[Paper Review] Production of light stabilized radion at high energy hadron collider

Uma Mahanta, Anindya Datta|arXiv (Cornell University)|Feb 17, 2000

Particle physics theoretical and experimental studies18 citations

TL;DR

This paper investigates the production and detection of a light radion in the Randall-Sundrum model at hadron colliders, showing that radion production via gluon fusion exceeds Higgs production by a factor of 6–8 due to enhanced couplings from QCD and QED conformal anomalies. The radion's branching ratios to diphotons and dijets are significantly enhanced—5–8 times larger than the SM Higgs—making the γγ channel a powerful discovery channel up to 1 TeV at the LHC for ⟨φ⟩ = 1 TeV.

ABSTRACT

In this paper we use the conformal anomaly in QCD to derive the coupling of light radion to gluons in the Randall-Sundrum model and use it to compute the radion production cross section at hadron colliders by gluon fusion. We find that the radion production cross section by gluon fusion at LHC would exceed that of the higgs boson by a factor that lies between 7 and 8 over most of the range. The decay modes of the radion are similar to that of the SM higgs boson. But the striking feature is the enhancement of radion to 2-photon and radion to 2-gluon branching ratio over the SM case. Utilising this, we then discuss the possible search strategies of such scalars at Tevatron and LHC. Using the $γγ$ decay mode one can explore/exclude radion mass upto 1 TeV. Even with the current collected data at the Tevatron, one can exclude radion mass upto 120 GeV for $\vphi$= 1 TeV.

Motivation & Objective

• To derive the radion coupling to gluons and photons in the Randall-Sundrum model using the conformal anomaly in QCD and QED.
• To compute the radion production cross section at hadron colliders via gluon fusion, comparing it to SM Higgs production.
• To analyze the decay branching ratios of the radion into SM particles, especially γγ and gg modes, and compare them to the SM Higgs.
• To evaluate the feasibility of detecting the radion at the Tevatron and LHC using the γγ final state, considering current and upgraded luminosities.
• To establish discovery and exclusion limits for the radion mass based on signal-to-background ratios in the γγ invariant mass distribution.

Proposed method

• Derive the radion-gluon coupling using the QCD trace anomaly, expressed as $\mathcal{L}_{\tilde{\phi}gg} = \frac{1}{\langle\phi\rangle} \frac{\beta(g_s)}{2g_s} \tilde{\phi} G^{a\mu\nu} G^a_{\mu\nu} $, with $ \frac{\beta(g_s)}{2g_s} \approx -3.84 \frac{\alpha_s}{4\pi} $ for $ n_f = 5 $ quarks.
• Compute the radion-photon coupling via the QED trace anomaly: $ \mathcal{L}_{\tilde{\phi}\gamma\gamma} = \frac{1}{\langle\phi\rangle} \frac{\beta(e)}{2e} \tilde{\phi} F_{\mu\nu} F^{\mu\nu} $, with $ \frac{\beta(e)}{2e} $ values depending on the radion mass relative to top and W boson thresholds.
• Calculate the radion branching ratios into various SM final states, noting that $ \tilde{\phi} \to gg $ and $ \tilde{\phi} \to \gamma\gamma $ are enhanced by a factor of 5–8 over the SM Higgs for $ \langle\phi\rangle = 1 $ TeV.
• Estimate signal and background events in the γγ invariant mass channel at the Tevatron and LHC, using cuts on photon transverse momentum (>20 GeV) and binning in 5 GeV intervals.
• Assess discovery and exclusion reach by comparing signal events to background, with a significance threshold of 5 for discovery and less than 1 background event per bin as a benchmark.

Experimental results

Research questions

• RQ1 How does the QCD conformal anomaly generate a coupling between the radion and gluons in the Randall-Sundrum model?
• RQ2 What is the radion production cross section via gluon fusion at the LHC relative to the SM Higgs boson?
• RQ3 How do the branching ratios of the radion into γγ and gg channels compare to those of the SM Higgs, and what is the enhancement factor?
• RQ4 What are the discovery and exclusion limits for the radion mass at the Tevatron and LHC using the γγ decay mode?
• RQ5 How does the radion mass dependence of the γγ branching ratio differ from that of the SM Higgs, and what are the implications for detection?

Key findings

• The radion production cross section via gluon fusion at the LHC exceeds that of the SM Higgs boson by a factor of 6–8 over most of the mass range.
• The branching ratio of the radion to two photons is enhanced by a factor of 5–8 compared to the SM Higgs when $ \langle\phi\rangle = 1 $ TeV.
• The branching ratio to two gluons is also significantly enhanced, reaching nearly 100% for certain radion masses.
• At the upgraded Tevatron, radion masses up to 160 GeV can be discovered and up to 165 GeV excluded using the γγ final state, assuming $ \langle\phi\rangle = 1 $ TeV.
• At the LHC with 30 fb⁻¹ luminosity, radion masses up to 1 TeV can be discovered via the γγ channel, with signal-to-background ratios favoring discovery across the mass range.
• For $ \langle\phi\rangle = 4 $ TeV, the discovery reach via γγ mode drops to 650 GeV due to reduced cross section scaling as $ 1/\langle\phi\rangle^2 $.