Complex decay chains of top and bottom squarks

TL;DR

This paper explores alternative decay modes of top and bottom squarks in supersymmetric models with light gauginos, proposing new search strategies and analyzing their potential to extend LHC discovery reach.

Contribution

It identifies dominant alternative decay channels of top squarks in specific supersymmetric scenarios and evaluates their discovery potential at the LHC.

Findings

Decay modes vary between 25% and 50% for squark masses over 500 GeV.

Top squark can be excluded up to 1040 GeV at 95% CL at 14 TeV LHC.

Discovery reach extends to 940 GeV with 5σ significance.

Abstract

Current searches for the top squark mostly focus on the decay channels of $\tilde{t}_1 \rightarrow t \chi_1^0$ or $\tilde{t}_1 \rightarrow b \chi_1^\pm \rightarrow bW \chi_1^0$, leading to $tt/bbWW+\not\mathrel{E}_T$ final states for top squark pair production at the LHC. In supersymmetric scenarios with light gauginos other than the neutralino lightest supersymmetric particle (LSP), different decay modes of the top squark could be dominant, which significantly weaken the current top squark search limits at the LHC. Additionally, new decay modes offer alternative discovery channels for top squark searches. In this paper, we study the top squark and bottom squark decay in the Bino-like LSP case with light Wino or Higgsino next-to-LSPs (NLSPs), and identify cases in which additional decay modes become dominant. We also perform a collider analysis for top squark pair production with mixed top squark decay final states of $\tilde{t}_1 \to t {\chi}_2^0 \to th {\chi}_1^0$, $\tilde{t}_1 \to b {\chi}_1^\pm \to bW {\chi}_1^0 $, leading to the $bbbbjj\ell+\not\mathrel{E}_T$ collider signature. The branching fraction for such decay varies between 25\% and 50\% for a top squark mass larger than 500 GeV with $M_2=M_1+150$ GeV. At the 14 TeV LHC with 300 ${\rm fb}^{-1}$ integrated luminosity, the top squark can be excluded up to about 1040 GeV at the 95\% C.L., or be discovered up to 940 GeV at 5$\sigma$ significance.