Evidence for rho^0(770)-f_0(980) mixing in pi(-)p->pi(-)pi(+)n from CERN measurements on polarized target

TL;DR

This study provides model-independent evidence for mixing between rho^0(770) and f_0(980) resonances in pion-proton scattering, revealing details of their interference and phase relationships through high-resolution amplitude analyses.

Contribution

It presents the first model-independent analysis demonstrating rho^0(770)-f_0(980) mixing in pion-proton scattering data at CERN, clarifying the resonance interference mechanisms.

Findings

Evidence of rho^0(770)-f_0(980) mixing in S- and P-wave amplitudes

Resonant phases of rho^0(770) observed in S-wave amplitudes

Interference effects explain apparent helicity-dependent width variations

Abstract

We present model independent high resolution amplitude analyses of CERN data on pi(-)p->pi(-)pi(+)n at 17.2 GeV/c for dipion masses 580-1080 MeV at small momentum transfers on polarized target (Analysis I) and unpolarized target (Analysis II). The results for S- and P-wave transversity amplitudes from the Analysis I are used in a model independent determination of helicity amplitudes. All three analyses provide similar evidence for rho^0(770)-f_0(980) mixing in S- and P-wave amplitudes. In Analyses I and II the S-wave amplitudes |S_d|^2 peak at rho^0(770) mass while the P-wave amplitudes |L_d|^2 dip at f_0(980) mass. In both analyses the S-wave amplitudes S_tau are nearly in phase with amplitudes L_tau for both transversitities tau=u(spin up) and d(spin down), indicating resonant phases of rho^0(770) also in the S-wave. The S-wave single flip amplitudes |S_1|^2 and the relative phases Phi(S_1)-Phi(L_1) show the same pattern. While the non-flip amplitudes |L_0|^2 are small below 960 MeV, there is a sudden rise above this mass that may reflect the presence of f_0(980) resonance. We show that the apparent dependence of rho^0(770) width on helicity in amplitudes |U_tau|^2 and |N_tau|^2 results from the interference of amplitudes with helicities lambda=+/-1 and not from the violation of rotational/Lorentz symmetry. This suggests that the production mechanism and the mechanism responsible for rho^0(770)-f_0(980) mixing have independent dynamical origins.