[Paper Review] Observability of the Higgs Boson in the Presence of Extra Standard Model Families at the Tevatron

E. Arık, Ö. Çakır+2 more|ArXiv.org|Feb 5, 2005

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper investigates the observability of the Higgs boson at the Tevatron in scenarios with additional Standard Model (SM) families (SM-4, SM-5, SM-6), focusing on the $WW^*$ decay channel. It shows that enhanced Higgs production cross sections due to extra fermion generations could allow the D0 and CDF experiments to observe an intermediate-mass Higgs boson before the LHC, with accessible mass limits extending up to 200 GeV at 8 fb⁻¹ luminosity for SM-4.

ABSTRACT

The observability of the Higgs boson via the WW^* decay channel at the Tevatron is discussed taking into account the enhancements due to the possible existence of the extra standard model (SM) families. It seems that the existence of new SM families can give the Tevatron experiments (D0 and CDF) the opportunity to observe the intermediate mass Higgs boson before the LHC

Motivation & Objective

• To assess whether the Tevatron could observe the Higgs boson before the LHC in the presence of additional SM families.
• To evaluate the impact of extra fermion generations (SM-4, SM-5, SM-6) on Higgs boson production cross sections and branching ratios.
• To determine the accessible Higgs mass ranges at the Tevatron under different luminosity scenarios (2 fb⁻¹ and 8 fb⁻¹) for models with extra families.
• To analyze the role of heavy neutrino masses (50 GeV or >100 GeV) in modifying Higgs signal observability.
• To explore the potential for fourth-family quark production via gluon fusion and single resonant production as indirect signatures.

Proposed method

• Uses flavor democracy and democratic mass matrix approaches to model the Yukawa couplings and fermion masses in extended SM families.
• Applies the assumption of equal Yukawa couplings across families to derive mass matrices and predict enhanced Higgs couplings.
• Calculates the Higgs production cross section times branching ratio into $WW^*$ final states, including enhancements from additional fermion generations.
• Performs statistical analysis using 95% confidence level (C.L.) exclusion limits based on theoretical predictions and expected Tevatron luminosity.
• Compares theoretical predictions with experimental exclusion limits for integrated luminosities of 2 fb⁻¹ and 8 fb⁻¹.
• Considers two neutrino mass scenarios: $m_\nu \approx 50$ GeV and $m_\nu > 100$ GeV, to assess sensitivity variations.

Experimental results

Research questions

• RQ1 Can the Tevatron observe the Higgs boson in the presence of extra SM families before the LHC?
• RQ2 How do additional SM families affect the Higgs boson production cross section in the $WW^*$ decay channel?
• RQ3 What are the accessible Higgs mass limits at the Tevatron for SM-4, SM-5, and SM-6 with 2 fb⁻¹ and 8 fb⁻¹ luminosity?
• RQ4 How does the mass of the heavy neutrino in the fourth family influence the observability of the Higgs boson?
• RQ5 Can the Tevatron detect signatures of fourth-family quarks via enhanced gluon fusion or single resonant production?

Key findings

• With 8 fb⁻¹ of integrated luminosity, the Tevatron can exclude or verify the SM-4 scenario for Higgs masses in the range 140 GeV < $m_H$ < 200 GeV.
• For SM-5 with $m_\nu \approx 50$ GeV, the Tevatron can probe Higgs masses above 150 GeV at 8 fb⁻¹, and above 155 GeV at 2 fb⁻¹.
• The SM-6* model (with $m_\nu \approx 50$ GeV) is excluded at 95% C.L. for Higgs masses between 165 GeV and 185 GeV.
• At 2 fb⁻¹, the Tevatron can exclude or verify SM-4 (with unstable neutrinos) for $m_H$ between 150 GeV and 180 GeV.
• The LHC is expected to cover the full Higgs mass range via the golden mode $H \to ZZ \to \ell\ell\ell\ell$ if the fourth SM family exists.
• The Higgs production cross section via gluon fusion is enhanced by up to ~8 times in the presence of a fourth SM family.