LHCb Collaboration Discovers New Proton-Like Particle with Two Charm Quarks

Physicists working on the LHCb experiment at CERN have announced the discovery of a remarkable new subatomic particle: the doubly charmed baryon, designated as the Xi_cc+ particle. This exotic baryon contains two heavy charm quarks and one down quark, making it fundamentally different from ordinary protons, which contain two up quarks and one down quark.

The discovery was made possible by the upgraded LHCb detector, which has been collecting data during Run 3 of the Large Hadron Collider. Researchers observed a clear peak of approximately 915 events around 3,620 MeV/c squared, with a statistical significance exceeding 7 sigma — far surpassing the 5 sigma threshold required to claim a discovery in particle physics.

“This exotic baryon contains two heavy charm quarks and one down quark, making it fundamentally different from ordinary protons, which contain two up quarks and one down quark.”

The new particle has roughly four times the mass of a proton, owing to the presence of two charm quarks, which are considerably heavier than the up quarks they replace. This makes the Xi_cc+ a valuable laboratory for studying how the strong nuclear force — one of the four fundamental forces of nature — binds composite particles together under different configurations of quark masses.

Understanding how quarks of different masses interact within baryons is crucial for refining quantum chromodynamics (QCD), the theory that describes the strong force. While QCD has been remarkably successful in predicting many aspects of particle behavior, doubly heavy baryons like the Xi_cc+ probe regions of the theory that have been difficult to test experimentally until now.

This marks the first new particle identified with the upgraded LHCb detector, a testament to the enhanced sensitivity and data-processing capabilities of the instrument after its extensive renovation. The LHCb experiment specializes in studying the differences between matter and antimatter, and its precision tracking systems make it uniquely suited to detecting rare and exotic particles.

The discovery has been met with enthusiasm across the physics community, as it opens new avenues for exploring the fundamental structure of matter. Future analysis of the Xi_cc+ particle's properties, including its lifetime and decay modes, will provide further tests of theoretical predictions and could reveal unexpected aspects of the strong force.