00 4 Four sorts of meson
نویسنده
چکیده
abstract An extensive spectrum of light non-strange q ¯ q states up to a mass of 2400 MeV has emerged from Crystal Barrel and PS172 data on ¯ pp → Resonance → A + B in 17 final states. These data are reviewed with detailed comments on the status of each resonance. For I = 0, C = +1, the spectrum is complete and very secure. Six 'extra' states are identified. Four of them have I = 0, C = +1 and spin-parities predicted for glueballs. Their mass ratios agree closely with predictions from Lattice QCD calculations. However, branching ratios for decays are not flavour blind and require mixing with neighbouring q ¯ q states. This mixing remains controversial. Two further states, η 2 (1870) and π 2 (1880), are candidates for a pair of hybrids. Their decay branching ratios BR[η 2 (1870) → f 2 (1270)η]/BR[η 2 (1870) → a 2 (1320)π] and BR[π 2 (1880) → a 2 (1320)η]/BR[π 2 (1880) → f 2 (1270)π] are much larger than predicted by SU(3) for q ¯ q states. A fourth category of anomalously light 0 + mesons is made of σ(540), κ(750), a 0 (980) and f 0 (980), forming a non-q ¯ q nonet. Their properties are reviewed using data from both Crystal Barrel and elsewhere.
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