The total cross sections of 18.7 GeV Σ − hyperons on protons and deutrons have been measured to be 34.0 ± 1.1 mb and 61.3 + 1.4 mb, respectively. The derived Σ − -neutron cross section is 30.0 ± 1.2 mb.
CROSS SECTIONS CORRECTED FOR FORWARD COULOMB AND NUCLEAR SCATTERING.
The magnetic moment of the Ξ− hyperon has been measured to be μ(Ξ−)=−0.69±0.04±0.02 nuclear magnetons, where the uncertainties are statistical and systematic, respectively.
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The magnetic moment of the Ξ0 hyperon has been measured to be μΞ0=−1.253±0.014 nuclear magnetons. A new measurement of μΛ is also reported.
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The polarization of 26 000 Σ+ hyperons produced by 400-GeV protons on Be has been measured. The polarizations of Σ+ and Λ hyperons have the opposite sign. The magnitude increases with momentum at 5-mrad production angle, and averages 22% over the momentum range 140 to 280 GeV/c.
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Polarization of the scattered Λ has been measured in the reaction Λ+p→Λ+p. A total of 90 000 elastic events was recorded. Polarization was observed which decreased in magnitude with increasing momentum. For 0.1<~|t|<~0.4 GeV2 the polarization is P=−0.21±0.07 for p=110 GeV/c and is +0.01±0.04 at p=320 GeV/c. Results for 860 Λ¯−p elastic scatterings are also presented.
90000 ELASTIC EVENTS.
860 ELASTIC EVENTS.
We have measured the forward production spectra of various neutral particles produced by π−, K−, p¯, and p at 200 GeV/c, and by π− at 290 GeV/c incident on a Be target. The salient features of these measurements are (1) copious production of KSo at large Feynman xL for incident π− and K−, (2) production of roughly equal fluxes of Λ0 and Λ¯0 for incident π−, and (3) close similarity of the following spectra: π−→n and K−→Λ0; π−→Λ0, π−→Λ¯0, and p→KS0; π−→KS0 and p→Λ0. The overall features of the various distributions seem to agree with the ideas of dimensional counting presented in the constituent-interchange model of quark collisions. Results are presented in terms of the invariant cross section Ed3σ(xL, PT=0)dp3 per Be nucleus for each inclusive reaction.
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A neutral beam designed to transmit a high flux of Λ0 hyperons with momenta above 50 GeV/c has been built and operated at Fermilab. Inclusive production cross sections per target nucleus have been measured for p+A→Λ0+X, p+A→KS0+X, and p+A→Λ¯0+X with 300-GeV protons incident on solid targets A=berylium,copper,andlead. The region of phase space covered is predominantly projectile fragmentation: 0.2<~x<~1, 0<~p⊥<~2 GeV/c. The A dependence of the inclusive cross sections is analyzed. The cross sections are compared to other work in pp collisions by extrapolating the A dependence to A=1. The results of measurements of Λ0 and Λ¯0 polarization from the beryllium target are presented.
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Inclusive production of Λ0 hyperons by 300-GeV protons has been measured at fixed production angles in the laboratory between 0 and 9 mrad and laboratory momenta from 65 to 300 GeV/c. Three different solid targets were used: beryllium, copper, and lead. The A dependence of the data is suggestive of a collision model in which the hadron loses energy and gains transverse momentum as it leaves the nucleus. The experimental results are compared to such a model, and the implications are discussed.
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Inclusive production cross sections have been measured for the processes p+A→Ξ0+X (A=Be, Cu, Pb) and for p+Be→Ξ¯0+X. Data were taken at angles of 0, 2, 3.5, 7.3, and 9.8 mrad between the incident 400-GeV proton beam and the outgoing hyperon beam. Production cross sections for Λ and Λ¯ production were measured at the same time. The A dependence of the Ξ0 cross sections is discussed, along with interpretations in terms of various models.
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The polarization of Ξ− hyperons produced by 400-GeV protons in the reaction p+Be→Ξ−+X has been measured as a function of momentum at two production angles. The average polarization for the full sample (192 110 events) was -0.108±0.007. Comparisons are made with polarization measurements for other hyperons produced under similar conditions. From the same data, αΛαΞ was measured to be -0.303±0.004±0.004, where αΛ is the asymmetry parameter in the decay Λ→pπ−, αΞ is the asymmetry parameter in the decay Ξ−→Λπ−, and the uncertainties are statistical and systematic, respectively. This yields αΞ=-0.472±0.006±0.011, where the systematic uncertainty is dominated by the uncertainty in αΛ. An updated test of the ΔI=1/2 rule in Ξ decay is presented.
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