Event and track cuts

In this step, event and track cuts are applied. The only event cut is a cut on the flag on the vertex fit (iflag==0). The cuts on tracks are: 30 or more $dE/dx$ points in the MTPC, more than half or the potential points in the main TPC, the $\phi$-wedge cut, and a cut to remove MTPC-only tracks. This last cut means that tracks that have more than 10 potential points in at least one of the VTPC are rejected if they have no points found in the VTPC. This constitutes a rather mild cut to reject MTPC-only tracks that should have VTPC points (MTPC-only tracks that have no potential points in the VTPC are accepted). The $\phi$-wedge cut selects tracks that are within 30 of the horizontal plane. The main goal of this cut is to reject tracks that leave the TPC thought the top or bottom, where the $dE/dx$ measurements can be distorted (this is mostly a concern for points close to the readout plane).