The B → πK puzzle revisited

Abstract

Abstract 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 → πK decays (B + → π+ K 0, B + → π0 K +, B d 0 → π − K +, B d 0 → π 0 K 0). In this paper, we re-examine this B → πK 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 the data. But if it is small, |C ′ /T ′| = 0.2, the SM cannot explain the B → πK puzzle —new physics (NP) is needed. The two types of NP that can contribute to B → πK at tree level are Z ′ bosons and diquarks. Z ′ models can explain the puzzle if the Z ′ couples to right-handed uū and/or dd¯ $$ d\overline{d} $$, with g R dd ≠ g R uu . Interestingly, half of the many Z ′ models proposed to explain the present anomalies in b → sμ + μ − decays have the required Z ′ couplings to uū and/or dd¯ $$ d\overline{d} $$. Such models could potentially explain both the b → sμ + μ − anomalies and the B → πK puzzle. The addition of a color sextet diquark that couples to ud can also explain the puzzle.

Keywords

• Beyond Standard Model
• Heavy Quark Physics
• CP violation