[Paper Review] Search for Higgs, Leptoquarks, and Exotics at Tevatron

Song Ming Wang|ArXiv.org|May 26, 2004

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper presents updated searches for the Standard Model Higgs boson, leptoquarks, and exotic particles at the Tevatron using 200 pb⁻¹ of proton-antiproton collision data at √s = 1.96 TeV. Despite no signal observed, the study sets stringent 95% confidence level limits on Higgs boson production, leptoquark masses above 240 GeV, and GMSB SUSY models with Λ > 78.8 TeV, significantly improving on Run 1 constraints.

ABSTRACT

This paper reviews some of the most recent results from the CDF and DZERO experiments on the searches for Standard Model and Non-Standard Model Higgs bosons, and other new phenomena at the Tevatron. Both experiments examine data from proton anti-proton collision at sqrt{s} = 1.96 TeV, of integrated luminosity ~200$ pb**-1 (per experiment), to search for Higgs predicted in the Standard Model and beyond Standard Model, supersymmetric particles in the Gauge Mediated Symmetry Breaking scenario, leptoquarks, and excited electrons. No signal was observed, and limits on the signatures and models are derived.

Motivation & Objective

• To search for the Standard Model Higgs boson in associated production with a W boson (W±H → lνbb̄) using 162 pb⁻¹ of CDF data.
• To probe large tanβ scenarios in the MSSM for neutral Higgs bosons decaying to bb̄ pairs via associated production with b-quarks.
• To search for non-Standard Model Higgs bosons decaying to diphotons in Fermiophobic and Topcolor models using 191 pb⁻¹ of DO data.
• To set limits on scalar leptoquark pair production in the bb̄ final state using 131 pb⁻¹ of DO data.
• To search for Gauge Mediated Supersymmetry Breaking (GMSB) signatures via mono-photon plus missing transverse energy, and to constrain excited electron compositeness via e*e → eγ final states.

Proposed method

• CDF and DO experiments used proton-antiproton collisions at √s = 1.96 TeV with integrated luminosity ~200 pb⁻¹ to search for rare signatures of new physics.
• Signal selection involved identifying final states with isolated leptons (e, μ), jets (especially b-tagged), photons, large missing transverse energy (E_T/), and invariant mass reconstruction.
• Backgrounds from QCD multijet, top quark pairs, and Drell-Yan processes were estimated using control samples and Monte Carlo simulations.
• Signal regions were optimized using cuts on transverse momentum, pseudorapidity (|η| < 1.1), and E_T/ > 20–40 GeV depending on channel.
• Limits were set at 95% confidence level using profile likelihood methods, with systematic uncertainties dominated by photon misidentification and b-tagging efficiency.
• Theoretical cross sections for GMSB models were calculated at leading order and corrected with K-factors to account for higher-order QCD effects.

Experimental results

Research questions

• RQ1 What are the 95% C.L. upper limits on the W±H production cross section times branching ratio for Higgs boson masses below 135 GeV?
• RQ2 What is the excluded region in the tanβ vs m_A parameter space for MSSM neutral Higgs bosons decaying to bb̄ pairs at high tanβ?
• RQ3 What are the 95% C.L. limits on the Higgs boson decay to diphotons in Fermiophobic and Topcolor models?
• RQ4 What is the lower limit on the leptoquark mass in the bb̄ final state for first- and second-generation scalar leptoquarks?
• RQ5 What are the 95% C.L. limits on the compositeness scale Λ and excited electron mass M_e* in contact and gauge-mediated interaction models?

Key findings

• No signal was observed in the W±H → lνbb̄ channel; the 95% C.L. upper limit on the cross section times branching ratio is reported as a function of Higgs mass, though no mass limit is set due to statistical limitations.
• The DO/ experiment excluded scalar leptoquarks with masses below 240 GeV at 95% C.L. in the bb̄ final state, based on 131 pb⁻¹ of data.
• For second-generation scalar leptoquarks, DO/ set a 95% C.L. mass limit of M > 186 GeV using 104 pb⁻¹ of data.
• In the GMSB SUSY search, DO/ derived a 95% C.L. lower limit of Λ > 78.8 TeV, corresponding to M_χ̃⁰₁ > 105 GeV and M_χ̃±₁ > 191 GeV, using 185 pb⁻¹ of data.
• CDF’s independent GMSB analysis using 202 pb⁻¹ data set a 95% C.L. limit of Λ > 68 TeV, with M_χ̃⁰₁ > 93 GeV and M_χ̃±₁ > 168 GeV.
• For excited electrons, the 95% C.L. exclusion regions in the M_e*/Λ vs M_e* plane (contact interaction) and f/Λ vs M_e* plane (gauge-mediated) were derived, with no observed resonance in the eγ invariant mass spectrum.