Likelihood maximiziation with 4 variables

Hello all,

In the following likelihood function, I want to add one more variable and the find the maximum:
L (X,Y,Z) = PI {f(N_MC, N_data)}
N_MC (X,Y, Z) = N_bkg + X*W(Y,Z)*N_signal

So far, I was using MINUIT to minimize -Log(L) which is in fact a TF3 . But now I want to change the L as follows:
L (X,Y,Z,T) = PI {f(N_MC, N_data)}
N_MC(X,Y,Z,T) = TN_bkg’ + XW(Y,Z)*N_signal.

Is there any way for such implementation (something like a TF4)?

Thanks a lot,

grep -r Minimize ${ROOTSYS}/tutorials