Observation of exotic meson production in the reaction pi(-)p -> eta 'pi(-)p at 18 GeV/c

An amplitude analysis of an exclusive sample of 5765 events from the reacti on pi (-) p --> eta ' pi (-) p at 18 GeV/c is described. The eta ' pi (-) p roduction is dominated by natural parity exchange and by three partial wave s: those with J(PC) = 1(-+), 2(++), and 4(++). A mass-dependent analysis of the partial-wave amplitudes indicates the production of the a(2)(1320) mes on as well as the a(4)(2040) meson, observed for the first time decaying to eta ' pi (-). The dominant, exotic (non-q (q) over bar) 1(-+) partial wave is shown to be resonant with a mass of 1.597 +/- 0.010(-0.010)(+0.045) GeV /c(2) and a width of 0.340 +/- 0.040 +/- 0.050 GeV/c(2). This exotic state, the pi (1)(1600). is produced with a t dependence which is different from that of the a(2)(1320) meson, indicating differences between the production mechanisms for the two states.