1. Alex Moiseev NASA/GSFC 12/16/2005 Some ACD Calibration issues I.ACD mip peak monitoring 1. ACD mip peak monitoring requires the measurements to be done at similar conditions. The best is to use normal incidence (to the ACD tile plane) single charged particles (mip) 2. In ACD standalone tests (TriggerOps): a) up-right position (Z up); quasi-normal incidence muons events are selected by coincidence of signals from any two pair of sides (top is also considered as a side). Main test, used for mip peak position monitoring b) horizontal position (X or Y up). Coincidence between upper and lower sides. Used for light yield measurements for the tiles on upper and lower sides These tests were performed at Goddard during environmental and pre-shipping tests, and at SLAC.

2. Alex Moiseev NASA/GSFC 12/16/2005 Now we have to find a way to compare mip peak positions obtained in ACD standalone tests with that obtained with up- right LAT triggered by L1T:  Select events by the incidence angle, or by the reconstructed trajectory pathlength in the tile AcdTkrIntSecPathLengthInTile (SVAC ntuple variable)  Do it for up-right ACD (Z up) with L1T and TriggerOps (need TrigOps!) Doing this we will make connection of all previous ACD standalone tests with that in LAT  Use obtained mip peak positions with L1T trigger as new reference values  The same event selection shall be done with LAT in orbit

3. Alex Moiseev NASA/GSFC 12/16/2005 What we will have with L1T? Top Tile All events (3 % of total statistics) Selected by the path in the tile 9.9mm < Path < 12mm Survive ~ 30% events Side Tile All events (1.7% of total statistics) Selected by the path in the tile 9.9mm < Path < 12mm Survive ~ 3.5% events ! See how mip peak moving with applying path length selections! To collect ~2000 events in side tile (needed for reliable mip peak fitting) we need to collect ~3.5 M events in total, which should take ~2 hours with the rate of 500Hz. Looks reasonable

4. Alex Moiseev NASA/GSFC 12/16/2005 II. Edge effect measurement Light yield from the tile decreases in the tile edge area. We run bench tests at Goddard and estimated that the light yield at the tile edge is ~70% of that in the tile center, and recovers to 100% at 3 cm from the center. But that measurements were rather crude, using scintillating fiber hodoscope to map the light yield edge effect. Here are MC simulation results on edge effect (based on bench tests results). Tests with LAT will provide us more accurate data. PHA vs. AcdActiveDist Edge effect PHA vs. AcdTkrIntSecLocalX(Y) Edge effect

5. Alex Moiseev NASA/GSFC 12/16/2005 ACD Tested TDA Triggering hodoscope Incident muon III. ACD tile efficiency measurement. Knowledge of tile efficiency is needed to estimate the absolute light yield (in photoelectrons), which is to be placed in ACD simulation to determine overall ACD efficiency. This is how it was done in ACD Performance tests at Goddard:

6. Alex Moiseev NASA/GSFC 12/16/2005 We want to do the same measurements with LAT to confirm our light yield knowledge. This is what I obtained from surface muon MC run: Top Tile: Selections applied: –TkrNumTracks=1 –9.9<AcdTkrIntSecPathLengthInTile<12 –AcdActiveDist>40 –AcdTkrIntSecTileId=current tile Seems that clean normal incidence tracks hitting the central part of the tile should pass these selections. But I cannot remove these events! I tried to select events with only one track, checked ChiSq, checked number of tracker hits – does not help. I cannot determine tile efficiency due to presence of these events!