Gluino decays with heavier scalar superpartners

TL;DR

This paper addresses how gluinos decay when scalar superpartners are heavier than the gluino (split SUSY) and generic flavor and CP violation are allowed. The authors derive complete decay-width formulas for the heavy-squark regime using a general quark-squark-ino coupling basis, enabling calculation of three-body decays and loop-induced two-body decays into a gluon and a neutralino. Numerical studies of simplified spectra show that, depending on $m_0$ and the higgsino mass, the radiative two-body channel can dominate and produce signals such as four tops plus missing energy or two jets plus missing energy; they also identify scenarios with near 100% branching to gluon plus LSP or to $t\bar t$ plus LSP. The work highlights the relevance of effective-theory considerations and provides a framework for analyzing split-SUSY gluino phenomenology at the LHC, with implications for displaced-vertex searches and diverse final-state signatures.

Abstract

We compute gluino decay widths in supersymmetric theories with arbitrary flavor and CP violation angles. Our emphasis is on theories with scalar superpartner masses heavier than the gluino such that tree-level two-body decays are not allowed, which is relevant, for example, in split supersymmetry. We compute gluino decay branching fractions in several specific examples and show that it is plausible that the only accessible signal of supersymmetry at the LHC could be four top quarks plus missing energy. We show another example where the only accessible signal for supersymmetry is two gluon jets plus missing energy.

Figures (6)

• Figure 1: Generic Feynman rules for "-ino"$-$quark$-$squark interactions.
• Figure 2: Diagrams contributing to the one-loop radiative gluino decay in MSSM. Due to the majorana nature of gluino and neutralino, two more diagrams contribute, but they differ only from a) and b) by having opposite fermion lines (the flow of charge inside the loop changes direction)
• Figure 5: Radiative two-body branchings of the gluino in mSUGRA (left) and AMSB (right) with $\mu=M_1$ and $\tan\beta=1.5$. These two plots illustrate the argument in the text that the heavier the $gluino$ mass, the larger the scalar masses need to be for the two-body decay to be sizeable.
• Figure 6: Branching Fractions of gluino decay for mSUGRA with $m_{1/2}=300$ GeV and $\mu=120$ GeV and with $\tan\beta=1.5$ (left) and $\tan\beta=30$ (right). The heavy scalar mass $m_0$ enables larger two-body final state branching fractions, as the Higgsino+gluon final state is enhanced by $\log m_0$ over other decay channels. The shaded band in the figure represents $1\,{\rm mm}<c\tau_{\tilde{g}} < 10\,{\rm m}$.
• Figure 7: $M_{2}=120$, $\tan\beta=1.5$$\mu= 120$ (left), $\mu= 700$ (right) AMSB. The heavy scalar mass $m_0$ enables larger two-body final state branching fractions, as the Higgsino+gluon final state is enhanced by $\log m_0$ over other decay channels. The shaded band in the figure represents $1\,{\rm mm}<c\tau_{\tilde{g}} < 10\,{\rm m}$. The two panels of this figure differ in $\mu$. As $\mu$ increase (right panel) the ability to decay into Higgsinos is diminished and the two-body final state branching fraction is reduced. In the right panel, lower case $q$ means that only the five lighter quarks, $u,d,c,s,b$ are included in the decay channel, while upper case $Q$ means all six Standard Model quarks are included.