CERN's LHC scientists closer to finding key to universe with discovery of doubly-charmed particle

Scientists at CERN’s Large Hadron Collider are one step closer to finding key to the universe with the discovery of a new ‘doubly-charmed’ particle, called Xicc++, that contains an unusual combination of quarks, a fundamental constituent of matter.

The discovery by the scientists working at the world’s largest and most powerful atom smasher will help investigate into the strong interaction, one of the four fundamental forces of nature. 

The newly-discovered particle consists of two charm quarks and one up quark. Current theories expected the existence of this particle from the baryon family. But for many years, physicists have been looking for such baryons with two heavy quarks.

The mass of the particle is about 3,621 Mega electron-Volt (MeV). This is almost four times heavier than the most familiar baryon, the proton, a property that arises from its doubly charmed quark content.

The discovery of the particle was announced at the EPS Conference on High Energy Physics in Venice.

According to scientists working with CERN’s LHC, this is the first unambiguously detected particle. CERN’s LHC is the largest and most powerful particle collider in the world.

Nearly all the matter found around us is made of baryons, which are common particles composed of three quarks, the best-known being protons and neutrons.

However, 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.

“Finding a doubly heavy-quark baryon is of great interest as it will provide a unique tool to further probe quantum chromodynamics, the theory that describes the strong interaction, one of the four fundamental forces,” said Giovanni Passaleva, spokesperson of the LHCb collaboration.

“Such particles will thus help us improve the predictive power of our theories,” said Passaleva.

“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,” said Guy Wilkinson, former spokesperson of the collaboration.

Measuring the properties of the Xicc++ will help to establish how a system of two heavy quarks and a light quark behaves.

Important insights can be obtained by precisely measuring production and decay mechanisms, and the lifetime of this new particle.

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 experiment, which can identify the decay products with excellent efficiency.

The Xicc++ baryon was identified via its decay into a Xic+ baryon and three lighter mesons K-, p+ and p+.

The observation of the Xicc++ in LHCb raises the expectations to detect other representatives of the family of doubly-heavy baryons. They will now be searched for at the LHC. 

(With inputs from PTI)