G. V. Borisov

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.

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.

Observation of the decaya 2 − (1320)→π−η′

The reactionπ−C→π−η′C has been studied at 36 GeV/c. A clear signal for the decaya2−(1320)→π−·′ is observed in theπ−η′ mass spectrum. The measured ratio of branchings is BR (a2−→π−η′)/BR(a2−→π−η);(3.4±0.8±0.5)·10−2.

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|

Study of the reaction π−p→η′η′n

The reaction π−p→η′η′n has been studied atpπ=37 GeV/c. Total of 14 events of this reaction have been selected. It has been shown that in the effective mass spectrum of the η′η′ system the events are concentrated mainly near the reaction threshold, which might be caused by the decayX(1910)→η′η′. The reaction cross-section has been evaluated: σ(π−p→η′η′n)=110±40 nb.

Latest results from the VES experiment

SummaryWe present here the results of the VES experiment obtained in 1992–1993: 1) The partial-wave analysis (PWA) has been performed for the reactionsnn