Study of sigma(750) and rho0(770) production in measurements of piN(polarized) -> pi(+)pi(-)n on a polarized target at 5.98,11.85 and 17.2 GeV/c

Abstract

We present a new and improved model independent amplitude analysis of reactions $π^+ n_\uparrow \to π^+ π^- p$ at 5.98 and 11.85 GeV/c and $π^- p_\uparrow \to π^- π^+ n$ at 17.2 GeV/c measured with transversely polarized targets at the CERN Proton Synchrotron. A clear signal for $σ(750)$ resonance emerges in all four solutions for $S$-wave intensity $I_S$ at 5.98 and 11.85 GeV/c and in both solutions for $S$-wave amplitude $|\overline S|^2Σ$ at 17.2 GeV/c. Its $π^+π^-$ decay width is estimated to be in the range 200--300 MeV. We find significant suppression of $ρ^0$ production in the amplitudes $|U|^2Σ$, $|\overline N |^2Σ$ and, at 17.2 GeV/c, in $|L|^2Σ$. The mass dependence of amplitudes $|\overline L |^2Σ$ and $|L|^2Σ$ shows unexpected structures within the $ρ^0$ mass region which correlate the mass spectra corresponding to opposite nucleon spins. These features of $P$-wave moduli reveal the essential role of nucleon spin in pion production process and contradict the factorization hypothesis. Our results emphasize the need for a systematic study of pion production on the level of amplitudes in a new generation of dedicated experiments with spin at the recently proposed high-intensity hadron facilities.