Topological search for the production of neutralinos and scalar particles
A search for scalar particles and neutralinos such as those predicted by supersymmetric models has been performed using a data sample of 4.4 million hadronic Z 0 decays recorded by the OPAL detector at the e + e − collider LEP. The production of such particles typically leads to event topologies consisting of an acoplanar pair of jets, or of a mono-jet, accompanied by sizeable missing energy owing to neutrinos and other undetectable neutral particles. Limits are obtained, at the 95% confidence level, on the masses and production rates of scalar particles produced in association with the Z 0 . Limits are also placed on neutralino production, for which an additional possible signature is also studied, events containing a single observed photon. Within the Minimal Supersymmetric Standard Model, the mass of the lightest neutralino is found to be larger than 12.5 GeV/ c 2 at 95% C.L., provided that tan β is larger than 1.5.

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: 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: 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: 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: 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 bound states for the Aharonov-Casher systems

title: Aharonov-Bohm-Casher Problem with a nonminimal Lorentz-violating coupling
abstract: The Aharonov-Bohm-Casher problem is examined for a charged particle describing a circular path in presence of a Lorentz-violating background nonminimally coupled to a spinor and a gauge field. It were evaluated the particle eigenenergies, showing that the LV background is able to lift the original degenerescence in the absence of magnetic field and even for a neutral particle. The Aharonov-Casher phase is used to impose an upper bound on the background magnitude. A similar analysis is accomplished in a space endowed with a topological defect, revealing that both the disclination parameter and the LV background are able to modify the particle eigenenergies. We also analyze the particular case where the particle interacts harmonically with the topological defect and the LV background, with similar results.

title: On Aharonov–Casher scattering in a CPT-odd Lorentz-violating background
abstract: The effects of a Lorentz symmetry-violating background vector on Aharonov?Casher scattering in the nonrelativistic limit are considered. Using the self-adjoint extension method, we find that there is additional scattering for any value of the self-adjoint extension parameter and non-zero energy bound states for negative values of this parameter. Expressions for the energy bound states, phase-shift and scattering matrix are explicitly determined in terms of the self-adjoint extension parameter. The expression obtained for the scattering amplitude reveals that the helicity is not conserved in this scenario.

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.