These counters, rather distinct in their functions, are so similar from the DAQ readout and software side, that all of them are described in this document.
The function of the counters is:
See the xfig drawing (EPS or GIF) of the external outlines of the DEA made by K.Olchanski in August of 1996.
See the drawings from R. Lindenbusch showing the correct sizes and postions of the DEA and CPV counters, using data from Hans and J. Dowd.
The counters are connected to an LeCroy 1881 ADC. This ADC is unpacked into the GROUP_MISC_ADCS.
During the 1993, 1994 and 1995 runs this ADC was run without zero suppression.
The counters are connected to a LeCroy 1876 TDC. This was done somewhere in the middle of the Summer 1994 run. This TDC is unpacked into the GROUP_TRIGGER_TDCS.
The routine unpackVetoes(event,eventLength) converts the separate ADC and TDC hits to counter hits in GROUP_VETO_HITS and GROUP_VETO_BITMAP.
Please read the documentation on both data groups before reading the rest of this document.
The DEA and CPVC are used offline to veto events with missing neutral particles.
When neutral particles go through DEA, they leave part of their energy in the detector. That energy is converted to electric pulses by scintillators/phototubes and then digitized by ADCs. Theoretically DEA can be used as a calorimeter. In practice, the detector was configured as a veto-only device by overdriving the ADCs to achieve the best-possible sensitivity to small signals. Larger signals overflow the ADC and cannot be digitized, precluding use of the detector as a calorimeter - during the 1995 data run, about 50% of the DEA hits overflowed the ADC.
To reject the events with missing neutral particles (particles that missed the CSI and the LGD), one would construct an offline veto that requires that none of the DEA section fires.
The situation however is complicated by the presense of charged particles in the data. The charged particles also produce hits in the DEA, so rejecting all the events that have hits in the DEA would cut into the acceptance for charged particles.
The DEA veto can be improved by ignoring the hits possibly created by charged particles. This can be done by tracking the reconstructed charged particles into the DEA and ignoring the corresponding sections of the DEA in a way similar to tagging the CSI.
We do not do it this way. Instead, we use CPVC to identify the sections of DEA hit by charge particles. Only charged particles produce hits in CPVC so we consider a section of DEA to have a hit from a neutral particle if the DEA section has a hit, but the corresponding CPVC section does not have a hit.
In terms of the GROUP_VETO_BITMAP, the combined DEA/CPVC veto is implemented as a bitwise and/not operation on the DEA and CPVC bitmaps:
vetoThisEvent = (~(veto->cpvc&0x3f)) & veto->dea;The "cpvc & 0x3F" operation is used to mask-off only the relevant 6 bits of CPVC ADC data, the "~ (cpvc & 0x3f)" operation requires that the CPVC ADC channels do not fire and the final bitwise "(~CPVC) & DEA" operation masks off all the DEA channels that have hits in CPVC.
//CO 1994-July-24, 1996-Apr-20
