Warning in <Fit>: Abnormal termination of minimization

Dear Experts,

I am trying to fit the Z peak with breit wigner+Crystal ball as signal and
background PDF as constant+linear+quadratic+linear.
By eye judgement the fit seems to be ok. Please find that attached.
But I get the warning as:[code]

Warning in <Fit>: Abnormal termination of minimization. FCN=40.5821 FROM MIGRAD STATUS=CALL LIMIT 2717 CALLS 2718 TOTAL EDM=0.000242378 STRATEGY= 1 ERROR MATRIX UNCERTAINTY 0.0 per cent EXT PARAMETER APPROXIMATE STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 BW width 4.25614e+00 1.63990e-01 2.58644e-04 4.26857e-01 2 BW mean 9.03080e+01 4.60907e-02 5.37866e-05 -1.36681e-02 3 integral 7.33987e+03 9.10546e+01 1.80412e-06 1.86584e+01 4 CB width 1.55001e+00 1.17678e-01 6.22649e-05 1.54124e-01 5 const bkg 6.74657e-02 6.50070e-02 1.11623e-07** at limit ** 6 linear bkg 1.27850e+01 1.08316e+01 -7.93476e-03 -7.16054e-03 7 quadratic bkg 3.58951e-02 4.32847e-02 -3.27019e-04 1.33683e-01 8 cubic bkg -8.22517e-03 6.07523e-03 4.03672e-06 9.52235e+00 9 bin width 2.00000e+00 fixed 10 Alpha of CB 9.44875e+00 5.27179e+00 -6.51159e-06 7.10543e-15 11 n of CB 5.00000e+01 8.97768e-01 -0.00000e+00 0.00000e+00

It seems that the const background has reached its limit and that is why fitter is giving this warning.
I tried varying the const bkg value many times but it didnt help. But everytime I see the fit roughly the same
as attached.
What would you advice me here: shall I ignore this warning ‘or’
try to tweak this parameter more (in this case what range of const bkg do you think
could be?)?

Thanks for your help,

I am not expert but just by looking at your fit. Problem seems to lie in N and alpha. It seems N stuck at upper limit. Also, this fit seems good but parameters can’t be trusted. So, in principle fit is NOT good. Please try by modifying N and alpha, also.
I hope it may help.

Thanks Vish, I will try that and see if that works.

Best Regards,