Observation of the Decay B0 => rho+ rho- and Measurement of the Branching Fraction and Polarization

TL;DR

This paper reports the first observation of the rare B0 => rho+ rho- decay, measuring its branching fraction and polarization with high significance using data from the BABAR detector.

Contribution

The study provides the first observation and precise measurements of the branching fraction and polarization for the B0 => rho+ rho- decay.

Findings

Observed the decay with 5.1 sigma significance

Measured branching fraction as (25 +7-6 +5-6) x 10^{-6}

Determined longitudinal polarization to be approximately 98%

Abstract

We have observed the rare decay B0 => rho+ rho- in a sample of 89 million BB pairs recorded with the BABAR detector. The number of observed events is 88 +23-21 +-9, with a significance of 5.1 standard deviations with systematic uncertainties included. The branching fraction and the longitudinal polarization are measured to be BR(B0 => rho+ rho-) = (25 +7-6 +5-6)*10^{-6} and Gamma_L/Gamma = 0.98 +0.02-0.08 +-0.03, respectively.