The Search Budget of the BSM Resonance Program

Abstract

Data-directed scans, anomaly searches and general searches probe many mass spectra at once, and for them the look-elsewhere effect sets the discovery bar. We count the trials factor of the ATLAS BSM resonance program in effective independent resolution elements, from public inputs alone, and then work out what a fully combinatorial scan would cost in the same units. The published record, summed over the 104 spectra it scans, amounts to $N_{\mathrm{trials}} = 7.9 \times 10^{3}$ looks, so a $5σ$ global discovery today costs a local $Z_{\mathrm{local}} = 6.55$. Scanning instead every mass built from up to four reconstructed objects, one event-level selection at a time and priced on Run 2 and Run 3 together, amounts to $3.6 \times 10^{5}$ looks and $Z_{\mathrm{local}} = 7.11$. A factor 46 more looks therefore costs $0.56σ$. If the trials factor cannot be enumerated because the estimator is itself imperfect, as in machine-learning searches, two-stage unblinding is a safeguard against its spurious signals: at the defect rate measured for a published bump-hunting network it is the more sensitive procedure.