The invariant mass spectrum of neutral final states produced in π − p charge-exchange scattering at 40 GeV/ c has been studied, searching for heavy particles decaying in 2γ. A peak is observed around 2.85 GeV/ c 2 . The cross section of the reaction π − p→X(2.85)+n, times the branching ratio of the X→2 γ decay, is measured to be σ × BR ⋍ 2 × 10 −34 cm 2 .
MEAN VALUE OF -T = 0.28 +- 0.04 GEV**2.
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The charge-exchange cross sections were measured for π − on Li, C, Al and Cu nuclei at momentum 48 GeV/ c . By comparing the data obtained for nuclei with those for hydrogen under the same conditions the effective numbers of protons are defined. The conclusion is made that η 0 mesons are absorbed in nuclei weaker then π 0 . The total cross section of η 0 interactions with the nucleon is determined to be σ tot ( η 0 N) = 15 ± 5 mb in agre ement with the quark model.
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The cross sections for the reaction π − p → X o n, X o → 2 λ are measured at 32.5 and 48 GeV c momenta. The cross spectrometer of γ -quanta is used to select events of reaction, whose cross section is only about 0.05 μbarn. The cross section energy dependence has the power form ( ≈ p −1.11±0.12 . conclusion on U(6) symmetry of quark model is made when comparing the differential cross sections at zero angle for the reactions π − p → X o and π − p → η o . The angle of octet-singlet mixing for pseudo-scalar mesons β = −(20.6 ± 2.2)° is defined.
FROM AVERAGE OF 32.5 AND 48 GEV/C DATA.
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Differential cross sections for π − p → η 0 n, η 0 → 2 γ have been measured from 20 to 50 GeV for four-momentum transfers − ≲ 3 (GeV/ c ) 2 . The cross sections decrease as a power of momentum and the forward scattering cone shrinks slowly. The parameters of the A 2 trajectory, which is considerably non-linear, have been determined.
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