A maximum likelihood method for particle momentum determination

We discuss a maximum likelihood method for determining a charged particleʹs momentum as it moves in a magnetic field. The formalism is presented in both rigorous and approximate forms. The rigorous form is valid when random processes include multiple scattering, energy loss and detector spatial resolution. When the measurement error is dominated by multiple scattering, it takes a particularly simple approximate form. The validity of both formalisms extends to include non-Gaussian multiple scattering distribution.