  This paper presents a statistical method to subtract background in maximum
likelihood fit, without relying on any separate sideband or simulation for
background modeling. The method, called sFit, is an extension to the sPlot
technique originally developed to reconstruct true distribution for each date
component. The sWeights defined for the sPlot technique allow to construct a
modified likelihood function using only the signal probability density function
and events in the signal region. Contribution of background events in the
signal region to the likelihood function cancels out on a statistical basis.
Maximizing this likelihood function leads to unbiased estimates of the fit
parameters in the signal probability density function.
