Search for new light resonances decaying to jet pairs and produced in association with a photon in proton-proton collisions at $\sqrt{s}=13$~TeV with the ATLAS detector

This note describes a search for new resonances decaying to pairs of jets in 3.2 fb$^{-1}$ of proton-proton collisions with a centre-of-mass energy of $\sqrt{s}=13$~TeV recorded during 2015 by the ATLAS detector at the Large Hadron Collider. The search requires the new resonance is produced in association with a high-$p_{\textrm{T}}$ photon, such as a photon radiated from the colliding partons, in order to efficiently trigger on light resonances. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the smoothly falling background. No evidence of anomalous phenomena is observed in the data, which are used to exclude effective cross-sections of processes with Gaussian-shaped contributions to the observed dijet mass distribution and regions of the parameter space of a lepto-phobic axial-vector $Z^\prime$ benchmark model. These results extend the limits on light dijet resonances obtained at lower centre-of-mass energies.