Confidence Level Computation for Combining Searches with Small Statistics

This article describes an efficient procedure for computing approximate confidence levels for searches for new particles where the expected signal and background levels are small enough to require the use of Poisson statistics. The results of many independent searches for the same particle may be combined easily, regardless of the discriminating variables which may be measured for the candidate events. The effects of systematic uncertainty in the signal and background models are incorporated in the confidence levels. The procedure described allows efficient computation of expected confidence levels.Comment: 17 pages, 2 figures, LaTeX, program available at http://home.cern.ch/~thomasj/searchlimits/ecl.html one replacement to fix a typo in a UR

Recent Heavy-Flavor Measurements from OPAL

A selection of recent heavy-flavor results from OPAL using the LEP1 data sample are presented. The average polarization of b baryons in hadronic Z^0 decay has been measured to be -0.56^{+0.20}_{-0.13} (stat.) +- 0.09(syst.) using semileptonic decays of Lambda_b baryons. A search has been conducted for the radially excited D*' and has produced a 95% CL upper limit on its production of f(Z^0 -> D*'+-(2629))xBr(D*'+- -> D*+- pi+ pi-) < 2.1x10^{-3}. Finally, the measurement of the product branching ratio $f(b -> Lambda_b)xBr(Lambda_b -> Lambda X)= (2.67 +- 0.38 (stat) ^{+0.67}_{-0.60}(syst.))% has been made. This measurement, along with an earlier measurement of the product branching ratio f(b -> Lambda_b)xBr(Lambda_b -> Lambda l X), has been used to compute an updated R_{Lambda l} = Br(Lambda_b -> Lambda l X)/Br(Lambda_b -> \Lambda X)= (8.0 +- 1.2 (stat.) +- 0.9 (syst.))%, consistent with the expected low semileptonic branching fraction of the Lambda_b inferred from its short lifetime compared to the other b hadrons.Comment: 9 Pages, LaTeX, 4 figures. Proceedings contributed to DPF'99, UCLA, Parallel session talk 3.0

Prospects for a low-mass Higgs boson

The SU(2){sub L} x U(1){sub Y} gauge theory of the electroweak interactions has enjoyed tremendous success over the past four decades, accurately predicting, or at least accommodating, all high-energy collider data. The gauge group must be broken somehow to U(1){sub EM}, because the unbroken theory predicts massless gauge bosons and massless fermions. The Standard Model incorporates a minimal Higgs sector with a single complex doublet field, to break the symmetry spontaneously, but it is not the only possibility. SUSY Higgses, general two-Higgs-doublet models, and other ideas may prove to model nature better than the minimal model. Many of these models, and even the SM, prefer a light Higgs boson, with a mass between the LEP limit of 114.4 GeV and 200 GeV. The Constrained MSSM favors masses under 120 GeV. A survey of the experimental work so far at LEP and the Tevatron, with estimations of the sensitivity of the upcoming LHC experiments is provided

Invariant amplitudes, unpolarized cross sections, and polarization asymmetries in (anti)neutrino-nucleon elastic scattering

At leading order in weak and electromagnetic couplings, cross sections for (anti)neutrino-nucleon elastic scattering are determined by four nucleon form factors that depend on the momentum transfer $Q^2$. Including radiative corrections in the Standard Model and potential new physics contributions beyond the Standard Model, eight invariant amplitudes are possible, depending on both $Q^2$ and the (anti)neutrino energy $E_\nu$. We review the definition of these amplitudes and use them to compute both unpolarized and polarized observables including radiative corrections. We show that unpolarized accelerator neutrino cross-section measurements can probe new physics parameter space within the constraints inferred from precision beta decay measurements.Comment: 65 pages, 89 figure

Tribromo(3,5-dimethyl-2-nitrophenyl-j2 C1 ,O)tellurium(IV), bromo(3,5-dimethyl-2-nitrophenyl-j2 C1 ,O)tellurium(II) and bromo(3,5-dimethyl-2-nitrosophenyl-j2 C1 ,O)tellurium(II)

All three title compounds, prepared from bis(3,5-dimethyl-2- nitrophenyl)ditellurium, exhibit high degrees of intramolecular TeÐO coordination. Their TeÐO distances increase in the order C8H8BrNOTe \u3c C8H8BrNO2Te \u3c C8H8Br3NO2Te, with distances of 2.165 (3), 2.306 (1) and 2.423 (6) AÊ , respectively, indicating that C8H8BrNOTe may be more aptly described as 1-bromo-4,6-dimethyl-2,1,3-benzoxatellurazole

(μ-Diazenediyldiphenyl-κ2C2, N2: κ2C2′, N1) bis [(3, 5-dimethylphenyl) tellurium (II)].

The title compound, C28H26N2Te2, prepared by reduction of (3,5-dimethylphenyl)(2-nitrophenyl)tellurium(II), is the first structurally characterized example of an azo group bridging two TeII centers. The compound is centrosymmetric and the Te—N distance [2.6916 (19) A ° ] is longer than in non-bridging azo compounds

Observation of Single Top Quark Production

The field of experimental particle physics has become more sophisticated over time, as fewer, larger experimental collaborations search for small signals in samples with large components of background. The search for and the observation of electroweak single top quark production by the CDF and DZero collaborations at Fermilab's Tevatron collider are an example of an elaborate effort to measure the rate of a very rare process in the presence of large backgrounds and to learn about the properties of the top quark's weak interaction. We present here the techniques used to make this groundbreaking measurement and the interpretation of the results in the context of the Standard Model.Comment: 33 pages, 14 figures, 4 tables, to appear in Annual Review of Nuclear and Particle Science, Vol. 61, November 201