Quantitative thresholds enable accurate identification of clostridium difficile infection by the luminex xTAG gastrointestinal pathogen panel

Clostridium difficile colonizes the gastrointestinal (GI) tract, resulting in either asymptomatic carriage or a spectrum of diarrheal illness. If clinical suspicion for C. difficile is low, stool samples are often submitted for analysis by multiplex molecular assays capable of detecting multiple GI pathogens, and some institutions do not report this organism due to concerns for high false-positive rates. Since clinical disease correlates with organism burden and molecular assays yield quantitative data, we hypothesized that numerical cutoffs could be utilized to improve the specificity of the Luminex xTAG GI pathogen panel (GPP) for C. difficile infection. Analysis of cotested liquid stool samples (n 1,105) identified a GPP median fluorescence intensity (MFI) value cutoff of 1,200 to be predictive of two-step algorithm (2-SA; 96.4% concordance) and toxin enzyme immunoassay (EIA) positivity. Application of this cutoff to a second cotested data set (n 1,428) yielded 96.5% concordance. To determine test performance characteristics, concordant results were deemed positive or negative, and discordant results were adjudicated via chart review. Test performance characteristics for the MFI cutoff of 150 (standard), MFI cutoff of 1,200, and 2-SA were as follows (respectively): concordance, 95, 96, and 97%; sensitivity, 93, 78, and 90%; specificity, 95, 98, and 98%; positive predictive value, 67, 82, and 81%;, and negative predictive value, 99, 98, and 99%. To capture the high sensitivity for organism detection (MFI of 150) and high specificity for active infection (MFI of 1,200), we developed and applied a reporting algorithm to interpret GPP data from patients (n 563) with clinician orders only for syndromic panel testing, thus enabling accurate reporting of C. difficile for 95% of samples (514 negative and 5 true positives) irrespective of initial clinical suspicion and without the need for additional testing

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

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.

Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2

The hadronic structure function of the photon F_2^gamma is measured as a function of Bjorken x and of the factorisation scale Q^2 using data taken by the OPAL detector at LEP. Previous OPAL measurements of the x dependence of F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted by QCD, the data show positive scaling violations in F_2^gamma. Several parameterisations of F_2^gamma are in agreement with the measurements whereas the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001, Ascona, Switzerlan

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

The XENONnT dark matter experiment.

The multi-staged XENON program at INFN Laboratori Nazionali del Gran Sasso aims to detect dark matter with two-phase liquid xenon time projection chambers of increasing size and sensitivity. The XENONnT experiment is the latest detector in the program, planned to be an upgrade of its predecessor XENON1T. It features an active target of 5.9&nbsp;tonnes of cryogenic liquid xenon (8.5&nbsp;tonnes total mass in cryostat). The experiment is expected to extend the sensitivity to WIMP dark matter by more than an order of magnitude compared to XENON1T, thanks to the larger active mass and the significantly reduced background, improved by novel systems such as a radon removal plant and a neutron veto. This article describes the XENONnT experiment and its sub-systems in detail and reports on the detector performance during the first science run

Low-energy Calibration of XENON1T with an Internal 37^{37}Ar Source

A low-energy electronic recoil calibration of XENON1T, a dual-phase xenontime projection chamber, with an internal $^{37}$Ar source was performed. Thiscalibration source features a 35-day half-life and provides two mono-energeticlines at 2.82 keV and 0.27 keV. The photon yield and electron yield at 2.82 keVare measured to be (32.3$\pm$0.3) photons/keV and (40.6$\pm$0.5) electrons/keV,respectively, in agreement with other measurements and with NEST predictions.The electron yield at 0.27 keV is also measured and it is(68.0$^{+6.3}_{-3.7}$) electrons/keV. The $^{37}$Ar calibration confirms thatthe detector is well-understood in the energy region close to the detectionthreshold, with the 2.82 keV line reconstructed at (2.83$\pm$0.02) keV, whichfurther validates the model used to interpret the low-energy electronic recoilexcess previously reported by XENON1T. The ability to efficiently remove argonwith cryogenic distillation after the calibration proves that $^{37}$Ar can beconsidered as a regular calibration source for multi-tonne xenon detectors.<br

Effective Field Theory and Inelastic Dark Matter Results from XENON1T

In this work, we expand on the XENON1T nuclear recoil searches to study theindividual signals of dark matter interactions from operators up todimension-eight in a Chiral Effective Field Theory (ChEFT) and a model ofinelastic dark matter (iDM). We analyze data from two science runs of theXENON1T detector totaling 1\,tonne$\times$year exposure. For these analyses, weextended the region of interest from [4.9, 40.9]$\,$keV$_{\text{NR}}$ to [4.9,54.4]$\,$keV$_{\text{NR}}$ to enhance our sensitivity for signals that peak atnonzero energies. We show that the data is consistent with the background-onlyhypothesis, with a small background over-fluctuation observed peaking between20 and 50$\,$keV$_{\text{NR}}$, resulting in a maximum local discoverysignificance of 1.7\,$\sigma$ for the Vector$\otimes$Vector$_{\text{strange}}$($VV_s$) ChEFT channel for a dark matter particle of 70$\,$GeV/c$^2$, and$1.8\,\sigma$ for an iDM particle of 50$\,$GeV/c$^2$ with a mass splitting of100$\,$keV/c$^2$. For each model, we report 90\,\% confidence level (CL) upperlimits. We also report upper limits on three benchmark models of dark matterinteraction using ChEFT where we investigate the effect of isospin-breakinginteractions. We observe rate-driven cancellations in regions of theisospin-breaking couplings, leading to up to 6 orders of magnitude weaker upperlimits with respect to the isospin-conserving case.<br

The Triggerless Data Acquisition System of the XENONnT Experiment

The XENONnT detector uses the latest and largest liquid xenon-based timeprojection chamber (TPC) operated by the XENON Collaboration, aimed atdetecting Weakly Interacting Massive Particles and conducting other rare eventsearches. The XENONnT data acquisition (DAQ) system constitutes an upgraded andexpanded version of the XENON1T DAQ system. For its operation, it reliespredominantly on commercially available hardware accompanied by open-source andcustom-developed software. The three constituent subsystems of the XENONnTdetector, the TPC (main detector), muon veto, and the newly introduced neutronveto, are integrated into a single DAQ, and can be operated both independentlyand as a unified system. In total, the DAQ digitizes the signals of 698photomultiplier tubes (PMTs), of which 253 from the top PMT array of the TPCare digitized twice, at $\times10$ and $\times0.5$ gain. The DAQ for the mostpart is a triggerless system, reading out and storing every signal that exceedsthe digitization thresholds. Custom-developed software is used to process theacquired data, making it available within $\mathcal{O}\left(10\text{ s}\right)$for live data quality monitoring and online analyses. The entire system withall the three subsystems was successfully commissioned and has been operatingcontinuously, comfortably withstanding readout rates that exceed $\sim500$ MB/sduring calibration. Livetime during normal operation exceeds $99\%$ and is$\sim90\%$ during most high-rate calibrations. The combined DAQ system hascollected more than 2 PB of both calibration and science data during thecommissioning of XENONnT and the first science run.<br