[Paper Review] Complementarity of a Low Energy Photon Collider and LHC Physics

D. M. Asner, S. Asztalos+8 more|arXiv (Cornell University)|Aug 9, 2003

Particle physics theoretical and experimental studies5 references3 citations

TL;DR

This paper proposes a low-energy photon collider (CLICHE) based on two-beam acceleration technology to complement the Large Hadron Collider (LHC) in precisely measuring Higgs boson properties. By exploiting clean γγ collisions, CLICHE enables model-independent measurements of Higgs couplings, spin, CP quantum numbers, and self-coupling—particularly critical for distinguishing between the Standard Model and New Physics like the MSSM, Littlest Higgs, and Randall-Sundrum models—offering unique sensitivity to anomalous couplings and Higgs-radion mixing.

ABSTRACT

We discuss the complementarity between the LHC and a low energy photon collider. We mostly consider the scenario, where the first linear collider is a photon collider based on dual beam technology like CLIC.

Motivation & Objective

• To establish the scientific and technical case for a low-energy photon collider (CLICHE) as a complementary facility to the LHC for detailed Higgs boson studies.
• To demonstrate that γγ collisions at CLICHE can provide model-independent measurements of Higgs couplings, spin, CP quantum numbers, and self-coupling, which are difficult to extract at the LHC.
• To explore the unique sensitivity of CLICHE to physics beyond the Standard Model, including the MSSM, Littlest Higgs model, and Randall-Sundrum model with Higgs-radion mixing.
• To validate the feasibility of using two-beam acceleration (TBA) technology for a compact, high-precision Higgs factory with polarized beams.
• To advocate for CLICHE as a staged, early-phase implementation of TBA technology that would provide critical physics output while testing key components for future multi-TeV colliders.

Proposed method

• Utilizes two 600 m two-beam acceleration (TBA) modules to produce electron beams of ~70–75 GeV, which are then converted into high-energy photon beams via Compton scattering with intense lasers.
• Employs a polarized electron beam to enhance sensitivity to Higgs couplings and quantum numbers, leveraging the high luminosity and clean environment of e⁺e⁻ and γγ collisions.
• Performs detailed Monte Carlo simulations to evaluate the discovery potential and precision of Higgs signal measurements, including H→γγ, H→bb̄, H→WW, and H→ZZ final states.
• Analyzes the ratio R_hgg = Γ(H→gg)Γ(H→γγ)/Γ_total^H as a key observable to distinguish between the Standard Model and New Physics models, especially in the context of the Littlest Higgs and Randall-Sundrum models.
• Considers the interplay between LHC and CLICHE: LHC detects Higgs via gluon fusion and decays to WW/ZZ, while CLICHE measures γγ couplings with high precision, enabling complementary constraints.
• Evaluates the detection reach for exotic Higgs-like states (e.g., φ in RS model) via γγ→φ→bb̄ or WW, showing that CLICHE can detect states invisible to the LHC.

Experimental results

Research questions

• RQ1 Can a low-energy photon collider like CLICHE provide model-independent measurements of Higgs couplings and quantum numbers that are inaccessible or imprecise at the LHC?
• RQ2 How does the precision of H→γγ coupling measurements at CLICHE compare to LHC measurements, and what is the combined sensitivity to New Physics?
• RQ3 In the context of the Littlest Higgs model, can CLICHE detect deviations in R_hgg from unity with sufficient accuracy to distinguish it from the Standard Model?
• RQ4 Can CLICHE detect and characterize a Higgs-like state decaying to two light pseudo-scalars, especially when the LHC signal is ambiguous?
• RQ5 In the Randall-Sundrum model with Higgs-radion mixing, can CLICHE measure anomalous γγ and gg couplings to the lightest Higgs and radion states, providing complementary information to the LHC?

Key findings

• CLICHE can measure the H→γγ partial width with a fractional accuracy of better than 0.2, which is sufficient to detect deviations from the Standard Model in the Littlest Higgs model for all but the smallest coupling parameters (ξ).
• The ratio R_hgg = Γ(H→gg)Γ(H→γγ)/Γ_total^H can be measured with high precision at CLICHE, providing a powerful discriminator between the Standard Model and New Physics, especially in scenarios with large new physics scales.
• For a Higgs boson decaying to two light pseudo-scalars (e.g., in the MSSM or Littlest Higgs), CLICHE can detect the signal via γγ→hh→bb̄bb̄, offering a crucial confirmation when the LHC signal is ambiguous or suppressed.
• In the Randall-Sundrum model, CLICHE can detect the φ resonance via γγ→φ→bb̄ when m_φ < 2m_W, and observe large deviations in R_φgg relative to the SM Higgs, even if the LHC only sees the h state.
• For m_φ > 2m_W, the b̄b final state becomes too rare for detection at CLICHE, but γγ→φ→WW/ZZ remains a viable channel, suggesting CLICHE can still probe the full mass range of the radion.
• CLICHE provides unique sensitivity to anomalous Higgs couplings in models with Higgs-radion mixing, where the LHC measures gg couplings and CLICHE measures γγ couplings, enabling a full reconstruction of the mixing parameters.