Signals for Minimal Supergravity at the CERN Large Hadron Collider II: Multilepton Channels

TL;DR

This study analyzes the LHC reach for supersymmetry within the minimal SUGRA framework using ISAJET, focusing on multilepton plus multijet final states arising from gluino/squark cascades and contrasting them with clean electroweak-signatures. By scanning the m0–m1/2 plane for fixed tanβ and μ, and applying ET^c-driven cuts, the authors show that the 1ℓ channel typically offers the strongest reach, with gluino masses up to ~1.5–1.8 TeV (m1/2 up to ~600–700 GeV) accessible at 10 fb^-1, while OS/SS dileptons and trileptons provide complementary channels for parameter localization and direct detection of sleptons and electroweak-inos. They quantify SM backgrounds (tt̄, W/Z+jets, WW/WZ/ZZ) and demonstrate that, with appropriate cuts, multiple lepton channels can be observed concurrently, enabling cross-channel cross-checks to identify SUSY sources. The work also explores clean multilepton channels from W̃1Z̃2 and slepton pair production, highlighting their potential to constrain or measure mass splittings (e.g., m̃Z2−m̃Z1) and to test model assumptions such as gaugino mass unification and radiative EWSB. Overall, the paper provides a framework for using a suite of multilepton observables at the LHC to probe, constrain, and potentially determine the underlying parameters of minimal SUGRA, with implications for SUSY dark matter scenarios and collider phenomenology.

Abstract

We use ISAJET to perform a detailed study of the multilepton signals expected from cascade decays of supersymmetric particle produced at the CERN LHC. Our analysis is performed within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking. We delineate the regions of parameter space where jets plus missing energy plus 1, 2 (opposite sign and same-sign dileptons), and 3 isolated lepton events should be visible above standard model backgrounds. We find that if any $\eslt$ signal at the LHC is to be attributed to gluino and/or squark production, and if $m_{\tg} \alt 1$~TeV, then several of these signals must be simultaneously observable. Furthermore, assuming $10\,\fb^{-1}$ of integrated luminosity, we find that the reach for supersymmetry in the 1$\ell + \jets +\eslt$ channel extends to $m_{\tg}\sim 2300\ (1600)$ GeV for $m_{\tq}\sim m_{\tg}$ ($m_{\tq} \sim 1.5m_{\tg}$), and exceeds the corresponding reach in the $0\ell+\eslt$ channel. We show that measurements of the various topological cross sections, jet and $B$-hadron multiplicities in these events, together with the charge asymmetry for single lepton and same-sign dilepton events, and flavor asymmetry for opposite sign dilepton events, serve to narrow the allowed range of underlying SUGRA parameter values. We also delineate parameter regions where signals with clean isolated dilepton (from slepton production) and trilepton events (from chargino/neutralino production) are visible at the LHC, and examine the extent to which these signals can be separated from other SUSY sources.

Figures (18)

• Figure 1: Contour plots of squark and gluino masses in the $m_0$ -- $m_{1/2}$ plane of the minimal SUGRA model. Frames are shown for a) $\tan\beta =2,\ \mu <0$, b) $\tan\beta =2,\ \mu >0$, c) $\tan\beta =10,\ \mu <0$, and d) $\tan\beta =10,\ \mu >0$. We take $m_t=170$ GeV and $A_0=0$. The bricked regions are excluded by theoretical constraints discussed in Paper I, while the shaded regions are excluded by experiment.
• Figure 2: Same as Fig. 1, except we plot contours of lightest chargino mass and contours of right slepton mass. Also shown by dotted contours are the kinematic limit for the neutralino spoiler decay modes, above which the decays $\widetilde{Z}_2\rightarrow\widetilde{Z}_1 H_{\ell}$ or $\widetilde{Z}_2\rightarrow \widetilde{Z}_1 Z$ are kinematically allowed.
• Figure 3: SM backgrounds to various SUSY search event topologies in fb, after cuts, but as a function of the cut parameter $E_T^c$ defined in the text. We show frames for a) $1\ell+{\rm jets}$ events, b) OS dilepton + jets events, c) SS dilepton + jets events and d) $3\ell +{\rm jets}$ events.
• Figure 4: SUSY signal cross sections for six SUSY cases listed in the text, and total SM background in fb, after cuts, as a function of the $E_T^c$ parameter, for the same event topologies as in Fig. 3.
• Figure 5: Contours of cross section (in fb) after cuts described in the text for $1\ell +{\rm jets}+E\hbox{/}_T$ events. The solid contours have $E_T^c=100$ GeV, while the dashed contours are for $1,2$ and $4$ fb cross sections with $E_T^c=400$ GeV, from which the maximum reach is derived. The frames are for the same SUGRA parameter choices as in Fig. 1.