Constraining the minimal supergravity model parametertanβby measuring the dilepton mass distribution at CERN LHC

Abstract

We study the dependence on $\mathrm{tan}\ensuremath{\beta}$ of the event kinematics of final states with ${e}^{+}{e}^{\ensuremath{-}}/{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}{/e}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\mu}}^{\ensuremath{\mp}}{+E}_{T}^{\mathrm{miss}}+\mathrm{jets},$ as expected in $\mathrm{pp}$ collisions at CERN LHC, within the framework of the minimal supergravity model. With an increase of $\mathrm{tan}\ensuremath{\beta},$ the third generation sparticle masses ${m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{1}}$ and ${m}_{{b}_{1}}$ decrease due to the increase of the tau and bottom Yukawa couplings. As a result, the gluino, top squark, sbottom, chargino, and neutralino decays to third generation particles and sparticles are enhanced. With $\mathrm{tan}\ensuremath{\beta}$ rising, we observe a characteristic change in the shape of the dilepton mass spectra in ${e}^{+}{e}^{\ensuremath{-}}/{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}{+E}_{T}^{\mathrm{miss}}+\mathrm{jets}$ versus ${e}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\mu}}^{\ensuremath{\mp}}{+E}_{T}^{\mathrm{miss}}+\mathrm{jets}$ final states, reflecting the presence of the decays ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}\ensuremath{\rightarrow}{l}_{L,R}^{\ifmmode\pm\else\textpm\fi{}}{l}^{\ensuremath{\mp}}\ensuremath{\rightarrow}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}{l}^{+}{l}^{\ensuremath{-}}, {\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}\ensuremath{\rightarrow}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}{l}^{+}{l}^{\ensuremath{-}},$ and ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}\ensuremath{\rightarrow}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\tau}}^{\ensuremath{\mp}}\ensuremath{\rightarrow}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}},$ ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0},$ respectively. We exploit this effect for constraining the value of $\mathrm{tan}\ensuremath{\beta}.$

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