# Search for W boson decays to three charged pions

## TL;DR

This paper reports the first search for the rare decay of the W boson into three charged pions using CMS data, setting an upper limit on its branching fraction at 13 TeV collision energy.

## Contribution

It presents the first experimental search for W boson decays to three charged pions and establishes an upper limit on the branching fraction, motivating further theoretical work.

## Key findings

- No significant excess observed above background
- Upper limit of 1.01 x 10^-6 on branching fraction
- Results motivate theoretical calculations of this decay mode

## Abstract

For the first time, a search for the rare decay of the W boson to three charged pions has been performed. Proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 77.3 fb$^{-1}$, have been analyzed. No significant excess is observed above the background expectation. An upper limit of 1.01 $\times$ 10$^{-6}$ is set at 95% confidence level on the branching fraction of the W boson to three charged pions. This provides a strong motivation for theoretical calculations of this branching fraction.