Likelihood fit fails to fit the tail

Hi RooFit experts,

I’m trying to build one 3rd order dijet function to fit the smooth background. With chi2 fit the fitting result looks good compared with data.

However, if I do a likelihood fit, the fit fails and the agreement in the tail region looks bad.


I attached my script and the histogram here. Could anyone take a look and see if something is wrong?

Thanks a lot.

Yongbin (1.6 KB)

test.root (6.5 KB)


I think this could be related to an open issue of binned likelihood fit in RooFit, see

The same fit works correctly in ROOT when using the binned likelihood fit there. Attached is your script extended to use ROOT


1 Like (3.0 KB)

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