Diffractive dissociation reaction np → Λ0K0p for incident neutron momenta between 30 and 70 GeV/c BIS-2 collaboration

We present results of the exclusive diffractive reaction np ⁰K⁰p at 0·08 < |t|< 0·53 GeV²/c² and momenta between 30–70 GeV/c at the Serpukhov neutron beam. Thet-dependence is exp (Bt) withB= 11·4± 2·3 (GeV/c)^–2 and it exhibits the diffractive minimum at ¦t¦ 0·28 GeV²/c² for ⁰K⁰ massesM < 1·8 GeV/c².B decreases with increasingM. Correlation with the beam direction is observed in the rest frame of the ⁰K⁰ system: the cross section rises for the forward-going ⁰. The rise is more pronounced for higherM. The cross section of reaction np ⁰K⁰p for 0<|t|< 0·53 GeV²/c² is 10·3 ± 2·5 ± 2·8 b.     

Measurement of np elastic scattering at high energies and very small momentum transfers

The np elastic differential cross section has been measured for incident neutron momenta 100–400 GeV/c in the |t| range 6 · 10^?6 ? 5 · 10^?1 (GeV/c)². The np data of this experiment provide a first direct measurement of the hadronic amplitude for |t| < 10^?2 (GeV/c)², which is consistent with the extrapolations from higher |t| values. Our data for |t| < 10^?4 (GeV/c)² are consistent with a rise which can be attributed to Schwinger scattering, caused by the interaction of the neutron magnetic moment with the proton.     

Associated production of φ-mesons and strange particles and double φ-meson production BIS-2 collaboration

Associated production of-mesons and strange particles by neutrons at energies of 30–70 GeV has been analysed. It has been found that at least 67% of inclusive-meson production in the kinematic regionx _F>0.1 andp _T<1 GeV/c proceeds via OZI-allowed processes with extra strange particles. Double-meson production has also been observed and its cross section in the full kinematic region is estimated to be 15 ± 9b.The authors are grateful to A. M. Baldin, E. I. Maltsev, I. A. Savin for supporting these investigations; H. Bottcher, Ch. Spiering and L. V. Schreiber for useful discussions; E. M. Likhacheva, L. V. Silvestrov, V. E. Simonov, G. G. Takhtamyshev, N. V. Vlasov for their participation in the experiment.     

Positron annihilation in alkali-halide crystals after electron irradiation

The effect of electron beam irradiation on the positron annihilation in KCl, KBr, NaCl single crystals was investigated. The narrowing of the angular correlation curves increases up to the saturation value with the absorbed radiation dose. The shape of the received narrow components differs from the narrow component measured in the additively colored samples. This phenomenon shows the considerable influence of the hole centres upon the positron annihilation in ionic crystals. Paper presented at 3rd Internat. Conf. Positron Annihilation, Otaniemi, Finland (August 1973).     

Positron annihilation in Si and GaAs crystals with an applied magnetic field

The narrow components in angular correlation curves of positron annihilation in Si and GaAs were observed. Hence it follows the formation of positronium-like states in semiconductors. Effects of mechanical and radiation treatment of the samples of Ps-states are discussed.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Parametric amplification of laser-driven electron acceleration in underdense plasma

A new mechanism is reported that increases electron energy gain from a laser beam of ultrarelativistic intensity in underdense plasma. The increase occurs when the laser produces an ion channel that confines accelerated electrons. The frequency of electron oscillations across the channel is strongly modulated by the laser beam, which causes parametric amplification of the oscillations and enhances the electron energy gain. This mechanism has a threshold determined by a product of beam intensity and ion density.     

Positron as a probe of cation vacancies in X-irradiated NaBr crystals

The temperature dependence of the ionic conductivity shows an increase of the free-cation vacancies concentration in X-irradiated NaBr single crystal. The 2γ angular correlation measurements confirm that positron bound state are formed preferably near the cation vacancies.     

On determination of effective mass of the delocalized positronium in NaCl crystals

The angular correlation of the photons of two-quantum annihilation in NaCl crystal was measured at temperatures ranging from 77 to 500 K. The data obtained clearly showed a narrow peak which was earlier observed only at low temperatures. The positronium nature of this peak was examined by applying a magnetic field. The positronium effective mass was found to be (1.5±0.2)2 m₀.     

A-dependence of inclusive Φ-meson production in neutron-nucleus interactions at 30–70 GeV

The production of -mesons on nuclear targets (carbon, aluminium and copper) by high-energy neutrons has been analysed. The dependence of the -production cross section ratios on the nuclear mass numberA was parametrized by the power lawA with=0.81±0.06. Within the sensitive kinematic rangex _F>0 andp _T<1 GeV/c we have not observed any dependence of the exponent on the longitudinal or transverse momentum. A possible interpretation of the measuredA-dependence is discussed in the Appendix.The authors are grateful to A. M. Baldin, E. I. Maltsev and I. A. Savin for supporting these investigations; E. M. Likhacheva, L. V. Silvestrov, V. E. Simonov, G. G. Takhtamyshev and N. V. Vlasov for their participation in the experiment.