Search

The s dependence of the electromagnetic proton form factors in the time-like region has been determined from the threshold (s = 4Mp2) up to s = 4.2 GeV2. Data were collected in a dedicated experiment performed at the LEAR antiproton ring at CERN, increasing by one order of magnitude the available statistics. Total and differential cross section of the p p → e − e + reaction have been measured. The electric and magnetic form factors are found to have comparable value. The observed form factor shows a clear steep s dependence close to the threshold.

The decays of 8.6 million J ψ produced at DCI in the DM2 detector are analyzed to measure baryon pair production. Angular distributions for J ψ → p p , Λ Λ , Σ 0 Σ 0 are in good agreement with first order QCD predictions. New measurements are given for the branching ratios of these decays.

The cross section for the KL0p elastic scattering has been measured for the first time. The incident momentum and momentum transfer ranges are 3 ⩽p⩽ 13 GeV/c, 0.1 ⩽ |t| ⩽ 1.3 GeV2. The results are compared to those of other experiments related to ours by isotopic spin conservation, finding agreement with some and discrepancies with others. The differential cross sections have been parametrized in the form Aebt. The coefficients show little or no dependence on energy, with A ≅ 9.8 mb · GeV−2and b ≅ 4.7 GeV−2. The effective linear trajectory has been determined and gives α0 = 0.95 ± 0.15, α′ = −0.35 ± 0.48 GeV−2, in good agreement with dominance by pomeron exchange.

We present experimental data on the K L 0 p → K S 0 p reaction between 4 and 14 GeV/ c in the range 0.1 ≲ | t | ≲ 2 GeV 2 . This experiment has been performed at the CERN PS, using spark chambers and a large aperture magnet. The results show a break of slope at t = −0.3 GeV 2 . The ω trajectory deduced from the data has an intercept α (0) = 0.5 and a slope α ′ = 0.88. A comparison with various models shows that the non-flip amplitude is dominant.

The e+e− → pp cross section has been measured in the energy interval (1975 ⩽ 2E ⩽ 2250) MeV for |cosθ| < 0.7. The measurement is based on ∼ 100 events, thus improving by a factor 3 on the previous existing statistics in this energy interval. The form factor |G|2 is given as a function of energy under the assumption |GE| = |GM|. We also give the first measurement of the differential cross section, averaged over the energy interval, and estimate the ratio GM|/|GE| from it.

We present a systematic study of SU(3) symmetry breaking in J ψ baryonic decays; first measurements are given for the forbidden processes J ψ → Ξ − (1530) Ξ + + c.c. and Ξ 0 (1530) Ξ 0 + c.c. Branching ratios for J gy → Σ ± (1385) Σ ∓ + c.c. are also obtained; they are consistent with published values and are given with better accuracy. All these decays are only 3 times weaker than SU(3) allowed decay modes: J ψ → Ξ − Ξ + , Σ ± (1385) Σ ∓ (1385) . In addition, upper limits are determined on purely electromagnetic transitions J ψ → Σ(1385) Λ + c.c. and J ψ → Δ + p + c.c. , both involving SU(2) and SU(3) breaking. The first observation of the isospin forbidden decay J ψ → Λ Λ π 0 is also presented.