Supersymmetry Reach of the Tevatron via Trilepton, Like-Sign Dilepton and Dilepton plus Tau Jet Signatures

TL;DR

The paper reassesses Tevatron Run II's reach for supersymmetry in three clean signatures—trileptons, like-sign dileptons, and dilepton plus tau-jet—using realistic background modeling and an invariant-mass edge cut to suppress WZ/ZZ contributions. It introduces a per-point cut optimization strategy that maximizes signal significance (S/√B) and demonstrates substantial reach gains over fixed-cut analyses. Across mSUGRA parameter space and for representative tanβ values, the study finds that backgrounds are larger than previously thought, limiting discovery potential, but optimized cuts and alternative channels (notably 2L and 2L1T) provide meaningful complementary reach, especially at high tanβ. The results underscore the importance of data-driven background estimates and justify further refinements, including NLO corrections, to sharpen Tevatron SUSY searches.

Abstract

We determine the Tevatron's reach in supersymmetric parameter space in trilepton, like-sign dilepton, and two lepton one tau-jet channels. We critically study the standard model background processes. We find larger backgrounds and, hence, significantly smaller reach regions than recent analyses. We identify the major cause of the background discrepancy. We improve signal-to-noise by introducing an invariant mass cut which takes advantage of a sharp edge in the signal dilepton invariant mass distribution. Also, we independently vary the cuts at each point in SUSY parameter space to determine the set which yields the maximal reach. We find that this cut optimization can significantly enhance the Tevatron reach.

Figures (10)

• Figure 1: The invariant mass distribution of any pair opposite sign, same flavor leptons for the signal events (with $M_0=700$ GeV, $M_{1/2}=160$ GeV, $\tan\beta=5$) and the PYTHIA $WZ$ background. We impose a set of cuts from Ref. BK: $p_T(\ell)>\{11,7,5\}$ GeV, central lepton with $p_T>11$ GeV and $|\eta|<1.0$, $\hbox{,/}E_T>25$ GeV and $|m_{\ell^+\ell^-}-M_Z|>10$ GeV. Each histogram is normalized to its cross section.
• Figure 2: $p_T$ distribution of isolated tracks in (a) $W+$jet production and (b) $Z+$jet production. The isolated tracks have $I<2$ GeV and are outside the $\Delta R=0.7$ cone around any jet. The events in the distributions potentially contribute to the 2L background: they have one real lepton with $p_T>11$ and $|\eta|<2$ and one same sign isolated track with $|\eta|<2$.
• Figure 3: Branching ratios of a chargino-neutralino pair into the 3L (solid), 2L (dash) and 2L1T (dot dot dash) channels versus the lightest stau mass (bottom axis), or alternatively, versus $M_0$ (top axis), with mSUGRA model parameters $\tan\beta=5$, $\mu>0$, $A_0=0$ and (a) $M_{1/2}=175$ GeV or (b) $M_{1/2}=250$ GeV. The arrows indicate the chargino threshold $m_{\tilde{\chi}_1^\pm}=m_{\tilde{\tau}_1}$. For the range of $M_0$ values shown the chargino mass varies from 118 to 139 GeV in (a), and from 187 to 201 GeV in (b).
• Figure 4: The same as Fig. \ref{['br_frac_lowtb']}, but for $\tan\beta=35$. This time the chargino mass varies from 126 to 140 GeV (in (a)), and from 192 to 201 GeV (in (b)).
• Figure 5: Tevatron reach in the 3L channel for mSUGRA models with $\mu>0$, $A_0=0$, and (a) $\tan\beta=5$ or (b) $\tan\beta=35$. We show the reach with both a standard set of soft cuts BK (dashed, for large $M_0$ only), as well as with the optimal set of cuts (solid) (see text). The reach is shown for 30 ${\rm fb}^{-1}$, 10 ${\rm fb}^{-1}$ and 2 ${\rm fb}^{-1}$ total integrated luminosity (from top to bottom). The cross-hatched region is excluded by current limits on the superpartner masses. The dot-dashed lines correspond to the projected LEP-II reach for the chargino and the lightest Higgs masses. In Fig. (a) the left dotted line shows where $m_{\tilde{\nu}_\tau}=m_{\tilde{\chi}_1^\pm}$ and the right dotted line indicates $m_{\tilde{\tau}_1}=m_{\tilde{\chi}_1^\pm}$. In Fig. (b) the dotted lines show where $m_{\tilde{e}_R}=m_{\tilde{\chi}_1^\pm}$ (left) and $m_{\tilde{\tau}_1}=m_{\tilde{\chi}_1^\pm}$ (right).