Measurement of the phase between strong and electromagnetic amplitudes of J/Psi decays

Using 16 energy points of e(+) e(-) annihilation data collected in the vicinity of the J/Psi resonance with the BESIII detector and with a total integrated luminosity of around 100 pb(-1), we study the relative phase between the strong and electromagnetic amplitudes of J/Psi decays. The relative phase between J/Psi electromagnetic decay and the continuum process (e(+) e(-) annihilation without the J/Psi resonance) is confirmed to be zero by studying the cross section lineshape of mu(+) mu(-) production. The relative phase between J/Psi strong and electromagnetic decays is then measured to be (84.9 +/- 3.6)degrees or (-84.7 +/- 3.1)degrees for the 2(pi(+) pi(-) )pi(0) final state by investigating the interference pattern between the J/Psi decay and the continuum process. This is the first measurement of the relative phase between J/Psi strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state eta pi(+) pi(-) with eta -> pi(+) pi(-) pi(0) , which provides additional information about the phase between the J/Psi electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/Psi -> 2(pi(+) pi(-) )pi(0) is measured to be (4.73 +/- 0.44)% or (4.85 +/- 0.45)%, and the branching fraction of J/Psi -> eta pi(+) pi(-) is measured to be (3.78 +/- 0.68) x 10(-4). Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.
For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.03.001