Jean Pierre Peigneux

Scattering of negative pions on carbon

Abstract Data are presented on elastic and inelastic differential cross sections as well as on total cross sections for negative pions on carbon in the energy range 120 MeV to 280 MeV.

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.

On the origin of the transmission damage in lead tungstate crystals under irradiation

The origin of the transmission damage in PWO crystals is discussed. It is shown that both electron and hole centers created on the basis of structural defects in PbWO 4 crystals contributed to the induced absorption of the crystals. The different aspects of the suppression of the recharge processes in PWO scintillation crystals are also discussed.

STRUCTURE IN THE ANGULAR DISTRIBUTION OF HIGH ENERGY PROTON--PROTON SCATTERING.

Abstract Results are presented on measurements of elastic proton-proton scattering at 19.2 and 21.1 GeV/c in the angular region where previously structure had been observed at lower energies.

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.

New channeling effects in the radiative emission of 150 GeV electrons in a thin germanium crystal

Abstract The orientation dependence of the radiative emission of 150 GeV electrons and positrons incident at small angles with respect to the 〈110〉 axial direction of a thin (0.185 mm) Ge crystal has been observed. The processes are well understood, except for channeled electrons, which radiate unexpected high energy photons.

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.

Coulomb-nuclear interference in π−-12C elastic scattering

Abstract The π − - 12 C elatic differential cross sections have beenmeasured at three kinetic energies around the ( 3 2 , 3 2 ) pion-nucleon resonance, namely 120, 180 and 260 MeV, in the small-angle region [ t ≤ 18 000 (MeV/ c ) 2 ] where the interference between Coulomb and nuclear amplitudes is most pronounced. An expression for the relative phase between Coulomb and nuclear amplitudes has been derived which takes into account a variation linear in t of the nuclear phase. Using this formula, the real part of the forward nuclear amplitude has been deduced from the data at each energy. The results are in good agreement with the predictions of pion-nucleus forward dispersion relations. The nuclear phase seems to vary significantly at 260 MeV.Abstract The π−-12C elatic differential cross sections have beenmeasured at three kinetic energies around the ( 3 2 , 3 2 ) pion-nucleon resonance, namely 120, 180 and 260 MeV, in the small-angle region [t ≤ 18 000 (MeV/c)2] where the interference between Coulomb and nuclear amplitudes is most pronounced. An expression for the relative phase between Coulomb and nuclear amplitudes has been derived which takes into account a variation linear in t of the nuclear phase. Using this formula, the real part of the forward nuclear amplitude has been deduced from the data at each energy. The results are in good agreement with the predictions of pion-nucleus forward dispersion relations. The nuclear phase seems to vary significantly at 260 MeV.

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.