Observation of B^{\pm} \to \chi_{c1} \pi^{\pm} and Search for Direct CP Violation

TL;DR

This paper reports the first observation of the decay B± → χc1 π±, measuring its branching fraction and charge asymmetry, and searches for direct CP violation using a large data sample collected at the Belle detector.

Contribution

The study provides the first observation and measurement of the branching fraction and charge asymmetry for B± → χc1 π± decay, expanding understanding of suppressed B meson decays.

Findings

First observation of B± → χc1 π± decay with 6.3σ significance.

Measured branching fraction: (2.2 ± 0.4 ± 0.3)×10⁻⁵.

Charge asymmetry consistent with zero within uncertainties.

Abstract

We report the first observation of $B^{\pm} \to \chi_{c1} \pi^{\pm}$, the Cabibbo- and color-suppressed decay in a data sample of $386\times 10^6$~$B\bar B$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe $55\pm10$ signal events with a statistical significance of $6.3\sigma$ including systematic uncertainties. The measured branching fraction and charge-asymmetry is $\mathcal {B}(B^{\pm} \to \chi_{c1} \pi^{\pm}) = (2.2\pm 0.4\pm 0.3)\times 10^{-5}$ and $\mathcal{A}_{\pi} = 0.07 \pm 0.18\pm 0.02$, respectively. We also determine the ratio $\mathcal {B}(B^{\pm} \to \chi_{c1} \pi^{\pm})/\mathcal {B}(B^{\pm} \to \chi_{c1} K^{\pm}) = (4.3\pm 0.8\pm 0.3) %$.