PENTAQUARK; TETRAQUARKS

About:

• The three “exotic” additions — a new kind of “pentaquark” and the first-ever pair of “tetraquarks” — to the growing list of new hadrons found at the LHC will help physicists better understand how quarks bind together into these composite particles.
• CERN — Conseil Européen pour la Recherche Nucléaire — is the original name of the European Organisation for Nuclear Research, which runs the particle accelerator complex that houses the LHC, the world’s largest and most complex collider.
• The LHC, re-ignited after three years in April, was cranked up to unprecedented levels of energy on July 5, and has begun smashing together protons at almost the speed of light, which could throw up “new” physics beyond the Standard Model.

What are quarks?

• Quarks are elementary particles that come in six “flavours”: up, down, charm, strange, top, and bottom. They usually combine together in groups of twos and threes to form hadrons such as the protons and neutrons that make up atomic nuclei.
• But they can also combine into four-quark and five-quark particles, called tetraquarks and pentaquarks. These exotic hadrons were predicted by theorists about six decades ago — around the same time as conventional hadrons — but they have been observed by LHCb and other experiments only in the past 20 years.