FDC Beam hole size

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Here is a brief simulation study aimed at helping give insight as to the affect the FDC beam hole size will have on the acceptance of forward going tracks.

A set of 20 simulations were done throwing 1000 events each with 1 π+ per event. The geometry of the FDC was modified to have both the Copper Kapton and the Rohacell backing extend all the way down to the beam line. This was done to allow software cuts on the radius of the beam hole.

The particles were thrown with a momentum of 0.25, 0.5, 1.0, 2.0, and 4.0 GeV/c for each of the following angles: 0.5, 1.0, 2.0, and 4.0 degrees.


The plots below show the number of hits per track as a function of the beam hole radius. These must be interpreted using some asumption about the minimum number of hits per track needed to find and fit the track. An assumption of 10-12 hits per track minumum may be a good place to start. The hits in these plots were taken from DMCTrackHit objects which are filled using "truth" information. No indication as to the quality of the hits is given. Also, the Lorentz effect is not taken into account which will push some hits outside of the fiducial area (and some hits inside). This should be a small peturbation though.



The following plots show the average distance from the beamline for π+ particles at specific momenta and angles.