Differential cross sections and density matrix elements are presented for K ∗− (890) and K ∗− (1400) produced in the reaction K − p→K O π − p at 3.95 GeV/ c . The cross sections are decomposed into contributions due to different exchange mechanisms.
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The production of the peripheral 3 π mass enhancement in the A 1 region is described. The differential cross section and its variation with 3 π mass is studied and the spin density matrix elements are given for the t -channel and s -channel helicity frames. As observed in π − p interactions t channel but not s channel helicity is conserved. A Deck type double Regge trajectory exchange amplitude gives good fits to the experimental distributions. Its use is supported by the equality of ϱ 0 0 for the A 1 and ϱ 00 for the ϱ in the t -channel, as noted by Donohue.
THE SPIN DENSITY MATRIX ELEMENTS FOR THE RHO (P=4) FROM A1 DECAY ARE IN THE RHO T-CHANNEL FRAME.
A search for N ∗ (1450) production has been made among the 904 selected examples of the reaction pd → pp π − (p sp ) obtained in a bubble chamber exposure at 5.9 GeV/ c incident momentum. The cross section for the reaction pn → pp π − is found to be 1.4 ± 0.1 mb. The peripheral data are in good agreement with the predictions of a single-pion exchange model. Approximately 8% of the events can be attributed to N ∗ (1450) production by some other mechanism.
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Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the ϱ , ω and φ production by e + e − annilations. Assuming a π + π − π 0 π 0 production by the quasi two-body process e + e − → ϱ → ωπ 0 we give the correspondi ng cross section σ (e + e − → π + π − π 0 π 0 ) = (1.1 ± 0.5) 10 −32 cm 2 . Since no events with 3 and 4 charged pions have been observed σ (e + e − → π + π − π 0 π − ) ⩽ 1.5 × 10 −33 cm 2 .
RATIO TO MUON PAIR PRODUCTION CALCULATED FROM CROSS SECTION. INCLUDING SYSTEMATIC ERRORS.
The Λ polarization in the reaction γp → K + Λ has been measured using the decay Λ → pπ − as an analyzer. It is found to be large and negative in the momentum transer range 0.2 ⩽ | t | ⩽ 1.0 (GeV/ c ) 2 .
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The Λp, Λn, Λ p, and Λ n total cross-sections were measured in the Λ momentum interval 6–21 GeV/ c . Within the experimental uncertainties the cross-sections are momentum-independent in this interval and the momentum-averaged cross-sections are found to be: σ ( Λp ) = 34.6 ± 0.4 mb : σ ( Λn ) = 34.0 ± 0.8 mb ; σ ( Λp ) = 56 ± 11 mb ; σ ( Λn ) = 46 ± 20 mb . The first two results are in agreement with charge symmetry, and with simple quark model sum rules applied to previous results on pp, K - n, and π + p total cross-sections.
NO SIGNIFICANT MOMENTUM DEPENDENCE OVER THIS INTERVAL. 2.8 +- 0.3 MB SHADOWING CORRECTION APPLIED FOR NEUTRON CROSS SECTION.
6 MB SHADOWING CORRECTION APPLIED FOR NEUTRON CROSS SECTION.
It is found in the reactions π ± p →( π ± π + π − )p, believed to be dominated by diffraction dissociation, that the d σ d t′ distributions show a “cross-over” effect at t ′ ≈ 0.15, similar to the effect observed in elastic scattering. This gives evidence for the interference of ( ϱ 0 , B 0 ,…)-exchanges with ( P , f 0 , …) -exchanges in pion diffraction dissociation reactions. No such evidence is found for baryon dissociation, π ± p → π ± (p π + π − ), at the same energy.
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The spin rotation parameter R has been measured at CERN, for π ± p at 6 GeV c and for π − p at 16 GeV c , with t ranging from −0.19 to −0.51 ( GeV c ) 2 . The parameter A was measured for π − p at 6 GeV c in the interval between t =−0.19 and minus;0.41 ( GeV c ) 2 . The averaged values are the following; R (+6) =−0.08±0.04, R (−6) =−0.23±0.05 and R (−16) =−0.23±0.05. The values obtained for A are close to +1.
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Multihadronic production has been observed at the Adone e + e − storage ring, in the c.m. energy range 1.4 - 2.4 GeV. The cross sections for the reactions e + + e − → 2 π ± + nπ o (1 ⩽ n ⩽ 4) and e + + e − → (4 π ± + nπ ± ) (0 ⩽ n ⩽ 2) have been measured, assuming that the produced particles are only pions with a pure phase space momentum distribution.
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Differential cross sections for single photoproduction of neutral pion on neutron have been measured at different c.m. angles for photon energies, between 450–800 MeV.
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