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ASSUMING ABS(GE)=ABS(GM).
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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.
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The cross section for the reaction e + e - →π + π - π + π - has been measured at the e + e - storage ring Adone, in the to tal c.m. energy range 1.42–2.20 GeV. The peak and the following descent of the ϱ′(1600) resonance is observed. Using also lower energy data, and assuming that only one resonant amplitude contributes to the observed cross section, the parameters of the ϱ′(1600) are deduced.
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POSSIBLE EVIDENCE FOR OMEGA(1670) RESONANCE.
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SINGLE CHARGED PARTICLE MOMENTUM DISTRIBUTION.
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The possible existence of new vector mesons above the ρ is investigated. The conclusion is that our data are compatible with the existence of the ρ′-meson only if we assume as a firm theoretical prediction the Gounaris-Sakurai tail of the standard ρ-meson. Furthermore our data are compatible with the existence of the ρ″-meson if we assume the validity of the\(\bar p\)p model for the calculation of the multihadron cross-section.
THESE MEASUREMENTS OF THE PION FORM FACTOR ARE GIVEN IN D. BOLLINI ET AL., NCL 14, 418 (1975).
THESE MEASUREMENTS OF THE FOUR CHARGED PION CROSS SECTION ARE GIVEN IN M. BERNARDINI ET AL., PL 53B, 384 (1974).
THESE MEASUREMENTS OF THE TOTAL HADRONIC CROSS SECTION ARE GIVEN IN M. BERNARDINI ET AL., PL 51B, 200 (1974).
We have measured the crosss section for the reaction e + e − → 4 π ± in the energy range 1 2–3.0 GeV.No statistically significant evidence for a new vector meson in the ϱ″ region is found.
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Multihadron production by electron-positron colliding beams has been investigated for total centre-of-mass energies ranging from 1.2 to 2.4 GeV. The total cross-section, σtot ≡ σ(e+e−→π+π−+ + anything), is of the order of σμμ ≡ σ(e+e−→μ+μ−), with a threshold near 1 GeV. Partial cross-sections for the various channels are also derived. The cross-section of the specific channel e+e−→π+π−π+π− exhibits an energy dependence which is suggestive of a heavier vector meson, ρ' (mρ,≈ 1.6 GeV,Гρ, ≈ 350 Mev), having the same quantum numbers as the ρ-meson. An upper limit is given for the coupling constantfρ′ (fρ′/4π<18, wherefρ′=mρ′2e/gγρ′). Final states withG+ parity are found to be much more abundant than those withG− parity. The average multiplicity (charged plus neutral final-state pions) is found to be betweet 4 and 5 over all the energy range explored.
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VALUES OF R CALCULATED FROM TOTAL CROSS SECTION.
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STATISTICAL ERRORS ONLY.