Physicists with LHCb Collaboration at CERN’s Large Hadron Collider (LHC) have detected the elusive Ωcc⁺ baryon, a particle containing two charm quarks and one strange quark, completing a long-sought family of doubly charmed baryons first predicted over half a century ago.
An artist’s impression of the doubly charmed Ωcc⁺ baryon. Image credit: Daniel Dominguez / CERN.
“Quarks are basic building blocks of matter,” said Dr. Paula Collins, incoming deputy spokesperson of the LHCb Collaboration.
“There are six types of quarks (up, down, charm, strange, top and bottom), which bond into pairs or triplets, known as mesons and baryons respectively.”
“Sixty years ago, as experiments started to reveal the underlying quark structure of matter, researchers began to build theoretical models to classify how quarks can combine into composite particles.”
“Soon, scientists were able to predict the properties of as-yet-undiscovered particles.”
“In 1964, the discovery of a new particle at Brookhaven National Laboratory marked a turning point.”
“Consisting of three strange quarks, this particle had already been predicted by theorists, and the experimental confirmation of its existence and properties showed the strength of these theoretical models.”
“In 1974, another discovery rocked the world of particle physics as it revealed a fourth quark, the charm quark,” they added.
“This meant that theorists now had to extend their models to accommodate the many new possible quark combinations.”
“Included in these predictions were the doubly charmed baryons.”
“These are particles that each consist of two charm quarks and either an up, a down or a strange quark as the third of the triplet.”
“Physicists are particularly interested in this family of particles as the large mass differences between the quarks could provide useful insight into the strong force, which binds quarks together into composite particles.”
“However, the experiments of the time were neither able to produce the doubly charmed baryons, nor did they have sensitive enough equipment to detect them.”
A reconstruction of how the doubly charmed Ωcc⁺ baryon was created and detected at the LHCb experiment. Image credit: CERN.
The LHCb physicists discovered the first of these doubly charmed baryons in 2017 and the second earlier this year.
The discovery of Ωcc⁺, the third and final member of this particle family, is based on data collected in 2024 from high-energy proton-proton collisions at the LHC.
These collisions produced the new doubly charmed baryons, which are short-lived, travelling a fraction of a millimeter in the detector before decaying into more stable particles.
The LHCb team traced the tracks left by these particles in the detector back to their points of origin.
This revealed the characteristic signature of the new short-lived particle with a distinct mass around four times heavier than a proton.
“This is a moment of beautiful historical significance,” Dr. Collins said.
“Out of the 85 composite particles discovered so far at the LHC, these three doubly charmed baryons are unique.”
“They decay by the weak force and live long enough to give measurable flight distances in our experiment.”
“The discovery was made possible thanks to the LHCb’s upgraded detector, with its powerful capabilities to track and identify particles.”
