The Casimir energy in the rigid string with massive ends is investigated. This system models the flux tube of finite thickness that connects the massive quarks. The string stiffness and quark mass give additive contributions to the Casimir energy, the second contribution being the same as in the Nambu-Goto string with massive ends. The string stiffness results in an additional positive contribution to the Casimir energy, however it alone does not compensate the negative Casimir energy in the Nambu-Goto string. Only common consideration of the string thickness and the quark mass enables one to get the positive Casimir energy, i.e. to remove the tachyon from the string spectrum.
The low energy antiproton ring (LEAR) is operating at CERN since August 1983. The operation of the machine is reviewed, and a status report is given of the experiments measuring polarization parameters and spin-spin correlation parameters in the [MATH]p system.
The integrable cosmological model with $n (n>1)$ spaces of constant curvature is investigated in the case when only one of them is not Ricci flat. This spacetime is minimally coupled with a massless scalar field. Two types of quantum wormholes with a continuous and discrete spectrum are found. The analogous result takes place for pure gravity also when the scalar field is absent.
The JETSET (PS202) experiment at CERN-LEAR uses a compact detector around a hydrogen-cluster jet target to perform spectroscopy of hadronic states in the mass range from 1.96 to 2.43 GeV. Main emphasis is on the reaction ppBAR --> phi-phi, where each phi-meson decays into a K+K- pair. Following two short test runs of the recently installed experiment, data analysis has clearly revealed a surprisingly copious production of phi-phi-events. This paper gives a brief introduction to the physics motivation of the experiment and an overview of results from some previous experiments, followed by a description of the JETSET detector and of the analysis that led to a preliminary estimate of 0.2 to 2.0-mu-b for the ppBAR --> phi-phi cross-section at a center-of-mass energy of 2.25 GeV.
The Weinberg-Salam model with fermion mixing is used to calculate the amplitude for the nondiagonal process f(i)gamma --> f(j)gamma with arbitrary fermions (quarks or leptons), both up and down. The only assumptions used are m(i)2, m(j)2 much less than m(w)2. It is shown that the total contribution of the counterterms to the amplitude of the process is zero. The expression obtained for the amplitude agrees with existing results in special cases.
The problem of the unitary addition of the resonance and background contributions is considered for the P-33 wave of pi-N scattering using the Lippmann-Schwinger equation in the on-shell approximation.
Classical Yang-Mills fields with a nonstandard Lagrangian (DF)2 + F3 are considered. It is shown that these fields are stochastic, and to a greater extent than in the case of the standard Lagrangian.
Breakup of nuclei into fragments in the proton-nucleus interaction is studied. It is assumed that breakup occurs in two stages. During the first stage the incident particle interacts with individual nucleons of the nucleus, and high-energy reaction products are emitted from the nucleus. This stage is described by means of the intranuclear-cascade model. During the second stage some of the nuclei, whose excitation energy is high, or whose density is very inhomogeneous, break up. This breakup is described by means of a percolation model which takes into account the spatial distribution of nucleons in the nucleus and which generalizes the percolation description of the "liquid-gas" phase transition for finite nuclei. Features of this breakup mechanism are studied. The analysis of the experimental data indicates that it is not sufficient to consider percolation only in the coordinate space, and that the momentum distribution of the nucleons in the nucleus must be taken into account.
Reflections of ultracold neutrons (UCN) from beryllium powder have been measured for various layer thicknesses and various packing densities. On the basis of the experimental data, the reduced UCN loss coefficient for the UCN reflected from the thermally untreated beryllium, eta, is found to be eta = ( 1.75 +/- 0.35) X 10(-4). The previously obtained data on the reflection of UCN from beryllium powder annealed at high temperature are reconsidered. The value obtained for eta at room temperature is (6.4 +/- 2.5) X 10(-5), which exceeds the theoretical value by an order of magnitude. The analysis of the experimental data was carried out by using a modified diffusion theory in which the albedo reflection depends on the packing density.
Low temperature of the phase transition into the quark-gluon plasma correspond to low values of the bag model constant and to absolutely stable strange quark matter. Some of the observed pulsars are identified quite reliably as neutron stars. If strange matter is stable, the central density of these pulsars is to be smaller that critical density of the phase transition into the nonstrange quark matter. The nonstrange quark matter being formed turns to more stable strange matter on a weak interaction timescale converting neutron stars into strange stars. The requirement of stability of old and newly born neutron stars is used to constrain the bag model constant and the critical temperature of the phase transition into the quark-gluon plasma at zero chemical potential.
Measurements have been made of the momentum and angular distributions of LAMBDA-particles in central Mg + Mg collisions. The angular distributions of the LAMBDA-particles in the center-of-mass system of the colliding nucleons is not isotropic. The kinematic properties of the pi--mesons in events with cumulative LAMBDA-particles are the same as in ordinary central collisions. The angular distributions of the pi--mesons in the center-of-mass system are not isotropic. Events with two detected decays of LAMBDA-particles were investigated.
The results are given of measurements of the doubly differential cross sections for the Si-28 (alpha, alpha-gamma) Si-28 reaction at E(alpha) = 25.0 MeV for 13 scattering angles of the alpha-particles from 20 to 160-degrees. A model-independent method has been used to reconstruct all components of the spin tensor of the density matrix of the state 1. 78 MeV (2+) and an appreciable part of it for the state 4.62 MeV (4+ ) of the final nucleus. A measurement has also been made of the angular dependence of the differential cross section for scattering of alpha-particles with excitation of low states of the nucleus Si-28 (0+, g.s.; 2+, 1.78 MeV; 4+, 4.62 MeV; 0+, 4.96 MeV) in the same interval of angles. The experimental results are compared with calculations made under the assumption of the mechanism of collective excitation of the Si-28 nucleus and the mechanism of formation of a compound nucleus.
A 100-mu-A 30 GeV facility, names KAON, could soon be developed at TRIUMF using the present cyclotron as an injector. A wide variety of beams would be provided which would accommodate a diversified physics program. A "flavour" of the experimental program will be given together with an outlook of the facilities currently planned for the initial program.
The CPLEAR experiment at CERN reports the first observation of the K0-K0BAR time-dependent decay rate asymmetry in the pi+-pi- decay channel. The aim of the experiment, the behavior of the detector, and the first physics results are presented.
A sharp structure at 1150 MeV/c2 in the invariant mass of the pi+-pi--pi+-pi- system is seen in the final state of antiproton-He-4 annihilation at 0.6 GeV/c incident momentum and of antiproton-He-3 annihilation at rest. These observations are confirmed by data on antiproton-He-4 annihilation at rest obtained in the Obelix (PS201) experiment. (See Ref. 1.)
