A. Berdoz

Measurement of the decay distribution of η′ → π+π−γ and evidence for the box anomaly

Abstract The distribution of m ( π + π − ) in the decay η ′ → π + π − γ has been measured with the Crystal Barrel detector. The results are based on a total of 7392 observed η′ decays. The box anomaly constant is extracted from this and its value is found to agree well with theoretical expectations. The pseudoscalar nonet parameters ( f 1 , f 8 and θ PS ) are determined. Finally, we find that there is a problem of consistency between QCD and the standard VDM assumption.

Observation of f0(1500) decay into KLKL

Abstract The f 0 (1500) is observed in its K K decay mode in an amplitude analysis of high statistics data in p p annihilation at rest into π 0 K L K L . The mass and width is found to be ( m , Γ ) = (1515 ± 20, 105 ± 15) MeV. A comparison of the decay rate into 2 π 0 shows that this state cannot be dominantly s s . The f ′ 2 (1525) has been observed for the first time in p p annihilation and its production rate is consistent with the expectation from the OZI rule.

A study of f0(1500) decays into 4π0 in pp → 5π0 at rest

Abstract Crystal Barrel data on p p → 5π 0 at rest are presented. Mass spectra for 2 π 0 combinations, 3 π 0 and 4 π 0 and decay angular distributions all differ significantly from phase space. We present several ways of fitting the data. All agree on the definite presence of the f 0 (1500), observed in its 4 π 0 decay mode. It can decay into ππ(1300) and into σσ where σ stands for the full ππ S-wave amplitude.

Further analysis of , ηηπ0 and ηπ0π0 at rest

Abstract A fresh analysis is reported of high statistics Crystal Barrel data on p p → 3π 0 , ηηπ 0 , ηπ 0 π 0 and ηη ′ π 0 at rest. This analysis is made fully consistent with CERN-Munich data on π + π − → π + π − up to a mass of 1900 MeV, with GAMS data on π + π − → π 0 π 0 , and with BNL and ANL data on π + π − → K K , which are fitted simultaneously. There is evidence for an I = 0, J PC = 2 ++ resonance with weak (≤ 7%) coupling to ππ, strong coupling to both ϱϱ and ωω and pole position 1534 - i90 MeV. This resonance agrees qualitatively with GAMS and VES data on ππ → ωω, previously interpreted in terms of a resonance at 1590–1640 MeV. New masses and widths for (A) ƒ 0 (1370) and (B) ƒ 0 (1500) , fitted to all eight data sets, are M A = 1300 ± 15 Mev, Γ A = 230 ± 15 MeV, M B = 1500 ± 8 MeV, Γ B = 132 ± 15 MeV. Branching ratios to ππ and ηη are given, and differ significantly from earlier determinations because of a new procedure.

Decay dynamics of the process η→3π0

Abstract The parameter α =−0.052±0.020 describing the shape of the η →3 π 0 Dalitz plot has been determined using the data from the Crystal Barrel detector at LEAR. The value is compared to predictions of chiral perturbation theory.

Momentum dependence of the decay η→π+π−π0

Abstract The π 0 momentum dependence of the decay η → π + π − π 0 has been measured with the Crystal Barrel detector. The analysis is based on 3230 events. The results of this independent measurement are compared to new chiral perturbation theory calculations and previous measurements.

High-mass ϱ-meson states from p̄d-annihilation at rest into π−π0π0pspectator

Abstract A study of p -annihilation in liquid deuterium into π − π 0 π 0 and a spectator-proton is presented. A cut on the proton-momentum of ≤ 100 MeV/ c ensures that annihilation takes place on a quasi-free neutron. A partial wave analysis shows contributions from three vector mesons, with masses and widths of (763.7 ± 3.2; 152.8 ± 4.3), (1411 ± 14; 343 ± 20); (1780 −29 +37 ; 275 ± 45) MeV/ c 2 , respectively.

Search for double-Λ hypernuclei and the H-dibaryon in the (K−,K+) reaction on 12C

Abstract A search for double- Λ hypernuclei ( 12 ΛΛ Be) and H -dibaryons using the 12 C( K − , K + ) reaction was performed at the BNL-AGS using a high-intensity 1.8 GeV/ c K − beam. A missing-mass analysis below the end point of the quasi-free Ξ − production was used to investigate these S =−2 systems. The upper limit obtained for the forward-angle cross section of 12 ΛΛ Be production is 6 to 10 nb/sr. This is the first search for the direct production of double- Λ hypernuclei to reach the sensitivity required to observe the signal predicted by theoretical calculations. For the H -production cross section, we have obtained an upper limit in the range of a few nb/sr to 10 nb/sr for the H mass below 2100 MeV/ c 2 . This upper limit is the most sensitive H search result to date for a tightly bound H .

Antiproton-proton annihilation at rest into KLKSπ0π0

Abstract The annihilation channel p p →K + K − π 0 in liquid hydrogen at rest has been studied with the Crystal Barrel detector at LEAR. The measured branching ratio is: BR ( p p → K + K − π 0 )=(2.37±0.15)×10 −3 . A partial wave analysis shows that this reaction is dominated by the π (K K ) S , K K ∗ (892) and π φ (1020) intermediate states. Weak signals are observed for π a 2 (1320), π f 2 (1270), π f 2 ′(1525) and K(Kπ) S . A satisfactory description of the Dalitz plot requires the introduction of π (K K ) P intermediate states with at least one pole.

ϱ-ω interference in pp-annihilation at rest into π+π−η

Abstract The π + π − invariant mass distribution produced in p p annihilation at rest and recoiling against η mesons exhibits large interference between the amplitudes for ϱη and ωη production. The interference can be quantitatively described within the framework of ϱ-ω interference. We find full coherence between the ϱω-ωη production amplitudes and a vanishing relative production phase. The implications of this result for p p annihilation dynamics are discussed.