Search for long-lived neutral particles in pp collisions at $\sqrt{s}=13\phantom{\rule{3.33333pt}{0ex}}\phantom{\rule{0.333333em}{0ex}}\text{TeV}$ that decay into displaced hadronic jets in the ATLAS calorimeter

This paper describes a search for pairs of neutral, long-lived particles decaying in the ATLAS calorimeter. Long-lived particles occur in many extensions to the Standard Model and may elude searches for new promptly decaying particles. The analysis considers neutral, long-lived scalars with masses between 5 and 400 GeV, produced from decays of heavy bosons with masses between $125$ and $1000$ GeV, where the long-lived scalars decay into Standard Model fermions. The analysis uses either $10.8\phantom{\rule{3.33333pt}{0ex}}{\text{fb}}^{-1}$ or $33.0\phantom{\rule{3.33333pt}{0ex}}{\text{fb}}^{-1}$ of data (depending on the trigger) recorded in 2016 at the LHC with the ATLAS detector in proton–proton collisions at a centre-of-mass energy of 13 TeV. No significant excess is observed, and limits are reported on the production cross section times branching ratio as a function of the proper decay length of the long-lived particles.