Exotic pentaquark particle found at CERN’s Large Hadron Collider

A new type of particle called the strange pentaquark has been found using the Large Hadron Collider. The particle could help researchers catalogue the states of exotic matter and figure out how fundamental particles stick together.

An illustration of a pentaquark
CERN/Science Photo Library

Researchers at the CERN particle physics laboratory’s Large Hadron Collider (LHC) in Switzerland have discovered a new type of particle called a strange pentaquark. Finding exotic particles like this could help us figure out how hadrons – subatomic particles such as protons and neutrons that are made up of quarks – are held together.

Pentaquarks, true to their name, are made up of four quarks and one antiquark, and they are not expected to form anywhere in nature, making them extraordinarily rare. “Usually conventional hadrons are made up of two or three quarks, so this is an exotic state,” says Elisabetta Spadaro Norella at the University of Milan in Italy, who was part of the team that found the new particle. “There have been very few states of this kind observed so far.”

This specific particle is different from others because it contains a strange quark – not a quark that is unusual, but one of the six “flavours” of the fundamental particle. The researchers found it by smashing two beams of protons together at extremely high energies and following the particles’ ensuing tracks as they decayed into their constituent parts.

Physicists have discovered several new tetraquarks, which are made up of four quarks, in recent years as well. “It’s like a renaissance of these particles because we are collecting more and more data and we are able to study more complex decays,” says Norella.

Each quark behaves slightly differently, so building up a catalogue of hadrons should help researchers understand the fundamental behaviour of the smallest building blocks of matter. For example, we don’t know how they all stick together to form the more complex particles that make up the world around us.

“It’s really important to study those exotic states because they help us to understand how quarks bond together inside particles,” says Norella. There are several ideas for how this might work, but we don’t yet have enough data to tell which is correct – the strange pentaquark and its kin should help with that.

Journal reference

Physical Review LettersDOI: 10.1103/PhysRevLett.131.031901