We have studied the production and decay of the D(1285) meson in the reaction K − p→ Λ D at an incident K − momentum of 4.2 GeV/ c . The cross section for this reaction is 11 ± 3 μ b and the branching ratios D→ KK π /D → ηππ and D → 4 π /D → ηππ are found to be 0.42 ± 0.15 and 0.7 ± 0.5, respectively. The proportion of D → ηπ + π − going through the intermediate δ ± π ∓ states is 0.72 ± 0.15. Forward and backward exchange mechanisms are found to contribute in the ratio 3 : 2.
ABOUT 60 PCT OF THE D(1285) PRODUCTION OCCURS IN THE FORWARD HEMISPHERE.
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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The polarization in K + n↑ → K 0 p has been measured at 6 and 12 GeV/ c in the interval 0.1 < |t| < 1.0 using a polarized deuteron target. The results are compared to predictions from SU(3), exchange degeneracy (EXD) and line reserval, and from various phenomenological models.
NARROW BINS.
WIDE BINS.
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Data on Λ and\(\bar \Lambda \) polarization inK±p interactions at 32 GeV/c are presented. A comparison is made between the results of these two experiments as well as with the data at lower energies. The contribution of the different production mechanisms to the Λ(\(\bar \Lambda \)) polarization are discussed.
Data are presented on figures only. DATA NOT ENCODED.
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Inclusive Λ production has been studied in K − p interactions at 8.25 GeV/ c using about 69 000 events; the total cross section is found to be 3.35 ± 0.20 mb. A comparison has been made with Σ 0 and Σ(1385) inclusive production. Their influence on the inclusive Λ production is discussed. The inclusive Λ cross section and polarization is interpreted in terms of the triple-Regge model. In the target fragmentation region an effective Regge trajectory is determined which lies closer to the K than to the K ∗ . In the beam fragmentation region the cross-section data indicate an effective Regge trajectory which corresponds to the nucleon, while the polarization data require additional Regge exchanges to be present.
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Inclusive production of ifπ ± , K ± and p has been studied near charm threshold for c.m. energies between 3.6 and 5.2 GeV. Differential and scaling cross sections together with particle multiplicities have been determinated. By comparing data below and above charm threshold the charm contribution to if π ± and K ± production has been extracted. A comparison has been made between inclusice p production and inelastic electron-proton scattering. To study differences between three-gluon annihilation and two-quark production of the spectra from J/ decay and from non-resonant production at 3.6 GeV has been compared.
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The magnetic moment of the Λ0 hyperon has been measured to be μΛ=(−0.6138±0.0047)μN.
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Approximately 350 A 2 + events have been observed in the reaction π + p → K + K S 0 p ( K S 0 → π + π − ) at an incident π + laboratory momentum of 12.7 GeV/ c . The events are distributed over a range of four-momentum transfer squared 0.01 ⩽ − t ⩽ 0.60 (GeV/ c ) 2 and K + K S 0 mass 1.11 ⩽ m K + K S 0 ⩽ 1.51 GeV . A Breit-Wigner fit to the mass spectrum yields a mass for the A 2 + , m A 2 + = 1.324 ± 0.005 GeV, and a width Γ 0 = 0.110 ± 0.018 GeV. We find a cross section σ ( π + p → A 2 + p) = 1.71 ± 0.30 μb referring to the above-mentioned mass and t range and A 2 + → K + K S O with K S 0 → π + π − . The spin-space density matrix in the Gottfried-Jackson frame is practically saturated by ϱ 11 ⋍ ϱ 1−1 = 1 2 suggesting natural parity exchanges only. There is a forward dip in the angular distribution consistent with dominance of s -channel net helicity flip amplitudes and ϱ and f Regge exchanges suffice to describe adequately our differential cross sections.
SUBTRACTED BACKGROUND IS PHASE SPACE. FITTED D(SIG)/DT SLOPE IS 9.5 +- 0.9 GEV**-2.
SUBTRACTED BACKGROUND IS AN S-WAVE WITH SLOPE OF 8 GEV**-2. FITTED D(SIG)/DT SLOPE IS 6.9 +- 0.6 GEV**-2.
FROM D(SIG)/DT. ERROR INCLUDES 15 PCT SCALE ERROR ADDED QUADRATICALLY.
We have determined the coherent KS regeneration amplitudes on various nuclei, from 20 to 140 GeV/c, using a particularly systematics-free technique. Our results are well represented by |(f−f¯)k|=2.23A0.758p−0.614 mb. This p dependence corresponds to an effective "nuclear" intercept ``αω(0)''=0.386±0.009, whereas the elementary value is αω(0)=0.44±0.01. Comparisons are made with data below 25 GeV/c, and with optical-model predictions. The latter work only if "αω(0)" is postulated to hold for the elementary amplitudes.
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