CERN Physicists Find Evidence of Long-Sought Quasiparticle: Odderon

Physicists from the TOTEM experiment at CERN’s Large Hadron Collider have uncovered evidence of a subatomic quasiparticle dubbed an ‘odderon’ that — until now — had only been theorized to exist. The results will be published in two papers in the journal Physical Review D.

View of the tunnel where the TOTEM experiment’s proton detectors are located. Image credit: TOTEM Collaboration.

View of the tunnel where the TOTEM experiment’s proton detectors are located. Image credit: TOTEM Collaboration.

“We’ve been looking for this since the 1970s,” said University of Kansas’ Professor Christophe Royon, a member of the TOTEM (TOTal cross section, Elastic scattering and diffraction dissociation Measurement) Collaboration.

The findings concern hadrons, the family of particle that includes protons and neutrons, which are composed of quarks ‘glued’ together with gluons.

This particular experiment involves ‘collisions’ where the protons remain intact after the interaction. In all previous experiments, physicists detected collisions involving only even numbers of gluons exchanged between different protons.

Professor Royon and colleagues now report evidence of an odd number of gluons, without any quarks, exchanged in the collisions.

“Until now, most models were thinking there was a pair of gluons — always an even number,” Professor Royon said.

“Now we measure for the first time the higher number of events and properties and at a new energy. We found measurements that are incompatible with this traditional model of assuming an even number of gluons.”

“It’s a kind of discovery that we might have seen for the first time, this odd exchange of the number of gluons. There may be three, five, seven or more gluons.”

The odderon can be seen as the total contribution coming from all types of odd gluon exchange. It represents the involvement of all of three, five, seven or other odd number numbers of gluons.

By contrast, the older model assumes a contribution from all even numbers of gluons, so it includes contributions from two, four, six or more even-numbered gluons together.

“Our findings give fresh detail to the Standard Model of particle physics, a widely accepted physics theory that explains how the basic building blocks of matter interact,” the researchers said.

“This doesn’t break the Standard Model, but there are very opaque regions of the Standard Model, and this work shines a light on one of those opaque regions,” said Dr. Timothy Raben, a particle theorist at the University of Kansas.

Physicists have imagined the existence of the odderon for many decades, but until the Large Hadron Collider began operating at its highest energies in 2015, the odderon remained mere conjecture.

The data presented in the new papers were collected at 13 teraelectronvolts (TeV), the fastest scientists have ever been able to collide protons.

“These ideas date back to the ‘70s, but even at that time it quickly became evident we weren’t close technologically to being able to see the odderon, so while there are several decades of predictions, the odderon has not been seen,” Dr. Raben said.

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G. Antchev et al (TOTEM Collaboration). 2018. First measurement of elastic, inelastic and total cross-section at s?=13 TeV by TOTEM and overview of cross-section data at LHC energies. Phys. Rev. D, in press; arXiv: 1712.06153

G. Antchev et al (TOTEM Collaboration). 2018. First determination of the ? parameter at ?s = 13 TeV – probing the existence of a colourless three-gluon bound state. Phys. Rev. D, in press; CERN-EP-2017-335

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