Determining the Mass of Supersymmetric Scalars at the CLIC Multi-TeV e+e- Collider

The determination of the smuon mass at the CLIC multi-TeV e+e- linear collider has been studied for two CMSSM benchmarks. Results are given for both the analysis of the muon energy spectrum and the threshold scan method. The effects of detector resolution, beam-beam interactions and accelerator- induced backgrounds are discussed. The energy spectrum technique is also applied to the \~t -> t ~g process to determine the scalar top mass, in scenarios with the gluino lighter than the squarks.Comment: 8 pages, 2 figures, To appear in the proceedings of International Workshop on Linear Colliders (LCWS 2002), Jeju Island, Korea, 26-30 Aug 200

The NOMAD Experiment : Status Report

The NOMAD experiment has been designed to search for neutrino-tau appearance in the CERN wide-band neutrino beam . The detector is now completed and has been further improved. All subdetectors are working well. The experiment, where the search for oscillation is based on kinematical criteria, will reach the sensitivity dm2 > 0.7 eV2 for maximal mixing and dm2 > 50 eV2 for mixing angles sin2 2\theta > 3.8E-4 after 2 years of running, making possible to explore a region of cosmological interest. Preliminary measurements are presented from the 1994 and 1995 data samples.Comment: 5 pages, An invited talk at the IV International Workshop on Theoretical and Phenomenological Aspects of Underground Physics TAUP'95, Toledo (Spain). September 17-21,1995. To appear in Nucl. Phys. B (Proc. Suppl.) Presented on behalf of the NOMAD Collaboration. Latex format (including figures), 6 eps figures (tar'ed and gzip'ed

Origins and renormalization of the superparticle spectrum

The importance of Yukawa contributions to the renormalization of the spectrum in non-minimal supersymmetric models is illustrated in the cases of explicit lepton number violation (leading to the possibility of singly produced sneutrinos at LEP energies), an intermediate scale singlet neutrino and negative mass squared parameters (possibly modifying fine-tuning considerations), and a grand-unified sector. The relevance of model-dependent renormalization to the supersymmetric flavor problem is emphasized. Sources of the flavor problem, some of which are newly identified, as well as possible solutions, are discussed and classified. It is then shown that gravitational interactions could lead (via a quadratically divergent singlet) to simple realizations of some of the low-energy frameworks that attempt to resolve the flavor problem.Comment: 11 pages. LaTex + espcrc2.sty (included). Talk presented at Supersymmetry 9

TeV Right-handed Neutrinos and the Flavor-symmetry-improved Seesaw Mechanism

Horizontal flavor symmetries can drastically suppress Dirac neutrino masses well below those of the corresponding charged leptons. We show that models can be constructed where the light neutrino mass eigenvalues are small enough to give the MSW solution to the solar neutrino problem, with a right-handed neutrino scale no larger than a TeV. We present a model of this type where the right-handed neutrino scale is generated by the spontaneous breakdown of gauged U(1)$_{B-L}$, in a radiative breaking scenario driven by the right-handed neutrino Yukawa couplings. The model allows for a solution to the $\mu$ problem, and predicts the existence of a $Z'$ boson within the reach of the LHC or the Tevatron.Comment: 16 pp. LaTe

Three Neutrino Flavors are Enough

It is shown that it is possible to account for all three experimental indications for neutrino oscillations with just three neutrino flavors. In particular, we suggest that the solar and atmospheric neutrino anomalies are to be explained by the same mass difference and mixing. Possible implications and future tests of the resulting mass-mixing pattern are given.Comment: 15 pages, LATEX format. 5 figures. Replaced 1 figure and corrected typographical error

Colour reconnection in e+e- -> W+W- at sqrt(s) = 189 - 209 GeV

The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies in the range sqrt(s) ~ 189-209 GeV using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles in hadronic decays of W+W-. Measurements of inclusive charged particle multiplicities, and of their angular distribution with respect to the four jet axes of the events, are used to test models of colour reconnection. The data are found to exclude extreme scenarios of the Sjostrand-Khoze Type I (SK-I) model and are compatible with other models, both with and without colour reconnection effects. In the context of the SK-I model, the best agreement with data is obtained for a reconnection probability of 37%. Assuming no colour reconnection, the charged particle multiplicity in hadronically decaying W bosons is measured to be (nqqch) = 19.38+-0.05(stat.)+-0.08 (syst.).Comment: 30 pages, 9 figures, Submitted to Euro. Phys. J.

Search for R-Parity Violating Decays of Scalar Fermions at LEP

A search for pair-produced scalar fermions under the assumption that R-parity is not conserved has been performed using data collected with the OPAL detector at LEP. The data samples analysed correspond to an integrated luminosity of about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An important consequence of R-parity violation is that the lightest supersymmetric particle is expected to be unstable. Searches of R-parity violating decays of charged sleptons, sneutrinos and squarks have been performed under the assumptions that the lightest supersymmetric particle decays promptly and that only one of the R-parity violating couplings is dominant for each of the decay modes considered. Such processes would yield final states consisting of leptons, jets, or both with or without missing energy. No significant single-like excess of events has been observed with respect to the Standard Model expectations. Limits on the production cross- section of scalar fermions in R-parity violating scenarios are obtained. Constraints on the supersymmetric particle masses are also presented in an R-parity violating framework analogous to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.

W+W- production and triple gauge boson couplings at LEP energies up to 183 GeV

A study of W-pair production in e+e- annihilations at Lep2 is presented, based on 877 W+W- candidates corresponding to an integrated luminosity of 57 pb-1 at sqrt(s) = 183 GeV. Assuming that the angular distributions of the W-pair production and decay, as well as their branching fractions, are described by the Standard Model, the W-pair production cross-section is measured to be 15.43 +- 0.61 (stat.) +- 0.26 (syst.) pb. Assuming lepton universality and combining with our results from lower centre-of-mass energies, the W branching fraction to hadrons is determined to be 67.9 +- 1.2 (stat.) +- 0.5 (syst.)%. The number of W-pair candidates and the angular distributions for each final state (qqlnu,qqqq,lnulnu) are used to determine the triple gauge boson couplings. After combining these values with our results from lower centre-of-mass energies we obtain D(kappa_g)=0.11+0.52-0.37, D(g^z_1)=0.01+0.13-0.12 and lambda=-0.10+0.13-0.12, where the errors include both statistical and systematic uncertainties and each coupling is determined setting the other two couplings to the Standard Model value. The fraction of W bosons produced with a longitudinal polarisation is measured to be 0.242+-0.091(stat.)+-0.023(syst.). All these measurements are consistent with the Standard Model expectations.Comment: 48 pages, LaTeX, including 13 eps or ps figures, submitted to European Physical Journal

A Measurement of Rb using a Double Tagging Method

The fraction of Z to bbbar events in hadronic Z decays has been measured by the OPAL experiment using the data collected at LEP between 1992 and 1995. The Z to bbbar decays were tagged using displaced secondary vertices, and high momentum electrons and muons. Systematic uncertainties were reduced by measuring the b-tagging efficiency using a double tagging technique. Efficiency correlations between opposite hemispheres of an event are small, and are well understood through comparisons between real and simulated data samples. A value of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is statistical and the second systematic. The uncertainty on Rc, the fraction of Z to ccbar events in hadronic Z decays, is not included in the errors. The dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the deviation of Rc from the value 0.172 predicted by the Standard Model. The result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the Standard Model.Comment: 42 pages, LaTeX, 14 eps figures included, submitted to European Physical Journal

Search for the Standard Model Higgs Boson with the OPAL Detector at LEP

This paper summarises the search for the Standard Model Higgs boson in e+e- collisions at centre-of-mass energies up to 209 GeV performed by the OPAL Collaboration at LEP. The consistency of the data with the background hypothesis and various Higgs boson mass hypotheses is examined. No indication of a signal is found in the data and a lower bound of 112.7GeV/C^2 is obtained on the mass of the Standard Model Higgs boson at the 95% CL.Comment: 51 pages, 21 figure