Recent measurements of branching fractions and $CP$ asymmetries of charmless hadronic $B$ meson decays at Belle

TL;DR

This paper presents final measurements of branching fractions and CP asymmetries in specific charmless hadronic B meson decays at Belle, providing insights into CP violation and constraints on the CKM angle phi_2, with findings challenging existing theoretical models.

Contribution

It reports new experimental measurements of B meson decay properties that improve constraints on the CKM unitarity triangle and reveal unexpected CP violation patterns.

Findings

Improved constraints on the CKM angle phi_2 from B0 → pi0 pi0 measurements.

Evidence of large CP violation in B± → K+ K− π± decays.

Observation of a significant yield increase at low K+ K− invariant mass.

Abstract

Hadronic $B$ decays without a charm quark constitute a powerful probe to search for physics beyond the standard model as well as to provide constraints on $CP$ violation parameters. We report final measurements from Belle of the branching fractions and $CP$ asymmetries for the decays $B^{0} \rightarrow \pi^{0} \pi^{0}$ and $B^{\pm} \rightarrow K^{+} K^{-} \pi^{\pm}$. The $B^{0} \rightarrow \pi^{0} \pi^{0}$ measurements enable us to improve constraints on the angle $\phi_{2}$ of the CKM unitarity triangle. For $B^{\pm} \rightarrow K^{+} K^{-} \pi^{\pm}$ we measure $CP$ asymmetry as a function of the invariant mass of the $K^{+}K^{-}$ system, where we find a strong evidence for large $CP$ violation and a large increase in yield at low mass region. This result challenges conventional theoretical approaches as it requires a large enhancement in both tree and loop level diagrams in the same small region of phase-space.