[Paper Review] W and Z Production and Standard Model Higgs Search from the Fermilab Tevatron

A. Patwa|arXiv (Cornell University)|May 17, 2006

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper presents updated measurements of W and Z boson production cross sections and charge asymmetries from CDF and DØ at the Fermilab Tevatron, along with a comprehensive search for the Standard Model Higgs boson across multiple decay channels. Using up to 0.4 fb⁻¹ of data, the experiments set 95% confidence level upper limits on Higgs production cross sections, with sensitivity still 2–3 times below the target of the 2003 Higgs sensitivity study, highlighting the need for further optimization and data integration to reach discovery potential.

ABSTRACT

This paper reviews recent measurements by the D0 and CDF collaborations in pbarp collisions at the Fermilab Tevatron at sqrt{s} = 1.96 TeV of W and Z boson production cross sections and asymmetries. Results from both experiments for the search of the Higgs boson predicted by the standard model in four different decay channels are also presented.

Motivation & Objective

• To measure W and Z boson production cross sections and charge asymmetries in p¯p collisions at √s = 1.96 TeV to test Standard Model predictions.
• To search for the Standard Model Higgs boson in four decay channels: e⁺e⁻, eμ, μ⁺μ⁻, and ττ, using data from CDF and DØ.
• To establish 95% confidence level upper limits on Higgs production cross sections in the absence of a signal, assessing sensitivity relative to theoretical expectations.
• To evaluate the current experimental sensitivity gap relative to the 2003 Higgs Sensitivity Study, identifying paths to improve reach through analysis optimization and data combination.

Proposed method

• CDF and DØ use leptonic decay signatures: W → ℓν (ℓ = e, μ, τ) and Z → ℓ⁺ℓ⁻ (ℓ = e, μ) for W/Z cross section measurements, applying triggers and offline selection cuts on pT, η, and missing transverse energy.
• For W → τν, CDF reconstructs τ candidates via isolated energy clusters and π⁰ matching, applying topology and invariant mass cuts to suppress QCD and W+jets backgrounds.
• Higgs searches are conducted in four channels: e⁺e⁻, eμ, μ⁺μ⁻, and ττ, with event selections optimized for signal-to-background ratios using kinematic and topological criteria.
• For the WH → WWW(*) channel, like-sign lepton final states (ee, eμ, μμ) are selected with pT > 15 GeV and E_T^miss > 20 GeV, with charge flip and QCD backgrounds mitigated via track quality and topology cuts.
• Systematic uncertainties from lepton identification (1–2%), energy scale (1–2%), and E_T^miss (2–3%) are propagated into cross section and limit calculations.
• Combined results from CDF and DØ use integrated luminosities of up to 360 pb⁻¹ (CDF) and 325 ± 21 pb⁻¹ (DØ) to set 95% C.L. upper limits on Higgs production cross sections as a function of mass.

Experimental results

Research questions

• RQ1 What are the measured W and Z boson production cross sections and charge asymmetries in p¯p collisions at √s = 1.96 TeV, and how do they compare to Standard Model predictions?
• RQ2 What are the 95% confidence level upper limits on the Higgs boson production cross section in the four main decay channels at the Tevatron?
• RQ3 How does the current experimental sensitivity to the Higgs boson compare to the target sensitivity outlined in the 2003 Higgs Sensitivity Study?
• RQ4 What are the dominant backgrounds in the WH → WWW(*) search channel, and how are they suppressed in the like-sign lepton final states?
• RQ5 Can the combination of data and optimized analysis techniques bridge the sensitivity gap between current limits and the expected discovery reach?

Key findings

• CDF and DØ measured W and Z production cross sections in leptonic decay modes, with results consistent with Standard Model expectations within systematic uncertainties.
• For the Z → ττ channel, CDF observed 504 candidate events with a 37% QCD background estimate, using 350 pb⁻¹ of data and τ identification via isolated clusters and π⁰ matching.
• In the WH → WWW(*) channel, DØ observed 1 ee, 3 eμ, and 2 μμ events—all consistent with expected backgrounds—using 363–384 pb⁻¹ of data and stringent lepton and E_T^miss cuts.
• CDF’s simpler analysis in the WH → WWW(*) channel observed no signal events in the signal region, with a total expected background of 0.95 ± 0.80 events from 194 pb⁻¹.
• The combined Higgs search results set 95% C.L. upper limits on the production cross section across all channels, with sensitivity still 2–3 times below the 2003 Higgs Sensitivity Study target.
• The experiments conclude that further optimization of analysis techniques, channel combination, and data integration (especially with full 1 fb⁻¹) are essential to achieve discovery sensitivity for a light Higgs boson.