The Large Hadron Collider’s subatomic discoveries didn’t stop with the Higgs boson: This week, scientists at Europe’s CERN research center announced that the collider’s LHCb experiment has detected a doubly charmed particle that’s like a proton, but four times as weighty.
The particle is known as the Ξcc⁺, or “Xi-cc-plus.” It flashes in and out of existence in less than the blink of an eye, but just knowing that it exists — and knowing how massive it is — could give physicists a more solid sense of how matter is put together.
The discovery of the Xi-cc-plus baryon marks a milestone for the LHCb team. “This is the first new particle identified after the upgrades to the LHCb detector that were completed in 2023,” Vincenzo Vagnoni, the spokesperson for the experiment, said in a news release.
It also resolves a 20-year-old mystery. Back in 2002, physicists working at Fermilab in Illinois said they saw hints of a particle that might be the Xi-cc-plus — but the particle was much lighter than predicted by theory, and the confidence level for the mass estimate fell short of the 5-sigma standard for a subatomic discovery.
In 2017, the LHCb team discovered a similar type of baryon known as the Ξcc++, or “Xi-cc-plus-plus,” and physicists expected that Xi-cc-plus would have a similar mass. The newly reported observations confirm those expectations, at a confidence level of 7-sigma.
The Large Hadron Collider smashes protons together at velocities that are close to the speed of light, and four detectors — including the LHCb — gather data to help scientists learn how all the subatomic pieces are put together.
Protons and other types of particles in the category known as hadrons consist of quarks that are bound together by the strong nuclear force, one of the four fundamental forces known to physics.
Quarks come in six “flavors,” and different combinations of quarks give rise to different types of hadrons. For example, protons are made up of two up quarks and one down quark. The double-charmed Xi that was previously discovered is heavier than a proton because it has two weighty charm quarks and one up quark, while the newly discovered Xi-cc-plus has two charm quarks and one down quark.
“Despite the similarity, the new particle has a predicted lifetime that is up to six times shorter than its counterpart, due to complex quantum effects,” CERN said. “This makes it even more challenging to observe.”
CERN said the new particle brings the total number of hadrons discovered by the LHC’s experiments up to 80.
The most famous subatomic particle on that list is the Higgs boson, which was discovered at the LHC in 2012 and filled in one of the biggest blank spots in the Standard Model for particle physics. The discovery of Xi-cc-plus isn’t as groundbreaking, but Vagnoni said it will expand the frontiers of physics nevertheless.
“The result will help theorists test models of quantum chromodynamics, the theory of the strong force that binds quarks into not only conventional baryons and mesons but also more exotic hadrons such as tetraquarks and pentaquarks,” he said.
And the LHC isn’t done yet: An overhaul known as the High-Luminosity Large Hadron Collider project is expected to boost the accelerator’s capacity for particle collisions by a factor of 10 compared to its original design value. When that upgrade is completed, in 2030 or so, physicists will be able to delve more deeply into past discoveries — and perhaps push ahead into whole new frontiers.
“We are looking for where the cracks are in our theory,” Jorgen D’Hondt, director of the Dutch National Institute for Subatomic Physics, told VRT NWS. “We are beginning to understand our collisions better, our method of simulation, and in doing so, we are getting better tools to explore uncharted territory.”
This report was published on Universe Today with the headline “CERN Adds a New Particle to Large Hadron Collider’s Subatomic Zoo.” Licensed for republication under Creative Commons Attribution 4.0 International License.
