Motivated by the plots shown by Philippe in the last beam test VRVS meeting on the distribution of CalZDir (see ) I spent some time inspecting the reconstruction of the direction of muons (which is far simpler than electrons) in the calorimeter of the calibration unit. In this page you find a comparison of the FRED event displays and also the distributions of Trk1ZDir and CalZDir for muon events detected with the calibration unit (Pisa, July 2006) and with the full LAT detector (SLAC, April-May 2006).
The events discussed below (both distributions and FRED images) were selected with the following criteria:
TCut cut = "TMath::Abs((acos(Tkr1ZDir)*(180./3.14159))-180.) < 5 && CalEnergyRaw>10";
Muon events from Cosmic Ray runs taken with full LAT (SLAC, April-May 2006)
The image MuonWithFullLAT shows the distribution of energy deposited in the calorimeter when a muon goes through it. This is a typical image. The muon deposites energy (11.2 MeV in average) in a crystal from each layer. A clear track is visualized, and consequently the direction of the muon event can be (up to some precision) reconstructed for a large fraction of the events using only information from the calorimeter. The plot Re
distribution of the energy deposited in the cal follows the same
"track" that one can see in the tracker. Consequently, the reconstruction
of the direction in the cal matches quite well (in general)
with that one of the tracker
Muon Data from CERN
David please include run numbers
Electrons @ 5 GeV
David please include run numbers