Simultaneous fit in separated ranges with the same pdf

goodmorning everybody. i’m doing a blind analysis on a Michel Spectrum of the muon decay. i cut the data in a signal region between 51.92 MeV and 53.72 MeV, so a histogram with this data shows a hole in this region. i need to do a simultaneous fit in the two remaining sidebands SB1 (50, 51.92) and SB2 (53.72,56). i proceded in this way:
i defined
RooDataHIst binned(“binned”,“binned”,RooArgSet(E),data) where data is a RooDataSet filled in this way data.add(RooArgSet(E))

then i tried with the likelihood fit

RooFitResult *res=bkg.fitTo(binned, Range(“SB1,SB2”),SplitRange(kTRUE))

where bkg is my pdf with 12 parameters. i tried severl times to change the number of free parameters, but nothing!

then i tried modifing the class RooChi2Var, just saying that if it founds bin with zero values (the hole) to continue fitting. but nothing!

i tried several times in other ways, but till now i didn’t obtain a convergent fit!

please help me!