Yu.A. Khokhlov

Study of π−N→ηπ−N and π−N→η′π−N reactions at 37 GeV/c

Abstract A partial-wave analysis of the ηπ− and η′π− systems produced in the reactions π−N→η(η′)π−N on a berylium target at a beam momentum of pπ− = 37 GeV/c is performed. It is shown that (1) all the waves with negative exchange naturality are negligibly small for both systems; (2) the matrix element squared of the P+ wave with JPC = 1−+ for the η′π− system significantly exceeds that for the ηπ− system, which could testify to the dominance of systems with a valence gluon (q q g) in the JPC = 1−+ wave formation; (3) the ratio R = Br(a2−→η′π−)/BR(a−2→ηπ−) = (4.7±1.0(stat.) ±0.4(syst.)) × 10−2 has been obtained.

Observation of a resonance with mass M=1814 MeV, decaying into π−ηη

Abstract The reaction π−N→π−ηηN off a carbon nucleus at Pπ=36 GeV/c has been studied with the help of the wide aperture magnetic spectrometer VES. In the π−ηη system a resonance with M=1814±10 (stat.)±23 (syst.) MeV, Γ=205±18 (stat.)±32 (syst.) MeV has been observed. Its most probable quantum numbers are IG=1+ or 2−.

Study of resonance production in diffractive reaction π−A → π+π−π−A

Abstract The results of the partial wave analysis of the diffractive reaction π − A → π + π − π − A at the momentum 36 GeV/ c on the scintillator target are presented. A resonance at m = 1.8 GeV with J PC = 0 − + (π(1800)) is clearly seen in this reaction. The characteristics of π(1800) point to the possible exotic nature of this object.

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.

Study of the reaction π− A → K+K−π−A at 37 GeV/c

Abstract The reaction π − A → K + K − π − A was studied at the momentum of 37 GeV/c on the beryllium target at the wide aperture VES spectrometer. The partial-wave analysis of the K + K − π − system produced at low | t ′| 2 was performed. It is shown that in the wave with J P = 0 − there exists an object withmass 1.79±0.014 GeV/c 2 and width 0.21±0.07 GeV/c 2 decaying into κK − and | 0 (975) π − .

Study of the wave with JPC=1−+ in the partial‐wave analysis of ήπ−, ηπ−, f1π−, and ρ0π− systems produced in π−N interactions at pπ−=37 GeV/c.

The wave with exotic quantum numbers JPC=1−+ is studied in η’π−, ηπ−, f1π−, and ρ0π− systems produced in π−N interactions at pπ−=37 GeV/c in the high‐statistics experiment at IHEP VES setup. The magnitude of JPC=1−+ wave in η’π− system significantly exceeds that in ηπ− system. Resonance‐like structure with mass M=1.62±0.02 GeV and with Γ=0.24±0.05 GeV is observed in ρ0π− system.

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.