* Astronomy

Title: Evidence for Exotic Meson Production in the Reaction \pi^{-} p \to \eta \pi^{-} p at 18GeV/c
Authors: The E852 Collaboration
(15 May 1997)

The \eta \pi^{-} system has been studied in the reaction \pi^{-} p \to \eta \pi^{-} p$ at 18 GeV/c. A large asymmetry in the angular distribution is observed indicating interference between L-even and L-odd partial waves. The a_{2}(1320) is observed in the J^{PC} = 2^{++} wave, as is a broad enhancement between 1.2 and 1.6 GeV/c² in the J^{PC} = 1^{-+} wave. The observed phase difference between these waves shows that there is phase motion in addition to that due to a_{2}(1320) decay. The data can be fitted by interference between the a_{2}(1320) and an exotic 1^{-+} resonance with M = (1370 ±16 {+50}\atop{-30}) MeV/c² and \Gamma =(385 ±40 {+65}\atop{-105}) MeV/c².

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Non-quark model mesons include

    exotic mesons, which have quantum numbers not possible for mesons in the quark model;
    glueballs or gluonium, which have no valence quarks at all;
    tetraquarks, which have two valence quark-antiquark pairs; and
    hybrid mesons, which contain a valence quark-antiquark pair and one or more gluons.
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