Constraints on the nonuniversal Z^\prime couplings from B\to\pi K, \pi K^{\ast} and \rho K Decays

TL;DR

This paper investigates how a nonuniversal Z' model can explain CP asymmetry discrepancies in B meson decays, identifying specific new couplings and phases that address the πK puzzle and are constrained by experimental data.

Contribution

It provides a detailed analysis of nonuniversal Z' couplings in B decays, identifying key parameters and phases that resolve CP asymmetry puzzles and are constrained by decay measurements.

Findings

New couplings ξ^{LL} and ξ^{LR} with a phase ~-86° are crucial for the πK puzzle.

The couplings ξ^{LL} and ξ^{LR} are unequal and opposite in sign.

A measurement of A_{CP}(B^-→ρ^0 K^-) constrains Z' contributions to QCD penguin operators.

Abstract

Motivated by the large difference between the direct CP asymmetries $A_{CP}(B^-\to \pi^0 K^-)$ and $A_{CP}(\bar{B}^{0}\to \pi^{+} K^{-})$, we combine the up-to-date experimental information on $B\to\pi K$, $\pi K^{\ast}$ and $\rho K$ decays to pursue possible solutions with the nonuniversal $Z^{\prime}$ model. Detailed analyses of the relative impacts of different types of couplings are presented in four specific cases. Numerically, we find that the new coupling parameters, $\xi^{LL}$ and $\xi^{LR}$ with a common nontrivial new weak phase $\phi_L\sim-86^{\circ}$, which are relevant to the $Z^{\prime}$ contributions to the electroweak penguin sector $\triangle C_9$ and $\triangle C_7$, are crucial to the observed "$\pi K$ puzzle". Furthermore, they are found to be definitely unequal and opposite in sign. We also find that $A_{CP}(B^-\to \rho^0 K^-)$ can put a strong constraint on the new $Z^{\prime}$ couplings, which implies the $Z^{\prime}$ contributions to the coefficient of QCD penguins operator $O_3$ involving the parameter $\zeta^{LL}$ required.