Two (Δ(1238)ππ) enhancements at 1.93 and 2.12 GeV have been observed in an analysis of the invariant-mass spectra of Δ++(1238)π-π0 and Δ++(1238)π-π- from π-p→π-pπ+π-π0 events in 4.5 GeV/c π-p interactions. An enhancement at 2.2 GeV is also seen with a dominant branching to the Δ(1238)ρ system. The 1.93 and 2.12 enhancements seem to be produced mainly through a ρ-meson exchange process. The 2.2 GeV enhancement seems to be produced diffractively and is considered to correspond to theG17(2190) state.
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EXPONENTIAL FITS TO T-DISTRIBUTIONS.
The reaction K − n → K − π + π − n has been studied in the SLAC 82″ liquid deuterium bubble chamber with a beam momentum of 12 GeV/ c . Although the kinematic fit for this final state has only one constraint, nonetheless a reasonably pure sample has been obtained. The cross section for the reaction is 1.02 ± 0.10 mb. The process K − n → K ∗0 890 Δ − is observed with cross section 36 ± 9 μ b and t -slope of 10 ± 2 (GeV/ c ) −2 . A kaon diffraction dissociation sample has been obtained, although the Q-signal is not so strong as in experiments with proton targets. Neutron dissociation into n π + π − is also observed with similar properties to those of proton dissociation into p π + π − , but with a broader t -distribution.
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SLOPE FROM FIT TO DN/DT FOR -TP < 0.3 GEV**2.
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We study the reactions π + p → π + p nπ 0 ( n = 2, 3) at 3.5 GeV/ c , with 940 and 143 events, respectively. Complete final states are recorded and measured in a heavy liquid bubble chamber. We find the cross sections: sigma;(π + p → π + p 2π 0 ) = 1300 ± 210 μ b , σ(π + p → π + p 3π 0 ) = 320 ± 70 μ b , below the values predicted by statistical models from charged pion data. The mass spectra are given and channel separations are performed using Van Hove variables. Our results are in agreement with charged pion experiments. We present a description of the 3 π 0 system, with 61 events. Under certain hypotheses a spin-parity analysis favours 0 − at low mass and 1 − at high mass.
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The ωπ − mass spectrum, in the reaction π −p → ωπ − pat 11.2 GeV/ c , shows the production of the B − meson with a cross section of 27 ± 5 μb as well as a clear enhancement around 1670 MeV. In the differential cross section for B − production, there is a strong forward peak and a change of slope at t ' t 0.2 GeV 2 .
CORRECTED FOR BACKGROUND AND OMEGA TAILS.
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ABS(D-WAVE/S-WAVE) = 0.4 +- 0.1 FOR B DECAY.
The analysis of A2−→ηπ− at 11.2 GeV/c confirms that A2− is essentially produced by natural-parity exchange. In the differential cross-section as a function oft′ there is evidence of the dip at smallt′ values. The branching ratio (A2→ηπ)/(A2→ϱπ) is 0.18±0.05.
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NUMERICAL VALUES SUPPLIED BY G. THOMPSON. 100 EVENTS IN A2 REGION DEFINED BY 1.18 < M(ETA PI-) < 1.44 GEV.
ROUGH BACKGROUND SUBTRACTION TO REMOVE NON-TRUE ETA EVENTS. FIRST THREE DENSITY MATRIX COMBINATIONS ARE NATURAL-PARITY EXCHANGE, THE REMAINDER BEING UNNATURAL-PARITY EXCHANGE.
We present a systematic analysis of the production of K ∗+ (892) and Δ ++ (1236) resonances in the K + p → K 0 p π + reaction at 5, 8.25 and 16 GeV/ c . We have measured total cross sections, differential cross sections, density matrix elements and examined resonance production mechanisms in terms of the exchange of states with definite naturality. Some results on the reaction K + p → K ∗+ (1420) p are also given.
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Approximately 12 000 examples of the reaction pp→Δ++(1236)n have been identified at 6 GeV / c in a spark-chamber experiment performed at the Argonne National Laboratory Zero Gradient Synchrotron. The experimental invariant-mass and momentum-transfer-squared distributions are in agreement with predictions of the Chew-Low one-pion-exchange model, suitably modified to account for form factors or absorption. The data have been extrapolated from the physical region to the pion pole. It is found that the Dürr-Pilkuhn and Benecke-Dürr models, in conjunction with quadratic extrapolations in t, reproduce the known on-mass-shell dependence of the cross section for the elastic π+p scattering.
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A partial-wave analysis has been performed on the (K − π − π + ) system produced in the reaction K − p → K − π − π + p at 10 and 16 GeV/ c . In the Q mass region it is found that the two dominant states, K ∗ π and Kπ, both in 1 + S wave, are produced with different polarisations, helicity being approximately conserved in the t -channel for K ∗ π and in the s -channel for Kπ. This is in contradiction with the assumption that the amplitude can be factorised into “production” and “decay” parts, and hence that the two amplitudes are fully coherent. The phase variation of the two states do not indicate simple resonance behaviour. It is concluded that the Q-mass enhancement is composite.
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A sample of 43000 two-prong events obtained at a momomentum of 11.7 GeV/c is used to determine the cross-sections of the fitted channels, and to study the reaction π+p→π+pπ0. We investigate in particular the quasi-two-body channels π0Δ++ and ρ+p.
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