Search for a scalar top quark using the OPAL detector
A search for a supersymmetric partner of the top quark (t 1 ) has been performed by the OPAL experiment in e + e - collisions at LEP. The integrated luminosity of the data sample analysed was 69.1 pb −1 , which corresponds to 1.68 × 10 6 produced Z 0 → qq events. No t 1 candidates have been found. This study excludes the existence of the t 1 with a mass below 45.1 GeV at 95% C.L., where the mixing angle of left- and right-handed partners is smaller than 0.85 rad or greater than 1.15 rad, and the mass difference between the t 1 and the lightest neutralino is greater than 5 GeV.

title: A measurement of strange baryon production in hadronic Z0 decays
abstract: The production of the octet and decuplet baryons Λ, Ξ − , Σ (1385) ± , Ξ(1530) 0 and Ω − and the corresponding antibaryons has been measured in a sample of 485 000 hadronic Z 0 decays. Results on differential and integrated cross sections are presented. The differential cross section of Λ baryons is found to be softer than the one predicted by the Jetset and Herwig Monte Carlo generators. The measured decuplet yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is used. Comparisons of the momentum spectra for Λ and Ξ − with the predictions of an analytical QCD formula are also presented.

title: A SILICON TRACKER FOR TRACK EXTRAPOLATION INTO NUCLEAR EMULSIONS
abstract: This paper describes the construction of a silicon tracker built to investigate how well silicon detectors can predict the position of particles in nuclear emulsions over a large area. The tracker consists of 72 single-sided silicon microstrip detectors with a total surface of 0.13 m2 distributed over four layers, providing two x and two y coordinate measurements. The set-up was installed in a CERN PS pion beam in September 1997. ( 1999 Elsevier Science B.V. All rights reserved.

title: Measurement of the $B^0$ - $\bar{B}^0$ mixing, Gamma (Z0 $\to b \bar{b}$) / Gamma (Z0 $\to$ hadrons) and semileptonic branching ratios for $b$ flavored hadrons in hadronic z0 decays
abstract: From a sample of about 450 000 hadronicZ 0 decays, measurements of the average\(B^0 - \bar B^0 \) mixing parameter, χ, the branching fraction ofZ 0 bosons into hadrons containing bottom quarks,\({{\Gamma (Z^0 \to b\bar b)} \mathord{\left/ {\vphantom {{\Gamma (Z^0 \to b\bar b)} {\Gamma (Z^0 \to hadrons)}}} \right. \kern-\nulldelimiterspace} {\Gamma (Z^0 \to hadrons)}}\), the average semileptonic branching ratios for such hadrons,B(b→l) andB(b→c→l), and the mean scaled energy of these hadrons, 〈xE〉, are presented. The measurements were obtained using a simultaneous fit to single-lepton and dilepton events collected with the OPAL detector at LEP, including both electrons and muons. The results are 
 
where the errors are statistical and systematic, respectively, in each case. The result forB)b→c→l) excludes decays of the typeb→→l.

title: The OPAL silicon strip microvertex detector with two coordinate readout
abstract: The OPAL experiment at the CERN LEP collider recently upgraded its silicon strip microvertex detector from one coordinate readout (φ only) to two coordinate readout (φ and z). This allows three dimensional vertex reconstruction and should improve lifetime measurements as well as b quark jet identification. This paper describes the new microvertex detector system with emphasis on the novel techniques and new components used to obtain the second coordinate information. These include the use of back-to-back single-sided detectors with orthogonally oriented readout strips, a gold printed circuit on a thin glass substrate to route the z strip signals to the electronics at the end of the detector, and the use of MX7 readout chips. Results on the performance of the new detector are presented.

title: Search for massive, unstable photinos that violate R parity
abstract: A search for unstable, massive photinos pair produced in e + e − collisions has been performed using the OPAL detector at LEP. The data sample corresponds to an integrated luminosity of 21 pb −1 collected at center-of-mass energies near the Z 0 resonance. The unstable photino is assumed to decay into τ ± / gn l ( l = e or μ ) final states, thereby violating individual lepton numbers and R parity. This search is inspired by a particular model of supersymmetry which is of interest within the context of solar neutrino experiments because it allows for a large neutrino magnetic moment. The present search excludes a large portion of the parameter space allowed by the model.

title: Finiteness of the noncommutative supersymmetric Maxwell-Chern-Simons theory
abstract: Within the superfield approach, we prove the absence of UV/IR mixing in the three-dimensional noncommutative supersymmetric Maxwell-Chern-Simons theory at any loop order and demonstrate its finiteness in one, three, and higher loop orders.

title: He–McKellar–Wilkens effect and scalar Aharonov–Bohm effect for a neutral particle based on the Lorentz symmetry violation
abstract: In this contribution, we discuss the He–McKellar–Wilkens effect and the scalar Aharonov–Bohm effect for neutral particles based on the Lorentz symmetry violation background, by showing that the background of the Lorentz symmetry violation yields Abelian quantum phases for a neutral particle. We also study the non-relativistic bound states for a neutral particle interacting with a Coulomb-like potential based on the Lorentz symmetry violation background given by a fixed vector field parallel to the radial direction.

title: The effect of singular potentials on the harmonic oscillator
abstract: We address the problem of a quantum particle moving under interactions presenting singularities. The self-adjoint extension approach is used to guarantee that the Hamiltonian is self-adjoint and to fix the choice of boundary conditions. We specifically look at the harmonic oscillator added of either a δ -function potential or a Coulomb potential (which is singular at the origin). The results are applied to Landau levels in the presence of a topological defect, the Calogero model and to the quantum motion on the noncommutative plane.

title: Effects of quantum deformation on the spin-1/2 Aharonov–Bohm problem
abstract: In this Letter we study the Aharonov–Bohm problem for a spin-1/2 particle in the quantum deformed framework generated by the κ -Poincare–Hopf algebra. We consider the nonrelativistic limit of the κ -deformed Dirac equation and use the spin-dependent term to impose an upper bound on the magnitude of the deformation parameter e . By using the self-adjoint extension approach, we examine the scattering and bound state scenarios. After obtaining the scattering phase shift and the S -matrix, the bound states energies are obtained by analyzing the pole structure of the latter. Using a recently developed general regularization prescription 2012) 041701(R)], the self-adjoint extension parameter is determined in terms of the physics of the problem. For last, we analyze the problem of helicity conservation.

title: Symmetry approach and the generalized Korteweg-de Vries equation with variable coefficients