Abstract
Searches for high-mass resonances in the dijet invariant mass spectrum with one or two jets identified as $b$-jets are performed using an integrated luminosity of $3.2$ fb$^{-1}$ of proton--proton collisions with a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% credibility level, excited $b^{*}$ quarks with masses from 1.1 TeV to 2.1 TeV and leptophobic $Z'$ bosons with masses from 1.1 TeV to 1.5 TeV. Contributions of a Gaussian signal shape with effective cross sections ranging from approximately 0.4 to 0.001 pb are also excluded in the mass range 1.5-5.0 TeV.
Highlights
Many extensions to the Standard Model (SM) predict the existence of new massive particles that couple to quarks or gluons
Due to the absence of a signal, 95% credibility-level upper limits are set on the cross section for new processes that would produce a contribution to the dijet mass distribution with b-tagging
The Bayesian credible intervals were calculated using a posterior probability density from the likelihood function for the observed mass spectrum obtained by a fit to the background (Eq (1)), while the signal shape was derived from Monte Carlo (MC) simulations
Summary
Many extensions to the Standard Model (SM) predict the existence of new massive particles that couple to quarks or gluons. If produced in proton–proton (pp) collisions at the Large Hadron Collider (LHC), these new beyond-the-SM (BSM) particles could decay into quarks (q) or gluons (g), creating resonant excesses in the two-jet (dijet) invariant mass distributions [1,2,3,4,5,6]. All benchmark model decays are expected to result in a narrow resonance superimposed on a smoothly falling dijet invariant mass distribution. This search divides the events into samples with one or two jets identified as b-jets to enhance the signal sensitivity to the benchmark models b∗ → bg and Z → bb. The results, presented in terms of the cross section times acceptance times branching ratio (σ × A × BR), are quoted for contributions with widths of up to 15% of the resonance mass
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