Measurement of $B^0 \to J/\psi \eta^{(}{}'{}^{)}$ and Constraint on the $\eta-\eta'$ Mixing Angle

TL;DR

This study measures the branching fractions of specific B meson decays involving J/psi and eta or eta' particles using Belle data, and constrains the eta-eta' mixing angle based on these measurements.

Contribution

It provides the first precise measurements of these branching fractions and sets a new upper limit on the eta-eta' mixing angle.

Findings

Branching fraction for B0 → J/ψ η is (12.3 ± 1.8 (stat) ± 0.7 (syst)) × 10^{-6}

Upper limit for B0 → J/ψ η' is < 7.4 × 10^{-6} at 90% CL

Eta-eta' mixing angle constrained to be less than 42.2° at 90% CL

Abstract

We measure the branching fractions of $B^{0} \to J/\psi \eta^{(}{}'{}^{)}$ decays with the complete Belle data sample of $772 \times 10^{6}$ $B\bar{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The results for the branching fractions are: ${\cal B}(B^{0} \to J/\psi \eta)=(12.3 \pm ^{1.8}_{1.7} \pm 0.7) \times 10^{-6}$ and ${\cal B}(B^{0} \to J/\psi\eta') < 7.4 \times 10^{-6}$ at 90% confidence level. The $\eta-\eta'$ mixing angle is constrained to be less than $ 42.2^{\circ}$ at 90% confidence level.