Amplitude analysis of reactions pi(-)p->etapi(-)p and pi(-)p->etapi(0)n on polarized target and the exotic 1-+ meson

Abstract

Recently several experimental groups analysed data on $π^- p \to ηπ^- p$ and $π^- p \to ηπ^0 n$ reactions with exotic $1^{-+}$ $P$-wave and found a conflicting evidence for an exotic meson $I=1 1^{-+} (1405)$. High statistics data on these reactions are presently analysed by BNL E852 Collaboration. All these analyses are based on the crucial assumption that the production amplitudes do not depend on nucleon spin. This assumption is in sharp conflict with the results of measurements of $π^- p \to π^- π^+ n$, $π^+ n \to π^+ π^- p$ and $K^+ n \to K^+ π^- p$ on polarized targets at CERN which find a strong dependence of production amplitudes on nucleon spin. To ascertain the existence of exotic meson $1^{-+} (1405)$, it is necessary to perform a model-independent amplitude analysis of reactions $π^- p \to ηπ^- p$ and $π^- p \to ηπ^0 n$. We demonstrate that measurements of these reactions on transversely polarized targets enable the required model independent amplitude analysis without the assumption that production amplitudes are independent on nucleon spin. We suggest that high statistics measurements of reactions $π^- p \to ηπ^- p$ and $π^- p \toηπ^0 n$ be made on polarized targets at BNL and at Protvino IHEP, and that model-independent amplitude analyses of this polarized data be performed to advance hadron spectroscopy on the level of spin dependent production amplitudes.