Prof. Dr. Wojciech Broniowski (INP Cracow, Jan Kochanowski U): Baryon inside the pion

It is shown that although (obviously) pions carry no net baryon number, its distribution is polarized when the isospin symmetry is broken due to the current quark mass splitting and the elecromagnetic effects. As a result, the baryon form factor of charged pions is nonzero. Estimates for this basic feature are obtained in a wide range of approaches, from simple constituent quark models, to vector meson dominance fits of the e+e- -> pi+pi- data. All methods yield a positive baryonic mean square radius for pi+, <r2>B = (0.04-0.07fm)^2, hence an intuitive picture emerges where the outer region of pi+ has a net baryon, and the inner region a net antibaryon density, both compensating each other such that the total baryon number is zero. For pi- the effect is equal and opposite.
[1] P. Sanchez, E. Ruiz Arriola, W. Broniowski, Phys. Lett. B 822 (2021) 136680.
[2] W. Broniowski, E. Ruiz Arriola, P. Sanchez, Phys. Rev. D 106 (2022) 036001.