Search for the minimal standard model Higgs boson
A search for the Minimal Standard Model Higgs boson (H0) has been performed with data from e+e− collisions collected by the OPAL detector at LEP. The search was made for events of the types e+e−→(e+e−,μ+μ− or νν)H0, H0→qq and was based on approximately 78 pb−1 of data taken at center-of-mass energies between 88 and 95 GeV in the years 1990–1993. The present study, combined with previous OPAL publications, excludes the existence of a Minimal Standard Model Higgs boson with mass below 56.9 GeV at the 95% confidence level.

title: Measurement of the multiplicity of charm quark pairs from gluons in hadronic Z0 Decays
abstract: We have measured the multiplicity of charm quark pairs arising from gluon splitting in a sample of about 3.5 million hadronic Z0 decays. By selecting a 3-jet event topology and tagging charmed hadrons in the lowest energy jet using leptons, we established a signature of heavy quark pair production from gluons. The average number of gluons splitting into a c c pair per hadronic event was measured to be n g→c c =(2.27±0.28±0.41) × 10 −2 .

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: A model independent measurement of quark and gluon jet properties and differences
abstract: AbstractThree jet events are selected from hadronic Z0 decays with a symmetry such that the two lower energy jets are produced with the same energy and in the same jet environment. In some of the events, a displaced secondary vertex is reconstructed in one of the two lower energy jets, which permits the other lower energy jet to be identified as a gluon jet, with an estimated purity of about 93%. Comparing these gluon jets to the inclusive sample of lower energy jets from the symmetric data set yields direct, model independent measurements of quark and gluon jet properties, which have essentially no bias except from the jet definition. Results are reported using both thek⊥ and cone jet definitions. For thek⊥ algorithm, we find
$$\frac{{\left\langle {n_{k_ \bot }^{ch.} } \right\rangle gluon}}{{\left\langle {n_{k_ \bot }^{ch.} } \right\rangle quark}} = 1.25 \pm 0.02(stat.) \pm 0.03(syst.)$$
 for the ratio of the mean charged particle multiplicity of gluon to quark jets, while for the cone algorithm, we find
$$\frac{{\left\langle {n_{cone}^{ch.} } \right\rangle gluon}}{{\left\langle {n_{cone}^{ch.} } \right\rangle quark}} = 1.10 \pm 0.02(stat.) \pm 0.02(syst.)$$
 using a cone size of 30°. We also report measurements of the angular distributions of particle energy and multiplicity around the jet directions, and of the fragmentation functions of the jets. Gluon jets are found to be substantially broader and to have a markedly softer fragmentation function than quark jets, in agreement with our earlier observations.

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: Relativistic Anandan quantum phase in the Lorentz violation background
abstract: We study the influence of a classical background based on the violation of the Lorentz symmetry on the relativistic Anandan quantum phase. We show that the choice of the Lorentz symmetry violation background provides an abelian contribution for the relativistic Anandan quantum phase.

title: Remarks on the Aharonov-Casher dynamics in a CPT-odd Lorentz-violating background
abstract: The Aharonov-Casher problem in the presence of a Lorentz-violating background nonminimally coupled to a spinor and a gauge field is examined. Using an approach based on the self-adjoint extension method, an expression for the bound-state energies is obtained in terms of the physics of the problem by determining the self-adjoint extension parameter.

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

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: 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.