# Search for the $B \to Y(4260) K, ~Y(4260) \to J/\psi \pi^+\pi^-$ decays

## TL;DR

This study searches for B meson decays involving the Y(4260) state decaying to J/psi pi+ pi-, using Belle data, and sets upper limits on the branching fractions due to no significant signal detection.

## Contribution

First search for B to Y(4260) K decays with Y(4260) to J/psi pi+ pi- using Belle data, providing upper limits on branching fractions.

## Key findings

- No significant Y(4260) signal observed.
- Upper limits set on product branching fractions.
- Excesses observed with low significance (2.1 and 0.9 sigma).

## Abstract

We report the results of a search for the $B \to Y(4260) K, ~Y(4260)\to J/\psi\pi^+\pi^-$ decays. This study is based on a data sample corresponding to an integrated luminosity of 711~fb$^{-1}$, collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We investigate the $J/\psi\pi^+\pi^-$ invariant mass distribution in the range 4.0 to 4.6 GeV/$c^2$ using both $B^+ \to J/\psi \pi^+\pi^- K^+$ and $B^0 \to J/\psi \pi^+\pi^- K^0_S$ decays. We find excesses of events above the background levels, with a significances of 2.1 and 0.9 standard deviations for charged and neutral $B \to Y(4260) K$ decays, respectively, taking into account the systematic uncertainties. These correspond to upper limits on the product of branching fractions, ${\cal B}(B^+ \to Y(4260) K^+) \times {\cal B}(Y(4260) \to J/\psi \pi^+ \pi^-) <1.4 \times 10^{-5}$ and ${\cal B}(B^0 \to Y(4260) K^0) \times {\cal B}(Y(4260) \to J/\psi \pi^+ \pi^-) <1.7 \times 10^{-5}$ at the 90\% confidence level.