Researchers from the LHCb experiment at CERN recently presented a new discovery at the European Physical Society Conference on High Energy Physics. The team discovered a new particle they labeled as TCC+, which is a tetraquark. A tetraquark is an exotic hadron that contains two quarks and two antiquarks.
The particle is the longest-lived exotic matter particle ever discovered and the first to contain a pair of heavy quarks and two light antiquarks. Quarks are the fundamental building blocks matter is constructed of. They combine to form hadrons, primarily baryons, such as the proton and the neutron, consisting of three quarks and mesons formed in a quark-antiquark pair.
Scientists note that several so-called exotic hadrons, which are particles containing four or five quarks rather than the conventional two or three, have been discovered in recent years. The new discovery is particularly unique, with scientists noting that it could be considered an “exotic exotic hadron.”
The new particle has a pair of charm quarks and an up and down antiquark. Previously, several tetraquarks have been discovered, but this is the first with two charm quarks without charm antiquarks to balance them. Physicists consider the particle an “open charm,” noting particles with the charm quark and anticharm antiquark have “hidden charm” because the charm quantum number for the whole particle adds up to zero.
In this new particle, the charm quantum number adds up to two. The quark content of TCC+ has other interesting features. It’s the first particle to be discovered belonging to a class of tetraquarks sporting a pair of heavy quarks and two light antiquarks. Those particles decay, transforming into a pair of mesons, each formed by one of the heavy quarks and one of the light antiquarks.
Theoretical predictions suggest that the decay of this type of particle is not only unlikely but forbidden. The particle would not decay via the strong interaction. It would have to do so via the weak interaction making its lifetime several orders of magnitude longer than any previously observed exotic hadron.