Integral Error in Signal

ROOT
3

Here my code

#!/usr/bin/python

import sys
import ROOT

ROOT.gStyle.SetOptFit(11111)

ff = ROOT.TFile(sys.argv[1])
h2 = ff.Get("NDE_mmVSmp_exp")

c1 = ROOT.TCanvas('c1','c1',1100,800)
c1.Print('test.pdf[')
h2.Draw('colz')
c1.Print('test.pdf')
f1=ROOT.TF1("f1","gaus(0)+pol2(3)",0.81,1.02)
f1.SetParameters(1,1,0.2,1,1,1)
hy1 = h2.ProjectionY()
hy1.Draw()
hy1.Fit(f1,"R")
mu1,sig1 = f1.GetParameter(1), f1.GetParameter(2)
r11,r21 = mu1-3*sig1,mu1+3*sig1

fsig1 = ROOT.TF1("fsig","gaus",r11,r21)
fsig1.SetParameters(*[f1.GetParameter(i) for i in range(3)])
fsig1.SetLineColor(4)
fsig1.Draw('same')
ntot1 = abs(f1.Integral(r11,r21))/hy1.GetBinWidth(1)
nerrtot1 =abs(f1.IntegralError(r11,r21))/hy1.GetBinWidth(1)
nsig1 = abs(fsig1.Integral(r11,r21))/hy1.GetBinWidth(1)
nsigerr1 = abs(fsig1.IntegralError(r11,r21))/hy1.GetBinWidth(1)
hy1.SetTitle('ntot={:.2f}#pm {:.2f},nsig={:.2f},nsigerr={:.2f},ratio={:.2f}%;missing mass'.format(ntot1,nerrtot1,nsig1,nsigerr1,nsig1/ntot1*100))

c1.Print('test.pdf')

c1.Print('test.pdf]')