Extraction of Basic Information

Basic information is extracted from the laserball time histograms by
OCA_EXTRACT.FOR. If element $a$ of the control word is 1 or 3, then each laserball file specified to input stream 1 is opened and read in. If an error occurs here, the user is allowed to either try again or quit. Since laserball files can be quite large, this gives the user the opportunity to compress, decompress or move files as needed. The line-of-sight distance to each PMT is then computed to define a rough, 10ns wide time window within which the prompt pulse is expected. An additional overall fixed offset of 100ns is currently assumed, although the correct value(s) must clearly be specified to SNOMAN at a later date. For each file and PMT, the following parameters are computed and designated by index mnemonics listed in OCA_DATA.INC:

Index Mnemonic	Computed Quantity
OCA_NG	Gaussian fit number of entries in prompt peak
OCA_NSW1	Sliding 7ns window containing highest number
	of entries corresponding to prompt peak
OCA_NSW2	Sliding 7ns window containing 2nd highest
	number of entries
OCA_NPeak	Number of entries in prompt peak (currently=OCA_NG)
OCA_NW1	Number of entries contained in successive, 10ns windows
-OCA_NW10	starting from beginning of prompt peak window
OCA_ND2	Squared distance to PMT in cm
OCA_NCT	Cosine of PMT orientation with respect to line-of-sight
OCA_NP	Number of laser pulses actually fired
OCA_NPois	Poisson correction for the possibility of multiple hits
OCA_ND2O	Distance traversed by photons in D2O to get to PMT
OCA_NH2O	Distance traversed by photons in H2O to get to PMT
OCA_NACR	Distance traversed by photons in acrylic to get to PMT
OCA_NTILE	Acrylic tile number traversed by photon in getting to PMT
OCA_NLASR	Relative probability of photon to be emitted in the
	direction of PMT, based on laserball angular distribution

If element $a$ of the control word is 2, this information is read in from a previously saved OCA data structure stored in a file whose name is passed to input stream 2. If element $a$ of the control word is 3, this causes the parameters to be computed and signals the OCA data structure to be written out to the file specified on input stream 2.