The energy dependence of low energy K−-proton processes

Weak Interactions (Second Section) Chapter 8: Decays of Charged K Mesons

Cross section data for interactions of nucleons, antinucleons, mesons (K), and mesons ( pi ) are compiled and discussed. At high energies, specific features common to particles of different kinds exist. Information on phenomena occurring in the region of very small space-time scales may be obtained. Most of the data is obtained from experiments using accelerators in which large particle- beam densities facilitate precision measurements. Weak neutrino reactions at high energies are discussed. (L.N.N.)

Cross Sections for Elementary Particle Interactions

Λ0 hyperon polarization in inclusive production by 24 GeV protons on platinum

K− meson absorption in neon

The energy distribution of Λ0 coming from K capture stars has been obtained measuring Λ0 found by area scanning in two emulsion stacks. This distribution, compared to a theoretical one obtained with an optical model calculation, gives indication that the percentage of multi-nucleon captures in nuclear emulsions of the order of 30%. To the same conclusion we are led by the detailed study of 103 capture stars correlated to Λ0 decay. From the study of the missing energy in K- capture stars we deduce that the probability for a π0 of being absorbed in nuclear matter is very low. There is evidence that the probability for the emission of a Λ0 is not strongly dependent on the atomic weight of the nucleus in which the K- was absorbed. The upper limit for the cryptofragment formation is 15%. A search for the formation of Y1*- in the reaction\(K^ - + 2n \to Y_1^{ * - } + n\) at rest in the emulsion nuclei gives no conclusive result due to the low statistics.

Λ0 from K- capture in emulsion

The magnetic moment of the Δ-hyperon has been measured by observing the precession of the polarization vector of Δ-particles in a transverse pulsed magnetic field of 20 T (= 200 kG). The hyperons were produced in a polyethylene target by the reaction π−+p→+Δ+K0 at a pion momentum of 1.05 GeV/c; their decays were detected in stacks of nuclear emulsion at a distance of 11 em from the centre of the target. The angular distribution of the decay products in the rest frame of the Δ was used to determine the direction of the polarization at the time of the decay, and hence the magnetic moment. About 1300 Δ decays have been analysed, giving the result\(\mu _\Lambda = - 0.66\mu _{\mathcal{N}}\) (nuclear magnctons) with a statistical uncertainty of\( \pm 0.06\mu _{\mathcal{N}}\). The systematic error is less then\( \pm 0.03\mu _{\mathcal{N}}\), so that the total (68% confidence level) error is\( \pm 0.07\mu _{\mathcal{N}}\).

A new measurement of the magnetic moment of the Δ-hyperon

Study of 224 τ' + decays

Experimental data are given on the interaction of K−-mesons with hydrogen nuclei. These emulsion data do now agree with the new bubble chamber data. They indicate an essentially isotropic angular distribution, both for scattering and for absorption events, a slight decrease of the elastic scattering cross-section with energy and a larger one of the absorption cross-section.

W. Püschel

Papers

Λ0 from K- capture in emulsion

A new measurement of the magnetic moment of the Δ-hyperon

Study of 224 τ' + decays

On K−-hydrogen interactions

A measurement of the magnetic moment of the Λ0 hyperon