Yu Y.V. Rodnov

Evidence for a 1-+ exotic meson

Abstract A non q q ,J PC = 1 −+ , I G =1 − meson has been observed in the study of the exclusive reaction π − p→π 0 ηn at 100 GeV. Its mass is (1406±20) MeV. Its width is (180±30) MeV.

Production of G(1590) and other mesons decaying into η pairs by 100 GeV/c π− on protons

Abstract New data on the scalar G(1590) meson which decays into ηη have been obtained in an experiment at the CERN SPS. η pairs are detected with the electromagnetic calorimeter GAMS both through their decay into 4γ and into 8γ. ϵ(1300), f(1270), f′(1525) as well as the spin-4 h(2030) mesons have also been observed to decay in the same mode. Their branching ratios have been evaluated. The presence of high-mass spin-0 and spin-2 structures is discussed.

Hodoscope multiphoton spectrometer GAMS-2000

Abstract A hodoscope γ spectrometer comprising 1536 lead-glass cells is described. This detector allows the coordinates and the energies of a large number of gammas (up to ≈ 10) to be measured simultaneously and the masses (with an accuracy of 1%) and the momenta of particles decaying into photons to be determined. The use of fast processors allows selection of events by mass, energy and momentum transfer. The procedure for a fully automatic calibration of the spectrometer in an electron beam (with ∼ 1% accuracy) and for its control during long-term physical experiments is described.

Production of G(1590) in 300 GeV central

Abstract Significant production of G(1590), a scalar glueball candidate, is observed in a study of η pairs produced in π−N central collisions at 300 GeV/ c .

\pi^-

The partial widths of η-meson decays η→2γ, η→3π0 and η→π0γγ have been measured in a high accuracy experiment made at the IHEP accelerator with the hodoscope electromagnetic spectrometer GAMS-2000. An upper limit has been determined for the 3γ channel. The Dalitz plot of the η decay into 3π0 shows that the matrix element does not depend on the pion energy.

N collisions

Summaryη′η pair production in the charge exchange reaction π−p→η′ηn has been observed and studied in a search for glueballs with the 38 GeV/c pion beam of the 70 GeV IHEP accelerator. The γ-rays from the decay η′η→4γ were detected with the hodoscope spectrometer GAMS-2000. The η′η events in the mass range from threshold up to 1.8 GeV are decays of the scalar G(1590)-meson which has been already observed in its ηη decay mode. The measured ratio of the partial widths of the G→η′η and the G → ηη decay channels is 2.7±0.8 in agreement with the value expected for glueballs.RiassuntoÈ stata osservata e studiata la produzione di coppie η′η nella reazione di scambio di carica π−p→η′ηn nella ricerca di sfere di gluoni con il fascio di pioni a 38 GeV/c dell’acceleratore IHEP a 70 GeV. I raggi gamma derivanti dal decadimento η′η→4γ sono stati rivelati con lo spettrometro odoscopico GAMS-2000. Gli eventi η′η nell’intervallo di massa dalla soglia fino a 1.8 GeV sono decadimenti del mesone scalare G(1590) che è stato già osservato nel suo modo di decadimento ηη. Il rapporto misurato delle ampiezze parziali dei canadi di decadimento G→η′η e G→ηη è 2.7 ± 0.8 in accordo con il valore atteso per le sfere di gluoni.РезумеНаблюдается и исследуется рождение η′η пар в реакции перезарядки π−p→η′ηn с целью поиска «глюболов», используя пионный пучок с импульсом 38 ГэB/c ускорителя 70 ГэB IHEP. γ-лучи из распада η′η→→4γ детектируются с помощью спектрометра GAMS-2000. η′η события в области масс от порога вплоть до 1.8 ГэB представляют распады скалярного G(1590)-мезона, который уже наблюдался в моде распада ηη. Измеренное отношение парциальных ширин каналов распадов G→η′η и G → ηη, составляет 2.8±0.8, что согласуется с ожидаемой величиной для «глюбола».

Neutral decays of the η-meson

The decay η′ → ηπ0π0 → 6γ has been measured accurately with the GAMS-2000 spectrometer in a high statistics experiment performed at the 70 GeV IHEP accelerator. The parameters of a linear matrix element have been obtained which show that it is practically constant, with a slight dependence on only one of the Dalitz variables.

Study of π − p→η′ηn in a search for glueballs

Summaryη′η pair production in the charge exchange reaction π−p→η′ηn has been observed and studied in a search for glueballs with the 38 GeV/c pion beam of the 70 GeV IHEP accelerator. The γ-rays from the decay η′η→4γ were detected with the hodoscope spectrometer GAMS-2000. The η′η events in the mass range from threshold up to 1.8 GeV are decays of the scalar G(1590)-meson which has been already observed in its ηη decay mode. The measured ratio of the partial widths of the G→η′η and the G → ηη decay channels is 2.7±0.8 in agreement with the value expected for glueballs.RiassuntoÈ stata osservata e studiata la produzione di coppie η′η nella reazione di scambio di carica π−p→η′ηn nella ricerca di sfere di gluoni con il fascio di pioni a 38 GeV/c dell’acceleratore IHEP a 70 GeV. I raggi gamma derivanti dal decadimento η′η→4γ sono stati rivelati con lo spettrometro odoscopico GAMS-2000. Gli eventi η′η nell’intervallo di massa dalla soglia fino a 1.8 GeV sono decadimenti del mesone scalare G(1590) che è stato già osservato nel suo modo di decadimento ηη. Il rapporto misurato delle ampiezze parziali dei canadi di decadimento G→η′η e G→ηη è 2.7 ± 0.8 in accordo con il valore atteso per le sfere di gluoni.РезумеНаблюдается и исследуется рождение η′η пар в реакции перезарядки π−p→η′ηn с целью поиска «глюболов», используя пионный пучок с импульсом 38 ГэB/c ускорителя 70 ГэB IHEP. γ-лучи из распада η′η→→4γ детектируются с помощью спектрометра GAMS-2000. η′η события в области масс от порога вплоть до 1.8 ГэB представляют распады скалярного G(1590)-мезона, который уже наблюдался в моде распада ηη. Измеренное отношение парциальных ширин каналов распадов G→η′η и G → ηη, составляет 2.8±0.8, что согласуется с ожидаемой величиной для «глюбола».

Matrix element of the η′(958) → ηπ0π0 decay

Abstract A 208 channel hodoscope γ spectrometer, the cells of which are made of lead-glass, is described. This detector makes it possible to measure simultaneously the coordinates (with an accuracy of 1.5 mm), and energy (to a few percent) of a large number of gammas and to reconstruct the mass and momentum of the particles decaying into gammas. The characteristics of the spectrometer have been studied in an electron beam and also under the conditions of real experiments ( π 0 → 2 γ ).

Study of

The partial widths of the η′(958) decays into 2γ, ωγ, 3π0 andηπ0π0 have been measured with the GAMS-2000 spectrometer at the 70 GeV IHEP accelerator. Upper limits for the η′ decays into 3γ, π0γγ, 2π0 and 4π0 have also been obtained. The slope of a linear matrix element for theG-parity violating decayη′→3π0 has been determined.