For my Cosmic rays study, version 2 I was combining all possible pairs of tracks in events with 2 or more global tracks. I made some plots to understand where the tracks were going though the TPC and was surprised by some structures in the plots of z positions.

In these plots, z_outer is the z of the outermost (or last) hit on the track, and z_inner is the z of the innermost (or first) hit. The "matching" requirement is that tracks are back-to-back in both azimuth φ and polar angle θ.

Here are plots of:

Top-left: z_outer,1 vs. z_outer,2 {matching}

Top-right: z_inner,1 vs. z_inner,2 {matching}

Bottom-left: z_outer,1 vs. z_outer,2

Bottom-right: z_inner,1 vs. z_inner,2

Here we see structure in these distributions using the TOF group of data:

The structures seem particular to events with high multiplicity (some events have thousands of tracks). Here we see the structures for track pairs from events with 5 or more tracks:

I believe these are due to Au+X events at low energy, generated when C-AD was trying to see if it could deliver AuAu beams at 5 GeV.

After removing these events with 5 or more tracks, the distributions look much better. I include here both the TOF group of triggers (left) and MTD group (right). Such high multiplicity events are thus to be excluded from the cosmic ray study.

-Gene