From godfrey@slac.stanford.edu Sat Aug 12 14:27:15 2006 Date: Fri, 16 Jun 2006 10:51:39 -0700 From: "Godfrey, Gary L." To: D.A. Smith Subject: Comparing Muon Telescope GPS time to LAT time Hi Dave I was looking at your Friday meeting transparencies and saw your suggestion for a muon telescope with GPS to compare to the LAT time. We actually took many runs at SLAC with the external muon telescope DAQ recording data while the LAT muon runs were going on. Unfortunately, there was no GPS on the LAT yet, so I just used the EvtTicks (20 MHz xtal clock in the LAT)to find out which LAT event went with which Muon telescope event (each Muon telescope event has a GPS time in usec written out). I shifted the relative time between the two clocks until I got the maximum number of coincidences. I also slightly adjusted the sec/tick of each run so the clocks ran at the same rate. Attached is the analysis of one 2 tower run (135004388). On the third page you can see how stable (~+- 1 usec)the 20 Mhz clock is wrt GPS over the 1800 sec run. There was generally more curvature in this plot just after the LAT was turned on than at the end of the day when the temperature of the clock had stablized. Too bad there wasn't a GPS reference on the LAT at the time or we would have your data ! I was using the time coincidence to measure how efficient the LAT was for seeing muon telescope events. You can see the shapes of the muon telescope paddles (top and bottom) in the plots on the second to last page. The light blue rectangle is the outline of the two towers. This data may already answer some worries like "is the event time being written with the correct event". All that is missing is the 1 pps GPS in the LAT to calibrate the 20 MHz clock. Gary PS: I have lots of the Muon (asci data) files all syncd up with LAT runs (MathCad sheets) if you can think of something else to do with them ? [ Part 2, "Muon32_4388.pdf" Application/OCTET-STREAM (Name: ] [ "Muon32_4388.pdf") 196KB. ] [ Unable to print this part. ]