YAM2: Yet another library for the M2 variables using sequential quadratic programming
Chan Beom Park
The M2 variables are devised to extend MT2 by promoting transverse masses to Lorentz-invariant ones and making explicit use of on-shell mass relations. Unlike simple kinematic variables such as the invariant mass of visible particles, where the variable definitions directly provide how to calculate them, the calculation of the M2 variables is undertaken by employing numerical algorithms. Essentially, the calculation of M2 corresponds to solving a constrained minimization problem in mathematical optimization, and various numerical methods exist for the task. We find that the sequential quadratic programming method performs very well for the calculation of M2, and its numerical performance is even better than the method implemented in the existing software package for M2. As a consequence of our study, we have developed and released yet another software library, YAM2, for calculating the M2 variables using several numerical algorithms.