1. PMT time offset calibration (not completed) R.Sawada 27/Dec/2007

2. 2 Database to store time offset of each PMTs were prepared. This is similar to gain and Q.E. database. A task to compute time offset by using LED runs was prepared (XECPMTTimeOffsetCompute). This is available with “xec” affiliation. Time offset calibration during analysis was added to XECPMTFill task. This is used when DRS time is used for analysis. Time offset simulation was added to bartender. Time offset during simulation and analysis can be different.

3. 3 Time offset computation Multiple LED runs are used. In each runs, only one LED is activated so that position of light source is known. Event by event fluctuation of LED pulse. => Use time difference from one reference PMT (always same one during a run). Run by run fluctuation (Reference PMT is different run by run) => calibrate by using mean of all PMTs. Limited speed of light. => Fit “time v.s. distance” distribution. Jitters

4. 4 Procedure 1 (Estimation of time) At the end of these steps, following data is obtained. A point corresponds to a PMT in a run. Time offset [nsec] Distance [cm] Estimate time Correct run offset

5. 5 Procedure 2 (Minimization) Parameters : Speed of light, time offset of each PMTs. Minimization is done by Minuit. Parameter for Minuit is only the speed of light. Minimization of time offset of PMTs is done in fitting function. At the end of these steps, following data is obtained. A point corresponds to a PMT in a run. Time offset [nsec] Distance [cm]

6. 6 Result ? It seems there is still a problem to align time of different runs. The final result will be after the problem is solved. With current implementation, speed of light is faster than c. This might be solved by improving alignment of runs. Time offsets are shifted so that mean of all PMTs becomes zero.