New backgrounds in Trilepton, Dilepton and Dilepton plus Tau Jet SUSY Signals at the Tevatron

TL;DR

The paper addresses the Tevatron's sensitivity to supersymmetry in the MSUGRA framework, focusing on trilepton, like-sign dilepton, and dilepton+tau-jet channels. It uses a full detector-level simulation combining COMPHEP→PYTHIA→SHW and optimizes cuts on $m_{\ell^+\ell^-}$, $m_T(\ell,\nu)$, and a low-end $m_{\ell^+\ell^-}^\gamma$ threshold to maximize signal-to-background. A key finding is that the $W\gamma^\ast$ background dominates the background budget under standard cuts, requiring these optimized cuts; the study maps reach in the $M_0$–$M_{1/2}$ plane for 2, 10, and 30 fb$^{-1}$. Despite the larger background, the trilepton channel remains a leading SUSY discovery mode, with dilepton+tau-jet offering best reach at large $\tan\beta$ for small $M_0$, and combined channels extend sensitivity, though higher luminosity is essential. The results underscore the importance of realistic background modeling and parameter-space-driven optimization for interpreting Tevatron Run II capabilities.

Abstract

We determine the Tevatron's reach in supersymmetric parameter space in trilepton, like-sign dilepton, and dilepton plus tau-jet channels, taking all relevant backgrounds into account. We show results for the minimal supergravity model. With a standard set of cuts we find that the previously unaccounted for $Wγ^\ast$ background is larger than all other backgrounds combined. We include cuts on the dilepton invariant mass and the $W$-boson transverse mass to reduce the $Wγ^\ast$ background to a reasonable level. We optimize cuts at each point in supersymmetry parameter space in order to maximize signal-to-noise.

Figures (8)

• Figure 1: The diagrams for the $p\bar{p}\rightarrow W^+(Z/\gamma^\ast)\rightarrow {\ell'}^+\bar{\nu}_{\ell'}\ell^+\ell^-$ background. Here $u$ and $d$ stand for a generic up-type and down-type quark, respectively.
• Figure 2: The invariant mass distribution $m_{\ell^+\ell^-}$ of the opposite sign, same flavor leptons in (a) $\mu^\pm e^+e^-$ events and (b) $e^\pm e^+e^-$ events. The histograms show the results from COMPHEP and from PYTHIA (shaded). We have imposed nominal charged lepton cuts $p_T(\ell)>5$ GeV and $m_{\ell^+\ell^-}>10$ GeV. Each histogram is normalized to its cross section. In (b), we fill both invariant mass combinations, each with weight $1/2$.
• Figure 3: The same as Fig. \ref{['im2l']}, but for the $p_T$ distribution of the leptons possibly coming from the $Z$. In the case of $\mu^\pm e^+e^-$, we fill the $p_T$ of both $e^+$ and $e^-$, each with weight $1/2$. For the case of $e^\pm e^+e^-$ we fill the $p_T$ of the odd-sign lepton with weight $1/2$ and the $p_T$ of the like sign leptons with weight $1/4$ each.
• Figure 4: Tevatron reach in the trilepton channel in the $M_0-M_{1/2}$ plane, for fixed values of $A_0=0$, $\mu>0$ and (a) $\tan\beta=5$, or (b) $\tan\beta=35$. Results are shown for 2, 10 and 30 ${\rm fb}^{-1}$ total integrated luminosity.
• Figure 5: The same as Fig. \ref{['3l']}, but for the like-sign dilepton channel.