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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.)

A Wilson cloud chamber 22 inches in diameter in a magnet producing a magnetic field of 21,700 gauss at the center of the chamber is described. The magnet is pulsed in synchronism with the 184‐inch Berkeley cyclotron and can be operated with a steady field of 10,000 gauss. The use of the instrument for identifying light atoms is discussed briefly.

A diffusion cloud chamber 8 ft long, 4 ft wide, and 5 in. deep has been built and operated successfully for 540 hrs out of a continuous 720‐hr run. Though the actual area is 32 sq ft, the area photographed was 21 sq ft or approximately 2 sq m. A sensitive layer of good quality extending 2½ to 3 in. above the floor was easily maintained. The coolant temperature was held near −67°C and the air above the glass sheet forming the top was held at 30°C. A clearing field of 30 v (top negative) was found desirable to keep the chamber free from general rain. The chamber contained an air and methyl‐alcohol mixture operated at 1 atmos pressure. Tracks in the sensitive region were photographed through the top with the aid of several mirrors. The chamber was used to study the structure of the cores of cosmic‐ray air showers. It is now being used for studies with the bevatron.

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 propane bubble chamber with a sensitive volume of 30½ in. by 21½ in. by 6½ in. deep operating in a magnetic field of 14 000 gauss is described. Operating parameters and some engineering details are given. The part of the chamber containing the propane is hydrostatically supported in oil through which the chamber is photographed. This permits the use of small glass windows with a large safety factor.

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.

About 500 antiprotons in a partially purified antiproton beam have been observed to enter the 30-in. propane bubble chamber. An arrangement of counters identified the antiproton events, thus reducing scanning to a minimum and also providing a sample of antiprotons free of scanning bias. The antiprotons entered the propane at a kinetic energy of 220 Mev and were brought to rest. Scattering and annihilation interactions in both hydrogen and carbon have been observed as a function of antiproton energy. Differential scattering cross sections have been obtained, and the following total cross sections have been measured for antiproton kinetic energies, $T$, in the ranges 75 to 137.5 Mev and 137.5 to 200 Mev: The above results show satisfactory agreement with the Ball-Chew theory where comparison can be made.

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.

An experimental measurement of the angular distribution of protons scattered by neutrons in the neutron beam of the 184-inch Berkeley cyclotron has been made with a Wilson cloud chamber with magnetic field. The results show that the scattering is not isotropic in the center of mass system and that it is not symmetric about 90 degrees. The peak of protons in the forward direction indicates that a certain amount of charge exchange is taking place between the neutron and proton.

Bright‐field illumination using a beaded reflective screen is accomplished in the 30‐in. heavy liquid bubble chamber by using separate light sources for each lens. The resolution obtainable is about four times as great as with dark‐field illumination.

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

The measurements yielded information on the antiproton-carbon scattering cross section for scattering; angles of 5 deg (lab) or more. A total of 70 antiprotoncarbon scattering events were seen in a total antiproton path length of 179 meters of liquid propane (density = 0.42 g/cm/sup 3/). The high ratio of the total antiproton cross section observed at higher energies on several elements also extends to the lower energies considered. (M.H.R.)

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

A study has been made of eighty-two stars produced in a mixture of oxygen and helium when a cloud chamber filled with these gases and placed in a magnetic field of 13,000 gauss was bombarded by 90-Mev neutrons. Stars having up to five prongs were observed.Of the forty-eight 2-prong stars, 14 could be reasonably assigned to oxygen and 14 to helium. The remaining 20 were unidentified. It was found possible to make plausible identifications of all the fragments from only 7 helium stars and one 5-prong oxygen star. The general identification procedure is discussed and the arguments for the one 5-prong oxygen star are presented in some detail. Histograms of the ${H}_{\ensuremath{\rho}}$- and scatter-angle distributions of the star fragments are given.

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): Ely, Robert P.; Gidal, George; Kalmus, George E.; Powell, Wilson M.; Singleton, William J.; Henderson, Cyril; Miller, David J.; Stannard, R. Russell.

Observation of antiprotons in a propane or hydrogen bubble chamber offers the possiblity of studying several phenomena for which counter or photographic emulsion techniques are less suitable. Because there is a high ratio of pions, muons, and electrons to antiprotons in the available momentum-analyzed beams, these beams cannot be used in the bubble chamber without an initial purification, which increases the ratio of antiprotons to other particles. Such a purification has been achieved by utilizing the difference in rates of momentum loss in absorbers between antiprotons and other particles. The principle of the method is to pass a momentum-analyzed beam through an absorber. Since particles of unequal mass do not have the same specific ionization they lose different amounts of momentum, and a further magnetic deflection suffices to separate the particles physically according to mass. In this experiment a desirable momentum for antiprotons entering the bubble chamber was 684 Mev/c; however, at this momentum the ratio of undesirable particles to antiprotons at the target where they are produced is about 6 x 10{sup 5}. By starting with 970-Mev/c particles at the target and using the method of differential absorption, they decreased the ratio of undesirable particles (87% {mu}{sup -}, 105more » {pi}{sup -}, 3% e{sup -}) to antiprotons entering the bubble chamber at 684 Mev/c to 1.5 x 10{sup 4}. A system of counters indicatd when an antiproton entered the bubble chamber, and although the chamber was expanded on every Bevatron pulse, the lights were flashed and the chamber photographed only when an antiproton entered.« less

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

Several experiments have indicated a possible forward-backward asymmetry in the decay of /sub 2/ at 1880 /sup o/ hyperon. A recent exposure of the UCRL 30-inch propane bubble chamber to a 1.15-Bev/c separated K/sup -/ beam offers the opportunity to explore the question further. Several thousand K/sup -/ interactions were photographed. The initial resuits from a sample of 141 V/sup o/ decays are reported. (W.D.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

Observation of antiproton--proton collisions in a propane bubble chamber at an average energy of 120 Mev has been accomplished. The ratio of antiprotons to other particles in the beam has been increased by utilizing the differential rate of momentum loss in absorbers between antiprotons and other particles. The angular distribution of 33 p-p scattering events between 15 and 165 deg c.m. is presented. (W.D.M.)

A 36‐atmosphere diffusion cloud chamber has been constructed for use with the 184‐inch cyclotron and with the bevatron. Minimum‐ionizing particles leave dense, sharp tracks of good contrast with hydrogen filling at design pressure. In the operation described, one event is obtained every 15 minutes for a reaction cross section of 30 mb for negative pions on hydrogen. Among the unique features of the chamber are (a) the high pressure; (b) the high magnetic field; (c) the simple unit preassembly of the chamber and the upper pole piece; (d) the distortion‐free photography afforded by the small camera windows of good optical quality directly in front of the camera lenses and the absence of a large top glass near the sensitive region; (e) the thin window for collimated beams; (f) the supported cast Astrolite windows for illumination; and (g) the satisfactory sensitive layer obtained despite the large height‐diameter ratio of the pressure vessel.