CERN's LHCb Experiment Unveils New Subatomic Particle: The Ξcc⁺
Scientists at CERN's Large Hadron Collider (LHC) have announced the discovery of a new subatomic particle, the Ξcc⁺ (Xi-cc-plus), utilizing the upgraded LHCb detector.
This particle is characterized as a heavy, proton-like entity composed of two charm quarks and one down quark. The observation, which involved an international collaboration and significant contributions from the University of Manchester, confirms a particle whose existence had been theorized and unconfirmed for over two decades. This groundbreaking discovery also marks the first particle observation made with the upgraded LHCb detector.
Particle Composition and Discovery Context
The Ξcc⁺ particle is a member of the baryon family, similar to a proton, but distinguished by its unique quark composition. While a proton contains two up quarks and a down quark, the Ξcc⁺ replaces the lighter up quarks with two heavier charm quarks, alongside one down quark. This finding aligns perfectly with theoretical expectations for such a particle. The discovery was made during proton-proton collisions at the LHC in 2024, the first year of full operation for the LHCb Upgrade experiment.
Identification and Measurement
The identification of the Ξcc⁺ particle involved observing its distinct decay into three lighter particles: Λc⁺, K⁻, and π⁺. Approximately 915 such decay events were recorded, revealing a clear peak at a mass of 3619.97 MeV/c².
This measured mass is consistent with theoretical models and provides a definitive confirmation, resolving a claim of the particle's existence made over two decades prior that was incompatible with current findings.
This discovery also builds on a rich historical legacy, including the proton's discovery by Ernest Rutherford and the identification of a member of the Ξ (Xi) particle family by Manchester physicists in the 1950s.
International Collaboration and Manchester's Pivotal Role
The LHCb experiment is a truly international project, involving over 1,000 scientists from approximately 20 countries. Notably, the United Kingdom made the largest national contribution to the LHCb detector upgrade, with the University of Manchester playing a significant leadership role.
Leadership in the Upgrade
Professor Chris Parkes, who heads the University of Manchester's Department of Physics and Astronomy, led the international collaboration throughout the installation and initial operation phases of the LHCb Upgrade detector. He also spearheaded the UK's contribution for more than a decade.
Technological Contribution: Silicon Pixel Detectors
The Manchester LHCb group was instrumental in designing and building key components for the upgraded tracking system, specifically advanced silicon pixel detector modules. These detectors were crucial for accurately reconstructing the intricate particle decays that ultimately led to the Ξcc⁺ observation.
Module Production and Innovation
Dr. Stefano De Capua, also from the University of Manchester, led the essential production of these silicon detector modules. The detector itself functions by imaging particles produced at the LHC an astonishing 40 million times per second, utilizing a custom-designed silicon chip – a variant of which finds applications in medical imaging.
Future Research Horizons
The University of Manchester continues its deep involvement in the LHCb program, including the planning and development for the upcoming LHCb Upgrade 2. This next ambitious phase is intended to leverage the High-Luminosity LHC accelerator, paving the way for even more groundbreaking future research.