Conclusions

Abstract

For a natural solution of the hierarchy problem in the context of the supersymmetry, stop mass is expected to be small. This book reported a result of the search for the stop pair production at the LHC assuming the decay mode of $\tilde{t}_{1} \rightarrow b \tilde{\chi }^{\pm }_{1} \rightarrow b ff' \tilde{\chi }^{0}_{1}$. Assuming higgsino-like lightest supersymmetric particle, small mass difference between chargino and neutralino, typically $\Delta m=20\,{\mathrm {\ GeV}}$, is considered as a benchmark point. Two types of analyses focussing on (1) small mass difference between stop and neutralino ($\Delta M$) of less than 70 GeV and (2) moderate $\Delta M$ between 120 GeV and 500 GeV. As a result of the analysis, no significant excesses against the estimated Standard Model backgrounds are observed. The results are interpreted as limits on the masses of supersymmetric particles. The small $\Delta M$ channel has excluded the region with $\Delta M < 70\,{\mathrm {\ GeV}}$ in the range of stop mass less than 210 GeV for the first time. It has alaso excluded stop four-body-decay signal $\tilde{t}_{1} \rightarrow b ff' \tilde{\chi }^{0}_{1}$ for the first time in the region with $m_{\tilde{t}_{1}}< 250\,{\mathrm {\ GeV}}$. The moderate $\Delta M$ channel has excluded stop masses in the range of 200 to 600 GeV for neutralino masses less than 280 GeV. The limits on stop masses from the previous ATLAS analyses are improved by approximately 120 GeV in the higher stop mass direction. Taking a combination with other ATLAS stop searches, a wide range of the stop signals has been excluded below 600 GeV of stop mass. The result gives the strong constraints to physics beyond the Standard Model.