F. Laplanche

Multipion production below 1.1 GeV by e+e− annihilation

Abstract The production of multipion events by e + e − annihilation has been measured at centre of mass energies 915,990 and 1076 MeV. Both channels e + e − → π + π − π o and e + e − → π + π − π + π − have been analysed. An energy threshold effect analysed. An energy threshold effect around 919 MeV ( m ω + m π o ) has been evidenced for the π + π − π o π o channel and the cross section is consistent with the quasi two-body process e + e − → ωπ o . The cross section for π + π − π + π − is lower by an order of magnitude and increases with the energy.

Measurement of the radiative decay modes of the ω and φ with the Orsay storage ring

Abstract With a large solid angle detector, optimized to detect γ rays, we observed the radiative decay modes of the ω and φ, produced by e + e − annihilation. Our results are: Γ(φ → ηγ) Γ(φ → all = 2.6 ± 0.7)% , Γ(φ → π°γ) Γ(φ → all = (0.25 ± 0.12)%, Γ(ω → π°γ) Γ(ω → π + π − π°) = (10.9 ± 2.5)%, Γ(ω → πγ) Γ(ω → π°γ) with 90% of CL , Γ(ω → π° π° γ) Γ(ω → π° γ) with 90% of CL , without ϱ° contribution for the ω decay modes.

Evidence for an interference effect between ω and φ resonances in π+π−πo production by e+e− annihilation

Abstract The cross section e + e − → π + π − π o has been measured in the φ energy region and at three other energies (915, 990, 1076 MeV) chosen outside the ω and φ resonances. In the same experiment the energy position and the width of the φ resonance have been determined from the φ →K S o K L o channel. It is found that the magnitude and energy dependence of the experimental cross section are well described by coherent production of ω and φ in the whole energy range 770 to 1076 MeV. Our data clearly show an interference effect which corresponds to an opposite sign between the two products g γω g ω →3 π and g γφ g φ →3 π of the coupling constants.

Evidence for resonant structure near 1780 MeV in e+ e− annihilations observed with the new colliding beam ring at Orsay

Abstract We present evidence for the existence of a new J PC = 1 −− resonance with a mass of 1778 ± 14 (±12) MeV and 150 ± 40 (±30) MeV wide. We tentatively conclude that it is an I = 0 state.

New measurements of the radiative decay modes of the φ-meson

Abstract The radiative decay models of the φ-meson have been studied: e + e − → φ → ηγ →3 γ ; e + e − → φ → π o γ →3 γ . Cross sections σ φ → ηγ →3 γ and σ φ → π o γ →3 γ have been measured at five energies in the φ-meson energy region and clearly show the φ-resonance in the ηγ → 3 γ mode as well as in the π o γ → 3 γ mode. From a Breit-Wigner fit to the experimental data the values of the branching ratios are deduced: B φ → ηγ = (1.5 ± 0.4) × 10 −2 ; B φ → π o γ = (1.4 ± 0.5) × 10 −3 .

Hadronic production by e+e− collisions at the energy 990 MeV with the Orsay storage ring

Abstract Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the ϱ , ω and φ production by e + e − annilations. Assuming a π + π − π 0 π 0 production by the quasi two-body process e + e − → ϱ → ωπ 0 we give the correspondi ng cross section σ (e + e − → π + π − π 0 π 0 ) = (1.1 ± 0.5) 10 −32 cm 2 . Since no events with 3 and 4 charged pions have been observed σ (e + e − → π + π − π 0 π − ) ⩽ 1.5 × 10 −33 cm 2 .

π+π−πo and ππγ production by e+e− annihilation in the φ energy range with the Orsay storage ring

Abstract A large solid angle detector has been used to observe π+π−πo events produced at the φ energy by electron-positron collisions in the Orsay storage ring. Fitting our data with a Breit and Wigner curve, with a fixed width Γ = (3.8±0.4) MeV coming from KOSKOL analysis, we deduce σe+e−→π+π−πO = (0.70±0.13) μbat 2E = Mφ. Using our measurements on the other φ decay modes we deduce (φ→π+π−πo)/(φ→KoSKoL) = 0.47±0.06 and (φ→ηoγ)/(φ→KoSKoL) = 0.077±0.022. Assuming (φ→K+K−)/(φ→KoSKoL) = 1.60, we derive σTOT = (4.7±0.4)μb, Γe+e−= (1.27±0.11 keV and g2o/4π = 14.3±1.3 (without finite width correction). Furthermore (from the observation of the ππγ coplanar events) we put an upper limit to the mode e+e− → φ π+π−γ, Γ(φ → π+π−γ) ⩽ 0.007 Γ(φ→Total) with 90% C.L.

π+π− production by e+e− annihilation in the ϱ energy range with the Orsay storage ring

Abstract A large solid angle detector has been used to observe two body events produced by electron-positron collisions in the Orsay storage ring. From the π + π − excitation curve in the ϱ region we have deduced the amplitude and the phase of the ω-ϱ interference, and the ϱ resonance paramaters: M ϱ = (775.4±7.3) MeV, Γ ϱ = (149.6 ± 23.2) MeV, √ B ( ω → π + π − ) = 0.19 ± 0.05, φ = (85.7 ± 15.3) 0 , σ ( e + e − → ϱ ) = (1.00 ± 0.13) μ b at S = M ϱ 2 , B ( ϱ → e + e − = (4.1 ± 0.5) × 10 −5 , Γ ( ϱ → e + e − ) = (6.1 ± 0.7) keV, ( g ϱ 2 /4 π ) = 2.26 ± 0.25, ( g ϱππ 2 /4 π ) = 2.84 ± 0.50.

Evidence for ϱπ dominance in φ → 3 η decay

Abstract About seven hundred π + π − π o events produced by e + e − annihilation at the φ meson energy are analysed by comparing the experimental Dalitz-plot to the distributions predicted by either a Lorentz invariant phase-space production of the three pions or by a dynamical φ → ϱπ → π + π − π o process as given by the Gellman-Sharp-Wagner model. The result gives clear evidence for ϱπ dominance.

Some experimental evidence of virtual compton scattering obtained at 990 MeV with the orsay storage ring

Evidence is obtained for e- gamma events coming from the e/sup +/e/sup - / yields e/sup +/e/sup -/ gamma reaction in a particular kinematics where the cross section is well explained by a Williams-Weizsacker-type calculation for a quasi-real photon Compton scattering. It is suggested that such a reaction can provide a good test of QED in the timelike region at higher energies. (LBS)