T. Mouthuy

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.

First observation of neutrino trident production

Abstract We report on the first observation of neutrino induced production of muon pairs in the electromagnetic field of a nucleus. The data has been obtained using the CHARM II detector exposed to the CERN wideband neutrino and antineutrino beams. A clear signal of 55 ± 16 events is seen in a sample of dimuons of opposite charge without visible recoil at the vertex. The cross section is determined and found to be in agreement with the standard model prediction.

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 The fine granularity of the CHARM-II detector has been exploited to search, in the CERN-SPS wide band neutrino beam, for quasi-elastic ντ interactions followed by the decay τ → πντ. Since the sampling thickness of the target calorimeter corresponds to ∼ 1 9 of an interaction length, these events appear in the detector as a single track followed by a hadronic shower. The study of the “single pion” events is used to set limits on the νμ → ντ oscillation parameters. The maximum sensitivity to the mixing angle θ is reached for Δm2 = 50 eV2 allowing to exclude values of sin22θ greater than 6.4 × 10−3 at 90% CL.

in a Search for Glueballs

Abstract We are reporting on a determination of neutral current coupling constants from a study of differential cross sections of muon- (anti)neutrino-electron scattering. The results were obtained with the CHARM-II detector which was exposed to the CERN wide band neutrino beam in the years 1987–1990. A total of about 2100 ve and 2200 ve scattering events were observed. From a comparison between the data and predicted event distributions, the effective vector and axial-vector neutral current coupling constants of the electron were determined to be g e v =−0.025±0.019 and g e A =−0.503±0.018.

Search for νμ → ντ oscillation

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.