Stop-neutralino coannihilation in the light of the LHC

Abstract

We employ the ATLAS search results for events containing jets and large missing transverse momentum, corresponding to an integrated luminosity of $1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, to investigate the constrained minimal supersymmetric model with $b\ensuremath{-}\ensuremath{\tau}$ Yukawa coupling unification. In this scenario, one of the stops is the next-to-lightest supersymmetric particle (NLSP), which coannihilates with the lightest (LSP) neutralino to yield the desired dark matter relic abundance. The NLSP stop, here taken to be lighter than the top quark, is slightly ($\ensuremath{\lesssim}20%--30%$) heavier than the LSP neutralino, and it primarily decays into the LSP and a charm quark. We find that the multijets and monojet ATLAS searches are sensitive to this scenario if the stop pair production is accompanied by a hard QCD jet. The excluded limit for the NLSP stop mass from the ATLAS data can reach 160 GeV in the coannihilation region, with mass below 140 GeV essentially excluded. A significant region of the parameter space corresponding to large ${m}_{0}$ values, $8\text{ }\text{ }\mathrm{TeV}\ensuremath{\lesssim}{m}_{0}\ensuremath{\lesssim}16\text{ }\text{ }\mathrm{TeV}$, is excluded by our analysis. For LSP neutralino mass $\ensuremath{\sim}100\text{ }\text{ }\mathrm{GeV}$, the LHC constraints in some cases on the spin-dependent (spin-independent) neutralino-nucleon cross section are significantly more stringent than the current and expected bounds from Xenon, CDMS, and IceCube.