# Search for low-mass quark-antiquark resonances produced in association with a photon at $\sqrt{s} = $ 13 TeV

## TL;DR

This paper reports a search for low-mass quark-antiquark resonances produced with a photon at 13 TeV, setting new limits on such particles below 50 GeV using CMS data from the LHC.

## Contribution

It introduces a novel photon trigger strategy to search for low-mass resonances decaying to quark pairs at a hadron collider, providing the first direct constraints below 50 GeV.

## Key findings

- No evidence for low-mass quark-antiquark resonances was observed.
- Upper limits were set on the coupling strength of these resonances.
- First direct constraints on such resonances below 50 GeV at a hadron collider.

## Abstract

A search for narrow low-mass resonances decaying to quark-antiquark pairs is presented. The search is based on proton-proton collisions events collected at 13 TeV by the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$, recorded in 2016. The search considers the case where the resonance has high transverse momentum due to initial-state radiation of a hard photon. To study this process, the decay products of the resonance are reconstructed as a single large-radius jet with two-pronged substructure. The signal would be identified as a localized excess in the jet invariant mass spectrum. No evidence for such a resonance is observed in the mass range 10 to 125 GeV. Upper limits at the 95% confidence level are set on the coupling strength of resonances decaying to quark pairs. The results obtained with this photon trigger strategy provide the first direct constraints on quark-antiquark resonance masses below 50 GeV obtained at a hadron collider.