The effects of a family non-universal Z-prime boson on B--->pipi decays

TL;DR

This paper explores how a family non-universal Z' boson could explain discrepancies in B meson decay rates, particularly addressing the large $ar{B}^{0} o ext{pi}^0 ext{pi}^0$ branching ratio, by fitting new physics parameters to observed data.

Contribution

It introduces a specific Z' model with particular coupling parameters that can simultaneously explain the $ ext{pi} ext{pi}$ and $ ext{pi} ext{K}$ decay puzzles, refining the parameter space.

Findings

A Z' coupling parameter $oxed{ ext{zeta}_d^{LR} ext{~0.05}}$ with a phase $oxed{-50^ ext{o}}$ can reconcile decay discrepancies.

The Z' model's parameter space is constrained but still viable after fitting to multiple decay channels.

The model can accommodate both $ ext{pi} ext{pi}$ and $ ext{pi} ext{K}$ puzzles simultaneously.

Abstract

Motivated by the measured large branching ratio of $\bar{B}^{0}\to\pi^0\pi^0$ (the so-called "$\pi\pi$" puzzle), we investigate the effects of a family non-universal $Z^{\prime}$ model on the tree-dominated $B\to\pi\pi$ decays. We find that the $Z^{\prime}$ coupling parameter $\zeta_{d}^{LR}\sim0.05$ with a nontrivial new weak phase $\phi_d^L\sim-50^{\circ}$, which is relevant to the $Z^{\prime}$ contributions to the QCD penguin sector $\triangle C_5$, is needed to reconcile the observed discrepancy. Combined with the recent fitting results from $B\to\pi K$, $\pi K^{\ast}$ and $\rho K$ decays, the $Z^{\prime}$ parameter spaces are severely reduced but still not excluded entirely, implying that both the "$\pi\pi$" and "$\pi K$" puzzles could be accommodated simultaneously within such a family non-universal $Z^{\prime}$ model.