Improving Long-Lived R-hadron Simulation at the CMS Experiment

Supersymmetry (SUSY) is a theoretical framework that predicts a new set of particles whose spin differs by 1/2 relative to their corresponding Standard Model particle. Although decades of HEP searches have largely excluded promptly decaying SUSY particles, opportunities remain at the CMS experiment to detect long-lived SUSY particles that have evaded previous searches. R-hadrons, hadrons that contain at least one SUSY particle, are commonly searched for at CMS. Historically, CMS has performed two types of R-hadron searches: stable and displaced-vertex. Stable searches make the strict assumption that the R-hadron is stable, and displaced-vertex searches do not simulate R-hadrons before they decay. To improve sensitivity, our group is currently working to implement proper R-hadron simulation into the CMS software in preparation for a long-lived R-hadron search. Improvements to the simulation include corrections to the R-hadron–hadron interaction model, as well as the simulation of long-lived R-hadrons prior to their Pythia-generated decay. Once implemented, users will be able to simulate long-lived R-hadrons by providing a lifetime and a decay table for the underlying SUSY constituent—e.g., the gluino or stop squark.