Centrality definitions for P18ih Au+Au 200 GeV

Status of centrality definitions:
  - low/mid luminosity - preliminary centrality definition complete
  - high luminosity - no centrality definition

Low/mid luminosity centrality definition

Production: P18ih
Trigger sets: AuAu_200_production_low_2014, AuAu_200_production_mid_2014, AuAu_200_production_2014
Run IDs: 15076101-15167014
Cuts: |vz| < 30 cm, |vz - vpd vz| < 3 cm, zdcX < 60 kHz

Links
presentation
glauber model
centrality definition reference implementation

StRefMultCorr procedure/parameters

Luminosity correction:
Mean refmult as a function of ZDC coincidence rate is corrected for by a linear fit (see presentation)
parameters: 175.758, -0.307738
normalization point: 30 kHz
Vz correction:
The position of the high multiplicity tail in the refmult distribution changes as a function of Vz due to performance differences
throughout the TPC. The tail of the luminosity corrected refmult distribution is fit with an error function, and the mean of the
error function is plotted as a function of  Vz. This distribution is fit with a sixth order polynomial. (see presentation)
parameters: 529.051, 0.192153, 0.00485177, -0.00017741, -1.44156e-05, 3.97255e-07, -6.80378e-10
normalization point: 0 cm

Glauber fit:
Glauber model parameters are shown in the presentation. The Glauber model is fit to the corrected refmult distribution  by
optimizing the multilpicity model parameters (Npp, K, x) (see presentation for details). The best fit is selected by a chi2 test.
The centrality definition is defined by integrating out 5% bins of the Glauber distribution. 
centrality bounds (refmult): 7, 10, 15, 22, 31, 43, 58, 77, 100, 129, 163, 203, 249, 303, 366, 441

The reweighting for trigger inefficiency is calculated by fitting the ratio of the corrected refmult over glauber.
weight function parameters: 1.22692, -2.04056, 1.53857, 1.55649, -0.00123008, 193.648, 1.30923e-06