Search for charginos in e+e- interactions at sqrt(s) = 189 GeV

An update of the searches for charginos and gravitinos is presented, based on a data sample corresponding to the 158 pb^{-1} recorded by the DELPHI detector in 1998, at a centre-of-mass energy of 189 GeV. No evidence for a signal was found. The lower mass limits are 4-5 GeV/c^2 higher than those obtained at a centre-of-mass energy of 183 GeV. The (\mu,M_2) MSSM domain excluded by combining the chargino searches with neutralino searches at the Z resonance implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 31.0 GeV/c^2 for tan(beta) \geq 1.Comment: 22 pages, 8 figure

Hadronization properties of b quarks compared to light quarks in e+e- -> q qbar from 183 to 200 GeV

The DELPHI detector at LEP has collected 54 pb^{-1} of data at a centre-of-mass energy around 183 GeV during 1997, 158 pb^{-1} around 189 GeV during 1998, and 187 pb^{-1} between 192 and 200 GeV during 1999. These data were used to measure the average charged particle multiplicity in e+e- -> b bbar events, _{bb}, and the difference delta_{bl} between _{bb} and the multiplicity, _{ll}, in generic light quark (u,d,s) events: delta_{bl}(183 GeV) = 4.55 +/- 1.31 (stat) +/- 0.73 (syst) delta_{bl}(189 GeV) = 4.43 +/- 0.85 (stat) +/- 0.61 (syst) delta_{bl}(200 GeV) = 3.39 +/- 0.89 (stat) +/- 1.01 (syst). This result is consistent with QCD predictions, while it is inconsistent with calculations assuming that the multiplicity accompanying the decay of a heavy quark is independent of the mass of the quark itself.Comment: 13 pages, 2 figure

Updated precision measurement of the average lifetime of B hadrons

The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.

Unraveling COVID-19: A Large-Scale Characterization of 4.5 Million COVID-19 Cases Using CHARYBDIS

Purpose: Routinely collected real world data (RWD) have great utility in aiding the novel coronavirus disease (COVID-19) pandemic response. Here we present the international Observational Health Data Sciences and Informatics (OHDSI) Characterizing Health Associated Risks and Your Baseline Disease In SARS-COV-2 (CHARYBDIS) framework for standardisation and analysis of COVID-19 RWD. Patients and Methods: We conducted a descriptive retrospective database study using a federated network of data partners in the United States, Europe (the Netherlands, Spain, the UK, Germany, France and Italy) and Asia (South Korea and China). The study protocol and analytical package were released on 11th June 2020 and are iteratively updated via GitHub. We identified three nonmutually exclusive cohorts of 4,537,153 individuals with a clinical COVID-19 diagnosis or positive test, 886,193 hospitalized with COVID-19, and 113,627 hospitalized with COVID-19 requiring intensive services. Results: We aggregated over 22,000 unique characteristics describing patients with COVID-19. All comorbidities, symptoms, medications, and outcomes are described by cohort in aggregate counts and are readily available online. Globally, we observed similarities in the USA and Europe: More women diagnosed than men but more men hospitalized than women, most diagnosed cases between 25 and 60 years of age versus most hospitalized cases between 60 and 80 years of age. South Korea differed with more women than men hospitalized. Common comorbidities included type 2 diabetes, hypertension, chronic kidney disease and heart disease. Common presenting symptoms were dyspnea, cough and fever. Symptom data availability was more common in hospitalized cohorts than diagnosed. Conclusion: We constructed a global, multi-centre view to describe trends in COVID-19 progression, management and evolution over time. By characterising baseline variability in patients and geography, our work provides critical context that may otherwise be misconstrued as data quality issues. This is important as we perform studies on adverse events of special interest in COVID-19 vaccine surveillance. © 2022 Kostka et al.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Study of rare b decays with the DELPHI detector at LEP

Rare decays of beauty particles were studied in several charmless modes using the data collected with the DELPHI detector at LEP from 1991 to 1994. These decays are mediated by both tree level $b \rightarrow u$ and one-loop penguin $b \rightarrow s$, $d$ transitions. Evidence for charmless $B$ decays was obtained in two body hadronic modes. The branching ratios of $B^{0}_{d,s}$ to $\pi^+ \pi^-$ or $K^+ \pi^-$ and $B^{-}_{u}$ to $\rho^0 \pi^-$ or $K^{*0} \pi^-$ were found to be $(2.8 ^{+1.5}_{-1.0} \pm 0.2) \times 10^{-5}$ and $(1.7 ^{+1.2}_{-0.8} \pm 0.2) \times 10^{-4}$ respectively. The fraction of these decays with a charged kaon in the final state that is not from the spectator $s$ quark, was measured to be $0.58 \pm 0.18$. Upper limits were set at 90\% confidence level on the branching ratios %for other two body modes including the $\Lambda_b^0\to pK^-$ decay and for three and four body charmless hadronic decays in the range of \mbox{$(1 - 3)\times10^{-4}$}, for inclusive radiative $b \rightarrow s \gamma$ decays at $5.4\times10^{-4}$, for the exclusive radiative decays $B_{d}^{0} \rightarrow K^*(892)^0\gamma$ and $B_{s}^{0} \rightarrow \phi(1020) \gamma$ at $2.1\times10^{-4}$ and $7.0\times10^{-4}$ respectively, and for dineutrino decays, $b \rightarrow s \nu \bar \nu$, in the exclusive channels $B_{d}^{0} \rightarrow K^*(892)^0 \nu \bar \nu$ and $B_{s}^{0} \rightarrow \phi(1020) \nu \bar \nu$ at 1.0 $\times$ 10$^{-3}$ and 5.4 $\times$ 10$^{-3}$ respectively. The limits on dineutrino decays constrain theories with a new $U(1)$ gauge boson coupling predominantly to the third family of fermions

Search for neutralino pair production at √s = 189 GeV

A search for pair-production of neutralinos at a LEP centre-of-mass energy of 189 GeV gave no evidence for a signal. This limits the neutralino production cross-section and excludes regions in the parameter space of the Minimal Supersymmetric Standard Model (MSSM)

Search for pair-produced neutralinos in events with photons and missing energy from e+e- collisions at √s=130-183 GeV

The events with two photons and missing (transverse) energy collected by the DELPHI detector at centre-of-mass energies between 130 GeV and 183 GeV have been studied to search for processes of the type e+e- → YY with the subsequent decay Y → Xγ, where X is an undetectable neutral particle. Reactions of this kind are expected in supersymmetric models, where the Y particle can be either the lightest neutralino, decaying to a photon and a gravitino, or the next-to-lightest neutralino, decaying to a photon and the lightest neutralino. To study the case of long-lived Y particles, a search for single-photon events with the reconstructed photon axis pointing far from the beam interaction region has also been performed. No evidence for a deviation from Standard Model expectations has been observed in the data and upper limits have been derived on the signal cross-section as a function of the the X and Y masses and of the Y mean decay path

Measurement of the rate of b anti-b b anti-b events in hadronic Z decays and the extraction of the gluon splitting into b anti-b

The rate $Z \rightarrow b\overline{b}b\overline{b}$ was measured using about $2 x 10^6$ hadronic decays collected by the DELPHI experiment in 1994 and 1995. Events were forced into 3-jets with $y_{min} > 0.06$ and a b-tag was required for every jet. The rate was measured to be: $R_{4b} = BR(Z \to b\overline{b}b\overline{b}) / BR(Z \to hadrons) = (6.0 +- 1.9(stat) +- 1.4(syst.)) x 10^{-4}$ where the invariant mass of every $b\overline{b}$ system is above twice the b quark mass. Using the value of $R_{4b}$ the probability of secondary production of a $b\overline{b}$ pair from a gluon per hadronic $Z$ decay, $g_{bb}$, was extracted and found to be: $g_{bb} = (3.3+-1.0(stat.) +- 0.8(syst.)) x 10^{-3}$