M. Boutemeur

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) 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^-

Abstract The π − p→ ωω n reaction has been further studied at 38 GeV/ c with increased statistics. The peak at 2 GeV that has been previously observed in the ωω mass spectrum is due to two resonances. The first one is a tensor meson with a mass of 1920 MeV. The second is f 4 (2050). The branching ratio BR [f 4 (2050)→ ωω ] = 0.26±0.06 has been measured.

N collisions

Abstract The effective mass spectrum of π0 pairs produced in pp central collisions (pp → pfπ0π0ps) at 450 GeV/c, s = 29 GeV , below 1 GeV differs from that observed in peripheral charge exchange reactions. In particular, there is a large number of events between ππ-threshold and 1 GeV, that interfere with f0(980) destructively. The possible existence of a broad S-wave state is suggested.

Further study of mesons which decay into ωω

A high-statistics study of the π0π0-system produced in the π-p→π0π0n reaction at 38GeV/c has been carried out at the IHEP accelerator using the GAMS-2000 multiphoton spectrometer. A partial-wave analysis which includesS, D0, D− andD+ waves has been performed in the |t|-range up to 1 (GeV/c)2. TheS*/f0(980) resonance is seen as a dip in theS-wave amplitude at small |t|. A distinct peak with a mass of 997±5MeV and a width of 48±10MeV is observed in theS-wave at |t|>0.3 (GeV/c)2. The production cross sections are measured.

Study of the π0π0 system in pp central collisions at 450 GeV/c

Abstract The rare radiative decay ω → π 0 π 0 γ has been detected with the GAMS-2000 multiphoton spectrometer at the IHEP 70 GeV accelerator. The ω → π 0 γ decay events have been used for normalization. The measured branching ratio is BR( ω → π 0 π 0 γ )=(7.2±2.6)×10 −5 .

Study offo (995) resonance in the π0π0 decay channel

Abstract New data on the ν′ν system produced in the π−p charge exchange at 38 GeV c momentum confirm the existence of the narrow ν′ν resonance X(1910). The hypothesis of the X(1910) quantum numbers being a JPC = 1−+, forbidden for the q[ovbar|q] meson, is proposed to explain the extremely low limits obtained for X(1910) decays through π0π0, νν and K0sK0s channels and the flat t-dependence of the X(1910) production cross section.

Observation of the

The rare ηγ decay width of the ω-meson has been measured in a model-independent way, with ω produced in 38 GeV/c π−p charge-exchange. Large momentum transfer events have been selected in order to eliminate ω-ρ interference contribution. BR (ω→ηγ) =(8.3±2.1)·10−4. The gammas from ω→ηγ→3γ decay have been detected with the multiphoton spectrometer GAMS-2000 at the IHEP 70 GeV proton accelerator.

\omega\to\pi^{0}\pi^{0}\gamma

SummaryRecent results on ωπ0 partial-wave analysis from the GAMS Collaboration are presented. A partial-wave analysis of the 38 GeV/c π-p charge exchange data confirmed the existence of theρ(2200) radial-orbital excitation of theρ(770) ground-state observed earlier in the same experiment. A new 5−− state,π5(2350), was also observed in this analysis. Masses, widths and production cross-sections for these states are given.

decay

The exculsive production of π0, η, and η′ mesons in π+N central collisions has been studied with 300 GeV incident pions. The experiment has been performed at the CERN SPS. The gammas from decaying mesons were detected in the hodoscope multiphoton spectrometer GAMS-4000. The measured differential cross sections show a plateau in the longitudinal momentum interval 0.1