Physicists from the TOTEM (TOTal Cross Section, Elastic Scattering and Diffraction Dissociation) collaboration at CERN’s Large Hadron Collider (LHC) and the DØ Collaboration at Fermilab have found strong new evidence for odderon, an elusive three-gluon state predicted nearly five decades ago.
The states that comprise two, three, or more gluons are generally called glue balls 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.
However, proving their existence has been a major experimental challenge, requiring detailed measurements of the protons as they deflect from each other in high-energy collisions.
While most high-energy collisions cause protons to break apart into their constituent quarks and gluons, about 25% are elastic collisions where the protons remain intact but emerge via slightly different paths.
“Our result probes the deeper features of quantum chromodynamics, in particular that gluons interact with each other and that an odd number of gluons can be ‘colorless,’ thus protecting the strong interaction,” said TOTEM spokesperson Dr. Simone Giani, CERN physicist.
“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 in the Tevatron proton-antiproton (pp̄) collider.
The physicists compared the pp̄ data from the LHC (recorded at collision energies of 2.76, 7, 8, and 13 TeV and extrapolated to 1.96 TeV) with the pp̄ data from Tevatron measured at 1.96 TeV.
The odderon would be expected to contribute different signs to the pp and pp̄ dispersion.
Supporting this picture, the two data sets disagree at the 3.4σ level, providing evidence for the exchange of the t-channel of an odd colorless C gluonic compound.
“When combined with the ρ and the total cross section result at 13 TeV, the significance is in the range of 5.2-5.7σ and therefore constitutes the first experimental observation of the odderon,” said Dr. Christophe Royon, a physicist at the University of Kansas. “
“This is a great CERN / Fermilab discovery.”
The results appear on the prepress server arXiv.org.
VM Abazov et al. (Collaboration TOTEM and Collaboration DØ). 2021. Comparison of differential elastic cross-sections of pp and pp¯ and observation of the exchange of a colorless C odd gluonic compound. CERN-EP-2020-236, FERMILAB-PUB-20-568-E; arXiv: 2012.03981