Run 12 p+p 500 GeV SC and GL updates

Speaker : David Garand ( Purdue )


Talk time : 12:00, Duration : 00:20

Issues with SpaceCharge & GridLeak in Run 12 pp510 have been previously reported at an S&C meeting. This topic will be discussed today by David Garand (attached talk) and Gene Van Buren (this page's content).

Some things we sought to examine:

  • Distribution of space charge in the TPC (see David's attached talk)
  • Resolve problems with newer version of calibration macro (Calib_SC_GL.C) [unresolved]
  • Investigate using W candidate events for calibration [some statistics issues; may have bumped into the same problems with calibration macro]
  • Investigate regions of problematic signed DCAs [partially done]
    • Able to demonstrate uniformity between most sectors; still having a problem with looking at signed DCA in the sectors of most interest! (see Table 1 below)
  • Miscellany that arose:
    • Can include Jan B.'s work on calibrating GridLeak dependence on anode HV into next calibration round
    • Distortion correction code (StMagUtilities) improved for large distortions
    • New open questions about occupancy (affecting calibration?)...see next section...

Plan is to...

  1. Re-do the calibration: exclude questionable sectors, include modifications for charge distribution, anode HV dependence, and distortion code improvement.
  2. Cycle back and verify the charge distribution using the updated calibration since the charge distribution determination has a dependence on the calibration.
  3. Decide whether we need to exclude specific sectors from the production.

Table 1. Sector-by-sector calibration of SpaceCharge & GridLeak

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Other likely-to-be relevant issues...

Justin's presentation on the W analysis concluded the following:

  • Calibrations of TPC are sufficient for W analysis with regard to pT reconstruction
  • There is some problem with loss of efficiency at high luminosity (seen also in embedding tests)
    • Appears to be due to loss of hits on tracks (Nhits_fit / Nhits_possible), particularly at inner-most padrows
    • Theories:
      • Calibration issue: this is where distortions are largest
      • Reconstruction issue: this is where occupancy is highest
      • A difference between the two may be z dependence

I took a quick look at occupancy recently and see that ~45% of hits on inner padrows have the flag FCF_MERGED at high luminosity (see Figure 1 below). Tonko's definition of the FCF_MERGED flag: "The cluster was deconvoluted. This implies loss of precision, especially in the charge. Typically should not be used for dE/dx calculation." Perhaps these are our problem? This needs to be understood.

Figure 1. FCF_MERGED hit fraction vs. padrow (x axis) and luminosity (depth)


-Gene