Abstract
Hadrons with similar masses and same spin and parity are grouped in multiplets of the electric charge. For example, the two charged pions π + and π − (139.6 MeV) and the π 0 (135.0 MeV) form a triplet with similar masses. As Table 2.1 shows, the four kaons with masses \(m_{K^\pm }\) = 493.7 MeV and \(m_{K^0}\) = \(m_{\overline {K}^0}\) = 497.6 MeV form two doublets, (K 0, K +) and (K −, \(\overline {K}^0\)).
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Notes
- 1.
The electromagnetic repulsion acts in the opposite direction because it reduces the binding energy and hence increases the mass of the proton.
- 2.
The inequalities (3.6) lift the mass degeneracy in the isospin multiplet. This is analogous to the two-level splitting of a free electron when an external magnetic field is switched on: the spin precesses around the z-axis with constant projection m.
- 3.
The analysis of these radiative decays, in particular ω(→ ηγ)π 0, is complicated by ρ − ω mixing : the electromagnetic isospin violating decay ω → 2π (Sect. 3.4), with a branching ratio f of 1.5%, interferes with the 2π decay of the ρ 0 (f = 100%) through the transition ω → 2π → ρ 0. This interference must be taken into account when the ρ 0 production × decay rate is much larger than the corresponding ω one (see [1] for details).
- 4.
The C violating decay J∕ψ → γγ is forbidden by the Landau-Yang theorem. The experimental upper limit is 2.7 × 10−7 [6].
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Amsler, C. (2018). Isospin. In: The Quark Structure of Hadrons. Lecture Notes in Physics, vol 949. Springer, Cham. https://doi.org/10.1007/978-3-319-98527-5_3
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DOI: https://doi.org/10.1007/978-3-319-98527-5_3
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