Physicists from the TOTEM Collaboration at CERN’s Large Hadron Collider (LHC) and the DØ Collaboration at Fermilab have found strong new evidence for the odderon, an elusive three-gluon state predicted almost five decades ago.
States comprising two, three or more gluons are usually called glueballs, and are peculiar objects made only of the carriers of the strong force.
The advent of quantum chromodynamics (QCD) led theorists to predict the existence of the odderon in 1973.
Proving its existence has been a major experimental challenge, however, requiring detailed measurements of protons as they glance off one another in high-energy collisions.
While most high-energy collisions cause protons to break into their constituent quarks and gluons, roughly 25% are elastic collisions where the protons remain intact but emerge on slightly different paths.
“Our result probes the deepest features of quantum chromodynamics, notably that gluons interact between themselves and that an odd number of gluons are able to be ‘colorless,’ thus shielding the strong interaction,” said TOTEM spokesperson Dr. Simone Giani, a physicist at CERN.
“A notable feature of this work is that the results are produced by joining the LHC and Tevatron data at different energies.”
TOTEM measures small deviations in proton-proton (pp) scattering using two detectors located 220 m on either side of the CMS experiment, while DØ employed a similar setup at the Tevatron proton-antiproton (pp̄) collider.
The physicists compared LHC pp data (recorded at collision energies of 2.76, 7, 8 and 13 TeV and extrapolated to 1.96 TeV), with Tevatron pp̄ data measured at 1.96 TeV.
The odderon would be expected to contribute with different signs to pp and pp̄ scattering.
Supporting this picture, the two data sets disagree at the 3.4σ level, providing evidence for the t-channel exchange of a colorless, C-odd gluonic compound.
“When combined with the ρ and total cross-section result at 13 TeV, the significance is in the range 5.2-5.7σ and thus constitutes the first experimental observation of the odderon,” said Dr. Christophe Royon, a physicist at the University of Kansas.”
“This is a major discovery by CERN/Fermilab.”
Sources
V.M. Abazov et al. (TOTEM Collaboration & DØ Collaboration). 2021. Comparison of pp and pp¯ differential elastic cross sections and observation of the exchange of a colorless C-odd gluonic compound. CERN-EP-2020-236, FERMILAB-PUB-20-568-E; arXiv: 2012.03981
