Event Class Handling

Pass 5 and Prior Implementations (ST v9r4p2 and earlier)

• Prior to DC2, there was a separate event class designation for each section of the LAT where the event converted, e.g., DC1::FRONT, DC1::BACK were two distinct classes for otherwise identical event selections. These were given values of 0 and 1, respectively, in the EVENT_CLASS column of FT1. The CONVERSION_TYPE column was set to have the same values, indicating a front (thin) or back (thick) section conversion.
• For DC2, there were two distinct sets of cuts that divided the events into two classes, A and B. This resulted in 4 possible values for the EVENT_CLASS column, and two values for CONVERSION_TYPE:

  event class name	EVENT_CLASS	CONVERSION_TYPE
  DC2::FrontA	0	0
  DC2::BackA	1	1
  DC2::FrontB	2	0
  DC2::BackB	3	1

  Besides still containing redundant information, this required special code in gtselect and the Likelihood tools to handle.
• For Pass 5, Bill defined a new classification tree variable, CTBClassLevel, and proposed three different cuts corresponding to what he envisaged as the appropiate kind of science analysis:

  CTBClassLevel cut	science analysis designation
  > 0	"transient"
  > 1	"source"
  > 2	"diffuse"

  The mechanism used for DC2 was unwieldy, and so it was not modified to handle these new classes. A temporary ad hoc procedure was adopted in which a CTBCLASSLEVEL column was added to the FT1 files (outside of the FFD definition), and fcopy or some other tool besides gtselect was used to make the CTBCLASSLEVEL cuts. The EVENT_CLASS and CONVERSION_TYPE columnss simply indicated front (0) vs back (1), and three separate sets of IRFs were generated for each of the cuts. The principal disadvantage of this scheme is that gtdiffrsp needs to be run separately for each CTBCLASSLEVEL cut, and there was no DSS keyword handling implemented to account for which cut was applied for any given dataset.

Proposed New Scheme (25 Mar 2008)