Pomeron

Pomeron
Name	Pomeron
Type	Regge trajectory
Discovered	Theoretical proposal (1960s)
Associated	Isaak Pomeranchuk
Field	Particle physics, High energy physics

Pomeron The Pomeron is a theoretical construct in particle physics invoked to explain the behavior of scattering amplitudes at high center-of-mass energy and small momentum transfer. It was introduced to account for rising total cross sections and diffractive phenomena in collisions involving hadrons such as proton, pion, and kaon. The concept is central to descriptions used by collaborations at facilities like CERN, SLAC National Accelerator Laboratory, and Fermilab and figures in analyses connected to the Large Hadron Collider and experiments such as TOTEM and CDF.

History

The idea traces to work by Isaak Pomeranchuk and contemporaries in the 1950s and 1960s, building on the Regge theory program associated with Tullio Regge, Vladimir Gribov, and Geoffrey Chew. Early phenomenological fits to data from experiments at CERN ISR, Brookhaven National Laboratory, and DESY invoked a vacuum quantum number exchange to explain elastic scattering and diffraction, paralleling analyses by researchers at SLAC and University of Rochester. The advent of perturbative Quantum Chromodynamics calculations in the 1970s by groups including Giorgio Parisi and David Gross reframed the Pomeron within partonic language, motivating studies at DESY HERA by collaborations such as H1 and ZEUS that probed deep inelastic scattering and diffractive structure functions.

Theoretical Description

In theoretical accounts the Pomeron appears as a leading singularity in complex angular momentum (Regge) space, carrying the quantum numbers of the vacuum. Seminal contributions came from Vladimir Gribov and Lev Lipatov, and the perturbative picture was advanced via the Balitsky–Fadin–Kuraev–Lipatov (BFKL) approach by Ian Balitsky, Victor Fadin, Lev Kuraev, and Eugene Kuraev (often cited as Lipatov and colleagues). In Quantum Chromodynamics the Pomeron can be modeled as a color-singlet exchange predominantly built from gluons—linking to calculations by Yuri Dokshitzer and Valery Khoze—and contrasted with nonperturbative models such as those inspired by Veneziano amplitudes and the dual resonance model developed by Gabriele Veneziano and Miguel Virasoro.

Experimental Evidence

Evidence for Pomeron-like behavior appears in elastic and diffractive scattering measurements by experiments like TOTEM, ATLAS, CMS, CDF, D0, H1, and ZEUS. Observables include slow energy dependence of total cross sections measured at ISR, SPS, and Tevatron and diffractive mass spectra from HERA deep inelastic processes. Central exclusive production studies at LHCb and forward physics detectors such as ALICE provide additional constraints. Results are interpreted using Monte Carlo generators developed at institutions such as CERN and Fermilab and compared with predictions from phenomenological models advocated by groups including Donnachie and Landshoff and matrix-element-based frameworks used by PYTHIA developers.

Phenomenology and Applications

Phenomenological uses of the Pomeron span soft and hard scattering regimes, informing models for total cross sections, elastic slopes, single and double diffraction, and rapidity gap survival probabilities. Practical applications include background estimates for searches at Large Hadron Collider, design of forward detectors at CERN, and interpretation of cosmic-ray air shower data from facilities like Pierre Auger Observatory and IceCube. The Pomeron concept also influences models of vector meson photoproduction measured by collaborations such as HERA H1 Collaboration and LHCb and figures into theoretical frameworks used by researchers at Brookhaven National Laboratory and Oak Ridge National Laboratory.

Mathematical Formalism

Mathematically the Pomeron is represented by a Regge pole or a cut in the complex angular momentum plane characterized by an intercept and slope; classic parametrizations are associated with the Regge trajectory formalism developed by Tullio Regge and extended by Donnachie and Landshoff. In perturbative treatments the BFKL equation yields a Green’s function for leading-logarithm energy evolution, with kernels computed by Lipatov and collaborators and next-to-leading corrections analyzed by teams including V. S. Fadin and L. N. Lipatov. Other approaches use the eikonal formalism and unitarization schemes studied by Mandelstam and E. Eichten to enforce S-matrix constraints, while modern holographic treatments draw on ideas from Juan Maldacena and the AdS/CFT correspondence to model Pomeron exchange as a graviton trajectory in curved spacetime backgrounds studied by groups at Princeton University and MIT.

Modern Developments and Open Problems

Current research connects Pomeron physics to small-x evolution, saturation phenomena described by the Color Glass Condensate program led by Larry McLerran and Raju Venugopalan, and jet-gap-jet studies pursued by ATLAS and CMS collaborations. Open problems include precise determination of the Pomeron intercept and slope across soft and hard regimes, unambiguous identification of glueball states predicted by lattice calculations from groups at CERN and DESY, and reconciling nonperturbative Regge phenomenology with perturbative Quantum Chromodynamics evolution. Progress is driven by analyses from experimental teams at LHC, theoretical advances by researchers at Stanford University, Cambridge University, and Harvard University, and computational studies using lattice methods at Fermilab and Jefferson Lab.

Category:Particle physics