By combining new results obtained at C.M. energies of 1.2 and 1.3 GeV with previous data obtained at lower energies from the e + e − annihilation process e + e − → π + π − π o π o , we get an indication in favour of the existence of a new vector meson of the ϱ type, ϱ' (1250), the first daughter of the ϱ in the predictions of the Veneziano model. Further results on the annihilation process e + e − → π (1600) → π + π − π + π − are also presented.
NOTE THAT ABOVE 1.3 GEV, THE CROSS SECTION VALUES ARE CRITICALLY DEPENDENT ON THE ASSUMPTION OF A PHASE SPACE DISTRIBUTION FOR THE FINAL STATE. NOTE ALSO THAT THE RHOPRIME(1600)0 --> RHO EPSILON(700) --> PI+ PI- PI0 PI0 RESONANT CONTRIBUTION HAS BEEN SUBTRACTED OUT. THIS CORRECTION IS GREATEST (25 PCT) AT 1.5 GEV.
The average multiplicities 〈 n c 〉 and 〈n〉, of charged-plus-neutral pions produced in e + e − collisions, have been determined for total center-of-mass energies ranging from 1.2 to 2.4 GeV. No appreciable multiplicity variation is observed over this energy range, where the mean values 〈; n c 〉 = 3.3 +0.3 −0.2 and 〈 n 〉 = 4.4 +0.4 −0.2 are found.
No description provided.
VALUES OF R CALCULATED FROM TOTAL CROSS SECTION.
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.
No description provided.
VALUES OF R CALCULATED FROM TOTAL CROSS SECTION.
No description provided.
None
THIS HADRON PAIR CROSS SECTION PROVIDES ONLY AN UPPER LIMIT TO THE PION FORM FACTOR ABOVE 1.5 GEV SINCE KAON PRODUCTION IS NOT DISTINGUISHED.
None
STATISTICAL ERRORS ONLY.
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 | F π | 2 shows a deep minimum around 1.6 GeV/ c 2 and is better fit under the hypothesis of two ϱ-like resonance ⋍0.25 GeV/ c 2 wide with 1.42 and 1.77 GeV/ c 2 masses.
Statistical errors only.
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 − π 0 ν τ =(0.13 ± 0.02)% is deduced via CVC from the above measurement.
No description provided.
We present new high statistics data on hadron production in photon-photon reactions. The data are analyzed in terms of an electron-photon scattering formalism. The dependence of the total cross section of Q 2 , the four-momentum transfer squared of the scattered electron, and on the mass W of the hadronic system is investigated. The data are compared to predictions from Vector-Meson Dominance and the quark model.
DEPENDENCE ON VISIBLE HADRONIC INVARIANT MASS.
None
No description provided.
We have measured the production cross section for K s 0 in e + e − annihilation from 3.6 to 5.0 GeV center of mass energy. A substantial increase of the K s 0 yield is observed around 4 GeV in qualitative agreement with the charm hypothesis.
No description provided.