The hadronic structure of the decay of the tau lepton to three charged particles, tau --> 3 pi nu(tau), is studied using data collected by the DELPHI detector at LEP between 1992 and 1995. The invariant mass of the 3 pi system, m(3 pi), is fitted using the models of Kuhn and Santamaria, Isgur Morningstar and Reader, and Feindt. The 3 pi and pi(+)pi(-) mass spectra are compared with each model. Below m(3 pi)(2) = 2.3 GeV2, all are in good qualitative agreement. Above m(3 pi)(2) = 2.3 GeV2, anomalous behaviour is observed, consistent with the existence of a hitherto unseen decay mode of the tau through a radial excitation of the alpha(1) meson. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
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