Dear experts,

I have fitted the data sets with two Gaussian PDFs in roofit.

RooRealVar mean(“mean”,“mean”,1.777,1.75,1.79);

RooRealVar sigma1(“sigma1”,“sigma1”,0.00,0.0,0.1);

RooGaussian signal1(“signal1”,“signal1”,x,mean,sigma1);

RooRealVar sigma2(“sigma2”,“sigma2”,0.01,0.0,0.2);

RooGaussian signal2(“signal2”,“signal2”,x,mean,sigma2);

RooRealVar sfrac(“sfrac”,“Area fraction”,0.5,0.0 ,1.0);

RooAddPdf signal(“signal”,“model”,RooArgList(signal1,signal2),sfrac);

signal.fitTo(*data);

After the fit, there are two sigmas found as a result. Here my question is what will be the ideal way to calculate the effective uncertainty from the fit.

I am thinking to calculate the, Effective sigma = sfrac*sigma1 + (1-sfrac) sigma2 here in roofit. Please let me know someone whether the above way is correct or they will be added in quadrature Effective sigma = sqrt( sfrac(sigma1)^2 + (1-sfrac)*(sigma2)^2 ). I am somehow confused about this now.

Thanks in advance.

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