Constraining the minimal supergravity model parameter tan(beta) by measuring the dilepton mass distribution at LHC

Abstract

We study the dependence on $\tan\beta$ of the event kinematics of final states with $e^+e^- /\mu^+\mu^- /e^{\pm}\mu^{\mp} + E_T^{\rm miss} + jets$, as expected in $pp$ collisions at CERN LHC, within the framework of the minimal supergravity model. With increase of $\tan\beta$, the third generation sparticle masses $m_{\tilde{\tau}_1}$ and $m_{\tilde{b}_1}$ decrease due to the increase of the tau and bottom Yukawa couplings. As a result, gluino, stop, sbottom, chargino and neutralino decays to third generation particles and sparticles are enhanced. With $\tan\beta$ rising, we observe a characteristic change in the shape of the dilepton mass spectra in $e^+e^- /\mu^+\mu^- +E_T^{\rm miss} + jets$ versus $e^{\pm}\mu^{\mp} + E_T^{\rm miss} + jets$ final states, reflecting the presence of the decays $\tilde{\chi}_2^0\to \tilde{\ell}_{L,R}^{\pm}\ell^{\mp}\to \tilde{\chi}_1^0 \ell^+\ell^-, \tilde{\chi}_2^0\to \tilde{\chi}_1^0 \ell^+\ell^-$ and $\tilde{\chi}_2^0\to \tilde{\tau}^{\pm}_1\tau^{\mp}\to \tilde{\chi}_1^0 \tau^+ \tau^-$, $\tilde{\chi}_2^0\to \tau^+ \tau^- \tilde{\chi}_1^0$, respectively. We exploit this effect for constraining the value of $\tan\beta$.