Odderon

Lore & Background

The theoretical prediction of possible odderon exchange was first published in 1973 by Basarab Nicolescu and Leszek Łukaszuk. The name 'odderon' was coined in 1975 in a paper by Joynson, D.; Leader, E.; Nicolescu, B. and Lopez, C. The odderon corresponds to the exchange of an odd number of gluons in elastic proton–proton and proton–antiproton collisions, in contrast to the pomeron which involves an even number of gluons.

In December 2020, the DØ and TOTEM Collaborations made public a preprint later published in Physical Review Letters in August 2021. They extrapolated TOTEM proton–proton data from 13, 8, 7 and 2.76 TeV to 1.96 TeV and compared it to DØ proton–antiproton measurement at 1.96 TeV, finding an odderon significance of 3.4 σ. TOTEM observed an independent odderon signal at low four-momentum transfers at 13 TeV. Combining these results gave an at least 5.2 σ statistical significance, the first statistically significant observation of odderon exchange effects by experimental collaborations.

A Hungarian-Swedish scaling analysis introduced a new scaling function and showed, model dependently, that in a limited energy range the elastic proton–proton collisions are independent of energy, but significantly different from the scaling function of elastic proton–antiproton collisions, providing a statistically significant signal for the odderon. This analysis was made public in December 2019 and published in February 2021. A subsequent theoretical paper in July 2021 increased the statistical significance to at least 7.08 σ.

Reader's Guide

The odderon's discovery resolves a long-standing puzzle in strong interaction physics, confirming the existence of a color-singlet state with odd gluon number that mediates elastic scattering at high energies. Its observation required combining data from the TOTEM experiment at the LHC and the DØ experiment at the Tevatron, and relied on careful extrapolation and model-dependent scaling analyses. The odderon is the crossing-odd counterpart of the pomeron, and its confirmation validates theoretical predictions made in the 1970s. The statistical significance of the signal, reaching at least 7.08 σ in some analyses, establishes the odderon as a genuine feature of quantum chromodynamics. This discovery opens new avenues for studying the structure of the strong force and the nature of Regge trajectories in particle physics.

Did You Know?

• It took about 48 years from the first theoretical prediction in 1973 to a statistically significant experimental signal.
• The first statistically significant observation combined data from the TOTEM and DØ collaborations, achieving at least 5.2 σ significance.
• A Hungarian-Swedish scaling analysis used a direct data-to-data comparison to show that elastic proton–proton and proton–antiproton collisions scale differently, indicating odderon exchange.