Hello,
Sorry to ask this question again (And I think it is better to move here).
So, I followed Wouter’s instructions in
http://root.cern.ch/phpBB2/viewtopic.php?t=7539&highlight=
To be simple, I just used a single Gaussian for the K factor, but it doesn’t work. I expect that after doing the Mellin convolution, the k is ntegrated out, and the pdf (versus t) should be something like exponential convoluted with a Gaussian. But what I obtained is a flat line. Did I do something wrong?
[code]void tesMellinCov(){
using namespace RooFit;
RooRealVar *t = new RooRealVar( “t”, “proper time”, -0.5 , 10.0 , “ps” );
RooRealVar *st = new RooRealVar(“st”, “proper time resolution”, 0.05, 0.10, “ps” );
RooRealVar *k = new RooRealVar( “k”, “k factor”, 0.3 , 3.0 );
RooRealVar *Tau = new RooRealVar(“Tau”, “lifetime”, 1.5, 0.1, 3.0, “ps”);
RooRealVar *TauResScale = new RooRealVar(“TauResScale”,“resolutions scale”,1.185, 0.5, 3);
RooRealVar *TauResBias = new RooRealVar(“TauResBias”,“bias”,0.,-5,5);
RooRealVar *TauResBiasScale = new RooRealVar(“TauResBiasScale”,“bias scale”,1.0,0.5,3);
RooResolutionModel *TauRes = new RooGaussModel(“TauRes”,“resolution model”,
*t,*TauResBias,*st,*TauResBiasScale,*TauResScale);
// Exp(t|tau) fConv Gau(st) — fConv: Fourier convolution
RooAbsPdf *TauPdf = new RooDecay(“BcTauPdf”, “proper time pdf”, *t, *Tau, *TauRes,RooDecay::SingleSided);
TauResBias->setConstant(kTRUE);
TauResBiasScale->setConstant(kTRUE);
// Take into account K factor
RooFormulaVar PseudoTau = new RooFormulaVar(“PseudoTau”, “pseudo lifetime”, "kTau", RooArgSet(*k,*Tau));
RooAbsPdf *PseudoTauPdf = new RooDecay(“PseudoTauPdf”, “proper time pdf”, *t, *PseudoTau, *TauRes, RooDecay::SingleSided);
// K factor distribution, one Gaussian
RooRealVar *gauMean = new RooRealVar( “gauMean” , “mean” , 1.0, 0.8, 1.2 );
RooRealVar *gauSigma = new RooRealVar( “gauSigma”, “sigma”, 0.2, 0.1, 0.3 );
RooAbsPdf *kPdf = new RooGaussian(“kPdf”, “k distribution”, *k, *gauMean, *gauSigma) ;
// [ Exp(t|k*tau) fConv Gau(st)] mConv Gau(k) — mConv: Mellin convolution, k integrated out
k->setBins(10000,“cache”) ;
RooAbsPdf *PseudoPdf = new RooFFTConvPdf(“PseudoPdf”, “PseudoPdf”, *k, *PseudoTauPdf, *kPdf );
RooPlot *tframe = t->frame();
PseudoPdf->plotOn(tframe);
tframe->Draw();
}[/code]
Thank you very much.
Cheers, Jibo
