A Search for Boosted Low Mass Resonances Decaying to the $b\bar{b}$ Final State and Produced in Association with a Jet at $\sqrt{s} = 13~\mathrm{TeV}$ with the ATLAS Detector

A search in the high momentum regime for new resonances, produced in association with a jet, decaying into a pair of bottom quarks is presented using an integrated luminosity of $80.5~\mathrm{fb}^{-1}$ of proton-proton collisions at center-of-mass energy $\sqrt{s}=13~\mathrm{TeV}$ recorded by the ATLAS detector at the Large Hadron Collider. The search was performed for low mass resonances, including the Standard Model Higgs boson and leptophobic $Z^{\prime}$ dark matter mediators, in the mass range of $100~\mathrm{GeV}$ to $200~\mathrm{GeV}$. For the Standard Model Higgs boson, the observed signal strength is $\mu_{H} = 5.8 \pm 3.1~\mathrm{(stat.)} \pm 1.9~\mathrm{(syst.)} \pm 1.7~\mathrm{(th.)}$, which is consistent with the background-only hypothesis at $1.6$ standard deviations. No evidence of a significant excess of events beyond the expected background is found and competitive limits on leptophobic $Z^{\prime}$ boson axial-vector couplings to Standard Model quarks with democratic couplings to all quark generations are set for the mass range considered. The dominant background in this analysis is irreducible multijet events from QCD interactions, which I modeled using a parametric function that was robust to fitting bias and spurious signals.