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| Pomeron (physics) | |
|---|---|
| Name | Pomeron |
| Field | High energy physics, Quantum chromodynamics, Regge theory |
| Discovered | 1960s |
| Discoverer | Isaak Pomeranchuk |
| Related | Regge trajectory, Diffractive scattering, Total cross section |
Pomeron (physics) The Pomeron is a theoretical construct used to describe the exchange responsible for slow energy dependence in certain high‑energy scattering amplitudes, notably hadron–hadron and photon–hadron collisions. It appears in frameworks connecting Regge theory, S‑matrix theory, and Quantum chromodynamics, and is central to understanding diffractive scattering, the rise of total cross sections, and vacuum quantum number exchanges. The concept links historical analytic S‑matrix ideas with modern perturbative and nonperturbative techniques in particle physics.
In high‑energy processes such as proton–proton scattering at the Large Hadron Collider and electron–proton collisions at HERA, amplitudes exhibiting approximate exchange of vacuum quantum numbers are modeled by the Pomeron. The Pomeron carries no conserved charges associated with Noether's theorem and manifests as an effective trajectory in Regge theory paralleling trajectories like the ρ and ω families. In Quantum chromodynamics analyses it is often represented by ladder diagrams dominated by gluon exchanges and is compared with the perturbative Balitsky–Fadin–Kuraev–Lipatov formalism and nonperturbative models such as the soft Pomeron and hard Pomeron.
The Pomeron concept originates from analytic S‑matrix studies developed in the 1950s–1960s amid work by figures including Lev Landau, Stanley Mandelstam, and Geoffrey Chew. Its eponymous name honors Isaak Pomeranchuk, whose theorem on asymptotic equality of particle and antiparticle total cross sections motivated a vacuum exchange interpretation. The integration of Pomeron ideas into Regge theory followed analyses by Tullio Regge and others, while later efforts by Vladimir Gribov, Alan White, and Serguei M. Troshin clarified unitarity and multi‑Pomeron contributions. The rise of Quantum chromodynamics in the 1970s led to reinterpretations of the Pomeron in terms of gluonic degrees of freedom explored by researchers such as Lipatov, Kuraev, Fadin, and Balitsky.
Multiple complementary models describe the Pomeron. In Regge phenomenology it is an effective pole or cut on the complex angular momentum plane characterized by an intercept and slope similar to the Regge trajectory of the f2 and a2 families. In perturbative Quantum chromodynamics the leading‑logarithm BFKL Pomeron arises from resummed gluon ladder diagrams computed by Balitsky–Fadin–Kuraev–Lipatov, with an intercept above unity leading to rapid growth of parton densities, connecting to deep inelastic scattering at small Bjorken‑x studied at HERA. Nonperturbative "soft Pomeron" models employ Regge pole fits and eikonal unitarization inspired by approaches of Donnachie and Landshoff and Veneziano dual amplitudes. Modern approaches use the AdS/CFT correspondence and gauge/gravity duals introduced by Juan Maldacena to model strong‑coupling Pomeron dynamics via graviton Regge trajectories in Anti‑de Sitter space. Unitarity constraints motivate multi‑Pomeron exchanges, triple‑Pomeron vertices, and cuts analyzed within the Good–Walker formalism and eikonal models developed by practitioners including Mueller, Pumplin, and Donnachie.
Empirical signatures attributed to Pomeron exchange include diffractive peaks, large rapidity gaps, low momentum transfer elastic scattering, and the slow rise of total cross sections measured by experiments at facilities such as CERN, Fermilab, SLAC, HERA, and the Large Hadron Collider. Measurements by collaborations like TOTEM, ATLAS, CMS, ZEUS, and H1 have probed elastic slopes, single and double diffraction, and hard diffractive processes involving jets or vector mesons. The diffractive structure functions and exclusive vector meson production provide constraints on the gluonic content associated with the Pomeron, while total cross section data from ISR, Spp̄S, and Tevatron feed into global fits. Observables such as rapidity gap survival probabilities and the triple‑Pomeron limit are tested in measurements of diffractive dissociation and central exclusive production investigated by experiments including CDF and LHCb.
The Pomeron framework is applied to model backgrounds and signals in searches for central exclusive production of states like the Higgs boson and beyond‑Standard‑Model resonances at the LHC. It interfaces with parton distribution function determinations, small‑x evolution equations like Dokshitzer–Gribov–Lipatov–Altarelli–Parisi and BFKL, and event generators such as PYTHIA and Herwig that incorporate diffractive modules. Related theoretical constructs include the Odderon proposed by Lukaszuk and Nicolescu for odd charge‑conjugation exchange, the Balitsky–Kovchegov equation for saturation phenomena studied by Iancu and McLerran, and color glass condensate models used in heavy‑ion programs at RHIC and LHC. The Pomeron also appears in phenomenological descriptions of cosmic‑ray air showers analyzed by collaborations such as Pierre Auger Observatory.
Key open issues include the reconciliation of soft and hard Pomeron descriptions across scales, quantitative unitarization of BFKL dynamics, precise determination of the Pomeron intercept and slope from global fits, and the microscopic understanding of multi‑Pomeron vertices in Quantum chromodynamics. Active research addresses nonperturbative modeling via lattice studies, applications of AdS/CFT to strong‑coupling scattering, constraints from new precision data from LHC Run 3, and connections to saturation phenomena encoded in the Color Glass Condensate and Balitsky–Kovchegov frameworks. Experimental programs at future facilities and planned forward detectors aim to refine measurements of diffractive processes and test predictions about Odderon contributions and exclusive production mechanisms.