Top polarization in stop production at the LHC

Abstract

Abstract:We survey the expected polarization of the top produced in the decay of a scalar top quark,t → tχ 0 i , i = 1 − 2. The phenomenology is quite interesting, since the expected polarization depends both on the mixing in the stop and neutralino sectors and on the mass differences between the stop and the neutralino. We find that a mixed stop behaves almost like a right-handed stop due to the larger hypercharge that enters the stop/top/gaugino coupling and that these polarisation effects disappear, when mt. After a discussion on the expected top polarization from the decay of a scalar top quark, we focus on the interplay of polarization and kinematics at the LHC. We discuss different probes of the top polarization in terms of lab-frame observables. We find that these observables faithfully reflect the polarization of the parent top-quark, but also have a non-trivial dependence on the kinematics of the stop production and decay process. In addition, we illustrate the effect of top polarization on the energy and transverse momentum of the decay lepton in the laboratory frame. Our results show that both spectra are softened substantially in case of a negatively polarized top, particularly for a large mass difference between the stop and the neutralino. Thus, the search strategies, and the conclusions that can be drawn from them, depends not just on the mass difference mt − mχ0 i due to the usual kinematic effects but also on the effects of top polarization on the decay kinematics the extent of which depends in turn on the said mass difference.

Mass effects in the Higgs-gluon coupling: boosted vs. off-shell production

“…One example of new physics which can generate sizable perturbative corrections to the Higgs-gluon coupling are light supersymmetric top squarks [62][63][64][65][66][67][68]. Because of the non-decoupling structure of the Standard Model with Yukawa couplings we can integrate out the top quark in the low-energy limit, which describes the interactions between gluons and any Higgs bosons in a simple effective Lagrangian [39][40][41][42].…”

Precise Predictions for Top-Quark–Plus–Missing-Energy Signatures at the LHC

“…While it appears for our choice of g L and g R that spin correlations are less than 50% of the effect of higher-order corrections, this could change for different coupling choices, as has been studied for example in Ref. [20]. We leave a more detailed study of this dependence for future work.…”

Tasting the SU(5) nature of supersymmetry at the LHC

“…Performing top polarimetry on a decaying stop potentially gives access to the stop mixing angle [96][97][98]. Here we point out that the same kind of procedure also provides a SU(5)-test.…”