Two-Body Decays of the Lightest Stop in Supergravity with and without R-Parity

TL;DR

This paper investigates the decay modes of the lightest stop in supergravity models, revealing that R-parity violation can lead to dominant decays into bτ, offering new experimental signatures.

Contribution

It demonstrates that R-parity violation causes the lightest stop to decay mainly into bτ, even above chargino thresholds, highlighting new decay channels and signatures.

Findings

The decay $ ilde t_1 o b au$ can dominate over traditional modes.

R-parity violation affects decay patterns regardless of threshold conditions.

New signatures for stop detection at LEP and Tevatron are proposed.

Abstract

We study the decays of the lightest top squark in supergravity models with and without R-parity. Using the simplest model with an effective explicit bilinear breaking of R-parity and radiative electroweak symmetry breaking we show that, below the threshold for decays into charginos $\tilde t_1\to c\chi^+_1$, the lightest stop decays mainly into third generation fermions, $\tilde t_1\to b\tau$ instead of the R-parity conserving mode $\tilde t_1\to c\chi^0_1$, even for tiny tau--neutrino mass values. Moreover we show that, even above the threshold for decays into charginos, the decay $\tilde t_1\to b\tau$ may be dominant. We study the role played by the universality of the boundary conditions on the soft supersymmetry breaking terms. This new decay mode $\tilde t_1\to b\tau$ as well as the cascades originated by the conventional $\tilde t_1\to c\chi^0_1$ decay followed by the R-parity violating neutralino decays can provide new signatures for stop production at LEP and the Tevatron.