Combined measurements of Higgs boson production and decay using up to $80$ fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=$ 13 TeV collected with the ATLAS experiment (1909.02845v2)

Abstract: Combined measurements of Higgs boson production cross sections and branching fractions are presented. The combination is based on the analyses of the Higgs boson decay modes $H \to \gamma\gamma$, $ZZ^\ast$, $WW^\ast$, $\tau\tau$, $b\bar{b}$, $\mu\mu$, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to $79.8$ fb$^{-1}$ of proton-proton collision data collected at $\sqrt{s}=$ 13 TeV with the ATLAS detector are used. Results are presented for the gluon-gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength is determined to be $\mu = 1.11^{+0.09}_{-0.08}$. The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of $6.5\sigma$ ($5.3\sigma$). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models and in the simplified Minimal Supersymmetric Standard Model. No significant deviations from Standard Model predictions are observed.

• The paper combines up to 80 fb⁻¹ of LHC data to precisely measure Higgs boson production cross sections and decay branching fractions.
• The analysis uses multiple decay channels, including rare muon pairs and invisible decays, to rigorously test the electroweak symmetry breaking mechanism.
• Significant signals, such as 6.5σ for VBF and over 5σ for t̄tH, benchmark the study and set the stage for exploring potential new physics.

Combined Measurements of Higgs Boson Properties Using ATLAS Data

The paper from the ATLAS Collaboration provides a comprehensive analysis of the Higgs boson by combining measurements of its production cross sections and decay branching fractions using a substantial dataset collected at CERN's Large Hadron Collider (LHC). The dataset corresponds to an integrated luminosity of up to 79.8 fb$^{-1}$ from years 2015 to 2017 at a center-of-mass energy of $\sqrt{s}=13$ TeV. The measurements elucidate various Higgs boson decay modes, including $H \to \gamma\gamma$, $H \to ZZ^\ast$, $H \to WW^\ast$, $H \to \tau\tau$, $H \to b\bar{b}$, $H \to \mu\mu$, and Higgs decays into invisible states.

Numerical Results and Interpretations

The global signal strength, a ratio of observed to Standard Model (SM) predicted rates, was determined to be $\mu = 1.11^{+0.09}_{-0.08}$. This indicates good alignment with the SM expectations. The vector-boson fusion (VBF) process showed an observed (expected) significance of 6.5σ (5.3σ). Additionally, the associated production with vector bosons ($VH$) demonstrated a significance of 5.3σ (4.7σ). Notably, the combined production of $t\bar{t}H$ and $tH$ exceeded 5σ.

Measured Cross Sections

The cross sections for various Higgs boson production processes were measured in different kinematic regimes. Measurements conformed primarily to the SM, setting a fundamental foothold for examining potential deviations or extensions to the SM. Key measurements include:

• Gluon-gluon fusion ($ggF$), VBF, and associated production processes with a $W$ or $Z$ boson.
• The cross-section times branching ratios for different decay channels were explored, including challenging measurements such as Higgs to muon pair decays.

Theoretical Implications

Measured deviations consistent with expectations provide a stringent test of electroweak symmetry breaking and the validity of the Higgs mechanism. The compatibility of measured Higgs couplings with the SM offers constraints on alternative models such as 2HDM and MSSM.

Future Research Directions

This comprehensive dataset coupled with high-precision measurements will be instrumental in future exploration of potential new physics scenarios. Analysis of additional decay channels and increased precision in complex processes like $tH$ and rare decays could present avenues for uncovering beyond-the-Standard-Model phenomena. As LHC continues to gather data, the precision of these measurements will improve, possibly revealing subtle effects not currently distinguishable.

This paper serves as a pivotal reference for researchers focusing on the properties of the Higgs boson and how these align with theoretical predictions. The methodologies highlighted pave the way for advancements in both experimental techniques and theoretical frameworks aimed at understanding the fundamental particles of the universe.