Tagging single muons and other long-flying relativistic charged particles by ultra-fast timing in air Cherenkov telescopes

摘要

Atmospheric air Cherenkov telescopes are successfully used for ground-based,very high-energy (VHE) gamma ray astronomy. Triggers from the so-called singlemuon and other long-flying relativistic charged particle events are an unwantedbackground for the Cherenkov telescope. Because of low rate at TeV energies themuon background is unimportant. It is much more intense for telescopes withhigh photon sensitivity and low energy threshold. Below a few hundred GeVenergy, the so-called muon background becomes so intense, that it candeteriorate the sensitivity of telescopes (the so-called muon-wall problem). From general considerations it can be anticipated that the signature of theseparticles should be a light pulse with a narrow time structure. In fact,simulations show that the pulses from muons have a very narrow time profilethat is well below the time resolutions of nearly all currently operatingtelescopes. In this report we elaborate on the time profile of Cherenkov lightfrom the so-called single muons and show that a telescope with ultra-fast timeresponse can open a new dimension allowing one to tag and to reject thoseevents.