Wall stops

For the incoming muons themselves, before any diffusion effects, there should be a negligible problem with wall stops. The resolution of the TPC is about 4 mm in z, 6 mm in x and 4 mm in y. We always make a fiducial cut about 1.5 cm or more from any wall materials. With the near 100% tracking efficiency for muons this is well under control. Furthermore we will make special analysis of events closer to the walls to establish the distance at which wall effects occur and what the fall-off is with distance. Diffusion into the walls of $\mu d$ atoms is a real concern and is handled in detail below.