{l}^{+}{l}^{-}$ in Low Invariant Mass Region