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The results of an extensive campaign of measurements of the pi -> pi pi process in the nucleon and nuclei at intermediate energies are presented. The measurements were motivated by the study of strong pi pi correlations in nuclei. The analysis relies on the composite ratio C_{pi pi}^A, which accounts for the clear effect of the nuclear medium on the (pi pi) system. The comparison of the C_{pi pi}^A distributions for the (pi pi)_{I=J=0} and (pi pi)_{I=0,J=2} systems to the model predictions indicates that the C_{pi pi}^A behavior in proximity of the 2m_pi threshold is explainable through the partial restoration of chiral symmetry in nuclei.
We show that both the linear and the non-linear chiral models give an enhancement of the pi-pi cross section near the 2pi threshold in the scalar-iso-scalar (I=J=0) channel in nuclear matter. The reduction of the chiral condensate, i.e., the partial
The N*(1440) -> N pi pi decay is studied by making use of the chiral reduction formula. This formula suggests a scalar-isoscalar pion-baryon contact interaction which is absent in the recent study of Hern{a}ndez et al. The contact interaction is intr
The COMPASS collaboration at CERN has investigated the pi^- gamma -> pi^- pi^- pi^+ reaction at center-of-momentum energy below five pion masses, sqrt(s) < 5 m(pi), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Excha
We propose a measurement on the elastic $pipi$ scattering phase shift difference $delta^0_0-delta^2_0$ through $Psito J/Psi pi^+ pi^-$ process in future high statistics BES-III experiment. The decay amplitude is constructed with seven Lorentz invaria
The e+e- -> pi+pi-pi+pi- cross section has been measured using 5.8/pb of integrated luminosity collected with the CMD-2 detector at the VEPP-2M collider. Analysis of the data with a refined efficiency determination and use of both three- and four-tra