The reactions π − p → p π − and π − p → p ϱ − ( ϱ − → π − π 0 ) at 10 GeV/ c with the proton in the forward direction in the c.m.s. are discussed on the basis of 953 elastic scattering events and 2240 events of the reaction π − p → p π − π 0 . The total backward cross sections are 0.52±0.10 and 1.52±0.28 μ b, respectively. In both cases the production mechanism is compatible with the dominance of the baryonic Δ δ Regge trajectory exchange. The ϱ − decay angular distributions are studied in the u -channel helicity frame and the spin density matrix elements are presented as functions of u .
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DATA FROM PRIV COMM WITH B. GHIDINI.
DATA FROM PRIV COMM WITH B. GHIDINI.
The reactionsπ−p→K0(890) Λ,K0(890)Σ0 andK0(890)Σ0 are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to ∼90 events/μb. The differential cross sections, density matrix elements of the vector meson and hyperon polarizations are presented. A transversity amplitude analysis is performed for each of the reactions. The results are compared with those obtained for the SU(3) related processesK−p→ϕΔ, ϕΣ0, ϕΣ0(1385) andϱ−Σ+(1385) and with predictions of the additive quark model and SU(6) sum rules.
BREIT-WIGNER FIT WITH BACKGROUND POLYNOMIAL.
BACKWARD CROSS SECTION.
TOTAL CROSS SECTION USING SLICING TECHNIQUE. FORWARD (-TP < 1.2 GEV**2) CROSS SECTION IS 25 +- 2 MUB: DOUBLE MASS CUT GIVES 20 +- 7 PCT BACKGROUND CONTAMINATION.
Exotic exchange processes observed in K − p and π − p scattering in the neighbourhoood of 4 GeV/ c are analysed in terms of standard models. Some new data on π − p induced processes are presented and used in the analysis. Regge-Regge cut predictions are found to be smaller than the data up to these energies. Baryonium exchange models are shown to be indistindistinguishable from Regge cut models as regards their phenomenological predictions. The double scattering quark model of Białas and Zalewski is compatible with data on the exotic exchange production of Σ and Y ∗ (1385), but fails for Ξ and Ξ ∗ (1530) production. Modifications of this model are discussed.
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FORWARD (SMALL -T) CROSS SECTIONS. THE K- P CROSS SECTIONS ARE COMPUTED FROM THE ACNO DATA AT 4.2 GEV/C, M. MAZZUCATO ET AL., NP B178, 1 (1981).
BACKWARD (SMALL -U) CROSS SECTIONS.
The reactions π−p→K0Λ,K0Σ0 are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to ∼90 events/μb. The differential cross sections and hyperon polarizations are presented and compared with existing data from earlier electronic experiments. The data in the forward hemisphere are used to perform an amplitude analysis of the 0−1/2+→0−1/2+ hypercharge exchange processes.
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Results are presented for the quasi two-body hypercharge exchange reactions of the type 0−1/2+→2+1/2+:$$\begin{gathered}
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Data on the reactions π − p → p π − , p p → π + π − , K − p → pK and p p → p p at 8 and 12 GeV/ c are presented. Our results agree with line reversal symmetry (between π − p → p π − and p p → π + π − ), Regge pole behaviour for non-exotic reactions ( π − p → p π − , p p → π + π − ), and universal behaviour for exotic reactions ( p p → p p , K − p → pK − ) with d σ /d u | u =0 ∼ s −10 excluding the existence of a “glory” mechanism in p p elastic backward scattering in our energy range.
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We present differential cross-section measurements for π−p elastic scattering in the backward direction, with −0.94>cosθc.m.>−1.0, for eleven beam momenta from 2.15 to 6 GeV/c.
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The π−+p→π0+n differential cross section at 180° has been measured for 52 values of π− momentum from 1.8 to 6.0 GeV/c using a constant-geometry detection system. The average statistical uncertainty is ∼5% and the systematic uncertainty is ∼10%. The details of the experiment and the data analysis are discussed. The data are compared with those of other experiments with which they are generally in agreement. One set of data disagrees with those presented here and a possible reason for this is discussed. A five-parameter fit of the predictions of a dual-resonance model to our data gave excellent agreement. The differential cross sections at 180° for π±p elastic scattering have been compiled and the moduli and relative phase of the T=12 and T=32 pion-nucleon s- and u-channel amplitudes (|A12|, |A32|, and cosδ) have a minimum at u=0.4 GeV/c and, in the s channel, a corresponding minimum at s=2.2 GeV/c.
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Differential cross sections for π−p elastic scattering over the angular range 155° to 177° in the center-of-mass system have been measured at 33 incident pion momenta in the range 600 to 1280 MeV/c. The experiment, which was performed at the Bevatron at the Lawrence Berkeley Laboratory, employed a liquid hydrogen target, a double-arm spectrometer, and standard counter techniques to detect the elastic events. The data from this experiment are compared to all other published data in this momentum region. The over-all agreement is good. The data of this experiment are also compared with the results of the recent phase-shift analysis by Almehed and Lovelace. In the momentum region between 700 and 900 MeV/c, the slope of the backward angular distribution goes rapidly through zero from negative to positive, and the magnitude of the differential cross section falls by more than a factor of 10. Momentum-dependent structure is seen in the extrapolated differential cross sections at 180°. Two prominent dips in the 180° differential cross sections appear at 880 and 1150 MeV/c. This structure is discussed in terms of a direct-channel resonance model that assumes only resonant partial waves are contributing to the cross sections for large scattering angles.
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Differential cross sections and density-matrix elements in ρ− decay have been measured at 6 GeV/c for p¯p→π+ρ− and its line-reversed partner π−p→pρ− in the range tmin>t>−1.5 (GeV/c)2. The reactions satisfy line-reversal symmetry and the ρ− decay is consistent with isotropy for −t≲0.5 (GeV/c)2. For −t≳0.5 (GeV/c)2, the differential cross sections show a weaker t dependence, and the decays become anisotropic.
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FROM ROUGHLY EQUAL NUMBERS OF RHO- EVENTS AND BACKGROUND (CONSISTENT WITH ISOTROPY FOR BOTH REACTIONS).
Forum