[RF] Bug with RooExtendPdf produces inconsistency in rf204b_extendedLikelihood_rangedFit.C between before 6.26 and after 6.28

[atsushi-icepp]

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Description

I am reporting a bug in RooExtendPdf, which can be seen in rf204b_extendedLikelihood_rangedFit.C of the tutorial. In the recent versions, the fit using RooExtendPdf class has wrong best-fit values of 𝑁 =4494 (and 𝛼 is biased as well) while the fit using the composite of signal and background PDFs implemented by RooAddPdf correctly fits the distribution with 𝑁 =9990.

Looking back into the past versions, this issue appears since version 6.28. With version 6.26, RooExtendPdf properly works.

Reproducer

ROOT tutorial: rf204b_extendedLikelihood_rangedFit.C.

ROOT version

Any versions after 6.28

Installation method

Built from source

Operating system

SLES15 and ALMA10

Additional context

No response