Geometry-based dilepton pairing in compressed electroweakino trilepton events at generator level

Abstract

Compressed electroweakino scenarios remain relevant because small mass splittings can produce soft-lepton signatures that are difficult to reconstruct with pairing rules based on an on-shell boson mass. We present a generator-level study of electron-channel trilepton events from chargino−neutralino production using a custom Rivet analysis. Signal samples were generated with PYTHIA 8.317 using SLHA-style SUSY inputs, while the Standard Model reference sample was generated with MadGraph5_aMC@NLO 3.7.0 and showered with PYTHIA. Events were exported in HepMC 2.06.11 format and analyzed with Rivet 4.0.2. The candidate dilepton pair is defined as the two leptons with the smallest angular separation ΔR. We compare compressed benchmarks with Δm=10 and 20 GeV at two heavy-mass scales, and use a real-Z/virtual-W benchmark together with a Standard Model trilepton sample as references. The geometry-selected dilepton mass stays in the low-mass region for the compressed benchmarks, shifts with the mass gap, and moves upward for the real-Z control. These results show that the smallest-ΔR pairing rule isolates a low-mass dilepton candidate in compressed trilepton events without relying on an on-shell mass target.