The phenomenology of central exclusive production at hadron colliders

TL;DR

The paper investigates central exclusive production at hadron colliders within the Durham perturbative framework, focusing on γγ and meson-pair final states to probe quantum numbers and QCD dynamics. It systematically analyzes uncertainties from unintegrated gluon densities, PDFs, NLO corrections, and soft survival (eikonal/enhanced) effects, including proton dissociation. By providing cross-section predictions across RHIC, Tevatron, and LHC energies and exploring both perturbative and non-perturbative contributions, the work identifies where measurements can best constrain theory and gluon densities. It also discusses strategies—such as using cross-section ratios and veto/forward-proton tagging—to reduce theoretical ambiguities and maximize the physics reach of CEP studies.

Abstract

Central exclusive production (CEP) processes in high-energy hadron-hadron collisions provide an especially clean environment in which to measure the nature and quantum numbers (in particular, the spin and parity) of new resonance states. Encouraged by the broad agreement between experimental measurements and theoretical predictions based on the Durham approach, we perform a detailed phenomenological analysis of diphoton and meson pair CEP final states, paying particular attention to the theoretical uncertainties in the predictions, including those from parton distribution functions, higher-order perturbative corrections, and non-perturbative and proton dissociation contributions. We present quantitative cross-section predictions for these CEP final states at the RHIC, Tevatron and LHC colliders.

Figures (11)

• Figure 1: The perturbative mechanism for the exclusive process $pp \to p\,+\, X \, +\, p$, with the eikonal and enhanced survival factors shown symbolically.
• Figure 2: Representative NLO virtual correction diagrams to the $\gamma\gamma$ CEP process.
• Figure 3: (a) Representative perturbative diagram for 'skewed' meson pair CEP. (b) Representative perturbative diagram for 'symmetric' meson pair CEP. In both cases, quarks with momenta $(l_1,l_4)$ and $(l_2,l_3)$ are collinear and form colourless meson states.
• Figure 4: Skewed and symmetric contributions to the $\pi^0\pi^0$ CEP cross section for different cuts $E_{\rm cut}$ on the $\pi^0$ transverse energy, $E_\perp$, and the differential cross section ${\rm d}\sigma/{\rm d}M_{\pi\pi}$ for $E_\perp(\pi^0)>2.5$ GeV, at $\sqrt{s}=7$ TeV. In both cases a pseudorapidity cut $|\eta(\pi^0)|<1$ is applied.
• Figure 5: Representative diagram for the non--perturbative meson pair ($M_3$, $M_4$) CEP mechanism, where $M^*$ is an intermediate off--shell meson of type $M$. Eikonal and (an example of) enhanced screening effects are indicated by the shaded areas.