The Measurement of Medicaid Coverage in the SIPP: Evidence from California, 1990-1996

This paper studies the accuracy of reported Medicaid coverage in the Survey of Income and Program Participation (SIPP) using a unique data set formed by matching SIPP survey responses to administrative records from the State of California. Overall, we estimate that the SIPP underestimates Medicaid coverage in the California population by about 10 percent. Among SIPP respondents who can be matched to administrative records, we estimate that the probability someone reports Medicaid coverage in a month when they are actually covered is around 85 percent. The corresponding probability for low-income children is even higher - at least 90 percent. These estimates suggest that the SIPP provides reasonably accurate coverage reports for those who are actually in the Medicaid system. On the other hand, our estimate of the false positive rate (the rate of reported coverage for those who are not covered in the administrative records) is relatively high: 2.5 percent for the sample as a whole, and up to 20 percent for poor children. Some of this is due to errors in the recording of Social Security numbers in the administrative system, rather than to problems in the SIPP.

Search for Higgs Bosons in e+e- Collisions at 183 GeV

The data collected by the OPAL experiment at sqrts=183 GeV were used to search for Higgs bosons which are predicted by the Standard Model and various extensions, such as general models with two Higgs field doublets and the Minimal Supersymmetric Standard Model (MSSM). The data correspond to an integrated luminosity of approximately 54pb-1. None of the searches for neutral and charged Higgs bosons have revealed an excess of events beyond the expected background. This negative outcome, in combination with similar results from searches at lower energies, leads to new limits for the Higgs boson masses and other model parameters. In particular, the 95% confidence level lower limit for the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA > 72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European Physical Journal

A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays

The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL detector at LEP. Lambda_b are selected by the presence of energetic Lambda particles in bottom events tagged by the presence of displaced secondary vertices. A fit to the momenta of the Lambda particles separates signal from B meson and fragmentation backgrounds. The measured product branching ratio is f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))% Combined with a previous OPAL measurement, one obtains f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European Physical Journal

Measurement of the Michel Parameters in Leptonic Tau Decays

The Michel parameters of the leptonic tau decays are measured using the OPAL detector at LEP. The Michel parameters are extracted from the energy spectra of the charged decay leptons and from their energy-energy correlations. A new method involving a global likelihood fit of Monte Carlo generated events with complete detector simulation and background treatment has been applied to the data recorded at center-of-mass energies close to sqrt(s) = M(Z) corresponding to an integrated luminosity of 155 pb-1 during the years 1990 to 1995. If e-mu universality is assumed and inferring the tau polarization from neutral current data, the measured Michel parameters are extracted. Limits on non-standard coupling constants and on the masses of new gauge bosons are obtained. The results are in agreement with the V-A prediction of the Standard Model.Comment: 32 pages, LaTeX, 9 eps figures included, submitted to the European Physical Journal

First Measurement of the Inclusive Branching Ratio of b Hadrons →ϕ\to \phi Mesons in Z0Z^{0} Decays

The inclusive production rate of phi mesons from the decay of b hadrons produced in Z0 decays was measured to be Br(b->phi+X) = 0.0282+-0.0013(stat.)+-0.0019(syst.), using data collected by the OPAL detector at LEP.The inclusive branching fraction of φ mesons from the decay of b hadrons produced in Z decays was measured to be Br(b→ φ X)=0.0282±0.0013 (stat.)±0.0019 (syst.), using data collected by the OPAL detector at LEP.The inclusive production rate of phi mesons from the decay of b hadrons produced in Z0 decays was measured to be Br(b->phi+X) = 0.0282+-0.0013(stat.)+-0.0019(syst.), using data collected by the OPAL detector at LEP

A Study of One-Prong Tau Decays with a Charged Kaon

From an analysis of the ionisation energy loss of charged particles selected from 110326 e+e- -> tau+tau- candidates recorded by the OPAL detector at e+e- centre-of-mass energies near the Z0 resonance, we determine the one-prong tau decay branching ratios: Br(tau- -> nu_tau K- >=0h0) = 1.528 +- 0.039 +- 0.040 % Br(tau- -> nu_tau K-) = 0.658 +- 0.024 +- 0.029 % where the h0 notation refers to a pi0, an eta, a K^0_S, or a K^0_L, and where the first uncertainty is statistical and the second is systematic.From an analysis of the ionisation energy loss of charged particles selected from 110326 e+e- -> tau+tau- candidates recorded by the OPAL detector at e+e- centre-of-mass energies near the Z0 resonance, we determine the one-prong tau decay branching ratios: Br(tau- -> nu_tau K- >=0h0) = 1.528 +- 0.039 +- 0.040 % Br(tau- -> nu_tau K-) = 0.658 +- 0.024 +- 0.029 % where the h0 notation refers to a pi0, an eta, a K^0_S, or a K^0_L, and where the first uncertainty is statistical and the second is systematic

Multiplicities of π0\pi^{0}, η\eta, K0K^{0} and of charged particles in quark and gluon jets

We compared the multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale Qjet which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Qjet for pizero, eta and Kzero was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of eta meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, C=2.27+-0.20(stat+syst),is about one standard deviation higher than the perturbative prediction.We compared the multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale Qjet which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Qjet for pizero, eta and Kzero was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of eta meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, C=2.27+-0.20(stat+syst),is about one standard deviation higher than the perturbative prediction

Measurements of RbR_{b}, AFBbA_{FB}^{b} and AFBcA_{FB}^{c} in e+e−e^{+}e^{-} Collisions at 130-189 GeV

The cross-section ratio Rb=sigma(e+e- to b-antib)/sigma(e+e- to q-antiq) andthe bottom and charm forward-backward asymmetries AFB^b and AFB^c are measuredusing event samples collected by the OPAL detector at centre-of-mass energiesbetween 130 and 189 GeV. Events with bottom quark production are selected witha secondary vertex tag, and a hemisphere charge algorithm is used to extractAFB^b. In addition, the bottom and charm asymmetries are measured using leptonsfrom semileptonic decays of heavy hadrons and pions from D*+ to D0pi+ decays.The results are in agreement with the Standard Model predictions.The cross-section ratio Rb=sigma(e+e- to b-antib)/sigma(e+e- to q-antiq) and the bottom and charm forward-backward asymmetries AFB^b and AFB^c are measured using event samples collected by the OPAL detector at centre-of-mass energies between 130 and 189 GeV. Events with bottom quark production are selected with a secondary vertex tag, and a hemisphere charge algorithm is used to extract AFB^b. In addition, the bottom and charm asymmetries are measured using leptons from semileptonic decays of heavy hadrons and pions from D*+ to D0pi+ decays. The results are in agreement with the Standard Model predictions

Measurement of the B+B^{+} and B0B^{0} lifetimes and search for CP(T) violation using reconstructed secondary vertices

The lifetimes of the B+ and B0 mesons, and their ratio, have been measured in the OPAL experiment using 2.4 million hadronic Z0 decays recorded at LEP. Z0 -> b bbar decays were tagged using displaced secondary vertices and high momentum electrons and muons. The lifetimes were then measured using well-reconstructed charged and neutral secondary vertices selected in this tagged data sample. The results are tau(B+) = 1.643 +- 0.037 +- 0.025 ps tau(B0) = 1.523 +- 0.057 +- 0.053 ps ratio tau(B+)/tau(B0) = 1.079 +- 0.064 +- 0.041 where in each case the first error is statistical and the second systematic. A larger data sample of 3.1 million hadronic Z0 decays has been used to search for CP and CPT violating effects by comparison of inclusive b and bbar hadron decays. No evidence for such effects is seen. The CP violation parameter Re(epsilon_B) is measured to be Re(epsilon_B) = 0.001 +- 0.014 +- 0.003 and the fractional difference between b and bbar hadron lifetimes is measured to be -0.001 +- 0.012 +- 0.00