The twist correction has been detailed in STAR notes and in blog entries (see Eric Hjort and Gene Van Buren's blogs). The entry is intended as a log of actions taken for the pp2009 calibration pass, and is not meant as a discussion of the physics motivation for the correction.

 Pass 1:

1) copied directory ~andrewar/tpc/tpcwrkExB_2008 to ~aarose/tpc/tpcwrkExB_2009

Note: local checkout of StRoot/StDbUtilities and StRoot/StGenericVertexMaker for cons to succeed

2) Gene has prepass ready under:

/star/institutions/bnl/genevb/FOR_TWIST/*.event.root

Note: there are 24 files for RFF

3) Refit results in 

 ~andrewar/tpc/tpcwrkExB_2009/outdirpp2009RFF10118_pass1

4) Build ntuple:

(cd outdirpp2009RFF10118_pass1; ls -1 *.root root.files)

root4star ~andrewar/tpc/tpcwrkExB_2009/StRoot/macros/make_res.C(10000,"outdirpp2009RFF10118_pass1")'

5) plot: (modify StRoot/macros/plot_vtx.C to point to the correct histos.root file)

root4star ~andrewar/tpc/tpcwrkExB_2009/StRoot/macros/plot_vtx.C

Output:

root4star [0]

Processing StRoot/macros/plot_vtx.C...

Info in <TCanvas::Print>: GIF file dvtxppzlt64.gif has been created

Info in <TCanvas::Print>: ps file dvtxppzlt64.ps has been created

Working on second plots...

done fitting Y slices...

starting gxe fit...

Fitting results:

Parameters:

NO. VALUE ERROR

0 3.126827e-01 3.247017e-03

1 1.481102e-03 1.744311e-04

done with gxe fit...

Fitting results:

Parameters:

NO. VALUE ERROR

0 3.125214e-01 3.516403e-03

1 1.369794e-03 1.950701e-04

still working...

still busy...

Fitting results:

Parameters:

NO. VALUE ERROR

0 -9.587691e-02 3.255975e-03

1 8.817128e-05 1.780517e-04

almost done...

Fitting results:

Parameters:

NO. VALUE ERROR

0 -1.044494e-01 3.596428e-03

1 1.149468e-04 2.041801e-04

Info in <TCanvas::Print>: GIF file bprofppzlt64.gif has been created

Info in <TCanvas::Print>: ps file bprofppzlt64.ps has been created

Conclusions:

The X intercept seems well calibrated, with only ~2um difference. However, keep in mind that the fit error is of order 10 um. The Y intercept has ~85um difference, but the error here is of the same order of magnitude. It would be best to have more data for the next pass.