A. Possoz

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.

Neutral decays of the η-meson

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.

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

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

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».

\pi^- p \to \eta^\prime \eta n

Abstract A data acquisition system with high amplitude resolution (12 bits), high speed conversion (clock frequency 50 MHz), used in an experiment with a large number of counters (∼ 4200) is described. Physical quantities (masses and momentum transfer) are computed during data transmission itself, allowing improved trigger selectivity.

in a Search for Glueballs

Abstract A structure has been observed at 2220 MeV in the mass spectrum of ηη ′ systems produced by 38GeV/ c and 100 GeV/ c ′ negative pions on protons. The angular distribution of the decay products shows that this structure is presumably a spin J ⩾ 2 meson.

Acquisition system for the hodoscope spectrometer GAMS-4000

Abstract A large cellular hadron calorimeter consisting of independent modular total aborption counters (iron-scintillator sandwiches) is described. Scintillation light is collected using light guides with a wavelength shifter. The characteristics of the detector have been studied in a 200 GeV hadron beam. The detector makes it possible to measure simultaneously the energy and coordinates of several particles.

2.22 GeV ηη′ structure observed in 38 GeV / c and 100 GeV / c π-p collisions

Abstract The production of χ particles in the reaction π−p → χ + … has been studied near threshold. The measurements have been performed at the 70 GeV IHEP proton synchrotron using the hodoscope spectrometer GAMS-2000. The χ particles have been identified through their decay χ → J/ψ + γ, J/ψ → e+e−. In the region XF ≳0.4 the fraction of obsered J/ψ particles which is obtained via the decay of χ states is 0.44 ± 0.16. The χ longitudinal and transverse momentum distributions are similar to those obtained for J/ψ. The inclusive production cross section of χ particles (3P1 and 3P2 states) at 38 GeV/c is σXF>0 (π−p → χ + …) = (28±11) nb.

Modular hadron calorimeter

Abstract The energy and spatial resolution and other characteristics of a combined detector permitting simultaneous detection of a large number of photons and hadrons has been studied in a 200 GeV/ c hadron beam at the CERN SPS. The detector consists of the GAMS-4000 spectrometer (4096 lead-glass cells) and a modular hadron calorimeter MHC-200 located behind it (240 total-absorption sandwich counters). A new method for adding the signals from the two calorimeters, which takes into account the difference in the development of hadron showers in photon and hadron calorimeters, has been developed. It permits substantial improvement of the energy resolution of the combined detector. The hadron coordinates are defined with a precision of several millimeters and the energy resolution is typical for steel-scintillator sandwiches with a wavelength-shifter readout. The effect of the gap between the photon and the hadron calorimeters has also been studied.