S. Jullian

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.

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.

Dm2: A Magnetic Detector for the Orsay Storage Ring DCI

DM2 is the magnetic detector built to study e+e- interactions in the c.m. energy range 1.2-3.7 GeV with the Orsay Storage Ring DCI. The magnet is a solenoid of 2 m diameter and 3 m length with a conventional aluminium coil producing a 0.5 T field. Inside the coil, the charged particles detector is made of two proportional chambers with anode and cathode read-outs, 13 layers of drift chambers, one layer of water Cerenkov counters and one layer of scintillation counters. Photon detection is provided outside the 1 rad length coil by stacks of 14 planes of wire tubes with longitudinal read-outs, separated by lead sheets, and by five layers of scintillation counters. Inside the coil, the end caps are covered by shower detectors made of lead sheets and MWPC planes. Muon separation uses the flux return iron or concrete absorbers, and planes of wire tubes with longitudinal read-out. The charged particle detector covers 87% or 4π and the photon detector 82% of 4π. Charged particle identification by time of flight and Cerenkov radiation can discriminate pions from kaons up to 600 MeV/c and kaons from protons up to 1100 MeV/c. The photon detection efficiency is 50% at 50 MeV and near 100% at 100 MeV. It allows a neutral trigger to be operated. The detector is starting operation on the storage ring DCI at Orsay.

>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

In a study of the radiative decay Jψ→γφφ→γK+K−K+K−, from the 8.6 million Jψ produced in the DM2 experiment at DCI, we found a large production of events with φφ mass below the ηc. The branching ratio, for mφφ < 2.9 GeV/c2, is BR(Jψ→γφφ) = (3.1 ± 0.3 ± 0.6) × 10−4. The angular analysis of the events with φφ mass below 2.5 GeV/c2 is consistent with a 2++ assignment. An enhancement near 2.2 GeV/c2 shows a preferred spin-parity JP = 0−.

for 1975-{MeV}

Abstract The 8.6 million J/ψ collected by the DM2 detector at DCI have been analysed looking for the J/ψ→γωω decay, both ωs decaying into π+π−π0. A clean signal of γωω events is observed with BR(J/ψ→γωω)=(1.41±0.20±0.42)×10 −3. The ωω invariant mass distribution shows a large bump peaked at 1.77 GeV/c2, associated with a pseudoscalar production, as first observed by a previous experiment. No evidence of further structures is found.

\le \sqrt{s} \le

AbstractThee+e−→K+K− cross section has been measured from about 750 events in the energy intervaln

Search of glueballs in the Jψ→γφφ decay

1350 leqq sqrt s leqq 2400 MeV