3 H̃e nuclei were observed in the negative beam, produced by 70 GeV protons on an Al target. Five 3 H̃e have been identified among 2.4 · 10 11 particles that passed through the apparatus. Scintillation and Čerenkov counters were used to measure the electrical charge and velocity of particles. The mass of 3 H̃e is found to be M 3 H ̃ e = (1.00 ± 0.03)3m p , the charge is z = (0.99 ± 0.03)2 e . The ratio of differential production cross sections of 3 H ̃ e (P = 20 GeV /c) and π − (P = 10 GeV/c ) equals 2 · 10 −11 . This corresponds to antihelium −3 production cross section d 2 σ 3 H ̃ e / d Ω d P = 2.0 · 10 −35 cm 2 / sr · GeV /c per Al nuclei and 2.2 · 10 −36 cm 2 sr · GeV/ c per nucleon.
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The results of the experiment searching for quarks with charge − 1 3 and 2 3 produced by 70 GeV protons on an aluminium target at zero angle are reported. For the selection of quarks the system of spectrometric scintillation counters, time-of-flight spectrometer, gas Cerenkov threshold counter and magnetic spectrometer with spark chambers were used. In the range of masses available at the IHEP accelerator, quarks were not found. The upper limit estimation of the differential cross-section for quark production with mass ⩽ 5 GeV /c 2− and charge −1 3 is 7×10 −38 cm 2 / ster GeV /c (with 90% confidence level). The total cross-section for quark production with charge −1 3 and mass 4.5–5 GeV /c 2 does not exceed 3×10 −39 cm 2 .
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Measured value of the pion form factor
Fitted peak cross section.
Hydrogen and deuterium gases have been bombarded in a gas target at a temperature of 77°K and at a pressure of about 140 atmospheres by the 318±10 Mev "spread-out" bremsstrahlung photon beam of the Berkeley electron synchrotron. The charged π-mesons which were produced were collimated at angles of 45°, 90°, and 135° to the beam direction. The π+ mesons were detected with trans-stilbene scintillation crystals using πμ, πβ, and πμβ delayed coincidences and π+ and π− mesons were detected with Ilford C-2 200-micron nuclear emulsions. The ratios of the numbers of π− to π+ mesons produced in deuterium were 0.96±0.10, 1.09±0.12, and 1.21±0.17 for the angles of 45°, 90°, and 135°, respectively. No variation of the ratio with meson energy, outside statistics, was observed. Absolute values for the π+ meson energy distribution functions from hydrogen and deuterium per "equivalent quantum" have been measured at each of the above production angles. The differential and total cross sections have been obtained by integrating over energy and angle, respectively. The experimental ratios of the deuterium to hydrogen cross sections are in good agreement with the phenomenological theory of Chew and Lewis when the Hulthén deuteron function with β=6α is used in the initial state, plane waves are used for the nucleons in the final state, and the bremsstrahlung cutoff is taken into account. The statistics of the data are, however, not sufficient to determine the amount of spin interaction. The excitation functions for hydrogen and deuterium and points on the angular distribution curves in the center-of-mass system have been obtained. An upper limit of 0.08 of the charged π-meson cross section was obtained for μ-meson production from deuterium.
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