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).
Muon events from Cosmic Ray runs taken with full LAT (SLAC, April-May 2006)
The data run used is 77003553.
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";
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 Calibration Unit (Pisa, July 2006)
The data run used is 700000460.
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";
Important Remark
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 can be found in the following two references:
- https://confluence.slac.stanford.edu/download/attachments/13893/Paneque_BeamTest_20060718.pdf?version=1
- https://confluence.slac.stanford.edu/display/BeamTest/CAL+Energy+Calibrations
The image MuonWithCUshows the distribution of energy deposited in the calorimeter when a muon goes through it. This is a typical image; not a rare event. Note that the track is "brocken"; every other layer there is a "hole" in the track, the energy deposited in that layer seems to show up off the track. The FRED Images 1,2,3 and 4 show the first 4 consecutive events from that run (after the application of the selection criteria described above). You can see the same behaviour in all them. The FRED image Evt0_4Views shows the event 0 from 4 different perspectives. Note that the Z-X perspective is different from the Z-Y perspective. In the first one the layers 1,3,.5,7 are alined and the layers 2,4,6,8 are off; whereas in the other the opposite occurs.
Anders and Leon atributed this effect to a wrong crystal diode relative calibration; since the position of the event along the crystal is determined comparing the signal produced in each of the diodes at the end of the crystal. This wrong relative-calibration seems to occur in all the layers.
This effect deteriorates the reconstruction of the direction of the event in the calorimeter; which is clearly observed in the distributions of the variables Trk1ZDir and CalZDir shown in MuonPisaReconstruction.gif, MuonPisaReconstruction.ps and MuonPisaReconstruction.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 ONLY a TINY FRACTION (3%) of the events.
Electrons @ 5 GeV
David please include run numbers