Fit Convergence with Status 5

Roofit and RooStats
1

Dear Experts,

I’m trying to minimize a given likelihood and obtained the following results, where the pulls seem reasonable and the uncertainties as well, but the status it gives is 5, meaning the Hessian failed.

Info in : VariableMetricBuilder Stop iterating after 194.74 ms
Warning in : CombinedMinimumBuilder Both migrad and method failed also at 2nd attempt; return simplex Minimum
Warning in : Minuit2Minimizer::Minimize Covar is not pos def
Minuit2Minimizer : Valid minimum - status = 5
FVAL = -898945.671385084046
Edm = 3.88594344258308411e-07
Nfcn = 155
deltaAy = 0.00096811 +/- 0.00245604
deltaAz = -0.000335685 +/- 0.0104327
deltaBz = 9.58189e-05 +/- 0.0202858
deltaBy = 0 (fixed)
kappa = 1 (fixed)

— Parameter Pulls —
deltaAy pull = 0.394175
deltaAz pull = -0.0321764
deltaBz pull = 0.00472344

Could you please explain why this is happening?

Best,

2

Dear @Mustaphaa ,

Thanks for reaching to the forum, maybe @jonas will be able to give you more insights about the result of your fit.

Cheers,
Vincenzo