Search for hadronic resonances below 100 GeV with ATLAS

by Lars Henkelmann (University of Cambridge (GB))

Wednesday 12 Mar 2025, 13:30 → 14:30 Europe/London

Small Lecture Theatre (Poynting)

Many proposed models of physics beyond the Standard Model predict new resonances. In particular, searches for resonances decaying into hadrons can probe any resonances that may be produced at the LHC. However, such dijet searches lose sensitivity at low masses due to transverse momentum trigger thresholds. This talk presents a recent ATLAS search for such low mass resonances using the invariant mass spectrum of large-radius (R=1) jets with two-pronged substructure. The jets recoil against an energetic photon from initial state radiation, which is used as a trigger, thus avoiding the issue of jet trigger thresholds. The large radius jets are clustered from inner detector tracks and narrow (R=0.2) calorimeter jets. Narrow jets are calibrated using a new in-situ method. Dedicated uncertainties on the energy scale and -resolution of these jets are derived and propagated to the large-radius jets. This enables a consistent calibration down to the lowest masses probed in the search. These techniques enable the search for boosted hadronically decaying resonances in the mass range 20-100 GeV hitherto unprobed by the ATLAS Collaboration. The observed data are found to agree with Standard Model predictions and 95% confidence level upper limits are set on the coupling of a hypothetical new spin-1 Z′ resonance with Standard Model quarks as a function of the assumed Z′-boson mass in the range between 20 and 200 GeV.