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Zeitschrift für Physik C
ISSN: 0170-9739 (printed version)
ISSN: 1431-5858 (electronic version)
Abstract Volume 74 Issue 3 (1997) pp 469-477
A partial wave analysis of the reaction $\gamma\gamma\to\pi^+\pi^-\pi^0$
H. Albrecht et al.ARGUS Collaboration
DESY, D-22603 Hamburg, Germany
Received: 11 July 1996
Abstract. The two-photon reaction $\gamma\gamma\to\pi^+\pi^-\pi^0$ was investigated by the ARGUS collaboration. The reaction is dominated by the formation of the $a_2(1320)$ meson. A value of $\Gamma _{\gamma \gamma} = (0.96 \pm 0.03 \pm 0.13)$ keV was obtained for its radiative width, in good agreement with the world average. The fraction of $\gamma\gamma$-helicity 0 in the $a_2$ two-photon width was found to be equal to $(6.7\pm 2.2)\%$. It allows a discrimination among models that describe the dynamics in the two-photon production of tensor mesons. An upper limit of $\Gamma _{\gamma \gamma} \cdot {\rm Br}(\rho ^{\pm} \pi ^{\mp}) < 0.54$ keV (90% c.l.) was obtained for the resonance $\pi (1300)$. The partial wave analysis revealed almost a complete absence of the wave with spin and parity $J^P=2^-$. We also observe no significant enhancement in the $\pi^+\pi^-\pi^0$ invariant mass spectrum that could be attributed to the two-photon production of the $\pi_2(1670)$. The obtained upper limit $\Gamma_{\gamma\gamma}(\pi_2(1670)) < 0.19$ keV at the 90% confidence level is in contradiction with two previous observations.
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