Update 04.23.2018 -- Pythia: pT Resolution Width (and Resolution / Efficiency Algorithm)
I wanted to check what the pT resolution [sigma = (pTmc - pTreco) / pTmc] looks like as implemented in our standalone Pythia8 simulation, so as to compare it to the resolution I calculated from the Run 9 dijet embedding:
https://drupal.star.bnl.gov/STAR/blog/dmawxc/update-04132018-run-9-pp-track-phi-eta-pt-resolution
https://drupal.star.bnl.gov/STAR/blog/dmawxc/update-04162018-run-9-pp-pt-resolution-width
By design, the resolution is symmetric about sigma = 0.
Let 'sig0' be the constant width and 'sig1' be the "linear" (pT-dependent) width, then the algorithm we used for calculating pTreco (a.k.a pTtrk):
r1 = gRandom -> Gaus(0., (sig1 * pTmc));
r2 = gRandom -> Gaus(0., sig0);
res = r1 + r2;
pTtrk = pTmc * (1.0 + res);
r2 = gRandom -> Gaus(0., sig0);
res = r1 + r2;
pTtrk = pTmc * (1.0 + res);
And with the smeared momentum in hand, the efficiency (recorded in a histogram 'hPtEff') is applied via:
iEff = hPtEff -> FindBin(pTtrk);
eff = hPtEff -> GetBinContent(iEff);
pass = gRandom -> Uniform(0., 1.);
eff = hPtEff -> GetBinContent(iEff);
pass = gRandom -> Uniform(0., 1.);
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