Higgs Physics at the HL-LHC and HE-LHC (1902.00134v2)

Abstract: The discovery of the Higgs boson in 2012, by the ATLAS and CMS experiments, was a success achieved with only a percent of the entire dataset foreseen for the LHC. It opened a landscape of possibilities in the study of Higgs boson properties, Electroweak Symmetry breaking and the Standard Model in general, as well as new avenues in probing new physics beyond the Standard Model. Six years after the discovery, with a conspicuously larger dataset collected during LHC Run 2 at a 13 TeV centre-of-mass energy, the theory and experimental particle physics communities have started a meticulous exploration of the potential for precision measurements of its properties. This includes studies of Higgs boson production and decays processes, the search for rare decays and production modes, high energy observables, and searches for an extended electroweak symmetry breaking sector. This report summarises the potential reach and opportunities in Higgs physics during the High Luminosity phase of the LHC, with an expected dataset of pp collisions at 14 TeV, corresponding to an integrated luminosity of 3 ab$^{-1}$. These studies are performed in light of the most recent analyses from LHC collaborations and the latest theoretical developments. The potential of an LHC upgrade, colliding protons at a centre-of-mass energy of 27 TeV and producing a dataset corresponding to an integrated luminosity of 15 ab$^{-1}$, is also discussed.

• The paper demonstrates significant advancements in precision measurements of Higgs properties at the HL-LHC and HE-LHC upgrades.
• It reveals that enhanced luminosity can uncover rare Higgs decay modes, potentially signaling phenomena beyond the Standard Model.
• The study emphasizes high-energy observables that may expose subtle deviations and extend our understanding of particle interactions.

Overview of Higgs Physics at the HL-LHC and HE-LHC

The discovery of the Higgs boson in 2012 by the ATLAS and CMS collaborations marked a significant milestone in particle physics, corroborating the last unverified component of the Standard Model (SM). The sequential phases of the Large Hadron Collider (LHC)—from its initial operations to the prospective upgrades—offer a probing ground for an array of Higgs boson properties, thus allowing a deeper examination of Electroweak Symmetry Breaking and potential new physics phenomena beyond the SM.

Study Objectives and Context

This document examines the Higgs physics prospects during the High Luminosity LHC (HL-LHC) phase, utilizing a dataset of proton-proton collisions with a center-of-mass energy of 14 TeV and an integrated luminosity of 3 ab$^{-1}$. Additionally, it evaluates the High Energy LHC (HE-LHC) upgrade, aimed at a 27 TeV center-of-mass energy, producing datasets corresponding to an integrated luminosity of 15 ab$^{-1}$. The analyses integrate recent LHC collaboration findings and the latest advancements in theoretical high-energy physics.

Experimental and Theoretical Richness

The report explores novel possibilities for higher precision in measurements, including but not limited to Higgs boson production, decay processes, exploration of rare decays and production modes, and investigation of new observables at unprecedented energies. Furthermore, it scrutinizes potential scenarios indicative of an extended Electroweak Symmetry Breaking sector. The theoretical implications, interwoven with experimental opportunities, designate a platform for broadening the current understanding and boundaries of the SM.

Key Findings and Numerical Results

• Precision Measurements: The HL-LHC promises substantial advances in precision measurements of the Higgs boson’s properties, vital for contrasts against SM predictions.
• Rare Decays: Enhancements in luminosity expand the frontier for detecting rare Higgs decay modes, functioning as potential harbingers of new physics.
• High Energy Observables: The HE-LHC’s elevated energy setting prepares the groundwork for exploring high-scale phenomena—vital for insights into particle interactions at the largest scales presently conceivable.

Theoretical and Practical Implications

The research catalyzes a progression in the fundamental understanding of particle physics, potentially uncovering deviations from the SM or confirming its robustness. The extensive datasets could surface minute discrepancies, suggesting new energy scales or interactions, postulating the presence of undiscovered particles or forces.

From an operational perspective, these insights can refine existing theoretical models or prompt development in experimental techniques necessary for charting these terra incognita. Illumination of the Higgs sector's unexplored properties could lead to technological and engineering advances, serving as exigencies for future collider designs.

Anticipations for Future Developments

As the HL-LHC and HE-LHC come to fruition, expectations tilt towards enriched datasets that will challenge theorists and experimentalists alike. The prospects include deciphering unsolved problems like electroweak naturalness and offering clues about dark matter and other fundamental questions.

In summarizing, the document is an expansive contemplation of how current and forthcoming collider experiments might cast new light on the Higgs boson narrative while questioning and possibly extending the Standard Model’s boundaries. The field looks forward to an era characterized by accelerated discoveries uncovered through refining techniques and novel theoretical insights.