G. Cosme

A measurement of e+e− → pp for (1975 ⩽ s ⩽ 2250) MeV

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.

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.

Experimental study of the triple-gluon vertex

Abstract In four-jet events from e+e− →Z0 →multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle θ NR ∗ and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor Nc to the fermionic Casimir operator C F : N c C F = 2.55 ± 0.55 ( stat. ) ± 0.4 ( fragm. + models ) ± 0.2 ( error in bias ) in agreement with the value 2.25 expected in QCD from Nc=3 and C F = 4 3 .

>A Measurement of

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.

e^+ e^- \to \bar{p} p

AbstractSearch for baryon pairs production ine+e− annihilation at

\le \sqrt{s} \le

\sqrt s = 2386 MeV