CERN experiment discovers a new, very charming particle

New particle observed at the LHCb, CERN (Credit: CERN)

Five years on from discovering the Higgs boson, an international team, including scientists from the University of Birmingham, has discovered a brand new heavy particle at the LHCb experiment at CERN’s Large Hadron Collider (LHC).

The new particle, named Xi-cc++ (pronounced Ksī-CC plus-plus), is part of a family of “doubly charmed baryons” that are predicted to exist by the Standard Model theory of particle physics, but this is the first time scientists have been able to confirm their existence.

The Xi-cc++ discovery follows the announcement earlier this year of unexpected decay mechanisms of B-meson particles in the LHCb experiment, in an analysis led by Dr Simone Bifani from the University of Birmingham’s School of Physics and Astronomy.

“The discovery of the Xi-cc++ is the latest in a long line of exciting areas being opened up by the LHCb experiment, and it follows closely on the heels of tantalising hints of physics beyond the Standard Model that we reported in April,” says Dr Bifani. “We are thrilled by both results!”

The latest findings open up a new field of particle physics research, with the potential for the further discovery of many more such doubly-charmed baryons.

Nearly all the matter that we see around us is made of baryons, which are common particles composed of three quarks, the best-known being protons and neutrons. But there are six types of existing quarks, and theoretically many different potential combinations could form other kinds of baryons. Baryons so far observed are all made of, at most, one heavy quark such as a bottom or charm quark.

Lead physicist Dr Patrick Spradlin from the University of Glasgow, who announced the findings at the European Physical Society Conference on High Energy Physics in Venice today, said “The properties of the newly discovered baryon shed light on a longstanding puzzle surrounding the experimental status of baryons containing two charm quarks, opening an exciting new branch of investigation for LHCb.”

“In contrast to other baryons, in which the three quarks perform an elaborate dance around each other, a doubly heavy baryon is expected to act like a planetary system, where the two heavy quarks play the role of heavy stars orbiting one around the other, with the lighter quark orbiting around this binary system,” added Guy Wilkinson, former Spokesperson of the collaboration.

The observation of this new baryon proved to be challenging and has been made possible owing to the high production rate of heavy quarks at the LHC and to the unique capabilities of the LHCb, one of the four main experiments at CERN solving the mysteries of our universe, which can identify the decay products with excellent efficiency. The Ξ_cc^(++) baryon was identified via its decay into a Λc+ baryon and three lighter mesons K-, π+ and π+.

The observation of the Ξ_cc^(++) in LHCb raises expectations that other representatives of the doubly charmed baryon family could be detected. They will now be searched for at the LHC.

This result is based on 13 TeV data recorded during run 2 at the Large Hadron Collider, and confirmed using 8 TeV data from run 1. The collaboration has submitted a paper reporting these findings to the journal Physical Review Letters.

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For more information, contact Liz Bell, Communiactions Manager for Science and Technology at the University of Birmingham, on +44 (0)121 414 5134. For out of hours enquiries please email the Press Office or call +44 (0) 7789 921 165.

Notes to editors

LHCb is one of the four main experiments at the Large Hadron Collider at CERN. LHCb was built in a cavern 100m below ground near Ferney-Voltaire in France. It is investigating the subtle differences between matter and antimatter in a bid to answer one of the most fundamental questions – why is our Universe made of matter?

UK participation in LHCb is funded by STFC, with contributions from the participating institutes, the Royal Society and European Union.

The UK participation in the international LHCb experiment is from eleven institutes. University of Birmingham, University of Bristol, University of Cambridge, University of Edinburgh, University of Glasgow, Imperial College London, University of Liverpool, University of Manchester, University of Oxford, STFC Rutherford Appleton Laboratory, University of Warwick.