# Search for $X(3872)$ and $X(3915)$ decay into $\chi_{c1} \pi^0$ in $B$ decays at Belle

## TL;DR

This paper searches for specific decay modes of the $X(3872)$ and $X(3915)$ particles in B meson decays, setting upper limits on their branching fractions and ratios, based on a large dataset from the Belle experiment.

## Contribution

It provides the first upper limits on the decay of $X(3872)$ and $X(3915)$ into $ ext{chi}_{c1} ext{pi}^0$ in B decays, improving understanding of these exotic states.

## Key findings

- Upper limit on $B^+ o X(3872) K^+$ with $X(3872) o ext{chi}_{c1} ext{pi}^0$
- Upper limit on $B^+ o X(3915) K^+$ with $X(3915) o ext{chi}_{c1} ext{pi}^0$
- Ratio $ ext{Br}(X(3872) o ext{chi}_{c1} ext{pi}^0)/ ext{Br}(X(3872) o J/\psi ext{pi}^+ ext{pi}^-)$ constrained to be less than 0.97

## Abstract

We report a search for $X(3872)$ and $X(3915)$ in $B^+ \to \chi_{c1} \pi^0 K^+$ decays. We set an upper limit of $\mathcal{B}(B^+ \to X(3872) K^+) \times \mathcal{B}(X(3872) \to \chi_{c1} \pi^0)$ $ < 8.1 \times 10^{-6}$ and $\mathcal{B}(B^+ \to X(3915) K^+) \times \mathcal{B}(X(3915) \to \chi_{c1} \pi^0)$ $ < 3.8 \times 10^{-5}$ at 90\% confidence level. We also measure $\mathcal{B}(X(3872) \to \chi_{c1} \pi^0)/\mathcal{B}(X(3872) \to J/\psi \pi^+ \pi^-) < 0.97$ at 90\% confidence level. The results reported here are obtained from $772 \times 10^{6}$ $B\overline{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.