Second stop and sbottom searches with a stealth stop

Abstract

Abstract:The top squarks (stops) may be the most wanted particles after the Higgs boson discovery. The searches for the lightest stop have put strong constraints on its mass. However, there is still a search gap in the low mass region if the spectrum of the stop and the lightest neutralino is compressed. In that case, it may be easier to look for the second stop since naturalness requires both stops to be close to the weak scale. The current experimental searches for the second stop are based on the simplified model approach with the decay modest 2 →t 1 Z andt 2 →t 1 h. However, in a realistic supersymmetric spectrum there is always a sbottom lighter than the second stop, hence the decay patterns are usually more complicated than the simplified model assumptions. In particular, there are often large branching ratios of the decayst 2 →b 1 W andb 1 →t 1 W as long as they are open. The decay chains can be even more complex if there are intermediate states of additional charginos and neutralinos in the decays. By studying several MSSM benchmark models at the 14 TeV LHC, we point out the importance of the multi-W final states in the second stop and the sbottom searches, such as the same-sign dilepton and multilepton signals, aside from the traditional search modes. The observed same-sign dilepton excesses at LHC Run 1 and Run 2 may be explained by some of our benchmark models. We also suggest that the vector boson tagging and a new kinematic variable may help to suppress the backgrounds and increase the signal significance for some search channels. Due to the complex decay patterns and lack of the dominant decay channels, the best reaches likely require a combination of various search channels at the LHC for the second stop and the lightest sbottom.

Exploring the nearly degenerate stop region with sbottom decays

“…In this case, searching for the asymmetric decay chains with one sbottom decaying tot W , the other decaying to tχ ± or bχ 2 could be useful. For larger values of the stop-neutralino mass gap, the stop decay products become more visible and it might be useful to look at channels with multiple b-jets or multiple leptons [56], or try to tag the charm quark from stop decay [23][24][25]. On the other hand, if the mass gap is smaller, the stop decay could exhibit displaced vertex, which can help reduce SM background in both the mono-jet search and the search with sbottom decays.…”

Uncover compressed supersymmetry via boosted bosons from the heavier stop/sbottom

“…Moreover, comparing to the method in Ref. [44,46] which utilise the leptons and b-jets in the final state, our search strategy can achieve a few times larger signal significance because of higher signal rate.…”

“…Moreover, one would expect two bottom quark jets in the final state if the flavor changing decay oft 1 → cχ 0 1 is suppressed. Studies [40,41,43,44,46] have shown that searching for final states with leptons and b-jets provides as a good probe to the light stop sector, especially when mt 1 ∼ m t +mχ0 1 . However, for some of our benchmark points, e.g.…”

“…This motivates the searches for the signal oft 2 pair production witht 2 →t 1 h/Z decay at the LHC run-I [40,41]. Moreover, through searching for the final state of multi-leptons and/or multi-b-jets [42], the heavier stop/sbottom with masses below ∼ 1 TeV decaying intot 1 and heavy bosons are found to be detectable at the 13/14 TeV LHC with an integrated luminosity of O(100) fb −1 [43][44][45][46].…”

Enhancing the discovery prospects for SUSY-like decays with a forgotten kinematic variable

“…This attitude is supported by the flurry of theoretical activity in recent years in designing models which "hide" the new physics from the LHC. One of the standard methods for doing so is to arrange for a "compressed" mass spectrum with a mass degeneracy of the relevant particles, such as supersymmetric (SUSY) partners, so that the resulting decay products are too soft to be triggered upon and tagged in the experimental analysis [4][5][6][7][8][9][10][11][12][13], or a "stealth" mass spectrum, where the new physics signature becomes identical to the SM background, since the additional particles are too soft to make any appreciable difference [14][15][16][17][18][19][20]. Our aim will be to highlight a kinematic variable that, either by itself or in conjunction with more conventional variables, can more effectively select signal over background when the signal spectrum is compressed and when signal events contain multi-stage cascade decays.…”