Observation of B^0 -> a_1^{+/-}(1260) \pi^{-/+}

TL;DR

This paper reports a new measurement of the branching fraction of a specific B meson decay involving the a1(1260) resonance, providing updated values for its mass and width based on data from the Belle detector.

Contribution

The study presents the first precise measurement of the branching fraction and resonance parameters of B^0 -> a1(1260) pi decay using a large data sample from Belle.

Findings

Branching fraction measured as (48.6 ± 4.1 (stat) ± 3.9 (syst)) x 10^-6

Mass of a1(1260) measured as 1197 ± 34 MeV/c^2

Width of a1(1260) measured as 305 ± 43 MeV/c^2

Abstract

We report a new measurement of the branching fraction of neutral $B$ meson decays $B^0\ra a_{1}^{\pm}(1260)\pi^{\mp}$ with \ensuremath{a_{1}^{\pm}(1260)\ra \rho^{0}\pi^{\pm}} and $\rho^0\ra pi^+\pi^-$ using $275\times 10^{6}$ BBar pairs collected by the Belle detector at the KEKBasymmetric-energy $e^{+}e^{-}$ collider. We measure the branching fraction $\mathcal{B}($B^0\ra a_{1}^{\pm}(1260)\pi^{\mp}=(48.6\pm 4.1(stat)\pm 3.9(syst)) \times 10^{-6}$. Using a relativistic Breit-Wigner parameterization, we measure the mass and width of the $a_{1}(1260)$ to be $m_{a_1}=1197\pm 34 MeV/c^2$ and $\Gamma_{a_1}=305\pm 43 MeV/c^2$, respectively.