Detection of long-lived neutral particles with Atlas

A number of extensions of the Standard Model results in particles that are neutral, weakly coupled and have macroscopic decay lengths comparable with Lhc detector dimensions. These long-lived particles occur in many models: gauge-mediated SUSY extensions of the MSSM (addition of one singlet field). MSSM with R-parity violation, split SUSY, inelastic dark matter and Hidden Valley (H V) Scenarios in which a new sector is weakly coupled to the Standard Model. In the H V models long-lived particles decaying to heavy quark pairs and tau pairs can be produced in SUSY processes, Z' decays and Higgs boson decays. For the purpose of exploring the challenges to the trigger posed by long-lived neutral particles, the Hidden Valley scenario serves as an excellent setting. Results are presented of a first study of the Atlas Detector performance for the Higgs decay h0 → π0υπ0υ, where π0υ is neutral and has a displaced decay mainly to bottom quarks. The initial goal of the study is to obtain benchmark triggers for processes with such non-standard signatures in the Atlas apparatus.