Spectator Scattering and Annihilation Contributions as a Solution to the ${\pi}K$ and ${\pi}{\pi}$ Puzzles within QCD Factorization Approach

TL;DR

This paper investigates how spectator scattering and annihilation contributions within QCD factorization can resolve the ${ m f extpi}K$ and ${ m f extpi} extpi$ puzzles by fitting relevant parameters to experimental data and achieving good agreement.

Contribution

It introduces a global fit of spectator scattering and annihilation parameters within QCD factorization to address the ${ m f extpi}K$ and ${ m f extpi} extpi$ puzzles, confirming the importance of these contributions.

Findings

Fitted parameters successfully resolve ${ m f extpi}K$ and ${ m f extpi} extpi$ puzzles.

Results are consistent with experimental measurements.

Parameter values support the difference between $X_A^i$ and $X_A^f$.

Abstract

The large branching ratios for pure annihilation $\bar{B}_s^0$ $\to$ $\pi^+ \pi^-$ and $\bar{B}_d^0$ $\to$ $K^+ K^-$ decays reported by CDF and LHCb collaborations recently and the so-called ${\pi}K$ and ${\pi}{\pi}$ puzzles indicate that spectator scattering and annihilation contributions are important to the penguin-dominated, color-suppressed tree dominated, and pure annihilation nonleptonic $B$ decays. Combining the available experimental data for $B_{u,d}$ ${\to}$ $\pi \pi$, ${\pi}K$ and $K \bar{K}$ decays, we do a global fit on the spectator scattering and annihilation parameters $X_H({\rho}_H$, ${\phi}_H)$, $X_A^i({\rho}_A^{i},{\phi}_A^{i})$ and $X_A^f({\rho}_A^{f},{\phi}_A^{f})$, which are used to parameterize the endpoint singularity in amplitudes of spectator scattering, nonfactorizable and factorizable annihilation topologies within the QCD factorization framework, in three scenarios for different purpose. Numerically, in scenario II, we get $({\rho}_A^{i},{\phi}_A^{i}[^{\circ}])=(2.88^{+1.52}_{-1.30},-103^{+33}_{-40})$ and $({\rho}_A^{f},{\phi}_A^{f}[^{\circ}])=(1.21^{+0.22}_{-0.25},-40^{+12}_{-8})$ at the $68\%$ confidence level, which are mainly demanded by resolving ${\pi}K$ puzzle and confirm the presupposition that $X_A^i\neq X_A^f$. In addition, correspondingly, the $B$-meson wave function parameter $\lambda_B$ is also fitted to be $0.18^{+0.11}_{-0.08}\, MeV$, which plays an important role for resolving both ${\pi}K$ and $\pi\pi$ puzzles. With the fitted parameters, the QCDF results for observables of $B_{u,d}$ $\to$ $\pi \pi$, $\pi K$ and $K \bar{K}$ decays are in good agreement with experimental measurements. Much more experimental and theoretical efforts are expected to understand the underlying QCD dynamics of spectator scattering and annihilation contributions.