What new particle, containing two charm quarks and one down quark, was discovered by CERN's LHCb experiment in March 2026?

In March 2026, CERN's LHCb experiment announced the discovery of a new subatomic particle, confirming the existence of a type of baryon containing two charm quarks and one down quark. Baryons are a class of composite particles made up of three quarks, the fundamental building blocks of matter. Familiar baryons include protons and neutrons, which form the atomic nuclei of all ordinary matter. The "doubly charmed" designation refers to the presence of two charm quarks, a heavier "flavor" of quark compared to the up and down quarks found in protons and neutrons.

This newly observed particle, officially named Ξcc⁺ (Xi-cc-plus), is like a heavier cousin to the proton. While a proton consists of two up quarks and one down quark, the Ξcc⁺ particle replaces the two lighter up quarks with two much heavier charm quarks, making it approximately four times as weighty as a proton. The detection of a particle with this specific quark configuration provides crucial data for physicists studying the fundamental forces that govern the universe.

The discovery of the Ξcc⁺ particle by the upgraded LHCb detector is a significant milestone, helping to resolve a mystery that puzzled scientists for over two decades following earlier, unconfirmed hints of such a particle. This observation offers a unique opportunity to test the Standard Model of particle physics and further our understanding of the strong nuclear force, which binds quarks together within baryons. It is only the second time a baryon with two heavy quarks has been observed, providing a valuable "laboratory" to explore how these exotic particles behave.