Abstract
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. The faithfulness of the estimated momenta to the true momenta is then tested in observables sensitive to top polarization and t-tbar spin correlations. Our method thereby provides a novel approach towards the evaluation of these observables, and towards testing t-tbar production beyond the level of the total cross section. While our discussion is confined to t-tbar production as a benchmark, the method is applicable to any process whose decay topology allows to construct MT2.
Highlights
Production of visibles plus missing energy) resembles the typical signatures of beyond-SM models with a dark matter candidate made stable by some discrete parity
We find that MAOScalculated distributions measuring top polarization and ttspin correlations have shapes and asymmetries always close to the ones obtained using the true top boosts, and that deviations can be systematically improved by just MT2 cuts
The interest of the MT2-assisted on-shell’ (MAOS) momenta (2.5) is in the observation [15] that kmi aos are distributed around the true ki, even when calculated with mY and mX values that differ from the true Y and X masses. ( these masses should still fulfill the inequality mY ≥ MT2(mX ) in order to ensure that the kinematics be in the physical region [11]
Summary
In order to make the discussion as self-contained as possible, it is worthwhile to shortly reproduce the line of reasoning [15, 28] leading to the definition of MAOS momenta. The interest of the MAOS momenta (2.5) is in the observation [15] that kmi aos are distributed around the true ki, even when calculated with mY and mX values that differ from the true Y and X masses. See corresponding discussion in the Introduction.) This observation makes MAOS momenta potentially valuable ‘estimators’ of the separate invisible momenta ki, in processes of the kind in eq (2.1). The question is how well these estimators represent the true, unknown, momenta of the two invisible particles This question heavily depends on the process and on the observable chosen. We will instead address in detail the different MAOS-momenta definitions that are possible in di-leptonic ttdecays
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
