I wanted to be sure that the simulations we're making for TPC alignment residual studies was really doing what we want it to do...

Log files have this output:

 Y2010: Y2010: BASELINE
 PHYS_OFF: NO PHYSICS: ONLY ENERGY LOSS

Also available is the kinetic energy (KE) of the particles reported at various sampled volumes printed as lines of text in the log files. Using a Pt = 0.5 GeV/c proton log file (which actually generates a spread in KE because a range of eta [-0.6,0.6] are allowed), I plotted a few quantities:

y vs. x, r vs. z:

First point y vs. x (essentially the primary vertex):

KE vs. transverse radius, and Pt vs. transverse radius:

There's a strong energy loss evident when we reach the BEMC (so energy loss is definitely working), but it's a little harder to see the energy loss in the TPC.

KE shows a bump in the above plots for radius just above because this is between the inner field cage and the first TPC padrow. The only reason we get a sample for these radii is if the track crosses the central membrane (CM, see the r vs. z plot earlier), which means there is a bias towards tracks with a specific range in eta. Since KE gets larger for a constant Pt as we increase eta, these CM samples show a bias in KE as well.

KE vs. transverse radius and z, Pt vs. transverse radius and z [TPC radii inward only]:

Again, the high eta tracks have higher KE for the same Pt. With the zoomed in scale, the energy loss in the TPC gas is also clear.

Using a pi+ sample instead, KE vs. transverse radius, and Pt vs. transverse radius:

These Pt = 0.5 GeV/c pions have less energy loss than the protons, and penetrate further into the BEMC and magnet. The rise in Pt near radius=300 is curious, but these again may be biased by pions that didn't interact with much before they got to the magnet. This plot of samples from the pion simulation for transverse radius > 196, out near the BEMC and magnet, show the structure out there nicely (the protons did not reach as far):

I conclude that the simulation is working fine.

-Gene