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Evidence for spin-one resonance production in the reaction γγ*→π+π−π0π0

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields1993Vol. 48(9), pp. 3976–3986

Abstract

Using data from the TPC/Two-Gamma experiment at the SLAC ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ storage ring PEP, a C=+1 resonance has been observed in the ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{0}$\ensuremath{\gamma} final state resulting from the fusion of one nearly real and one quite virtual photon. The actual decay channel is probably ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{0}$${\mathrm{\ensuremath{\pi}}}^{0}$, where one final-state photon is not detected, and the mass of the fully reconstructed state would be approximately 1525 MeV. A four-pion decay mode in turn implies that the resonance has even isospin. The nonobservation of this R(1525) when both initial-state photons are nearly real suggests a spin-1 assignment. Since the large measured value of the product of the branching ratio into ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{0}$${\mathrm{\ensuremath{\pi}}}^{0}$ and the \ensuremath{\gamma}\ensuremath{\gamma} coupling makes it unlikely that this state is the mostly s\ifmmode\bar\else\textasciimacron\fi{}s ${\mathit{f}}_{1}$(1510), its interpretation may lie outside of conventional meson spectroscopy. There is a second, less-significant enhancement observed in the same reaction at a four-pion mass centered around 2020 MeV.

Abstract

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