Is There Still a B -> pi K Puzzle?

Measurements of the combined branching ratios for $B^\pm \to \pi^\pm K$ and $B_d \to \pi^\mp K^\pm$ allow interesting constraints on the CKM angle $\gamma$, the ratio $r \equiv |T'|/|P'|$ of the current-current and penguin operator contributions to $B_d \to \pi^\mp K^\pm$, and the CP asymmetry in that decay. Present CLEO results for these branching ratios indicate where problems with consistency of the Standard Model may arise in the future. In this paper we discuss scenarios...

The recent observation of B_d -> pi^0 pi^0 at the B factories with a surprisingly large branching ratio represents a challenge for theory, and complements the amazingly small B_d -> pi^+ pi^- rate. We point out that all puzzling B -> pi pi features can be accommodated in the Standard Model (SM) through non-factorizable hadronic interference effects, extract the relevant parameters, and predict the CP asymmetries of B_d -> pi^0 pi^0. Using then SU(3) flavour-symmetry and plaus...

The discrepancies found in the B->pi K decays between theory and experiment suggest the presence of new physics in the electroweak penguin sector of the theory. We show that this hypothesis can be tested more efficiently including in the analysis the non-leptonic decays B_s->phi pi, B_s->phi rho.

Exploring correlations between the CP asymmetries of $B^0_d\to\pi^0K_{\rm S}$ following from an isospin relation, we uncover new tensions with the Standard Model in data for neutral $B\to\pi K$ decays. Should this intriguing picture originate from New Physics, a modified electroweak penguin sector provides a key scenario. It includes models with extra $Z'$ bosons, which offer attractive ways to resolve anomalies in $B\to K^{(*)}\ell^+\ell^-$ measurements. We present a new str...

Recent experiments suggest that certain B -> pi K branching ratios are inconsistent with the standard model expectations. We show that a flavor-changing Z' provides a solution to the problem. Electroweak penguin amplitudes are enhanced by the Z' boson for select parameters. We discuss implications for the Z' mass and its couplings to the standard model fermions. We also show that the solution is consistent with constraints from the CP asymmetries of the B -> phi K_S decay.

For a number of years, there has been a certain inconsistency among the measurements of the branching ratios and CP asymmetries of the four $B \to \pi K$ decays ($B^+ \to \pi^+ K^0$, $B^+ \to \pi^0 K^+$, $B^0 \to \pi^- K^+$, $B^0 \to \pi^0 K^0$). In this paper, we re-examine this $B \to \pi K$ puzzle. We find that the key unknown parameter is $|C'/T'|$, the ratio of color-suppressed and color-allowed tree amplitudes. If this ratio is large, $|C'/T'| = 0.5$, the SM can explain...

Motivated by the recent experimental data, we have revisited the $B\to \pi K,\pi \pi$ decays in the framework of QCD factorization, with inclusion of the important strong penguin corrections of order $\alpha_s^2$ induced by $b\to D g^\ast g^\ast$ ($D=d$ or $s$ and $g^\ast$ denotes an off-shell gluon) transitions. We find that these higher order strong penguin contributions can provide $\sim 30%$ enhancement to the penguin-dominated $B\to \pi K$ decay rates, and such an enhanc...

For about twenty years, $B\to\pi K$ decays are in the focus of $B$-decay studies. We show that a correlation between the CP asymmetries of $B^0_d\to\pi^0K_{\rm S}$ reveals a tension with the Standard Model. Should it be due to New Physics, a modified electroweak penguin sector provides particularly interesting possibilities. We present a new method to determine the electroweak penguin parameters, which uses an isospin relation and requires only minimal $SU(3)$ input. We apply...

An enhanced electroweak penguin amplitude due to the presence of unknown new physics can explain the discrepancies found between theory and experiment in the B -> pi K decays, in particular in A_CP(B^- -> pi^0 K^-) - A_CP(\bar{B}^0 -> pi^+ K^-), but the current precision of the theoretical and experimental results does not allow to draw a firm conclusion. We argue that the \bar{B}_s -> phi rho^0 and \bar{B}_s -> phi pi^0 decays offer an additional tool to investigate this pos...

The Standard-Model interpretation of the ratios of charged and neutral B-> pi K rates, R_c and R_n, respectively, points towards a puzzling picture. Since these observables are affected significantly by colour-allowed electroweak (EW) penguins, this ``B -> pi K puzzle'' could be a manifestation of new physics in the EW penguin sector. Performing the analysis in the R_n-R_c plane, which is very suitable for monitoring various effects, we demonstrate that we may, in fact, move ...