[Paper Review] Searches for New Phenomena with Lepton Final States at the Tevatron

T. Adams|ArXiv.org|May 31, 2007

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper presents the latest results from CDF and D0 collaborations at Fermilab's Tevatron, searching for new physics in final states with leptons. Using 0.4–1.3 fb⁻¹ of proton-antiproton collision data, the experiments set stringent 95% confidence level limits on supersymmetry, $W^\prime$, $Z^\prime$, Randall-Sundrum gravitons, excited electrons, and long-lived neutral particles, with the most sensitive limits being $M(\tilde{\chi}_1^\pm) > 141$ GeV and $m_{e^*} > 946$ GeV for $\Lambda = m_{e^*}$. These results represent the world's best constraints in several channels, significantly narrowing the parameter space for new physics beyond the Standard Model.

ABSTRACT

Numerous searches for new phenomena have been carried out using data from proton-antiproton collisions at Fermilab's Tevatron. Final states with leptons give signatures which are relatively unique and generally have small backgrounds. We present many of the latest results from the CDF and D0 collaborations from 0.4-1.2 fb^-1 of data. Topics include supersymmetry, extra gauge bosons, Randall-Sundrum gravitons, excited electrons and neutral, long-lived particles.

Motivation & Objective

• To search for new physics beyond the Standard Model using final states with leptons, which offer low backgrounds and high signature purity.
• To set the most stringent limits to date on supersymmetric chargino and neutralino pair production, especially in trilepton final states.
• To probe the existence of heavy gauge bosons ($W^\prime$, $Z^\prime$), Randall-Sundrum gravitons, excited leptons, and long-lived neutral particles.
• To improve sensitivity by combining multiple search strategies, including three-lepton, two-lepton+track, and same-sign dilepton final states.
• To interpret results in model-independent and phenomenologically motivated frameworks, such as mSUGRA and MSSM, to constrain new physics parameters.

Proposed method

• Utilized data from proton-antiproton collisions at $\sqrt{s} = 1.96$ TeV, with integrated luminosities ranging from 0.4 to 1.3 fb⁻¹.
• Applied multiple search techniques: full three-lepton reconstruction, two leptons plus an isolated track, and same-sign dilepton final states to enhance sensitivity.
• Employed kinematic variables such as transverse mass ($M_T$), missing transverse energy (MET), and invariant mass of lepton pairs to identify resonant signals.
• Used background estimation from control regions in data and Monte Carlo simulations, with systematic uncertainties propagated via data-driven methods.
• Combined results from CDF and D0 for enhanced sensitivity in searches for $Z^\prime$, RS gravitons, and $W^\prime$ bosons.
• Applied model-independent and simplified model interpretations to derive limits on cross-section times branching ratio as a function of new particle mass.

Experimental results

Research questions

• RQ1 What are the most stringent limits on chargino and neutralino pair production in trilepton final states at the Tevatron?
• RQ2 Can a $W^\prime$ boson decaying to $e\nu$ be excluded at high masses using transverse mass and missing energy signatures?
• RQ3 What is the exclusion limit on a $Z^\prime$ boson decaying to $e^+e^-$ in the di-electron invariant mass spectrum?
• RQ4 How do the combined CDF and D0 searches constrain the parameter space of Randall-Sundrum gravitons in di-lepton and di-photon final states?
• RQ5 What are the limits on the mass and compositeness scale of excited electrons ($e^*$) from $p\bar{p} \to ee^* \to ee\gamma$ processes?

Key findings

• CDF sets a 95% CL limit of $M(\tilde{\chi}_1^\pm) > 130$ GeV in an MSSM model without slepton mixing and $m_0 = 60$ GeV.
• D0 sets a 95% CL limit of $M(\tilde{\chi}_1^\pm) > 141$ GeV in the 3$\ell$-max model, representing the world's best limit for this channel.
• D0 excludes a $W^\prime \to e\nu$ boson with mass below 965 GeV assuming standard model couplings, based on 0.9 fb⁻¹ of data.
• CDF excludes a standard model-like $Z^\prime$ boson with mass below 923 GeV in the di-electron final state using 1.3 fb⁻¹ of data.
• CDF and D0 exclude Randall-Sundrum gravitons with masses below 889 GeV (CDF) and 865 GeV (D0) at $k/\bar{M}_{\text{pl}} = 0.1$.
• D0 sets a 95% CL limit of $m_{e^*} > 946$ GeV when $\Lambda = m_{e^*}$, and $m_{e^*} > 756$ GeV for $\Lambda = 1$ TeV, representing the most stringent limits on excited electrons.