pomeron

The Pomeron is a concept in high-energy physics used to describe a class of exchanges in the strong interaction that carry vacuum quantum numbers. It arises in Regge theory as a Regge trajectory with the quantum numbers of the vacuum, meaning it has no electric charge, isospin, baryon number, or color. The term was introduced in the 1960s to explain certain features of hadronic scattering and is named after Isaak Pomeranchuk.

In soft hadronic processes, the Pomeron leads to a nearly energy-independent or slowly rising total cross section at high energies. This behavior is often parameterized as sigma_tot ~ s^{alpha_P(0) - 1}, with the intercept alpha_P(0) slightly above 1 (commonly around 1.08 in fits). The associated trajectory also has a slope alpha'_P that governs the t-dependence of differential cross sections. The exchange is typically modeled as a colorless, vacuum-like object, effectively a gluon-rich ladder between interacting hadrons.

In quantum chromodynamics (QCD), the Pomeron is understood as a colorless exchange of gluons. In perturbative QCD, the BFKL framework describes a hard Pomeron arising from gluon ladders, leading to a stronger rise with energy, though higher-order corrections and confinement effects complicate a single universal picture. The soft and hard Pomeron descriptions reflect different regimes of QCD, and a unified treatment remains a topic of ongoing research.

Experimentally, Pomeron exchange accounts for diffraction, elastic scattering at high energies, and events with rapidity gaps. In deep inelastic scattering, diffractive processes imply a partonic structure carried by the Pomeron, influencing diffractive parton distributions.