Combined analysis of Belle and Belle II data to determine the CKM angle $ \phi_{3} $ using $B^+ \to D(K_{S}^0 h^- h^+) h^+$ decays

TL;DR

This paper reports a combined analysis of Belle and Belle II data to measure the CKM angle φ₃ using a model-independent Dalitz plot method in B⁺ decays, achieving a precise determination of φ₃ with multiple sources of uncertainty.

Contribution

First combined Belle and Belle II analysis of φ₃ using a model-independent Dalitz plot approach in B⁺ decays, improving measurement precision.

Findings

Measured φ₃ = (78.4 ± 11.4 ± 0.5 ± 1.0)°

Combined data from 711 fb⁻¹ and 128 fb⁻¹ datasets

First simultaneous Belle and Belle II analysis for this measurement

Abstract

We present a measurement of the Cabibbo-Kobayashi-Maskawa unitarity triangle angle $ \phi_{3} $ (also known as~$\gamma$) using a model-independent Dalitz plot analysis of \linebreak $B^+\to D\left(K_{S}^{0}h^{+}h^{-}\right)h^+$, where $D$ is either a $D^0$ or $\bar{D}{}^0$ meson and $h$ is either a $\pi$ or $K$. This is the first measurement that simultaneously uses Belle and Belle~II data, combining samples corresponding to integrated luminosities of \SI{711}{fb^{-1}} and \SI{128}{fb^{-1}}, respectively. All data were accumulated from energy-asymmetric $e^+e^-$ collisions at a centre-of-mass energy corresponding to the mass of the $\Upsilon(4S)$ resonance. We measure $\phi_3 = \left(78.4 \pm 11.4 \pm 0.5 \pm 1.0 \right)^{\circ}$, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the $D$-decay strong-phase parameters.