The a(0)(980) Meson Explained

One of the long standing mysteries in high energy physics is determining the internal structure of scalar mesons such as the a(0)(980) meson, and they aren't easily explained with a quark-antiquark model (apart from distinctive quarkonium cases, where the quark and antiquark are quarks of the same flavor, like a charm quark- anticharm quark meson).

The symbols "a" (isospin 1) and "f" or "f'" (isospin 0) apply to mesons with ground state JPC quantum numbers 0++ which are also known as (true) scalar mesons.

A new paper concludes with convincing reasoning that the a(0)(980) meson, a scalar meson, is a tetraquark. A key part of the abstract to the paper explains that:

The predicted branching fractions in the qq¯ model of a0(980) are too small by one to two orders of magnitude compared to experiment as the amplitude is suppressed by the smallness of the a0(980)+ decay constant, while those for D+→a0(980)0P and D0→a0(980)−P are usually too large. These discrepancies can be resolved provided that a0(980) is a tetraquark state.