Search for rare hadronic B decays
A search for rare decays of B hadrons has been performed using approximately two million hadronic Z 0 decays collected by the OPAL experiment between 1990 and 1993. The exclusive decay channels B d 0 → π + π − , B d 0 → K + π − , B s 0 → π + K − and B s 0 → K + K − have been studied. Such decays include contributions from flavour changing neutral current processes such as hadronic penguin decays. No significant excess of events has been observed in the π + π − , π + K − and K + K − invariant mass distributions. Consequently, upper limits on the B d 0 branching ratios, Br(B d 0 → π + π − ) −5 and Br(B d 0 →K + π − ) −5 , and on the B s 0 branching ratios, Br(B s 0 → π + K − ) −4 and Br(B s 0 →K + K − ) −4 , have been set at the 90% confidence level. These limits assume that the ratio of the partial decay widths of the Z 0 , λ (Z 0 → bb)/λ(Z 0 → hadrons), is 0.217 and that the fractions of B d 0 and B s 0 mesons produced during fragmentation are 39.5% and 12% respectively. The B s 0 branching ratio limits are the first such limits obtained.

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: 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: 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: 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: 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: On the spin- 1/2 Aharonov-Bohm problem in conical space: Bound states, scattering and helicity nonconservation
abstract: In this work the bound state and scattering problems for a spin-1/2 particle undergone to an Aharonov-Bohm potential in a conical space in the nonrelativistic limit are consider ed. The presence of a �-function singularity, which comes from the Zeeman spin interaction with the magnetic flux tube, is addressed by the self-adjoint extension method. One of the advantages of the present approach is the determination of the self-adjoint extension parameter in terms of physics of the problem. Expressions for the energy bound states, phase-shift and S matrix are determined in terms of the self-adjoint extension parameter, which is explicitly determined in terms of the parameters of the problem. The relation between the bound state and zero modes and the failure of helicity conservation in the scattering problem and its relation with the gyromagnetic ratio g are discussed. Also, as an application, we consider the spin-1/2 AharonovBohm problem in conical space plus a two-dimensional isotropic harmonic oscillator.

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: On the noncommutative fields method in the three-dimensional Yang-Mills theory
abstract: We apply the noncommutative fields method to the three-dimensional non-Abelian gauge theory. We find that, first, implementing the noncommutativity between the canonical momenta implies in generation of the non-Abelian Chern-Simons term, second, if one introduces the noncommutativity between the field operators, the higher derivative terms would arise.

title: On the superfield effective potential in three dimensions
abstract: We develop the superfield approach to the effective potential in three dimensions and calculate the one-loop and two-loop Kahlerian effective potential in commutative and noncommutative cases.

title: Physical regularization for the spin-1/2 Aharonov-Bohm problem in conical space
abstract: We examine the bound state and scattering problem of a spin-one-half particle undergone to an Aharonov-Bohm potential in a conical space in the nonrelativistic limit. The crucial problem of the \delta-function singularity coming from the Zeeman spin interaction with the magnetic flux tube is solved through the self-adjoint extension method. Using two different approaches already known in the literature, both based on the self-adjoint extension method, we obtain the self-adjoint extension parameter to the bound state and scattering scenarios in terms of the physics of the problem. It is shown that such a parameter is the same for both situations. The method is general and is suitable for any quantum system with a singular Hamiltonian that has bound and scattering states.