Hao Qiu was able to calibrate alignment of the TPC sectors for Run 8, but this has not yet been used for large scale data production as the calibration arrived too late to assess (and re-calibrate TPC SpaceCharge+GridLeak) in time for the start of the P08ic productions of Run 8 data. The decision not to wait for that assessment was based partially on a naive expectation that the alignment changes were likely inconsequential to physics.

A couple issues were identified in analyses of the P08ic production of dAu data: You do not have access to view this node and inexplicable h-/h+ & e-/e+ ratios. The topic was discussed at some S&C meetings (see You do not have access to view this node for example). Hopeful that solving the DCA problem would help solving the ratios problems, the P08ie production of Run 8 dAu data included some additional improvements in the TPC SpaceCharge correction, still using the old TPC sector alignment.

Unfortunately, the P08ie production appears not to have solved the h-/h+ ratio problem, while a test production processed using Hao's updated alignment for the TPC did appear to be helpful for both h-/h+ and e-/e+. The state of affairs was reviewed in mid-April by the S&C team and among the action items were to finish assessment of the TPC alignment calibrations, re-calibrate TPC SpaceCharge+GridLeak, and provide a new sample for re-evaluation.

Progress was made on the alignment assessment and You do not have access to view this node by performing the alignment calibration on both Run 7 and Run 9 data as well. The results gave confidence to the calibration, readying us for the next step of re-calibrating the Run 8 TPC SpaceCharge and GridLeak, which is what I present here.

In order to use the new PCA method of multi-scaler SpaceCharge calibration in combination with the older method of single scaler SpaceCharge+GridLeak calibration, I had to update the Calib_SC_GL.C macro to use luminosity measures which include several scalers. I also updated the code to try to exclude some pileup data via a cut that at used vertex have at least one track matched to the BEMC. The PCA method introduced three periods which needed to be calibrated separately (runs before 9004000, between 9004000 and 9016000, and after 9016000). I have chosen to re-calibrate the third period.

After several passes on the data, I have found the following calibration to be stable:

* Constraint on SC x GL =  9.024 +/-  5.916
* Guesses on SC =  0.984 , 0.9839 , 0.5583 , -0.5574
* Guesses on GL =  9.171 ,  16.16 ,  9.172 , -16.19
* Guesses on SO = -4.523e-05 , -3.997e-05

*** FINAL CALIBRATION VALUES: ***
SC = (2.563e-07*(zdcx-(-54.3)))+(-4.822e-08*zdcw)+(1.9094e-08*bbcw) with GL =  9.17

This is a slight increase in the GridLeak relation to SpaceCharge (by ~5%), and a slight increase in the SpaceCharge correction itself over the previously used measure (by ~1%):

SC = (3.56937e-07*(zdcx-582.871654))+(-4.04788e-08*zdce)+(1.20216e-07*bbcbb) with GL =  8.74

Perhaps also worthy of note is that the scaler offset from zero is small with the new calibration (~54 vs. ~583), likely reflecting that some of the previously calibrated offset was in fact alignment related.

Both the alignment and the SpaceCharge+GridLeak corrections have now been entered into the database with entryTimes of 2009-05-22. Note that for now, I have made the Run 8 alignment entries applicable for all of Run 8 (and Run 9), despite that the TPC SpaceCharge+GridLeak calibrations have not yet been re-done for earlier dAu data from Run 8, nor the pp & low energy AuAu running from later in Run 8.

-Gene

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Updated on May 27, 2009:

Period II spans days 004-015.

* Constraint on SC x GL =  8.652 +/-  1.087
* Guesses on SC =  1.002 ,      1
* Guesses on GL =  8.634 ,  8.649
* Guesses on SO = -1.829e-05 , -1.751e-05

*** FINAL CALIBRATION VALUES: ***
SC = (3.15e-7*(zdcx-(-1331)))+(-6.056e-08*zdcw)+(1.808e-08*bbcw)) with GL =  8.65

Now in the DB.

-Gene