Particle physicists at CERN have caught the first glimpse of a long-sought-after quasiparticle, which they've been hunting since the 1970s. The curious state, called an odderon, is made up of an odd number of gluons, the carriers of a strong nuclear force.
This force keeps protons and neutrons together and “glues” the quarks that these particles are composed of together. Protons are smashed into one another in the Large Hadron Collider and peculiar states of matter like quark-gluon plasma can form. The atom smasher can also create bound states, which are the so-called quasiparticles, peculiar objects that are not particles but behave like them nonetheless.
Pairs of gluons have been seen forming bound states, but scientists have never seen this happen for an odd number of gluons. However, the latest measurements suggest that this is possible. The findings are submitted for publication and can be read on the CERN preprint server in two papers (here and here).
"Until now, most models were thinking there was a pair of gluons – always an even number," team member Professor Christophe Royon, from the University of Kansas (KU), said in a statement. "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 findings from the experiment provide new insight into the Standard Model of particle physics, the theory that connects forces to fundamental particles. We know that the Standard Model is not perfect or complete (it doesn’t include gravity, for example) and there is probably a better theory out there somewhere. There are some hints of violation from some experiments, but so far we haven’t found a smoking gun. Any new findings might help us understand it better.
"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 Timothy Raben, a particle theorist at KU who has worked on the odderon.
The experiment that looks for these gluon bound states is called TOTEM and is CERN’s “longest” experiment, as its detectors spread across almost half a kilometer (1,640 feet). It measures the time-of-flight of protons and its work can be applied to a range of subjects, from space physics to the proton therapies used to treat cancer.