Motivated by the plots shown by Philippe in the last beam test VRVS meeting on the distribution of CalZDir (see http://polywww.in2p3.fr/~bruel/cernps_20060801.pdf
) 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 , as well as the distributions of Trk1ZDir and CalZDir, for muon events detected with the calibration unit Calibration Unit (Pisa, July 2006) and with the full Full LAT detector (SLAC, April-May 2006).
Muon events from Cosmic Ray runs taken with
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the Full LAT (SLAC, April-May 2006)
The data run used is 77003553.
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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 distributions of the variables Trk1ZDir and CalZDir are shown in MuonSLACReconstruction.gif, MuonSLACReconstruction.ps and MuonSLACReconstruction.root (gif, ps and root files). Note that (for this data and selection applied) the muon direction in the calorimeter (CalZDir) is properly reconstructed for most of the events, as expected.
Muon events from Cosmic Ray runs taken with the Calibration Unit (Pisa, July 2006)
The data run used is 700000460.
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The calibration of this run is not perfect, yet it is roughly ok , (within 10-20% (, estimated from the location of the muons peaks). I took this run because the calibration seems to be much better than in dedicated muon runs (700000276 to 286, 700000490 to 500). Details about this quick evaluation of the calibration constants for these specific runs can be found in the following two references:
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