Observation of single top-quark production.

We report observation of the electroweak production of single top quarks in pp[over ] collisions at sqrt[s]=1.96 TeV based on 2.3 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(pp[over ]--> tb + X, tqb + X) = 3.94 + or - 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10(-7), corresponding to a 5.0 standard deviation significance for the observation.

Search for resonant diphoton production with the D0 detector.

We present a search for a narrow resonance in the inclusive diphoton final state using approximately 2.7 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron pp Collider. We observe good agreement between the data and the background prediction, and set the first 95% C.L. upper limits on the production cross section times the branching ratio for decay into a pair of photons for resonance masses between 100 and 150 GeV. This search is also interpreted in the context of several models of electroweak symmetry breaking with a Higgs boson decaying into two photons.

Study of direct CP violation in B(+/-)-->J/psiK(+/-)(pi(+/-)) decays.

We present a search for direct CP violation in B(+/-)-->J/psiK(+/-)(pi(+/-)) decays. The event sample is selected from 2.8 fb(-1) of pp collisions recorded by D0 experiment in run II of the Fermilab Tevatron Collider. The charge asymmetry A_(CP)(B(+)-->J/psiK(+))= + 0.0075 +/- 0.0061(stat)+/-0.0030(syst) is obtained using a sample of approximately 40, 000 B(+/-)-->J/psiK(+/-) decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry A(CP)(B(+)-->J/psipi(+))=-0.09+/-0.08(stat)+/-0.03(syst).

Search for W' boson resonances decaying to a top quark and a bottom quark.

We search for the production of a heavy W' gauge boson that decays to third generation quarks in 0.9 fb-1 of pp collisions at square root(s)=1.96 TeV, collected with the D0 detector at the Fermilab Tevatron collider. We find no significant excess in the final-state invariant mass distribution and set upper limits on the production cross section times branching fraction. For a left-handed W' boson with SM couplings, we set a lower mass limit of 731 GeV. For right-handed W' bosons, we set lower mass limits of 739 GeV if the W' boson decays to both leptons and quarks and 768 GeV if the W' boson decays only to quarks. We also set limits on the coupling of the W' boson to fermions as a function of its mass.

Search for associated higgs boson production WH-->WWW*-->l+/-nul'+/-nu'+X in pp collisions at square root s=1.96 Te V.

We present a search for associated Higgs boson production in the process pp-->WH-->WWW*-->l;+/-nul'+/-nu'+X in final states containing two like-sign isolated electrons or muons (e+/-e;+/-, e+/-micro+/-, or micro+/-micro+/-). The search is based on D0 run II data samples corresponding to integrated luminosities of 360-380 pb-1. No excess is observed over the predicted standard model background. We set 95% C.L. upper limits on sigma(pp-->WH)xBr(H-->WW*) between 3.2 and 2.8 pb for Higgs boson masses from 115 to 175 GeV.

Search for supersymmetry via associated production of charginos and neutralinos in final states with three leptons.

A search for associated production of charginos and neutralinos is performed using data recorded with the D0 detector at a pp center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final states with missing transverse energy and three charged leptons, of which at least two are electrons or muons. No evidence for supersymmetry is found in a data set corresponding to an integrated luminosity of 320 pb-1. Limits on the product of the production cross section and leptonic branching fraction are set. For the minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95% C.L. is derived in regions of parameter space with enhanced leptonic branching fractions.

Search for neutral supersymmetric Higgs Bosons in multijet events at sqrt[s]=1.96 TeV.

We have performed a search for neutral Higgs bosons produced in association with bottom quarks in pp collisions, using 260 pb-1 of data collected with the D0 detector in Run II of the Fermilab Tevatron Collider. The cross sections for these processes are enhanced in many extensions of the standard model (SM), such as in its minimal supersymmetric extension at large tanbeta. The results of our analysis agree with expectations from the SM, and we use our measurements to set upper limits on the production of neutral Higgs bosons in the mass range of 90 to 150 GeV.

First-order phase transition from the vortex liquid to an amorphous solid.

We present a systematic study of the topology of the vortex solid phase in superconducting Bi2Sr2CaCu2O8 samples with low doses of columnar defects. A new state of vortex matter imposed by the presence of geometrical contours associated with the random distribution of columns is found. The results show that the first-order liquid-solid transition in this vortex matter does not require a structural symmetry change.

Direct measurement of the pion valence-quark momentum distribution, the pion light-cone wave function squared.

We present the first direct measurements of the pion valence-quark momentum distribution which is related to the square of the pion light-cone wave function. The measurements were carried out using data on diffractive dissociation of 500 GeV/c pi(-) into dijets from a platinum target at Fermilab experiment E791. The results show that the /q&q> light-cone asymptotic wave function describes the data well for Q2 approximately 10 (GeV/c)(2) or more. We also measured the transverse momentum distribution of the diffractive dijets.

Observation of color-transparency in diffractive dissociation of pions.

We have studied the diffractive dissociation into dijets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t(min)-->0), we find that when the per-nucleus cross section for this process is parametrized as sigma = sigma0Aalpha, alpha has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.

Ratio of jet cross sections at square root of s = 630 GeV and 1800 GeV.

The D0 Collaboration has measured the inclusive jet cross section in barpp collisions at square root of s = 630 GeV. The results for pseudorapidities (eta)<0.5 are combined with our previous results at square root of s = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute magnitude, the dependence of the ratio on jet transverse momentum is very similar for data and theory.

Search for large extra dimensions in dielectron and diphoton production.

We report a search for effects of large extra spatial dimensions in pp collisions at a center-of-mass energy of 1.8 TeV with the D0 detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% C.L. on the effective Planck scale between 1.0 and 1.4 TeV for several formalisms and numbers of extra dimensions.

Enterobacter cloacae and Pseudomonas aeruginosa polymicrobial bloodstream infections traced to extrinsic contamination of a dextrose multidose vial.

OBJECTIVE: To identify risk factors for polymicrobial bloodstream infections (BSIs) in neonatal intensive care unit (NICU) patients during an outbreak of BSIs. DESIGN: During an outbreak of BSIs, we conducted a retrospective cohort study, assessed NICU infection control practices and patient exposure to NICU healthcare workers (HCWs), and obtained cultures of the environment and HCW hands. PATIENTS: During the period May 3 to 7, 1996, 5 infants contracted BSIs caused by both Enterobacter cloacae and Pseudomonas aeruginosa, and one infant contracted a BSI caused by E cloacae only. For each pathogen, all isolates were identical on DNA typing. RESULTS: Infants exposed to the following were more likely than nonexposed infants to have BSI: umbilical venous catheters (6/14 vs 0/7, P = .05), total parenteral nutrition given simultaneously with a dextrose/electrolyte solution (6/12 vs 0/9, P = .02), or one HCW (5/7 vs 1/13, P = .007). Neither environmental nor HCW hand cultures yielded the outbreak pathogens. Quality control cultures of intravenous solution bags were negative. CONCLUSIONS: We speculate that a dextrose multidose vial became contaminated during manipulation or needle puncture and that successive use of this contaminated vial for multiple patients may have been responsible for BSIs. Aseptic techniques must be employed when multidose vial medications are used. Single-dose vials should be used for parenteral additives whenever possible to reduce the risk of extrinsic contamination and subsequent transmission of nosocomial pathogens.

Culturally sensitive validation of screening questionnaires for depression in older African-Caribbean people living in south London.

BACKGROUND: We tested the validity of two screens for depression in older African-Caribbean adults, the 15-item Geriatric Depression Scale (GDS) and a new Caribbean Culture-Specific Screen for emotional distress (CCSS). Two independent criteria were used for validity: (a) a psychiatric diagnosis derived from GMS-AGECAT, and (b) a culturally sensitive assessment of mental disorder, derived from a tool developed with local African-Caribbean religious healers. METHOD: One hundred and sixty-four consecutive African-Caribbean primary care users, aged 60 years or older, were screened with the GDS and the CCSS. Diagnostic interviews were carried out on 80% of high scorers and 20% of low scorers. RESULTS: The number of cases detected by the two separate diagnostic approaches was similar. However, the agreement between who was and who was not a case was only modest. At a cut-off of > or = 5, the GDS was an adequate case detector for psychiatric depression, and, at a cut-off of > or = 4, for 'depressed/lost spirit', as defined by culture-specific criteria. It performed as well as the new CCSS. CONCLUSIONS: At a cut-off of > or = 4 the 15-item GDS can be recommended as a case detector for significant forms of depression in older African-Caribbean people living in south London.