# Search for $B^0 \to X(3872) \gamma$

## TL;DR

This study searches for the rare decay of B0 mesons into X(3872) and a photon, using a large data sample, but finds no evidence and sets an upper limit on the decay probability.

## Contribution

First search for the decay B0 to X(3872) gamma with a large data sample, establishing an upper limit on its branching fraction.

## Key findings

- No evidence for the decay was observed.
- An upper limit on the branching fraction was set at 5.1 x 10^{-7}.
- The results constrain theoretical models of X(3872) production.

## Abstract

We report the results of a search for the decay $B^0 \to X(3872)(\to J/\psi \pi^+ \pi^-) \gamma$. The analysis is performed on a data sample corresponding to an integrated luminosity of $711\,{\rm fb}^{-1}$ and containing $772 \times 10^6 B\bar{B}$ pairs, collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider running at the $\Upsilon(4S)$ resonance energy. We find no evidence for a signal and place an upper limit of $\mathcal{B}(B^0 \to X(3872)\gamma)\times \mathcal{B}(X(3872) \to J/\psi \pi^+ \pi^-) < 5.1 \times 10^{-7}$ at 90% confidence level.