[Halld-cal] Update to BCAL low level constants

[Elton Smith]

Dear collaborators,

I have updated GlueX-doc-2618 "Low-level calibration constants for BCAL" 
to match our current implementation in the analysis. There are two main 
changes:
1. change definition of gain constants so that they are normalized to 
attenuated energies at the end of the module.
2. The time-walk corrections reference time is given by the c0 constant 
determined in fits for the reference time.

These two modifications are intended to match what is currently 
implemented in the code. Will, Mike, Mark, and others, please check that 
the documentation correctly reflect the analysis.

Thanks, Elton.

p.s. I note that presently the code in DBCALPoint.cc to compute energies 
assumes a single exponential, which is consistent with the set of 
constants in ccdb. However, if a two attenuation length parameterization 
is implemented, the code will have to be generalized to include the full 
parameterization.




-- 
Elton Smith
Jefferson Lab MS 12H3
12000 Jefferson Ave STE 4
Newport News, VA 23606
(757)269-7625
(757)269-6331 fax