MT2-reconstructed invisible momenta as spin analizers, and an application to top polarization

Understand

Full event reconstruction is known to be challenging in cases with more than one undetected final-state particle, such as pair production of two states each decaying semi-invisibly.

• On the other hand, full event reconstruction would allow to access angular distributions sensitive to the spin fractions of the decaying particles, thereby dissecting their production mechanism.
• We explore this possibility in the case of Standard-Model t-tbar production followed by a leptonic decay of both W bosons, implying two undetected final-state neutrinos.
• We estimate the t and tbar momentum vectors event by event using information extracted from the kinematic variable MT2.