Last modified: 7-OCT-1999
On-line pedestal subtraction and zero-suppression is essential to prevent excessive data volumes. The DAQ group's ASIC will do this in the real system, but it is only implemented in i960 software for the TPC Cosmic-Ray tests.
The current algorithm allows the user to vary requirements on the number of sequential pixels that must meet or exceed threshold, and the number of pre- and post-samples. This approach differs somewhat from that of the ASIC.
There are obviously trade-offs between noise suppression and hit resolution in the choice of zero-suppression parameters, but these have not been studied systematically. The DAQ ASIC allows some flexibility in their choice.
In general, one would expect better resolution for large average dE/dx, while hits with much higher than expected energy loss probably indicate that a delta-ray deposited abnormally large ionization in a clump. We should check our data against our expectations and our slow simulator.
Many minimum-ionizing hits contain 2-pad hits; however, these are 3-pad hits in the sense that a measurement usually was made on the third pad, but simply failed the threshold requirement. Therefore, information does exist on the third pad; we might be able to exploit it to improve our resolution.
The tcl cluster finder attempts to estimate the pad crossing angle, and there are also estimates from the width of the hit. These should be compared to the reconstructed track angle.