  A method to directly determine the Wilson coefficients for rare $b\to s$
transitions using $B^0\to K^{*0}\mu^+\mu^-$ decays in an unbinned maximum
likelihood fit is presented. The method has several advantages compared to the
conventional determination of the Wilson coefficients from angular observables
that are determined in bins of $q^2$, the square of the mass of the dimuon
system. The method uses all experimental information in an optimal way and
automatically accounts for experimental correlations. Performing
pseudoexperiments, we show the improved sensitivity of the proposed method for
the Wilson coefficients. We also demonstrate that it will be possible to use
the method with the combined Run 1 and 2 data sample taken by the LHCb
experiment.
