Parameterization of deflections/preliminary momentum resolution results

Using the 1500 Amp TOSCA map provided by Paul Brindza, I ran Garfield calculations over a grid in z and r corresponding to the dimensions of the FDC to compute the deflections of the avalanches along the wire due to the Lorentz force. The behavior of this deflection for ionizations throughout a given FDC cell is well-described by a plane:

The two slope (tangent) parameters describing the deflection planes are shown as a function of r and y=z'(beam direction in GlueX coordinate system) here:

Here r is the same as x in the GlueX coordinate system. For interactions in the FDC for other phi values, the tan(theta_x=theta_zbeam) component is multiplied by cos(phi).

The hitFDC.c routine in HDGeant has been modified to read in a table of these tangent values and interpolate the amount of deflection as a function of the point of closest approach to the avalanche wire on a wire-by-wire/event-by-event basis.

Next I generated npi+ events with 9 GeV photon beam and t-slope of 0.25 GeV^-2 to mostly populate the forward region and ran the events through HDGeant. One caveat is that the current version of the B-field in the repository has slightly less magnitude (~2T in the central region of the bore as compared to ~2.2 T) than the one I used to generate the deflection table.