Measurement of the CKM parameter cos(2phi_1) using time-dependent Dalitz analysis of B0bar -> D[Ks pi+ pi-] h0

TL;DR

This paper measures the CKM angle phi1 using a time-dependent Dalitz analysis of B meson decays, providing a direct determination of 2phi1 and resolving a key ambiguity in CP violation measurements.

Contribution

It introduces a method to directly extract 2phi1 from B meson decays, improving the understanding of CP violation in the quark sector.

Findings

Measured sin 2phi1 as 0.78±0.44±0.22

Determined cos 2phi1 as 1.87+0.40+0.22-0.53-0.32

Confirmed positive sign of cos 2phi1 at 98.3% confidence level

Abstract

We present a measurement of the angle phi1 of the CKM Unitarity Triangle using time-dependent Dalitz analysis of D -> Ks pi+ pi- decays produced in neutral B meson decay to a neutral D meson and a light meson (B0bar -> D(*) h0). The method allows a direct extraction of 2phi1 and, therefore, helps to resolve the ambiguity between 2phi1 and pi-2phi1 in the measurement of sin 2phi1. We obtain sin 2phi1=0.78+-0.44+-0.22 and cos 2phi1=1.87+0.40+0.22 -0.53-0.32 The sign of cos 2phi1 is determined to be positive at 98.3% C.L.