Search

The regeneration of Kl from K2 neutral mesons and the mass difference between the two mesons were studied by passing a K/sup 0/ beam through 1.5- and 6- in. iron plates. About 200,000 pictures were made of the events, and they were analyzed for two-prong events where the primary momentum was equal to the beam momentum. The Q( pi , pi ) distribution of these selected events showed a peak around the expected value of 220 Mev, thus proving the regeneration of K1. The angular distribution of K1 decay events is plotted; the diffraction was computed from an optical model method and subtracted from the distribution to give the transmission peak, which was found to be confined to angles smaller than 2.5 deg (angle between primary K2 beam and regenerated K1). The mass difference is calculated to be zero for the 1.5-in. plate and 0.85 for the combination of the 1.5- and 6-in. plates. (D.L.C.)

The interaction of 5-Bev negative pions with protons has been studied by exposing a 36-atmosphere hydrogen-filled diffusion cloud chamber to ${\ensuremath{\pi}}^{\ensuremath{-}}$ beams from the Berkeley Bevatron. One hundred and thirtyseven interactions producing charged outgoing particles were observed. Of these, 27 were elastic scattering events, 64 were inelastic collisions having two charged outgoing prongs, 39 had four prongs, 3 had six prongs, and 4 involved the production and visible decay of heavy unstable particles. The total cross section is estimated to be 22.5\ifmmode\pm\else\textpm\fi{}2.4 mb. The elastic scattering cross section is 4.7\ifmmode\pm\else\textpm\fi{}1.0 mb. The angular distribution of the elastic events is consistent with that expected for diffraction scattering from a sphere with radius (0.9\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm and opacity 0.6. Analysis of the inelastic events shows that multiple, rather than single, pion production is the predominant process occurring at this energy. An average of 2.3 secondary pions were produced in the inelastic events. This average multiplicity can be fitted by the Fermi statistical theory only by increasing the interaction radius occurring in the theory by 20%. The statistical theory, however, fails to account for the rather marked asymmetry found in the c.m. angular distributions of some of the particles emitted in inelastic events. A combination of the four observed strange-particle production events with 11 similar events obtained in exposures to high-energy neutron and proton beams shows that pion emission accompanies strange-particle production in at least 60% of elementary-particle collisions at Bevatron energies.

A beam of ${K}_{2}$ mesons was produced by passing a beam of 1.1-Bev/c negative pions through a liquid hydrogen target and accepting the neutral reaction products in the forward direction after allowing the ${K}_{1}$ component to decay. The resultant beam was observed in a 30-in. propane bubble chamber fitted with lead and iron plates. About 200 regenerated ${K}_{1}$ mesons were identified by their characteristic $Q$ value and decay rate. All three types of regeneration were observed: by transmission in the plates, by nuclear diffraction, and by interaction with single nucleons. The detection of the first two types of regeneration constitutes strong evidence for the correctness of the Gell-Mann and Pais particle mixture theory. Comparison of the transmission and diffraction regeneration effect, using the method of M. L. Good, gives the ${K}_{1}\ensuremath{-}{K}_{2}$ mass difference $\ensuremath{\delta}$. Two important corrections must be applied to Good's formula: One originates from the nuclear scattering of the transmission component, the other from the multiplicity of scatterings in a thick plate. The independence from nuclear parameters, which was an advantageous property of Good's formula, is no longer rigorously valid; but due to the sharp dependence of the transmission intensity upon the mass difference, the nuclear properties of ${K}^{0}$ and ${\overline{K}}^{0}$, as derived from ${K}^{+}$ and ${K}^{\ensuremath{-}}$ data, still allow a measurement of $\ensuremath{\delta}$. We find that $\ensuremath{\delta}$ is ${0.84}_{\ensuremath{-}0.22}^{+0.29}$ in units of $\frac{\ensuremath{\hbar}}{{\ensuremath{\tau}}_{1}}$, where ${\ensuremath{\tau}}_{1}$ is the ${K}_{1}$ mean lifetime. With 90% confidence level, the difference is between 0.44 and $1.2 \frac{\ensuremath{\hbar}}{{\ensuremath{\tau}}_{1}}$. The probability that the transmission peak we observe is due to a statistical fluctuation is one in a million.

The first observed production of negative cascade particles at an accelerator is reported. A 30 in. propane bubble chamber was exposed to a beam of negative pions of 5.5 GeV/c. Two cascades were identified, indicating a production cross section of 2.3−1.6+3.1 µb. TheQ values found were (49.5±7.9) MeV and (53.6±11.3) MeV. The lifetimes were (1.9±0.1) · 10−10 s and (5.2±0.4) · 10−10 s. Both Θ’s were produced backwards in the center-of-momentum system. The identification process and background is discussed.

Author(s): Fowler, William B.; Birge, Robert W.; Eberhard, Phillippe; Ely, Robert; Good, Myron L.; Powell, Wilson M.; Ticho, Harold K.

Author(s): Kernan, Anne; Powell, Wilson M.; Sandier, Carl L.; Knight, William L.; Stannard, P. Russell.

An experiment to study the $\overline{p}$ annihilation process at 1.05 Bev/c was performed with the Lawrence Radiation Laboratory 30-in. propane bubble chamber. It was observed that the $K$-meson production in annihilation events rises sharply with the increase in energy, namely from 4\ifmmode\pm\else\textpm\fi{}1% for annihilations at or near "rest" to 8\ifmmode\pm\else\textpm\fi{}1%. On the other hand, the pion multiplicity was not observed to increase appreciably with the increase of available energy. We have found a pion multiplicity of 5.0\ifmmode\pm\else\textpm\fi{}0.2. These numbers are discussed in this paper and compared with existing models for the $\overline{p}$ annihilation process. It is pointed out that with further increase in bombarding energy different models may differ appreciably in the above quantities.We have observed a $\overline{p}$-H annihilation cross section of 51\ifmmode\pm\else\textpm\fi{}10 mb and a $\overline{p}$-C annihilation cross section of 368\ifmmode\pm\else\textpm\fi{}60 mb at a $\overline{p}$ momentum of 1.05 Bev/c. Crude determinations of the $\overline{p}$ charge-exchange process---which turns out to be forward peaked--- and of $\overline{p}$ inelastic-scattering events leading to pion production are also discussed.

Author(s): Goldhaber, Gerson; Fowler, William B.; Goldhaber, Sulamith; Hoang, T.F.; Kalogeropoulos, Theodore E.; Powell, Wilson M.

The interaction of 5-Bev negative pions with protons has been studied by exposing a 36-atmosphere hydrogen-filled diffusion cloud chamber to pi /sup -/ beams from the Berkeley Bevatron. One hundred and thirty-seven interactions producing charged outgoing particles were observed. Of these, 27 were elastic scattering events, 64 were inelastic collisions having two charged outgoing prongs, 39 had four prongs, 3 had six prongs, and 4 involved the production and visible decay of heavy unstable particles. The total cross section is estimated to be 22.5 plus or minus 2.4 mb. The elastic scattering cross section is 4.7 plus or minus 1.0 mb. The angular distribution of the elastic events is consistent with that expected for diffraction scattering from a sphere with radius (0.9 plus or minus 0.15) x 1O/sup -13/ cm and opacity 0.6. Analysis of the inelastic events shows that multiple, rather than single, pion production is the predominant process occurring at this energy. An average of 2.3 secondary pions were produced in the inelastic events. This average multiplicity can be fitted by the Fermi statistical theory only by increasing the interaction radius occurring in the theory by 20%. The statistical theory, however, fails to account for the rather markedmore » asymmetry found in the c.m. angular distributions of some of the particles emitted in inelastic events. A combination of the four observed strange-particle production events with 11 similar events obtained in exposures to highenergy neutron and proton beams shows that pion emission accompanies strange-particle production in at least 60% of elementary-particle collisions at Bevatron energies. (auth)« less