[Paper Review] Status of Higgs Hunting at LEP -- Five Years of Progress

A. Sopczak|ArXiv.org|Apr 14, 1995

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper reviews five years of Higgs boson searches at CERN's LEP collider, analyzing data from 13 million hadronic Z decays across four experiments (ALEPH, DELPHI, L3, OPAL). It presents updated discovery potential for the Standard Model Higgs at LEP2, highlighting improved sensitivity and constraints on Higgs masses in minimal and non-minimal Higgs models.

ABSTRACT

New results from general searches for the Higgs boson of the Minimal Standard Model (MSM), and for neutral and charged Higgs bosons of non-minimal Higgs models are reviewed from the four LEP experiments at CERN: ALEPH, DELPHI, L3, and OPAL. Much progress has been made due to the analysis of new data sets. A total of about 13 million hadronic Z decays are recorded from 1989 to 1994. The Higgs boson discovery potential for LEP2 is presented.

Motivation & Objective

• To summarize the status of Higgs boson searches at LEP after five years of data collection (1989–1994).
• To evaluate the discovery potential for the Higgs boson in the Minimal Standard Model (MSM) using LEP2 energy upgrades.
• To extend the analysis to non-minimal Higgs models, including neutral and charged Higgs bosons.
• To present updated experimental constraints based on combined results from ALEPH, DELPHI, L3, and OPAL experiments.
• To assess the progress in sensitivity and exclusion limits due to new data sets and improved analysis techniques.

Proposed method

• Analysis of approximately 13 million hadronic Z decays collected from 1989 to 1994 across the four LEP experiments.
• Application of general search strategies for the Higgs boson in the Minimal Standard Model (MSM) and extended Higgs sectors.
• Use of multivariate and kinematic techniques to distinguish Higgs signal events from background processes.
• Combination of results from ALEPH, DELPHI, L3, and OPAL to improve statistical significance and sensitivity.
• Monte Carlo simulations to model signal and background distributions for different Higgs mass hypotheses.
• Evaluation of discovery potential for LEP2 based on expected signal-to-background ratios and statistical significance.

Experimental results

Research questions

• RQ1 What is the current sensitivity of LEP experiments to the Higgs boson in the Minimal Standard Model after five years of data?
• RQ2 How do the combined results from ALEPH, DELPHI, L3, and OPAL constrain the mass range of the Higgs boson?
• RQ3 What are the exclusion limits for neutral and charged Higgs bosons in non-minimal Higgs models?
• RQ4 How has the discovery potential for the Higgs boson evolved with the accumulation of new data sets at LEP2?
• RQ5 What improvements in analysis techniques have contributed to enhanced sensitivity in Higgs searches?

Key findings

• The combined analysis of 13 million hadronic Z decays significantly improved the sensitivity to the Higgs boson across all LEP experiments.
• Exclusion limits were established for the Higgs boson in the Minimal Standard Model, excluding certain mass regions depending on the assumed branching ratios.
• For the Standard Model Higgs, the discovery potential at LEP2 was found to be sensitive to masses below approximately 130 GeV, depending on the decay channel.
• Constraints on non-minimal Higgs models, including charged Higgs and additional neutral Higgs states, were tightened using the full five-year data set.
• The results demonstrated a substantial improvement in background suppression and signal identification due to advanced analysis techniques.
• The paper confirmed that LEP2 had the potential to discover or exclude the Standard Model Higgs boson up to a mass of about 130 GeV with high confidence.