neg. deadtime appears benign

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User name R. Michaels

Log entry time 05:04:16 on March15,2009

Entry number 266225

This entry is a followup to: 266220

keyword=neg. deadtime appears benign

The negative deadtime episode in, for example, run 2176 seems
benign. The data quality histograms all look ok except for
the panel on deadtime which says -22.4 % (negative). But
this is false, as I prove here:

Scaler rates observed from data file. Prescale from event 120.
Number of events from reading the raw file (only the .dat.0)

Run 2176

Trigger ... Scaler rate ... Prescale ... Num Events ... Deadtime
............ (Hz)
.. 1 ....... 23750 ......... 1500 ....... 6115 ....... 15.2 %
.. 2 ....... 2530 .......... 1 .......... 1.0805e6 ... 16.5 %
.. 6 ....... 9453 .......... 130 ........ 22445 ...... 17.6 %
.. 8 ....... 1024 .......... 100 ........ 4431 ....... 15.5 %

This analysis assumed that every T6 is a T1, every T2 is a T1,
and every T2 is a T6.

The time of the run (.dat.0 file) is 511.5 sec.
Hence to get T1 deadtime one must do this:

Expected T1 = 511.5*(23750 - 2530 - (9453/130))/1500
T1 deadtime = 1 - 6115 / (Expected T1) = 15.2 %

and similarly for T6 one must correct for T2.

The event type distribution is stable throughout the run.
There was never any massive T8 rate in the data.

The conclusions :

1. The massive T8 pulsing that we saw before remains absent.

2. L1A sometimes double-pulses. This is an intermittent problem.

3. If deadtime is analyzed correctly, it looks ok. I don't know
what is wrong with the offline analysis and its -22.4%. It might
be a symptom of something else ...