README fdc_covariance_hists
April 22, 2009  David Lawrence


This plugin can be used to generate 2D histograms of the 
covariance of FDC layers using a file produced by hdgeant
as input.

This works by swimming a particle using the DMCTrajectoryPoint
parameters for the step closest to the first layer of the
FDC. The covariance is calculated from the residuals between
the swum track and the drift distance given by hdgeant. The
covariance is therefore measured relative to the particle
as it enters the FDC (as opposed to looking at the covariance
all the way back to the target.

This assumes that there is no position smearing of the drift
times so that the residuals are due purely to multiple scattering
(and energy loss if that is turned on as well).

The control.in file used for hdgeant should contain the following:

TRAJECTORIES 3
NOSECONDARIES 0
MULS 1
LOSS 1
DECAY 0