L. Montanet

The Crystal Barrel spectrometer at LEAR

The crystal Barrel spectrometer used at LEAR, CERN to study the products of pd annihilations is described. A 1380 element array of Csl crystals measures photons from the decay of π0, η, η′ and ω mesons. A segmented drift chamber in a 1.5T magnetic field is used to identify and measure charged particles. A fast on-line trigger on charged and neutral multiplicities and on the invariant mass of secondary particles is available. The performance of the detector is discussed.

Observation of two JPC=0++ isoscalar resonances at 1365 and 1520 MeV

From a simultaneous analysis of data on pp → π0π0π0 and pp → ηηπ0 at rest, two I = 0, JPC = 0++ resonances are identified above 1 GeV. The first has mass M = 1365−55+20 MeV and width г = 268 ± 70 MeV, close to the ƒ0(1400) of the Particle Data Group. The second has M = 1520 ± 25 MeV, г = 148−25+20 MeV.

Inclusive particle production in 400 GeV/c pp-interactions

AbstractWe report on a study of inclusive particle production in pp-interactions at 400 GeV/c. The data are based on 472 K reconstructed events recorded in the NA 27 experiment using the LEBC-EHS facility at CERN. The production cross sections are determined of pseudo scalar (π±,0, η andK±), scalar (f0(975)), vector (ρ±,0(770), ω(783), ϕ(1020),K*0(892), and

Coupled channel analysis of pp annihilation into π0π0π0, π0ηη and π0π0η

\bar K^{ * 0}

Production of three pions in pp annihilations at rest

(892)), and tensorf0 mesons, of protons and antiprotons, and theΔ++,+,0(1232), and Λ(1520) baryon resonances in the forward hemisphere of the center of mass system, as well as longitudinal and transverse momentum distributions. The results are compared with predictions of the FRITIOF model and with other experimental data.

Observation of a new IG(JPC)=1−(0++) resonance at 1450 MeV

Abstract A partial-wave analysis of the reaction p p →π 0 π 0 π 0 has been performed using a high-quality high-statistics data set of 712 000 events. In addition to the f0(975) and f0(1300), the scalar resonance with mass m = (1500 ± 15) MeV and width Γ = (120 ± 25) MeV is necessary to describe the data.

First measurement of the π+π- atom lifetime

We confirm the existence of the two IG(JPC) = 0+(0++) resonances f0(1370) and f0(1500) reported by us in earlier analyses. The analysis presented here couples the final states π0π0π0, π0π0η and π0ηη of pp annihilation at rest. It is based on a 3 × 3 K-matrix. We find masses and widths of M = (1390±30) MeV, Γ = (380±80) MeV; and M = (1500±10) MeV, Γ = (154 ± 30) MeV, respectively. The product branching ratios for the production and decay into π0π0 and ηη of the f0(1500) are (1.27 ± 0.33) · 10−3 and (0.60 ± 0.17) · 10−3, respectively.

Observation of a 2+ + resonance at 1515 MeV in proton-antiproton annihilations into 3π0

Abstract The presence of a structure in the pp total cross section at 1930–1940 MeV, with a narrow width of 9 MeV is confirmed. The interpretation of the effect as a single, non interfering, resonance is made difficult by the comparison of the elastic scattering with the charge exchange cross sections.