Cuts used:

  • st_centralpro files where available (all but the first 4 fills)
  • rank > -3.8
  • highest ranked vertex in the event (index==0)
  • # of daughters > 1000 (mult>1000)

Here are the results for 61 fills:

I was a little concerned about the notably different intercepts for the second fill (16779), but this was a very low luminosity fill with 12x12 bunches and looking at the individual vertices I found the half mm shift to be consistent across all z, independent of luminosity or multiplicity, so I left this point in. I don't think there's any UPC data until the fourth fill (16780) anyhow.

It should be noted that some luminosity depedence is still believed to exist in this data, most likely from remaining uncorrected luminosity-dependent distortions in the TPC. This has been documented elsewhere, but the below plot shows the intercepts from the above data color-coded by luminosity to demonstrate that a correlation remains at the level of ~0.05 cm (half a mm). NB: available for luminosity in the ntuples was the average of the ZDC coincidence rates from events used, though some of the ZDC-based rates are also known to have issues, and were not used in the TPC luminosity-dependent distortion corrections.