Cross-section of the reaction e+ e- ---> pi+ pi- pi+ pi- below 1-GeV at CMD-2

Using 3.07 pb −1 of data collected in the energy range 0.60–0.97 GeV by CMD-2, about 150 events of the process e + e − → π + π − π + π − have been selected. The energy dependence of the cross section agrees with the assumption of the a 1 (1260) π intermediate state which is dominant above 1 GeV. For the first time π + π − π + π − events are observed at the ρ meson energy. Under the assumption that all these events come from the ρ meson decay, the value of the cross section at the ρ meson peak corresponds to the following decay width: Γ(ρ 0 →π + π − π + π − )=(2.8±1.4±0.5) keV or to the branching ratio B(ρ 0 →π + π − π + π − )=(1.8±0.9±0.3)·10 −5 .

Note:

15 pages, 5 figures

electron positron: colliding beams
electron positron: annihilation
pi: multiple production
intermediate state: (a1(1260) pi)
rho(770)0: hadronic decay
rho(770)0: branching ratio
rho(770)0: width
channel cross section: energy dependence
magnetic detector: experimental results
Novosibirsk Stor2

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