Measurement of the branching fraction and time-dependent $CP$ asymmetry for $B^0\to J/\psi\pi^0$ decays

TL;DR

This paper reports the most precise measurement to date of the branching fraction and time-dependent CP asymmetry in B0 to J/psi pi0 decays, providing insights into CP violation in the B meson system.

Contribution

First measurement of the CP asymmetry parameters in B0 to J/psi pi0 decays with high precision using Belle data.

Findings

Branching fraction measured as (1.62 ± 0.11 (stat) ± 0.07 (syst)) × 10^{-5}

Mixing-induced CP asymmetry S = -0.59 ± 0.19 (stat) ± 0.03 (syst)

Direct CP asymmetry A = -0.15 ± 0.14 (stat) +0.04/-0.03 (syst)

Abstract

We measure the branching fraction and time-dependent $CP$-violating asymmetry for $B^0\to J/\psi\pi^0$ decays using a data sample of 711 ${\rm fb^{-1}}$ collected on the $\Upsilon(4S)$ resonance by the Belle experiment running at the KEKB $e^+e^-$ collider. The branching fraction is measured to be $\mathcal{B}(B^0\to J/\psi\pi^0) = [1.62\,\pm 0.11~({\rm stat}) \pm0.07~({\rm syst})]\times 10^{-5}$, which is the most precise measurement to date. The measured $CP$ asymmetry parameters are $\mathcal{S} = -0.59\,\pm 0.19~({\rm stat}) \pm 0.03~({\rm syst})$ and $\mathcal{A} = -0.15\,\pm 0.14~({\rm stat})\,^{+0.04}_{-0.03}~({\rm syst})$. The mixing-induced $CP$ asymmetry ($\mathcal{S}$) differs from the case of no $CP$ violation by 3.0 standard deviations, and the direct $CP$ asymmetry ($\mathcal{A}$) is consistent with zero.