Hi,
I am facing a strange problem in a 2D fit I am performing on a data set. I have defined a PDF, with all the parameters fixed (so, only area under the component will change, but not the PDF shape).
The
RooGenericPdf dsstCFrhoPolarization("dsstCFrhoPolarization",
"(1 - fLong)*(3/2)*(1 - rhoHelicity*rhoHelicity) + 2*fLong*rhoHelicity*rhoHelicity",
RooArgList(fLong, rhoHelicity));
RooRealVar d0("d0", "d0", -0.99),
d1("d1", "d1", 0.29),
d2("d2", "d2", -0.11),
d3("d3", "d3", 0.41),
d4("d4", "d4", 0.39),
d5("d5", "d5", 0.37),
d6("d6", "d6", 0.16),
d7("d7", "d7", 0.16);
RooChebychev dsstCFdsstAcceptance("dsstCFdsstAcceptance", "dsstCFdsstAcceptance",
dsstHelicity, RooArgList(d0, d1, d2));
RooChebychev dsstCFrhoAcceptance("dsstCFrhoAcceptance", "dsstCFrhoAcceptance",
rhoHelicity, RooArgList(d3, d4, d5, d6, d7));
// Dsst crossfeed Total PDF
RooProdPdf dsstCrossfeedTotal("dsstCrossfeelTotal", "dsstCrossfeedTotal",
RooArgList(dsstCrossfeedDE, dsstCFrhoPolarization, dsstCFdsstAcceptance, dsstCFrhoAcceptance));
The figure attached shows the fit results. The gray curve in the upper plot represents the PDF dsstCFdsstAcceptance, which is a 3rd order Chebyshev polynomial, with all the coefficients (d0, d1, d2) fixed.
This is strange and I am unable to understand why …
though it appears more as a conceptual problem than a fitting bug, I feel: If the component dsstCFrhoPolarization is removed, the above PDF recovers it’s original shape !!
BTW, this doesn’t happen in a similar fit in the other dimension.
TIA,
Nikhil
dsstrho-PolarizationFit-test.pdf (24.4 KB)