Could MT2 be a singularity variable?

The algebraic singularity method is a framework for analyzing collider events with missing energy. It provides a way to draw out a set of singularity variables that can catch singular features originating from the projection of full phase space onto the observable phase space of measured particle momenta. It is a promising approach applicable to various physics processes with missing energy but still requires more studies for use in practice. Meanwhile, in the double-sided decay topology with an invisible particle on each side, the MT2 variable has been known to be a useful collider observable for measuring particle masses from missing energy events or setting signal regions of collider searches. We investigate the relation between the two different types of kinematic variables in double-sided decay topology. We find that the singularity variables contain the MT2 variable in many cases, although the former is not a strict superset of the latter.

The light invisible boson in FCNC decays of B and $$B_c$$ mesons

In this paper, we study the FCNC decay processes of B and $$B_c$$ B c meson, in which one invisible particle is emitted. Both the spin-0 and spin-1 cases are considered. The model-independent effective Lagrangian is introduced to describe the coupling between the light invisible boson and quarks. The constraints of the coupling coefficients are extracted by experimental upper limits of the missing energy in B meson decays. The bounds are used to predict the upper limits of branching fractions of corresponding $$B_c$$ B c decays, which are of the order of $$10^{-6}$$ 10 - 6 or $$10^{-5}$$ 10 - 5 when final meson is pseudoscalar or vector, respectively. The maximum branch ratios are achieved when $$m_\chi \approx 3.5$$ m χ ≈ 3.5 –4 GeV, where $$m_\chi $$ m χ is the mass of the invisible particle.