Neutral decays ofη′(958)

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.     

Production of pseudoscalar mesons in 300 GeV central π+ N collisions

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 0.1F<0.3.     

Measurement of π−p → π0n at large momentum transfer

New results on a high statistics measurement of pion-nucleon charge exchange scattering at 40 GeV/c, extending in momentum transfer up to ?t = 1.8 (GeV/c)², are reported and compared with an optical impact parameter model, together with previous data for the reaction π^?p → ηn at the same energy. The imaginary part of the pole trajectory b₀(s) is determined from the slope of the tangent to the maxima of $\text{(?t)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{d}\text{σ}\text{d}\text{t}$. The linear increase of Im b₀(s) with log s, which has been observed at low energies, continues up to 40 GeV/c.     

Experimental study of direct photon emission in K/it− → π−π0γ decay using ISTRA+ detector

The branching ratio in the charged-pion-kinetic-energy region of 55 to 90 MeV for the direct photon emission in the K ⁻ → π⁻π⁰γ decay has been measured using in-flight decays detected with the ISTRA+ setup operating in the 25-GeV/c negative secondary beam of the U-70 PS. The value Br(DE)=[0.37±0.39(stat.)±0.10(syst.)]×10⁻⁵ obtained from the analysis of 930 completely reconstructed events is consistent with the average value of two stopped-kaon experiments, but it differs by 2.5 standard deviations from the average value of three in-flight-kaon experiments. The result is also compared with recent theoretical predictions. The text was submitted by the authors in English.     

Study of theω π + system

The mass spectra of theω π ⁰ system, produced inπ ^? p charge-exchange reactions at 38 GeV/c and 100 GeV/c, show a new neutral state with a mass of 2200±20 MeV and a width of 260±50 MeV. Likeρ ₃(1690), this meson,X(2200), is produced through one-pion-exchange.X(2200)J ^PC is likely 1^??. It might be a 2³ D ₁ radial-orbital excitation ofρ ⁰. Its production cross section falls with energy quadratically, in agreement with one-pion-exchange. The cross sections forb ₁(1235) andρ ₃(1690) production have also been measured; their energy dependences have been determined.     

Measurement of π−p→π0π0n at 25 GeV/c

The reaction π^?p→π⁰π⁰n has been measured with a 648 channel hodoscope spectrometer for the detection of the four γ's from the π⁰ decays. The π⁰π⁰ D-wave is fully compatible with the f⁰ contribution as it is determined in high-statistics π⁺π^? experiments. The magnitude of the π⁰π⁰ S-wave and the cosinus of its phase angle (relative to the known D-wave) are determined from fits to the π⁰π⁰ angular distributions. Argand diagrams for the I = 0 amplitude S₀ are given for the range 1000 to 1500 MeV/c². Two solutions exist. One exceeds the unitarity limit above 1200 MeV/c². The other remains within the unitarity limit and is nearly elastic up to 1450 MeV/c². It indicates an S₀ wave resonance around 1300 MeV/c².     

Study of multi-gamma final states from π−p interactions at 40 GeV/c with invariant mass above 2 GeV

Searching for new heavy particles, we have investigated the invariant mass spectra of neutral final states from π^?p interactions at 40 GeV/c incident momentum. No particles, in the mass region from 2 to 5 GeV, decaying in γ- rays, π⁰, η and X⁰ mesons, have been found to a level of about 10^?34 cm².     

χ particle production in π−p collisions at 38 GeV/c

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 X_F ?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 σ_XF>0 (π^?p → χ + …) = (28±11) nb.