Abstract
Supersymmetry is a strong candidate of physics beyond the Standard Model. New symmetry introduced between bosons and fermions can suppress the known hierarchy problem of the Standard Model. For a natural solution of the hierarchy problem, masses of scalar top quark (stop) and higgsino are required to be small. Evidence of ‘light’ stop signal, however, has not been found until today. There is a high possibility of that light stop hides in the parameter space not explored in previous analyses. This book reports a search result for stop pair production at the Large Hadron Collider (LHC), assuming the decay mode of stop into bottom quark and chargino. If the lightest supersymmetric particle has a large higgsino component, the mass difference between chargino and neutrino is expected to be small. In this case, chargino decays in three body into neutralino and low-momentum (‘soft’) fermion pair. Previous stop searches did not explore this signal model sufficiently due to the difficulty of the analysis using soft particles. This analysis aims to improve the sensitivity at this parameter space using the soft lepton as a probe of the signal, which can suppress the large amount of background. This chapter consists of (1) the theoretical background of the analysis—explanation about supersymmetry and significance to search for it at the LHC; (2) good summary of the current search results; and (3) clarification of the goal of this book.
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Notes
- 1.
We define e, \(\mu \) and \(\tau \) belong to charged lepton family, \(\nu _{e}\), \(\nu _{\mu }\) and \(\nu _{\tau }\) neutrino family; u, c and t up-type quark family; and d, s, and b down-type quark family.
- 2.
- 3.
The CKM matrix plays an important role to explain the observed CP violation [5], though it is not discussed in this thesis.
- 4.
Some GUT models e.g. SU(5) and SO(10) reduces number of parameters of the SM. Some combined models of the GUT and supersymmetry are considered, but they are not explained in this thesis on account of limited space.
- 5.
Procedure of the cross section calculation is explained in Sect. 3.2.1.
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Nobe, T. (2016). Introduction. In: Search for Scalar Top Quarks and Higgsino-Like Neutralinos. Springer Theses. Springer, Singapore. https://doi.org/10.1007/978-981-10-0003-4_1
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