Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at √s = 8 TeV with the ATLAS detector

• Autores: Alconada Verzini, María Josefina; Alonso, Francisco; Anduaga, Xabier Sebastián; Dova, María Teresa; Monticelli, Fernando Gabriel; Wahlberg, Hernán Pablo; The ATLAS Collaboration
• Año de publicación: 2014
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas; Física; hadron-hadron scattering; supersymmetry; top squark; proton-proton scattering
• Institución: Universidad Nacional de La Plata

The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1 fb−1 of proton-proton collision data at √s = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via $\stackrel{¯<!--\; ¯\; -->}{t}\to <!--\; \to \; -->t{\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0$ or $\stackrel{¯<!--\; ¯\; -->}{t}\to <!--\; \to \; -->b{\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^{\pm <!--\; \pm \; -->}\to <!--\; \to \; -->b{W}^{(\ast <!--\; \ast \; -->)}{\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0$, where ${\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0\left({\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^{\pm <!--\; \pm \; -->}\right)$ denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fullyhadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of $\stackrel{¯<!--\; ¯\; -->}{t}\to <!--\; \to \; -->t{\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0$. For a branching fraction of 100%, top squark masses in the range 270–645 GeV are excluded for ${\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0$ masses below 30 GeV. For a branching fraction of 50% to either $\stackrel{¯<!--\; ¯\; -->}{t}\to <!--\; \to \; -->t{\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0$ or $\stackrel{¯<!--\; ¯\; -->}{t}\to <!--\; \to \; -->b{\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^{\pm <!--\; \pm \; -->}$, and assuming the ${\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^{\pm <!--\; \pm \; -->}$ mass to be twice the ${\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0$ mass, top squark masses in the range 250–550 GeV are excluded for${\stackrel{¯<!--\; ¯\; -->}{\mathrm{\chi <!--\; \chi \; -->}}}_1^0$ masses below 60 GeV.
Facultad de Ciencias Exactas