The era of charmed resonance searches at the LHC

Abstract

The LHC dijet program has searched extensively for resonances decaying to inclusive jets and, more recently, to bottom-quark jets, where the sensitivity enhancement from suppression of the background outweighs the loss of signal efficiency in bottom-quark tagging. However, no dedicated search for dijet resonances containing charm-tagged jets has been performed. We study the charm-tagging performance required to make such searches competitive with the inclusive dijet search. Using the ATLAS 13 TeV dijet mass spectrum with 139 fb$^{-1}$, we predict the expected charm-tagged spectra from simulated jet-flavor fractions and parameterized charm-, bottom-, and light-jet tagging efficiencies, and estimate the sensitivity of a profile-likelihood search in exclusive one- and two-tag categories. At the loosest working point of the current tagger, charm-tagged searches improve the expected sensitivity to a resonance decaying to two charm quarks across the full resonance mass range considered, although the quantitative sensitivity depends on the poorly constrained high-$\pt$ behavior of charm-tagging efficiencies and on the simulated heavy-flavor composition of the dijet background. These results provide performance targets for charm taggers and motivate the development of dedicated charm-tagged dijet resonance searches at the LHC.