J. Bistirlich

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

Abstract Antiproton-proton annihilations at rest into 3 π 0 are analyzed in terms of π 0 π 0 final state interactions. A J PC = 2 + + resonance at a mass of 1515 ± 10 MeV with a width of 120 ± 10 MeV is required to explain the data. This result is supported by previous observations made on the ππ system in p p and p n annihilations which show that the resonance has I = 0. This resonance is practically degenerate in mass with the f′ 2 (1525) but the two resonances have very different production and decay characteristics.

The pseudoscalar mixing angle ΘPS from ν and ν′ production in p annihiltion at rest

Abstract We have determined ratios of branching ratios for p p annihilations at rest into π 0 η and π 0 η ′, into ηη and ηη ′, and into ωη and ωη ′. All reactins are observed in two different all-neutral final states. The ratios permit a determination of the pseudoscalar mixing angle. We find Θ PS = −(17.3±1.8)°.

Proton-antiproton annihilation into ηηπ-observation of a scalar resonance decaying into ηη

Abstract The results of a measurement of pp annihilation at rest into ηηπ 0 are presented. Assuming a resonance dominated model for the annihilation process an isoscalar J PC =0 ++ resonance decaying into ηη is observed with a mass of 1560±25 MeV/ c 2 and a width of 245±50 MeV/ c 2 .

Antiproton-proton annihilation at rest into ωπ0π0

The annihilation channel pp → ωπ0π0, where ω decays to π0γ, was studied with antiprotons stopped in liquid hydrogen. This reaction is dominated by the production of b10(1235) with contributions from f2(1270) and the ππ S-wave. The branching ratio for pp → ωπ0π0 is (2.00±0.21)% of all annihilations. The branching ratios for b10(1235)π0 (b1 → ωπ0) and f2(1270)ω (f2 → π0π0) are (0.92 ± 0.11)% and (0.57 ± 0.07)% of all annihilations, respectively. Upper limits for the production of vector mesons decaying to ωπ are given and the ππ mass distribution around 1 GeV is discussed.

Radiative protonium annihilation into γγ, γπ0, γη, γω and γη′

Abstract Radiative p p annihilation at rest into γγ , γπ 0 , γη , γω and γη′ has been measured with the Crystal Barrel detector at LEAR for antiprotons stopped in liquid hydrogen. The branching ratios are B γπ 0 =(44±4)×10 −6 , B γη =(9.3±1.4)×10 −6 and B γω =(68±18)×10 −6 , respectively. For B γγ and B γη ′ we find new upper limits of 0.63×10 −6 and 12×10 −6 (95% CL), respectively.

Upper limits for bound states and resonance behavior in the trineutron system

Abstract The trineutron mass spectrum was observed in the stopped pion radiative capture reaction 3H( π − , γ )3n by measuring the photon energy with a high-resolution spectrometer. The present experiment improves upon an earlier experiment by a factor of 27 in statistics and 2.2 in resolution. An improved upper limit (95 % confidence level) on the branching ratio (bound state)/(total radiative capture rate) is found to be 4 × 10 −3 . No resonant structure is observed beyond that predicted by the pairwise interaction of the outgoing nucleons. The upper limit on the branching ratio to resonances with Γ ≲ 5 MeV is 2 × 10 −2 .

The LEAR Crystal Barrel Detector

The features of the Crystal Barrel Detector which is in preparation for LEAR at CERN, are discussed. The physics aims include qq‐ and exotics‐spectroscopy and a detailed investigation of yet unknown pp‐anihilation channels. An eventual later use on the PSI‐B‐Meson‐Factory is discussed. The paper finishes with a description of the present status of the project.

PIONS PRODUCED NEAR THE CENTER-OF-MASS VELOCITY IN HEAVY-ION COLLISIONS

LBL-12585 Preprint i Submitted to Physical Review Letters i_.i PIONS PRODUCED NEAR THE CENTER-OF-MASS VELOCITY IN HEAVY-!ON COLLISIONS K.A. Frankel, J.A. Bistirlich, R. Bossingham, H.R. Bowman, K.M. Crowe, C.J .. Martoff, D. Murphy, J.O. Rasmussen, J.P. Sullivan, W.A. Zajc, J.P. Miller, 0. Hashimoto, M. Koike, J. P~ter, W. Benenson, G.M. Crawley, E. Kashy, J.A. Nolen, Jr., and J. Quebert August 1981 TWO-WEEK LOAN COPY This is a library Circulating Copy which may be borrowed for two weeks.· For a personal retention copy, call Tech. Info. Diu is ion, Ext. 6782 Prepared for the U.S. Department of Energy under Contract W-7405-ENG-48

Antiproton annihilation at rest in liquid deuterium into π−π0π0pS

SummaryWith the Crystal Barrel detector, the final state π−π0π0pS at rest in liquid deuterium was measured for the first time. A preliminary partial-wave analysis was performed, which required two interesting features: besides the ρ(770), a second pole was needed in the ππP-wave and a narrow resonance in the ππS-wave, slightly above 1500 MeV/c2. With the same parametrization a high-statistics π+π−π0 data set could also be well described.