Scientists celebrate the long-sought discovery of the odderon, a strange phenomenon that rarely occurs when high-energy protons collide, such as in particle accelerators. Although the odderon was first predicted in the early 1970s, physicists only recently gathered the data they needed from CERN’s Large Hadron Collider to confirm a true discovery.
The discovery contributes to physicists’ understanding of how all matter in the universe interacts at the smallest levels. Unlike the famous Higgs particle, which was officially discovered in 2012, the odderon is not really a particle. Instead, it’s the name for a compound of three gluons that are exchanged between protons (or a proton and its antimatter twin, the antiproton) when they collide violently but aren’t destroyed. Gluons are subatomic particles so named because they “glue” together other particles called quarks; quarks are the little things that make up the larger particles, such as protons and neutrons that make up the atoms we all know and love.
Gluons are funny because they don’t like to be alone; they are almost always found together. If it is an even-numbered group of gluons (two, four, etc.) we call it a pomeron. If the number of gluons in the group is odd (three, five, etc.), well, you guessed it: that’s an odderon. The odderon is, for mysterious reasons, very rarely produced, and while hints of it have surfaced over the decades, the evidence was never strong enough to say it definitely existed. But the generally accepted theory of quantum physics says Odderons should exist, so scientists have continued to hunt them.
An international team of physicists announced earlier this month that their data reached a level of statistical significance known as “ five sigma, ” a threshold that most scientists agree means you are 99,999 +% sure you really have a discovery done. After all, it’s not like physicists can just peek into their particle accelerator and see an odderon smile. Instead, they have to process dizzying amounts of data recorded when protons and anti-protons bounce off the walls of their detectors.
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If you put all that data on CDs and stack them on top of each other, “you will travel more than the distance between the Earth and the moon,” said Christophe Royon, a professor of physics and astronomy at the University of Kansas who is part of the team. behind the new research. “You collect an enormous amount of data. And then you have to do some analysis to identify among all this data what is interesting to you. ”
Where the protons and anti-protons hit the detector after they hit each other, it tells the researchers how the particles collided with each other. Physicists scour the records of millions and millions of these collisions, looking for enough of the correct data points to say with confidence that what they see can only be explained if the odderon exists. If they persisted in this research for years and never found evidence of the odderon, they would have to go back to the drawing board and come up with a new theory of how the universe works.
Fortunately, the researchers were able to collect their results from the particle accelerators before the Covid-19 pandemic ended personal work, and then the data analysis could be done remotely. But they haven’t been able to celebrate together yet.
“With the Covid situation, it’s a bit tricky – everyone works from home and so on,” Royon said in a video call. “But when we’re back to normal, I think we deserve a party.”
The study included a careful comparison of datasets: one created a decade ago during the now-closed DØ experiment at Fermilab, Illinois, and others conducted in 2015, 2019 and 2020 (before pandemic lockdowns) in the TOTEM experiment of Large Hadron Collider. The Fermilab experiment collided with protons and anti-protons, while the LHC work looked at protons hitting protons. By comparing the data from these two different colliders, they could be sure of the odderon’s existence.
While the team, which involved researchers in countries around the world, suspected they had something big last year, they didn’t want to rush an announcement. They asked independent researchers in the field to check their work for possible bias or concerns before making their paper public. The article is now published as a preprint by CERN and Fermilab and has been submitted to the journal Physical Review Letters.
“The odderon is a solid prediction of the theory of strong interactions made nearly half a century ago,” said Ohio State University physicist Yuri Kovchegov, who was not involved in the new work. “At the same time, it has avoided experimental detection for decades. If the new DØ and TOTEM result is correct, it probably indicates that the odderon has finally been found. “
Kovchegov said in an email that the paper appears to be “the first solid experimental evidence for the odderon’s existence,” although he would still like more experiments to confirm the finding. He said it was forthcoming Electron-Ion Collider, a major new experiment being built in New York and starting in the early 2030s, could potentially be able to answer ongoing questions about the odderon.
Royon agrees that studying the odderon is far from over. “It’s not something that we close and say we’re happy, done and done,” he said. “In physics, when you find something new, it’s usually a door that opens completely new domains.”