B. Polyakov

Measurement of form factors for the decay η′ å ηπ−π+

Form factors measured for the decay η′ å ηπ−π+ in π−A å η′π−A* reactions at a beam momentum of pπ = 28 GeV are presented. The distribution in Dalitz variables for 7000 decay events is described well within a linear and a nonlinear parametrization of the relavant matrix element. The slope parameter in the variable y differs from zero significantly. It is Reα = −0.072±0.012 (stat.)±0.006 (syst.) in the linear and a = −0.120±0.027 (stat.)±0.015 (syst.) in the nonlinear parametrization. In this decay, the C-violation parameter is compatible with zero, c = 0.021±0.024.

Search for the f1(1285) → π+π-π0 decay with the VES detector

The isospin violating decay f1(1285) → π ππ has been studied at VES facility. This study is based at the statistics acquired in πBe interactions at 27, 36.6 and 41 GeV/c in diffractive reaction πN → (f1π )N . The f1(1285) → πππ decay is observed. The ratio of decay probabilities BR(f1(1285) → πππ) to BR(f1(1285) → ηπ π) ·BR(η → γγ) is ∼ 1.4%.

Study of η′ Decays in the VES Experiment

Measurements of Dalitz plot parameters for η′ → ηπ+π− decay are presented. The data sample of ∼15000 events originates from charge‐exchange reaction π−p → η′N* at beam momentum of 28 GeV/c. Comparison with results from diffractive‐like reaction, π−A → η′π−A* and with theoretical expectations is given. Also a limit of Br(η′ → (π+π−π0)) is estimated.

Resonances in the ωω system

Results of a partial-wave analysis for the reaction π− → ωωn studied at the VES spectrometer (Institute for High Emergy Physics, Protvino) are presented. The behavior of the JPC = 2++ amplitudes in the ωω system is described by the f2(1565) and f2(1910) resonances, whose parameters were fixed at M = 1.590 ± 0.010 GeV and Γ = 0.140 ± 0.011 GeV for the former and at M = 1.890 ± 0.010 GeV and Γ = 0.165 ± 0.019 GeV for the latter. The decay f4(2050) → ωω was observed at parameters values of M = 1.960 ± 0.015 GeV, Γ = 0.290 ± 0.020 GeV.

Investigation of the reaction π−p → η′π0n at the VES spectrometer

Results obtained by investigating the reaction π−p → η′π0n at the VES spectrometer (Institute for High Energy Physics, Protvino) are presented. The effective-mass spectrum and angular distributions of η′π0 events are compared with their counterparts for ηπ0 and η′π− events selected from the same data sample. The ratio R of the branching fractions for the decays of a20(1320) mesons into η′π and ηπ is measured. The result is R=0.047±0.018, which agrees with the value measured previously for a2−. An investigation of P-wave production in the η′π0 and ηπ0 systems over the effective-mass interval 1.45–1.9 GeV/c2 leads to the conclusion that the coupling of the exotic object π1 (1600) to the ρπ channel is suppressed in relation to its coupling to the η′π or the b1(1235)π channel.

Natural parity resonances in ηπ+π−

Abstract Results of a partial wave analysis of the ηπ+π− final state are presented using 4.2×104 events with |t|

Dynamical selection rule in the decays of π(1800)

Combined analysis of π(1800) decays is performed using results of the VES experiment on its decays into f0(980)π, f0(1500)π, f0(600 ÷ 1300)π, κK, a0(ηπ)π, ηη′π, ρπ and K*K channels. Relative branching ratios of those decay modes are measured. It is shown that the OZI selection rule is strongly violated in π(1800) decays. Observed pattern of π(1800) decays can be explained in terms of assumption, that π(1800) decay proceeds via SU(3)‐singlet and SU(3)‐octet states.

Evidence for a scalar meson resonance in the {pi}{sup -}p{yields}n{omega}{phi} reaction

The charge‐exchange reaction π−p→nω(780)φ(1020) is studied with the VES setup. The (ωφ) system is observed at relatively low background. Its invariant mass distribution peaks near threshold. The two‐particles partial wave analyses shows that the Jpc = 0++ state dominates. This wave is compared with 0++ component in the (ωω) system at the comparable mass, which was measured earlier.

RECENT RESULTS FROM VES EXPERIMENT

The charge-exchange reaction π-p → ω(780)ɸ(1020)n is studied with the VES setup. The (ωΦ) system is observed at relatively low background. Its invariant mass distribution peaks near threshold. The two-particles partial wave analyses shows that the JPC = 0++ state dominates. Comparison with scalar wave in ωω system at the comparable mass gives evidence for violation of the OZI rule. Another subject is a search for possible transition f0(980) → a0(980), which violates the isospin symmetry.

Analysis of the reaction π−Be → π−π0π0Be at VES

We present the results of the analysis of diffractive reaction π−Be → π−π0π0Be measured with upgraded VES detector with the statistics of about 16 · 106 events. The mass-independent partial-wave analysis is performed using set of 70 partial waves corresponding to natural-parity exchange mechanism and restricting the rank of spin-density matrix Nr = 1. The data is divided into 40 MeV m(3π) bins and in 10 intervals of momentum transfer squared t′. The sub-density-matrix of mass independent PWA is subject to further mass dependent fits using Breit-Wigner resonant terms and coherent non-resonant backgrounds.