A non-iterative method for constraining masses in particle decays

To overcome the mass constraint problem of particle decays, a non-iterative method is developed as an alternative to relatively complicated and slow iterative methods. The new method can be applied to any two-body decay or a many-body decay which can be reduced to a two-body decay having well known daughter masses. By using a toy detector simulation and ALEPH full simulation data, the performance of the new method is compared with the traditional iterative chi-square method for several decay types. No significant difference is obtained between the two methods in terms of improvement in momentum resolution. However, the non-iterative method is found to be much faster than the chi-square method.