F. Mane

Study of the reaction e+e−→pp in the total energy range 1925–2180 MeV

The e+e− → pp cross section has been measured between 1925 and 2180 MeV. About 50 pp events were detected. The total cross section decreases from 1.31 ± 0.4 nb near 1937 MeV to 0.55 ± 0.2 nb near 2135 MeV. The proton form factors |GE|2 and |GM|2, assumed identical, decrease from 0.15 ± 0.05 to 0.043 ± 0.015. They are an order of magnitude higher than predicted by the well-known dipole fit. The energy range has been scanned in steps of about 2 MeV. No significant structure was found in this pp sample.

Study of the J/ψ decay into five pions

Abstract A high statistics study of the J/ψ → π+π−π+π−π0 decay is performed from the 8.6 million J/ψs produced by the DM2 experiment at DCI. ϱ- and ω-associated production is evidenced and branching ratios for ϱa2(1320), inclusive ωπ+π−, ωf2(1270) and b1±(1235)π∓ dynamics are given. In the ωπ+π− final state a bump is observed at a low (π+π−) mass and a possible ωf0(975) contribution is discussed. Moreover first measurement of J/ψ → ωπ0π0 is reported and branching ratios for this decay and for ωf2(1270) and b1(1235)π0 dynamics are given. Evidence is found of the low (ππ) mass bump observed in the charged mode.

The pion electromagnetic form factor in the time-like energy range 1.35 ⩽ s ⩽ 2.4 GeV

Abstract The e+e− → π+π− cross section has been measured from about 280 events (an order of magnitude more than the previous world statistics) in the energy interval 1.35 ⩽ s ⩽ 2.4 GeV with the DM2 detector at DCI. The pion squared form factor |Fπ|2 shows a deep minimum around 1.6 GeV/c2 and is better fit under the hypothesis of two ϱ-like resonance ⋍0.25 GeV/c2 wide with 1.42 and 1.77 GeV/c2 masses.

Measurement of the reaction e+e−→ηπ+π− in the center of mass energy interval 1350–2400 MeV

Abstract The e+e−→ηπ+π− reaction has been measured in the center of mass energy interval 1350–2400 MeV by the magnetic detector DM2 at the Orsay storage ring DCI. Under the hypothesis of only one large resonance the cross section is not fit in a satisfactory way. The branching ratio τ−→η−π0ντ=(0.13 ± 0.02)% is deduced via CVC from the above measurement.

Study of the reaction e+e− → 3π+3π− in the total energy range 1400–2180 MeV

Abstract The e + e − → K + K − cross section has been measured between 1400 and 2060 MeV. About 500 K + K − events were detected in the magnetic detector DM1 at the Orsay storage rings DCI. The charged kaon form factor is appreciably higher than predicted by only the ϱ, ω, o tails, suggesting contributions from higher vector mesons.

The Pion Electromagnetic Form-factor in the Timelike Energy Range 1.35-{GeV}

Abstract The e+e− → π+π− cross section has been measured from about 280 events (an order of magnitude more than the previous world statistics) in the energy interval 1.35 ⩽ s ⩽ 2.4 GeV with the DM2 detector at DCI. The pion squared form factor |Fπ|2 shows a deep minimum around 1.6 GeV/c2 and is better fit under the hypothesis of two ϱ-like resonance ⋍0.25 GeV/c2 wide with 1.42 and 1.77 GeV/c2 masses.

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Abstract The reactions e + e − → ρη , ρπ , φπ and φη have been studied with the magnetic detector DM1 at DCI in the total energy ranges between 1.4 and 2.18 GeV. The ρη signal is clearly seen. Upper limits for ρπ and φη channels as well as for the OZI forbidden φπ channel.

2.4-{GeV}

Abstract New measurements of thee + e − → π + π − π + π − cross section have been performed by the magnetic detector DM1 at DCI (ORSAY) in the 1.4−2.18 GeV total energy range with statistics of 11000 events. Assuming the4 π ± production is dominated by the ϱ′(1.6) we determine its parameters: M = 1.57 ± 0.02 (stat.) −0.00 +0.06 (syst.) GeV,Γ = 0.51 ± 0.04 (stat.) −0.01 +0.04 (syst.)GeV,Γ ρ ′ee B ϱ′→ ρ 0 π + π − = 2.67 ± 0.19 (stat.) −0.36 +0.27 (syst.)keV.

Study of the reactions e+e− → ρη, ρπ, φπ and φη for total energy ranges between 1.4 and 2.18 GeV

Abstract First measurements of the e+e− → KS0K±π∓ reaction in the 1.4–2.18 GeV energy range have been performed with the magnetic detector DM1 at the Orsay storage rings DCI. The cross section is rather large. The production is mainly K∗0K0 which reveals an interference between isovector and isoscalar amplitudes. These results show again the existence of an isoscalar vector at 1.65 GeV shown to be a φ′ meson.

Study of thee+e− →π+π−π+π− reaction in the 1.4–2.18 GeV energy range

Abstract The reactions e + e − → ρη , ρπ , φπ and φη have been studied with the magnetic detector DM1 at DCI in the total energy ranges between 1.4 and 2.18 GeV. The ρη signal is clearly seen. Upper limits for ρπ and φη channels as well as for the OZI forbidden φπ channel.