2006 TPC Drift Velocity Investigation
Preliminary analyses of the 2006 data have shown an abnormally large DCA for tracks from a 4-day period following a purge of the TPC on the evening of May 18th. TPC experts have suggested that a recalculation of the drift velocity measurements using the procedure developed for Run 7 may allow for better reconstruction of these tracks. Here's my first attempt at the recalculation, using Yuri's codes "out-of-the-box".Procedure
- Restore st_laser DAQ files from HPSS
- cons StRoot/StLaserAnalysisMaker
- Run a simple BFC chain: root.exe -q -b 'bfc.C(9999,"LanaDV,ITTF","path_to_st_laser_daq_file")'
- execute LoopOverLaserTrees.C+("./st_laser_*.tags.root") to generate drift velocity measurements
Results
Here are the drift velocity measurements currently in the Calibrations_tpc database and the ones that I recalculated from the st_laser DAQ files. I'm only showing measurements from the 10 days around the purge:
I'm not sure how much attention should be paid to the original East laser measurements. The West laser measurements in the DB track pretty closely with the new ones. The significant difference is that there are more new measurements covering the period where the D.V. was changing rapidly:
So what we're really interested in is, for a given event, how different will the D.V. returned by the database be? The way to calculate that is to compare each new measurement to the DB measurement with the closest preceding beginTime:
In the West ratio plot one can clearly see the effect of the additional measurements. For comparison I've plotted the time period where we see problems with the track DCAs and <nTracks> / jet. See for example
http://deltag5.lns.mit.edu/~kocolosk/protected/drupal/4036/summary/bjp1_sum/bjp1_sum_dcaG.gif
http://drupal.star.bnl.gov/protected/spin/trent/jets/2007/apr06/problem_highlights.gif
http://cyclotron.tamu.edu/star/2006Jets/apr23_2007/driftVelocityProb.list
Next Steps
As I mentioned, I didn't tweak any of the parameters on Yuri's codes to get these numbers, so it may be possible to improve them. I looked at the sector-by-sector histograms in the file and the values for the drift velocities looked generally stable. The values for the slopes jumped around a bit more. Assuming there are no additional laser runs that I missed, we could look into interpolating between drift velocity measurements to get even more fine-grained records of the period when the gas mixture was still stabilizing. Here's an example of a fit to the new combined drift velocity measurement in the rapidly-varying region: