Flemming asked me to look for any observable event-by-event differences, so I looked at 14126 events from run 25292005 (taken this morning), file st_physics_25292005_raw_2000014. I then counted hits, sampling hits whose center position is in one of four patches:

• Patches 1 & 2: 4 rows (25-28) by 9 pads in RDO 3 & RDO 4 respectively
• Patches 3 & 4: 4 rows (37-40) by 19 pads in RDO 3 & RDO 4 respectively

I was conservative in my patch sizes because there are lots of dead areas in both of these RDOs. A hit can span RDOs for some padrows, so I also restricted the minimum and maximum pad of any hit to be within the same RDO. What I see:

First observation: no significant spans of events without hits in any of the RDO patches. It should be noted that the events in the DAQ files are however not immediately consecutive.

	Using patches 1 & 2	Using patches 3 & 4
Ratio of hits in RDO3/RDO4	262287/225816 = 1.16	371307/168015 = 2.21
Fraction of events with hits in RDO3 but none in RDO4	2539/14126 = 0.180	3136/14126 = 0.222
↳ Fraction of those events   followed by another with   none in RDO4	444/2539 = 0.175	690/3136 = 0.220
Fraction of events with hits in RDO4 but none in RDO3	1637/14126 = 0.116	1391/14126 = 0.098
↳ Fraction of those events   followed by another with   none in RDO3	171/1637 = 0.104	129/1391 = 0.093
Fraction of events with hits in both RDOs	9302/14126 = 0.659	8905/14126 = 0.630
↳ Ratio of hits in RDO3/RDO4   for events with   hits in both RDOs	1.07	1.58

Conclusions:

1. The probabilities for seeing zero hits in RDO 4 patches is significantly higher than for RDO 3! This appears to be a real difference.
2. The probabilities for two events in a row without hits in any of the patches is reasonably consistent with their single event probabilities repeating randomly, i.e. there is no clear sign in this data of RDO 4 being dead for spans of time.
3. While the strongest bias appears to be seeing no hits in a patch in RDO 4 vs. RDO 3, there is also a weaker bias towards more hits in RDO 3 when there are hits in both RDOs.
4. My over-arching conclusion is that it doesn't appear to be that RDO 4 is dead for certain events, but rather that RDO 4's efficiency for finding hits is simply lower overall, for all events. That would be consistent with the cut-off for zero suppression for RDO 4 being wrong by a small amount for the entire run.

-Gene