I am using RooJohnson+Gauss to describe the mass distribution of my signal and one background. I see there is a difference in the results when updating the root version from 6.18 to 6.20. Mainly, a drop of the mass distribution in the lower mass side is observed in the new version (see the red and the magenta distributions in the attachment, left is the new version, I do here a simultaneous MC-data fit). I could figure out that the difference is somehow related to the setting of the massThreshold. So, setting the massThreshold to be equivalent to my lower limit of the mass fit range, will result in the drop. To fix it in the new version, I had to go to a lower massThreshold than the low limit of my fit range.
My questions would be then: was there a bug in the old version that has been fixed recently, for example, the massThreshold was ignored so that I haven’t seen this drop earlier, or are you aware of other reasons? Shall I go to lower massThreshold than the actual fit range?
By comparing the RooJhonson class, I could see this line is newly added https://root.cern/doc/v620/RooJohnson_8cxx_source.html#l00079, not sure though if related!