Measurement of CP Asymmetry in a Time-Dependent Dalitz Analysis of B^0 \to (\rho \pi)^0 and a Constraint on the Quark Mixing Matrix Angle \phi_2

TL;DR

This paper measures CP asymmetry in B0 decays using a time-dependent Dalitz plot analysis, providing constraints on the CKM angle φ2 and testing the Standard Model with data from the Belle detector.

Contribution

First measurement of CP asymmetry in B0 --> pi+pi-pi0 decays using a time-dependent Dalitz analysis, constraining the CKM angle φ2 with Belle data.

Findings

Constraint on φ2: 68° to 95° at 68.3% confidence

Evidence supporting the Standard Model within certain φ2 ranges

Large region remains disfavored by the Standard Model

Abstract

We present a measurement of CP asymmetry using a time-dependent Dalitz plot analysis of B0 --> pi+pi-pi0 decays based on a 414/fb data sample containing 449M BB pairs. The data was collected on the $\Upsilon$(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. Combining our analysis with information on charged B decay modes, we perform a full Dalitz and isospin analysis and obtain a constraint on the CKM angle $\phi_2$, 68 deg. < $\phi_2$ < 95 deg. as the 68.3% confidence interval for the $\phi_2$ solution consistent with the standard model (SM). A large SM-disfavored region also remains.