Tetraquark Discovered

Updated: Oct 2, 2021

This short article is so complicated that it will make your nose bleed, but in a strange way it's difficulty to comprehend also makes it quite amusing. So, if you want to give your brain a workout, then go ahead...

Scientists have just discovered tetraquarks. What is it? A tetraquark is an exotic hadron containing two quarks and two antiquarks. It's the longest-lived exotic matter particle ever discovered, and the first to contain two heavy quarks and two light antiquarks.

Quarks are the fundamental building blocks from which matter is constructed. They combine to form hadrons, namely baryons, such as the proton and the neutron, which consist of three quarks, and mesons, which are formed as quark-antiquark pairs. In recent years a number of so-called exotic hadrons - particles with four or five quarks, instead of the conventional two or three - have been found. Today's discovery is of a particularly unique exotic hadron, an exotic exotic hadron if you like.

The new particle contains two charm quarks and an up and a down antiquark. Several tetraquarks have been discovered in recent years (including one with two charm quarks and two charm antiquarks), but this is the first one that contains two charm quarks, without charm antiquarks to balance them. Physicists call this "open charm" (in this case, "double open charm"). Particles containing a charm quark and a charm antiquark have "hidden charm" - the charm quantum number for the whole particle adds up to zero, just like a positive and a negative electrical charge would do. Here the charm quantum number adds up to two, so it has twice the charm!



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