[Paper Review] Combined CDF and D0 upper limits on gg->H W+W- and constraints on the Higgs boson mass in fourth-generation fermion models with up to 8.2 fb-1 of data

Tevatron New Phenomena|arXiv (Cornell University)|Aug 16, 2011

Particle physics theoretical and experimental studies7 citations

TL;DR

This paper combines CDF and D0 data from 8.2 fb⁻¹ of proton-antiproton collisions at √s = 1.96 TeV to set combined upper limits on the gluon fusion production of a Higgs boson decaying to W+W−. At 95% confidence level, it excludes a standard-model-like Higgs boson with mass between 124 and 286 GeV in models with a fourth-generation fermion sector.

ABSTRACT

We combine results from searches by the CDF and D0 Collaborations for a standard model Higgs boson (H) in the processes gg->H->W+W- and gg->H->ZZ in p-pbar collisions at the Fermilab Tevatron Collider at sqrt(s)=1.96 TeV. With 8.2 fb-1 of integrated luminosity analyzed at CDF and 8.1 fb-1 at D0, the 95% C.L. upper limit on sigma(gg->H)xBr(H->W+W-) is 1.01 pb at m_H=120 GeV, 0.40 pb at m_H=165 GeV, and 0.47 pb at m_H=200 GeV. Assuming the presence of a fourth sequential generation of fermions with large masses, we exclude at the 95% Confidence Level a standard-model-like Higgs boson with a mass between 124 and 286 GeV.

Motivation & Objective

• To improve constraints on Higgs boson production in the H→W+W− decay channel using combined data from CDF and D0 experiments.
• To assess the impact of a fourth-generation fermion sector on Higgs boson mass exclusion limits.
• To set stringent 95% confidence level upper limits on the cross-section times branching ratio for gg→H→W+W− across a range of Higgs masses.
• To test the consistency of the standard model Higgs boson with fourth-generation fermion models using updated Tevatron data.

Proposed method

• Combines results from CDF and D0 Collaborations using 8.2 fb⁻¹ of integrated luminosity at the Fermilab Tevatron.
• Applies statistical combination techniques to merge observed upper limits on σ(gg→H) × Br(H→W+W−) from both experiments.
• Uses observed event yields and background estimates in the W+W− final state to compute 95% confidence level upper limits.
• Assumes a standard-model-like Higgs boson and evaluates exclusion limits in the context of a fourth-generation fermion model with heavy fermions.
• Applies standard model Higgs production cross-section predictions for gluon fusion to set limits across a range of Higgs masses.
• Performs a model-dependent exclusion analysis assuming the presence of a fourth generation of fermions with large masses.

Experimental results

Research questions

• RQ1 What is the combined 95% confidence level upper limit on the production cross-section times branching ratio for gg→H→W+W− at m_H = 120 GeV?
• RQ2 How do the combined CDF and D0 results constrain the mass of a standard-model-like Higgs boson in the presence of a fourth-generation fermion sector?
• RQ3 What is the upper limit on σ(gg→H) × Br(H→W+W−) at m_H = 165 GeV and m_H = 200 GeV using the combined dataset?
• RQ4 To what extent does the inclusion of a fourth-generation fermion model alter the exclusion limits for the Higgs boson mass?

Key findings

• The 95% confidence level upper limit on σ(gg→H) × Br(H→W+W−) is 1.01 pb at a Higgs boson mass of 120 GeV.
• At 165 GeV, the upper limit decreases to 0.40 pb, indicating stronger constraints at higher masses.
• At 200 GeV, the upper limit is 0.47 pb, showing consistent sensitivity across the high-mass range.
• With the inclusion of a fourth-generation fermion sector, a standard-model-like Higgs boson is excluded at 95% confidence level for masses between 124 and 286 GeV.
• The combined analysis improves sensitivity compared to individual experiments, enhancing exclusion reach in the context of fourth-generation models.
• The results represent a significant constraint on Higgs boson masses in models with extended fermion generations.