[Paper Review] Particle Physics at Future Colliders

John Ellis|ArXiv.org|Oct 22, 2002

Particle physics theoretical and experimental studies4 references3 citations

TL;DR

This paper argues that future high-energy colliders, particularly the LHC and linear $e^{+}e^{-}$ colliders like CLIC, are essential for discovering new physics beyond the Standard Model, such as the Higgs boson and supersymmetric particles. It emphasizes that high luminosity—$\mathcal{L} \sim 10^{34}$ to $10^{35}$ cm$^{-2}$s$^{-1}$—is critical to produce and precisely measure heavy new particles, with $e^{+}e^{-}$ colliders enabling detailed mass and coupling measurements that complement the LHC's discovery potential.

ABSTRACT

The search for physics beyond the Standard Model motivates new high-energy accelerators, which will require high luminosities in order to produce interesting new heavy particles. Using the Higgs boson and supersymmetry as examples, we discuss the capabilities of the LHC and $e^+ e^-$ linear colliders in the TeV and multi-TeV energy ranges to discover and study new particles.

Motivation & Objective

• To evaluate the necessity of high-luminosity colliders for discovering new physics beyond the Standard Model.
• To compare the complementary discovery and precision capabilities of the LHC and future $e^{+}e^{-}$ linear colliders.
• To assess the feasibility and physics potential of multi-TeV $e^{+}e^{-}$ colliders such as CLIC for studying the Higgs boson and supersymmetric particles.
• To establish luminosity scaling requirements based on cross-section suppression with energy, ensuring sufficient event rates for new particle production.

Proposed method

• Uses theoretical cross-section scaling ($\sigma \sim 1/E_{\rm CM}^2$) to argue that luminosity must increase with center-of-mass energy to maintain event rates.
• Applies the Higgs-Brout-Englert mechanism to explain how a Higgs boson with mass $\sim 115$ GeV could resolve the hierarchy problem and give mass to gauge bosons and fermions.
• Proposes that $e^{+}e^{-}$ colliders at $\sim$500 GeV and 3–5 TeV can precisely measure Higgs and sparticle properties, including couplings and masses.
• Analyzes beamstrahlung and detector signatures to assess the viability of $e^{+}e^{-}$ colliders at high energies, such as CLIC.
• Uses global fits to precision electroweak data to constrain the Higgs boson mass to $<193$ GeV at 95% CL, supporting its search at future colliders.
• Compares the LHC's discovery potential with $e^{+}e^{-}$ colliders' precision measurements to test models of supersymmetry breaking.

Experimental results

Research questions

• RQ1 What luminosity is required for future colliders to produce sufficient events for new heavy particles, given that cross sections decrease with energy?
• RQ2 How can $e^{+}e^{-}$ colliders at $\sim$500 GeV and 3–5 TeV complement the LHC in discovering and precisely measuring the Higgs boson and supersymmetric particles?
• RQ3 What is the role of beam polarization and collider type (e.g., $e^{+}e^{-}$, $\gamma\gamma$, $e^{-}e^{-}$) in enhancing the discovery and study of new physics?
• RQ4 Can $e^{+}e^{-}$ colliders at multi-TeV energies resolve the full supersymmetric spectrum and test GUT-scale unification models?
• RQ5 What are the technical and luminosity requirements for future colliders, such as CLIC, to achieve the necessary precision for new physics discovery?

Key findings

• The LHC with a luminosity of $\mathcal{L} \sim 10^{34}$ cm$^{-2}$s$^{-1}$ is capable of producing $\sim$1 TeV mass particles, such as the Higgs boson or supersymmetric partners.
• An $e^{+}e^{-}$ collider at $\sim$500 GeV with $\mathcal{L} \sim 10^{34}$ cm$^{-2}$s$^{-1}$ can measure Higgs boson decay modes with high precision, enabling tests of its couplings and potential deviations from the Standard Model.
• A multi-TeV $e^{+}e^{-}$ collider like CLIC, operating at $E_{\rm CM} = 3$–5 TeV with $\mathcal{L} \sim 10^{35}$ cm$^{-2}$s$^{-1}$, can complete the supersymmetric spectrum and measure sparticle masses with high accuracy.
• Precision measurements of sparticle masses at $e^{+}e^{-}$ colliders can be evolved to high scales to test models of supersymmetry breaking, such as universal GUT-scale masses.
• Despite beamstrahlung effects, CLIC can still distinguish supersymmetric missing-energy signatures and perform detailed mass and decay mode measurements.
• The paper concludes that $e^{+}e^{-}$ colliders with $E_{\rm CM} \sim 1$ TeV or higher are essential for precision physics and complementarity with the LHC, especially for probing the full supersymmetric parameter space.