We report on the results of a partial-wave analysis of the 3π system produced by baryon exchange in the reaction K − p→ Σ − π + π + π − at 4.2 GeV/ c . We confirm the existence of an enhancement in the 1 + S( ϱπ ) wave as previously established from a Dalitz plot analysis of the same data. The phase variation of this wave is found to be consistent with that expected for a resonance and thus the enhancement is identified with A 1 production. No clear signal for this state is found in either the reaction K − p→ Σ + π + π + π − π − or K − p→ Λπ + π − π 0 . We also find production via baryon exchange of the A 2 in all three reactions and the ω and ω ∗ (1975) in the third reaction.
SIMPLE BREIT-WIGNER RESONANCE FITS. CORRECTED FOR UNOBSERVED DECAY MODES.
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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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Cross-section values or upper limits are presented for twenty-five two-body hypercharge-exchange reactions in K − p and π + p interactions at 10 and 16 GeV/ c . The 16 GeV/ c results are compared with some predictions of line-reversal plus exchange-degenerate Regge poles, of SU(3) and of the additive quark model. Agreement is found in all cases.
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Lambda production is studied in K − p interactions at 10.1 GeV/ c , where the dominant reaction is K − p → Λ + pions. General characteristics such as the distributions of the double differential cross section in the lab system, of the variable x = p L ∗ p max ∗ , of p ⊥ 2 and of the missing mass to the lambda are presented. Total cross sections for Λ production and for the various channels are given. Differential cross sections d σ d t , d σ d t′ and d σ d u′ are presented. Forward and backward peaks are observed in the d σ d t′ and d σ d u′ distributions, respectively. It is found that the exponential slope of these distributions decreases with increasing missing mass to the lambda and, for d σ d t′ , also for increasing multiplicity in the final state. The polarization of the lambdas is studied as a function of multiplicity, p L ∗ , (Λπ ± ) effective mass, t ′ and u ′. The forward lambdas show
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POSSIBLE FORWARD DIP.
The vector meson production, hypercharge exchange reactions K − p → ( φ , ω , ϱ ) Λ and ( φ , ϱ ) Σ 0 are studied at 4.2 GeV/ c incident momentum. The data come from a high statistics bubble chamber experiment with a sensitivity of ∼ 120 events/μb. Total and differential cross sections are presented. The vector meson density matrix elements and hyperon polarization are investigated as functions of momentum transfer. Amplitude analyses are performed for all five reactions. The results are compared with duality and quark model predictions, as well as used to test current ideas in two-body phenomenology.
ERRORS INCLUDE THE 5 PCT MODEL ERROR BUT NOT THEORETICAL RESONANCE PARAMETRIZATION ERRORS.
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Evidence is presented for production of Ξ* resonances, decaying into Ξπ, Ξ(1530)π, ΛK¯, and ΣK¯, in K−p interactions at 2.87 Gev/c. The data represent final combined results from a 30-events/μb hydrogen exposure and an 18-events/μb exposure in deuterium designed to study Ξ* production in the mass interval 1.46-2.07 GeV/c2. In addition to Ξ(1820) and Ξ(1940), signals have been observed at masses of 1630 MeV/c2 and 1860 MeV/c2 decaying into Ξ−π+ and YK¯, respectively. Reaction cross sections have been measured for all final states containing two visible signs of strangeness, and for the final states ΛK−K+ and Σ0K−K+.
CROSS SECTIONS ARISING FROM VARIOUS TOPOLOGIES.
K- P CROSS SECTIONS FROM DEUTERIUM TARGET EXPERIMENT. RESULTS ARE IN GOOD AGREEMENT WITH THE HYDROGEN DATA.
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Cross sections are given for the various exclusive reactions K − p→ Λ 0 + n pions, as well as for quasi two-body final states involving ϱ 0 , ω 0 and Y 1 ∗ (1385) resonance production. The general features of Λ 0 production are presented as a function of the pion multiplicity n . Production of Y 1 ∗+ (1385) is clearly observed at all multiplicities while the Y 1 ∗− (1385) signals grow with the multiplicity, as expected in a non-exotic exchange picture. The polarisation of the Λ 0 is consistent with zero everywhere, except when it is a decay product of Y 1 ∗ (1385), when non-zero values are found for odd values of n . The reactions Λ 0 + 2π and Λ 0 + 3π are analysed in terms of the Plahte-Roberts model and good overall agreement is obtained for the various effective mass distributions and the p L ∗ , p T and cos θ distributions for the individual particles.
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The differential cross sections and density matrix elements for the φ and ϱ 0 mesons have been measured in the reactions K − p → K − K + ( Λ , Σ 0 ) and K − p → π − π + ( Λ , Σ 0 ) at 13 GeV using a wire chamber spectrometer. The analysis shows that while the vector meson production is dominated by the natural parity exchange amplitude, some unnatural parity exchange is also required. Furthermore the φ and ϱ natural exchange cross sections are identical in shape and have the 2:1 relative strength expected in the quark model with K ∗ and K ∗∗ exchange degeneracy. The analysis of the clear peak-dip ϱ 0 − ω interference pattern observed in the π − π + data indicates that the ω production is in phase with the ϱ and of similar magnitude. Both the S ∗ and f′ meson are clearly observed in this experiment. The S ∗ data are found to be consistent with S ∗ parameters deduced from ππ scattering analyses. The f′ density matrix elements and a new limit of the f′ → π − π + branching ratio are presented.
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CROSS SECTIONS CORRECTED FOR EVENTS OUTSIDE THE PHI MASS CUT. <T-CHANNEL>.
CROSS SECTIONS CORRECTED FOR EVENTS OUTSIDE THE PHI MASS CUT. <S-CHANNEL>.
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