Fast Tracker

Improving Single Muon Trigger at High Luminosity

The problem: As pile-up increases, calorimeter isolation requirements loose some of their power since real isolated leptons can have calorimeter energy from the pile-up. The idea is to replace calorimeter isolation (or augment a weaker calorimeter isolation requirement) with a track-based isolation that only uses tracks pointing to the z0 of the lepton. This could significantly reduce the effect of pile-up, but of course would be relying entirely on the charged component of nearby energy and thus might not do better.

For muon triggers: The low-pT regime it is dominated by muons from K and π decays, while muons from semileptonic b and c decays dominate in the intermediate-pT range. The contribution from W and Z decays becomes important in the high-pT range (pT above 20-30 GeV/c). In this pT range the component of muon rates from semileptonic b and c decays is the largest source of background in the trigger. The rejection of these muons is difficult since they are real and produced close to the interaction point. On the other hand muons from π/K or b/c decays are produced in jets while muons from heavy object decays (like W →μν ) are isolated – i.e. not surrounded by other particles, except for those from pile-up collisions.

Muon Reconstruction: Staco is the standard reconstruction (MuId is mentioned as a comparison). The overlap between the high and low Pt algorithms is removed (such that there is no double counting)

-- MonicaDunford - 27 Feb 2009