Researchers from the LHCb experiment announced today at the Beauty2026 conference in Maastricht the discovery of a long-sought-after third particle containing two charm quarks.
This omega-cc particle was discovered through precise studies of the tracks of particles created during proton collisions in the LHC accelerator at CERN. Data collected up through 2024 were used for the discovery.
The discovery adds an important piece to the puzzle of quark physics, in which matter particles consist of triplets of quarks. In ordinary matter, these are up or down quarks. But all combinations with heavier quarks, such as charm and strange, are also theoretically possible.
Many of these combinations have already been found in numerous accelerator experiments. A combination of two charm quarks with a strange quark had not yet been demonstrated. This nearly completes the tableau of baryons with two charm quarks.
Only a particle with a third charm quark has not yet been discovered. According to the presentation in Maastricht, it is quite possible that this will still turn up if all measurements up to and including 2026 are included. “A wonderful result that can actually be identified in the particle tracks,” says LHCb researcher Niels Tuning of Nikhef.
LHCb is one of the four large detectors at the LHC accelerator where protons collide. Nikhef is closely involved in the international experiment, particularly through the construction of the VELO detector, which can determine the exact starting point of particle tracks.
In some proton collisions, a pattern emerges in the detector consisting of a new proton, two kaons, and a pion, which, upon closer examination, does not originate precisely from the collision point. Instead, it appears that two other particles are produced first, one of which was previously unknown.
This unknown particle is the omega particle with two charm quarks and one strange quark. Its signal is unmistakable in the LHCb measurements through 2024. Statistically, the significance is 8 sigma, jargon for a genuine discovery.
According to the measurements, the new omega-cc particle is four times as heavy as a proton and is estimated to exist for 170 femtoseconds before it decays further. That is enough to produce a small but telling dip in the particle tracks in the detector.
At the Beauty2026 conference in Maastricht this week, approximately one hundred experts in the field of quark physics from around the world have gathered to discuss new results, analyses, and theory. The Nikhef LHCb group is partly affiliated with Maastricht University.
