[en] We investigated a gas jet issued from a rectangular slit nozzle. Such jets can be made to dynamically converge by interacting with the residual, lower density, gas inside the accelerator vacuum vessel. Densities of up to few times 10¹⁵ atoms cm^-2 were achieved. We describe the experimental facility, the diagnostics used and present the result of our data analysis. (orig.)

[en] To measure the spin structure of the nucleon, the HERMES experiment is planned at the HERA electron beam using a polarised internal gas target. A tracker is being built to reconstruct the vertex of the exciting particles. It consists of two drift chambers and two microstrip gas counter (MSGC) systems. The MSGC systems are housed into two gas gatight containers surrounding the beam pipe and located immediately after the exit flange of the target housing. The active area of the upper MSGC system covers an angular range of 40 mrad≤θ_v≤ 140 mrad by -170 mrad≤θ_h≤170 mrad. Below the beam pipe a second system is situated with the same acceptance. Each track within the acceptance is measured by two stations of three MSCGs having a strip orientation, of 0 , and +30 and -30 respectively with respect to the vertical axis. (HSI)

[en] A tracker consisting of 16 MSGCs has been installed in the high intensity muon beam of the SMC experiment at CERN. Each MSGC has an active surface of 10 x 10 cm², covered by 496 anode strips. As a front-end amplifier the APC 64 is used. Results are presented about the efficiency, both at a high rate and at a low rate, and the position resolution. Using the data of the MSGC tracker the definition of the beam tracks in SMC significantly improved. (orig.)

[en] A tracker consisting of 16 MSGCs has been installed in the high intensity muon beam of the SMC experiment at CERN. Each MSGC has an active surface of 10x10cm², covered by 496 anode strips. As a front-end amplifier the APC 64 is used.Results are presented about the efficiency, both at a high rate and at a low rate, and the position resolution. Using the data of the MSGC tracker the definition of the beam tracks in SMC significantly improved. (orig.)

[en] The set of modular invariants that can be obtained from Galois transformations is investigated systematically for WZW models. It is shown that a large subset of Galois modular invariants coincides with simple current invariants. For algebras of type B and D infinite series of previously unknown exceptional automorphism invariants are found. ((orig.))

[en] We present the analytical α_s³ correction to the Z⁰ decay rate into hadrons. We calculate this correction up to (and including) terms of the order (m_Z²/m_top²)³ in the large top quark mass expansion. We rely on the technique of the large mass expansion of individual Feynman diagrams and treat its application in detail. We convert the obtained results of six-flavour QCD to the results in the effective theory with five active flavours, checking the decoupling relation of the QCD coupling constant. We also derive the large charm quark mass expansion of the semihadronic τ lepton decay rate in the α_s³ approximation. ((orig.))

[en] The New Muon Collaboration has measured deep inelastic muon scattering simultaneously on hydrogen and deuterium at incident muon energies of 90 and 280 GeV. The data cover a wide kinematic range 0.008< x<0.7 and 0.8< Q²<50 GeV². Preliminary results are presented on the nucleon structure functions F₂^p and F₂^d. In the region of kinematic overlap the data are in good agreement with previous results from SLAC and BCDMS (x>0.07) but disagree with those obtained from a recent analysis of the NMC data. Good agreement is found between theory and data. The flavour non-singlet and singlet quark distributions as well as the gluon distribution are extracted with good precision down to low values of x (0.008). These results are compared to low-x extrapolations based on recent parton distribution fits. Also given is a preliminary result on the strong coupling constant α_S. 16 refs.; 7 figs

[en] The recently introduced Galois symmetries of rational conformal field theory are generalized, for the case of WZW theories, to 'quasi-Galois symmetries'. These symmetries can be used to derive a large number of equalities and sum rules for entries of the modular matrix S, including some that previously had been observed empirically. In additions, quasi-Galois symmetries allow us to construct modular invariants and to relate S-matrices as well as modular invariants at different levels. The also lead us to a convenient closed expression for the branching rules of the conformal embeddings g→ so(dim anti g). (orig.)

[en] We examine a recently made claim that an unphysical coupling associated with the longitudinal component of the gauge field appears in the Dirac quantization condition thus rendering QED inconsistent in the presence of Dirac monopoles. We point out that a conventional quantization condition can still be obtained. (orig.)

[en] We show that Galois theory of cyclotomic number fields provides a powerful tool to construct systematically integer-valued matrices commuting with the modular matrix S, as well as automorphisms of the fusion rules. Both of these prescriptions allow the construction of modular invariants and offer new insight in the structure of known exceptional invariants. (orig.)