Determining the time zero of PIBETA trigger is crucial in extracting the PIBETA decay branching ratio. Essentially what we need to do is determining the offset of each channel so that same signal from different channel will arrive at the same time.

Method Currently Used

Two methods were compared:
In one method, each run was analyzed with its online odb file loaded; in the other method, only one odb file was used for all runs. TDC offset for each channel was calculated and adjusted accordingly. Then same runs were analyzed again with new TDC offsets. Results and explainations are presented below.

Run21100 to run21136 were used. Cuts were:

      trig[0] & TRIG_PIBETA_HI   &&
      mwpc->wc1_n_hits==0        &&
      mwpc->wc2_n_hits==0        &&
so that gammas from decay of nutral pion generated from prompt events were used to set time zero. The timing of the clump which registered the largest energy depositon would be filled into histogram corresponding to this specific channel. The time offset then was determined as following:
we labelled peak around -20ns as P0 and peak at around 20ns as P1, then P2, P3... etc. for each peak after P1. we omitted peak at time 0 because it was distorted by beam veto.
Suppose T0 is at offset t0, then we have:
t0 = (Pm+m*P0)/(m+1)
to = (n*Pm-m*Pn)/(n-m)       n,m>0
we then average all t0's we got from above to get T0 for this specific channel . Three programms were used to get above work done, namely,slix.kumac which is used to fit 6 peaks for each channel and write data to tof.dat. which reads tof.dat and calculates the timing offset for each channel and then write results to time0.dat. reads time0.dat and a runxxx.odb file to calculate new odbfile and write data into ntofxxx.odb. There is a README file explaining how to use these programms in detail.


1. Loading odb files for each runs:
With online odb.
After adjusting TDC offsets once.

2. Using only run21136.odb
All runs were analyzed with run21136.odb.
After adjusting TDC offsets once.

© 22, January 20001. by Weidong Li for PIBETA collaboration.