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.
Highlights
JHEP07(2015)075 been studied [11, 12], with limits for stop masses around 240 to 270 GeV
Current searches for the top squark mostly focus on the decay channels of t1 → tχ01 or t1 → bχ±1 → bW χ01, leading to tt/bbW W + ET final states for top squark pair production at the LHC
Searches based on sbottom decay ofb1 → bχ02 → bZ/hχ01 exclude sbottom masses between 340 and 600 GeV [19, 20]. ̃b1 → tχ±1 → tW χ01 decay has been studied in multi-lepton final states [20,21,22,23], which excludes sbottom masses around 440–590 GeV
Summary
We work in the MSSM and focus primarily on the third generation squark sector. Given the large top Yukawa coupling, the stop sector provides the dominant contribution to the radiative corrections of the SM-like Higgs mass in the MSSM. In the general MSSM when M32SQ = M32SU , to provide a SM-like Higgs mass of 125 GeV, the light stop t1 can still be as light as 200 GeV. A large mass splitting between the stop mass eigenstates (and a large At term), is typically needed, resulting in mt 500 GeV in general [37, 38]. Given the suppression of the off-diagonal terms by the small bottom mass, mixing among the sbottom mass eigenstates is typically small. Since the stop sector provides the dominant contribution to the Higgs mass corrections, we decouple the right-handed sbottom in our analysis. Given mbAb, M32SQ M32SD, the light sbottom mass eigenstate is mostly left-handed: ̃b1 ∼ ̃bL. The sbottom corrections to the Higgs mass are small compared to the stop corrections, there can be significant modifications to the Higgs couplings, especially the bottom Yukawa coupling [39]
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