Effects of Single Counter Efficiencies on Mu2e Sensitivity and Mitigation Strategy for Individual Counter Efficiency Deficits
Jo Lynn Tyner
Austin Peay State University
Mentored by Dr. Tim Bolton and Dr. Glenn Horton-Smith
The mission of the Mu2e (Muon to Electron Conversion) experiment is to observe a muon to electron conversion. This observation would be evidence of a charged lepton flavor violation process, thereby putting into question some parts of the Standard Model. Cosmic Rays interfering with the detection devices in Mu2e create background that can hide electron conversion events in noise. The Cosmic Ray Veto will measure cosmic ray strikes and veto the events from the final data. The Cosmic Ray veto covers the entire Detection Solenoid of Mu2e and is made of four layers of scintillation counters. The Cosmic Ray veto must be incredibly efficient (99.99% efficient), and the efficiencies of the individual counters affect the overall efficiency. To model this affect, we simulated a cosmic ray hit across four layered counters. We included a gap hit probability wherein the cosmic ray hits a gap between counters instead of a counter. Using a 0.37% gap hit rate, the individual efficiency needed to meet the high overall efficiency standard is 99.65%. Manufacturing and electronic malfunctions could cause some counters to be dead, thereby dropping the individual counter efficiency for a dead counter to 0%. We added this into our simulation and found that an individual efficiency of 99.8% with a dead counter rate of 0.1% would meet the overall efficiency requirement. To mitigate these deficits in dead counters, we determined a local drop in passing and failing event rates would allow for a lower individual counter efficiency. Usually events with three of four hits out of four total hits are considered passing events. In the local drop fix, the passing event criteria are three or two hits when a counter in the event is dead, and failing events have two, one, or zero hits. This strategy allows the individual efficiency to drop back to 99.65% and allows up to 2% of the counters to be dead.
We would like to thank our Mu2e collaborators both at Fermilab and Kansas State University. This project is funded by the National Science Foundation (NSF) and the Air Force Office of Scientific Research (AFOSR) through NSF grant number PHYS-1461251.