Scientists at the University of Manchester have played a key role in identifying previously unknown elementary particles at CERN’s Large Hadron Collider (LHC). The particle, called Ξcc⁺ (Xi-cc-plus), is a heavy proton-like particle composed of two charm quarks and one down quark.
This will be the first particle discovery using the upgraded LHCb detector. The upgrade is part of a larger international effort involving more than 1,000 researchers from 20 countries. Britain contributed more than any other country, and Manchester provided important leadership.
Heavier relatives of protons
The newly discovered Ξcc⁺ is part of the same family of protons that were first identified in Manchester by Ernest Rutherford and colleagues between 1917 and 1919. A proton contains two up quarks and one down quark, but Ξcc⁺ replaces the up quark with a heavier charm quark.
The discovery also builds on Manchester’s long history of particle physics research. In the 1950s, university scientists first identified members of the Ξ (Xi) particle family, laying the foundation for discoveries like this one.
Manchester’s role in LHCb detector upgrade
Professor Chris Parkes, head of the University’s Department of Physics and Astronomy, led the international collaboration in the installation and initial operation of the upgraded LHCb detector. He also oversaw UK project involvement for over 10 years, guiding projects from initial approval to completion.
The Manchester LHCb team designed and built key parts of the upgraded tracking system, including the silicon pixel detector module, which was assembled in the university’s Schuster Building. These components are important for accurately tracking particle decay and identifying signals such as Ξcc⁺.
Professor Parkes said: “Rutherford’s gold foil experiment in Manchester’s basement changed our understanding of matter, and this discovery builds on that legacy using cutting-edge technology at CERN. Both milestones show how far curiosity-driven research can take us. This discovery demonstrates the extraordinary capabilities of the upgraded LHCb detector and the strength of the UK and Manchester’s contribution to the experiment.”
Advanced detectors capture particle collisions
Dr Stefano De Capua from the University of Manchester led the fabrication of the silicon detector module. He explained that the detector works like a high-speed camera.
“This detector is a type of ‘camera’ that images particles produced at the LHC, taking pictures 40 million times per second. It utilizes a custom-designed silicon chip, and also has variations for use in medical imaging applications.”
how ξcc⁺ particle has been identified
The researchers detected Ξcc⁺ by observing how it decays into three lighter particles: Λc⁺ K⁻ π⁺. These decay events were recorded during proton-proton collisions at the LHC in 2024, the first year the upgraded LHCb experiment was in full operation.
A clear signal of about 915 events was measured with a mass of 3619.97 MeV/c2. This result is consistent with predictions based on previously discovered related particles Ξcc⁺⁺.
Solving a 20-year mystery in particle physics
For more than 20 years, scientists have debated previous claims that this particle had been observed, but those findings were never confirmed. New measurements from LHCb show that the particle’s mass does not match previous claims, but does match theoretical expectations based on its partner particles.
Future developments for CERN and Manchester
Looking forward, the University of Manchester will continue to play a leading role in the next phase of the LHC programme, known as LHCb Upgrade 2. This upgrade will utilize the high-luminosity LHC accelerator to collect more data and study rare particles in more detail.
Details of the Ξcc⁺ discovery will be presented at the Rencontres de Moriond Electroweak conference.
