Biomedical subjects

J Chapman

Publications and source records attributed to J Chapman.

At least 37 records · Page 2Linked to original sources

PubMed2006

Top-quark mass measurement from dilepton events at CDF II.

We report a measurement of the top-quark mass using events collected by the CDF II detector from pp collisions at square root of s = 1.96 TeV at the Fermilab Tevatron. We calculate a likelihood function for the top-quark mass in events that are consistent with tt --> bl(-)nu(l)bl'+ nu'(l) decays. The likelihood is formed as the convolution of the leading-order matrix element and detector resolution functions. The joint likelihood is the product of likelihoods for each of 33 events collected in 340 pb(-1) of integrated luminosity, yielding a top-quark mass M(t) = 165.2 +/- 6.1(stat) +/- 3.4(syst) GeV/c2. This first application of a matrix-element technique to tt --> bl+ nu(l)bl'- nu(l') decays gives the most precise single measurement of M(t) in dilepton events. Combined with other CDF run II measurements using dilepton events, we measure M(t) = 167.9 +/- 5.2(stat) +/- 3.7(syst) GeV/c2.

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PubMed2006

Measurement of the inclusive jet cross section using the kT algorithm in pp collisions at (square root s)=1.96 TeV.

We report on a measurement of the inclusive jet production cross section as a function of the jet transverse momentum in pp collisions at (square root s)=1.96 TeV using data collected with the upgraded Collider Detector at Fermilab in run II, corresponding to an integrated luminosity of 385 pb-1. The measurement is carried out for jets with rapidity 0.1</yjet/<0.7 and transverse momentum in the range 54<pjetT<700 GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross section after the necessary nonperturbative parton-to-hadron corrections are included.

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PubMed2006

Measurement of the dipion mass spectrum in decays.

We measure the dipion mass spectrum in X(3872)--> J/psipi(+) pi(-) decays using 360 pb(-1) of pp collisions at square root s= 1.96 TeV collected with the CDF II detector. The spectrum is fit with predictions for odd C-parity ((3)S(1), (1)P(1), and (3)D(J)) charmonia decaying to J/psipi(+) pi(-), as well as even C-parity states in which the pions are from rho(0) decay. The latter case also encompasses exotic interpretations, such as a D(0)D(*0) molecule. Only the (3)S(1) and J/psirho hypotheses are compatible with our data. Since (3)S(1) is untenable on other grounds, decay via J/psirho is favored, which implies C= +1 for the X(3872). Models for J/psi - rho different angular momenta L are considered. Flexibility in the models, especially the introduction of rho - omega interference, enables good descriptions of our data for both L = 0 and 1.

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PubMed2006

Search for Higgs bosons decaying to bb and produced in association with W bosons in pp collisions at square root of s = 1.96 TeV.

We present a search for Higgs bosons decaying into bb and produced in association with W bosons in pp collisions at square root of s = 1.96 TeV. This search uses 320 pb(-1) of the data set accumulated by the upgraded Collider Detector at Fermilab. Events are selected that have a high-transverse momentum electron or muon, missing transverse energy, and two jets, at least one of which is consistent with the hadronization of a b quark. Both the number of events and the dijet mass distribution are consistent with standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching ratio for the Higgs boson or any new particle with similar decay kinematics. These upper limits range from 10 pb for mH = 110 GeV/c2 to 3 pb for mH = 150 GeV/c2.

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PubMed2006

Evidence for the exclusive decay B(c)+- --> J/psi pi+- and measurement of the mass of the B(c)+- meson.

We report the first evidence for a fully reconstructed decay mode of the B(c)+- meson in the channel B(c)+- --> J/psi pi+-, with J/psi --> mu+ mu-. The analysis is based on an integrated luminosity of 360 pb(-1) in pp collisions at 1.96 TeV center of mass energy collected by the Collider Detector at Fermilab. We observe 14.6 +/- 4.6 signal events with a background of 7.1 +/- 0.9 events, and a fit to the J/psi pi+-mass spectrum yields a B(c)+- mass of 6285.7 +/- 5.3(stat) +/- 1.2(syst) MeV/c2. The probability of a peak of this magnitude occurring by random fluctuation in the search region is estimated as 0.012%.

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PubMed2006

Search for charged Higgs bosons from top quark decays in pp collisions at square root s=1.96 TeV.

We report the results of a search for a charged Higgs boson in the decays of top quarks produced in pp collisions at a center-of-mass energy of 1.96 TeV. We use a data sample corresponding to an integrated luminosity of 193 pb-1 collected by the upgraded Collider Detector at Fermilab. No evidence for charged Higgs production is found, allowing 95% C.L. upper limits to be placed on BR(t-->H+b) for different charged Higgs decay scenarios. In addition, we present in the minimal supersymmetric standard model (mH+/-, tanbeta) plane the first exclusion regions with radiative and Yukawa coupling corrections.

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PubMed2006

Precision top-quark mass measurement in the lepton+jets topology in p p collisions at square root s=1.96 TeV.

We report two measurements of the top-quark mass M(top) using the CDF II detector at the Fermilab Tevatron in a 318 pb(-1) data sample of tt events in the lepton+jets final state. One method uses an event-based likelihood technique resulting in M(top) = 173.2(-2.4)(+2.6)(stat) +/- 3.2(syst) GeV/c2 or 173.2(-4.0)(+4.1) GeV/c2. The second method reconstructs a top-quark mass in each event using the measured invariant mass of the hadronically decaying W boson to constrain the jet energy scale to obtain a value for M(top)of 173.5(-3.6)(+3.7)(stat) +/- 1.3(syst) GeV/c2 or 173.5(-3.8)(+3.9) GeV/c2 . We take the latter, which is more precise, as our result.

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PubMed2006

Search for neutral Higgs bosons of the minimal supersymmetric standard model decaying to tau pairs in pp collisions at square root of s = 1.96 TeV.

We present a search for neutral supersymmetric Higgs bosons decaying to tau pairs produced in pp collisions at square root of s = 1.96 TeV. The data, corresponding to 310 pb(-1) integrated luminosity, were collected with the Collider Detector at Fermilab in run II of the Tevatron. No significant excess above the standard model backgrounds is observed. We set exclusion limits on the production cross section times branching fraction to tau pairs for Higgs boson masses in the range from 90 to 250 GeV/c2.

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PubMed2006

Low 1-year cyclosporine microemulsion doses are associated with better 5-year renal graft function: an insight from MOST, a multinational observational study.

BACKGROUND: In earlier registry analyses, cyclosporine at doses of < 3 mg/kg/d at 1 year post-renal transplantation has been associated with significant graft loss or reduction in renal function. Improvements in cyclosporine formulation with increased bioavailability, plus the use of more efficient comedications, may now confer better outcomes. To determine the effect of the 1-year cyclosporine microemulsion (CsA-ME) dose on renal allograft function at 5 years, we analyzed data collected from 2889 patients with documented graft survival to year 5 in a prospective, multinational, observational study-Neoral MOST. RESULTS: Glomerular filtration rate (GFR) at year 1 was 63 +/- 20 mL/min and 59 +/- 22 mL/min at year 5. The multivariate analysis including year 1 CsA-ME dose as factor and GFR at 1 year as covariate revealed the most significant factors affecting GFR at year 5 were 1-year GFR, donor age > 60 years, and CsA-ME dose at 1 year. Risk factors associated with reduction in 5-year GFR (<65 mL/min) included donor or recipient age >60 years, delayed graft function, cadaveric donor, previous graft, and acute rejection. CsA-ME dose <3 mg/kg/d was found to protect GFR. Analysis of GFR at each year posttransplantation (Wilcoxon model) found 1-year CsA-ME (cutoff 3 mg/kg/d) had a significant effect at each time point. CONCLUSIONS: Compared to higher doses, CsA-ME <3 mg/kg/d at year 1 posttransplantation is associated with increased preservation of renal allograft function at year 5.

Aged↗

PubMed2006

Apolipoprotein epsilon4 advances appearance of psychosis in patients with Parkinson's disease.

BACKGROUND: Psychosis is one of the most serious complications of advanced parkinsonism, but many patients are spared. The genetic factors predisposing to psychosis are unclear. OBJECTIVES: To assess the association between apolipoprotein E (APOE) polymorphism and the development of psychosis in patients with Parkinson's disease (PD). METHODS: Eighty-seven patients with advanced PD were assessed. Psychosis was diagnosed in 50 patients who manifested paranoid delusions, hallucinations without insight, or disorders of perception. Time of onset of psychosis was retrieved from the medical records and caregivers' recall. APOE genotype was determined by restriction enzyme digests of amplified alleles. Cox models of logistic regression and Kaplan-Meier survival curves were used to assess factors determining early development of psychosis. RESULTS: APOE epsilon3/epsilon4 allele was carried by 20 patients (14 with psychosis), epsilon2/epsilon3 by 11 patients (10 with psychosis), epsilon3/epsilon3 by 55 patients (25 with psychosis) and epsilon2/epsilon4 by one patient who had psychosis. The mean age of onset of PD symptoms was 60.0 +/- 12.5 years. The mean duration of motor symptoms at the onset of psychosis was 7.3 +/- 4.3 years for the 15 patients harboring an APOE epsilon4 allele and 10.1 +/- 6.2 years among those who did not carry APOE epsilon4 (n = 35). The APOE epsilon4 allele was significantly associated with earlier onset of psychosis (P < 0.05) when the age of onset of motor symptoms and presence of dementia were included in the Cox regression model. Carrying the APOE epsilon4 allele was a significant risk factor for earlier appearance of psychosis with a hazard ratio of 3.24 (95% CI 1.62-6.46) while dementia by itself did not increase the risk. CONCLUSION: Parkinson's disease patients who carry the APOE epsilon4 allele develop psychosis earlier.

Age of Onset↗

PubMed2005

Search for new high-mass particles decaying to Lepton pairs in pp collisions at square root s = 1.96 TeV.

A search for new particles (X) that decay to electron or muon pairs has been performed using approximately 200 pb(-1) of pp collision data at (square root) s = 1.96 TeV collected by the CDF II experiment at the Fermilab Tevatron. Limits on sigma(pp --> X)BR (X --> ll) are presented as a function of dilepton invariant mass m(ll) > 150 GeV/c2, for different spin hypotheses (0, 1, or 2). The limits are approximately 25 fb for m(ll) > GeV/c2. Lower mass bounds for X from representative models beyond the standard model including heavy neutral gauge bosons are presented.

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PubMed2005

Search for [corrected] B0(s) --> mu+ mu- and B0(d) [corrected] --> mu + mu- decays in pp collisions with CDF II.

We report on a search for B0(s) --> mu+ mu- and B0(d) --> mu + mu- decays in pp collisions at square root(s) = 1.96 TeV using 364 pb(-1) of data collected by the CDF II detector at the Fermilab Tevatron Collider. After applying all selection requirements, we observe no candidates inside the B0(s) or B0(d) mass windows. The resulting upper limits on the branching fractions are B(B0(s) --> mu+ mu-) < 1.5 x 10(-7) and B(B0(d) --> mu+ mu-) < 3.9 x 10(-8) at 90% confidence level.

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PubMed2005

Search for new physics using high-mass tau pairs from 1.96 TeV pp collisions.

We present the results of a search for anomalous resonant production of tau lepton pairs with large invariant mass, the first such search using the CDF II Detector in Run II of the Tevatron pp collider. Such anomalous production could arise from various new physics processes. In a data sample corresponding to 195 pb(-1) of integrated luminosity we predict 2.8+/-0.5 events from standard model background processes and observe 4. We use this result to set limits on the production of heavy scalar and vector particles decaying to tau lepton pairs.

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PubMed2005

Measurement of B(t --> Wb)/B(t--> Wq) at the collider detector at fermilab.

We present a measurement of the ratio of top-quark branching fractions R = B(t --> Wb)/B(t --> Wq), where q can be a b, s, or a d quark, using lepton-plus-jets and dilepton data sets with an integrated luminosity of approximately 162 pb(-1) collected with the Collider Detector at Fermilab during Run II of the Tevatron. The measurement is derived from the relative numbers of tt events with different multiplicity of identified secondary vertices. We set a lower limit of R > 0.61 at 95% confidence level.

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PubMed2005

Evoked potential studies in the antiphospholipid syndrome: differential diagnosis from multiple sclerosis.

BACKGROUND: The CNS manifestations of the antiphospholipid syndrome (APS) can mimic multiple sclerosis both clinically and radiologically. OBJECTIVE: To compare evoked potential studies in APS patients and patients with multiple sclerosis with similar neurological disability. METHODS: 30 APS patients with CNS manifestations and 33 patients with definite multiple sclerosis and similar neurological disability underwent studies of visual evoked potentials (VEP), somatosensory evoked potentials (SSEP) in the upper and lower limbs (UL, LL), and sympathetic skin responses (SSR) in the upper and lower limbs. RESULTS: The neurological manifestations in the APS patients included stroke (n = 17), transient ischaemic attacks (n = 10), and severe headache with multiple white matter lesions on brain MRI (n = 3). Abnormal SSEP (LL), and SSR (UL; LL) were seen in APS patients (37%, 27%, and 30%, respectively) but VEP and UL SSEP were rarely abnormal (10% and 6%, respectively in APS v 58% and 33% in multiple sclerosis; p = 0.0005, p = 0.008). Mean VEP latencies were more prolonged in multiple sclerosis (116 ms v 101 ms, p<0.001). Only one APS patient had abnormal findings in all three evoked potential studies, compared with seven patients in the multiple sclerosis group (p = 0.04) CONCLUSIONS: Abnormal VEPs are uncommon in APS in contrast to multiple sclerosis. Coexisting abnormalities in all other evoked potentials were similarly rare in APS. In patients with brain MRI findings compatible either with multiple sclerosis or APS, normal evoked potential tests, and especially a normal VEP, may support the diagnosis of APS.

Adult↗

PubMed2005

Search for long-lived doubly charged Higgs bosons in pp collisions at sqrt[s] = 1.96 TeV.

We present a search for long-lived doubly charged Higgs bosons (H(+/- +/-)), with signatures of high ionization energy loss and muonlike penetration. We use 292 pb(-1) of data collected in pp collisions at sqrt[s] = 1.96 TeV by the CDF II detector at the Fermilab Tevatron. Observing no evidence of long-lived doubly charged particle production, we exclude H(+/- +/-)(L) and H(+/- +/-)(R) bosons with masses below 133 GeV/c(2) and 109 GeV/c(2), respectively. In the degenerate case we exclude H(+/- +/-) mass below 146 GeV/c(2). All limits are quoted at the 95% confidence level.

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PubMed2005

Search for Higgs bosons decaying into bb and produced in association with a vector boson in pp collisions at square root of s = 1.8 TeV.

We present a new search for H0V production, where H0 is a scalar Higgs boson decaying into bb with branching ratio beta, and V is a Z0 boson decaying into e+e-, mu+mu-, or nunu. This search is then combined with previous searches for H0V where V is a W+/- boson or a hadronically decaying Z0. The data sample consists of 106 +/- 4 pb(-1) of pp collisions at square root of s = 1.8 TeV accumulated by the Collider Detector at Fermilab. Observing no evidence of a signal, we set 95% Bayesian credibility level upper limits on sigma(pp --> H0V) x beta. For H0 masses of 90, 110, and 130 GeV/c2, the limits are 7.8, 7.2, and 6.6 pb, respectively.

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PubMed2005

Evidence for B0 s-->phiphi decay and measurements of branching ratio and A(CP) for B+ -->phiK+.

We present the first evidence of charmless decays of the B(0)(s) meson, the decay B(0)(s)--> phiphi, and a measurement of the branching ratio BR(B(0)(s)--> phiphi) using 180 pb(-1) of data collected by the CDF II experiment at the Fermilab Tevatron collider. In addition, the BR and direct CP asymmetry for the B+-->phiK+ decay are measured. We obtain BR(B(0)(s)--> phiphi)=[14(+6)(-5)(stat)+/-6(syst)] x 10(-6), BR(B+-->phiK+)=[7.6+/-1.3(stat)+/-0.6(syst)] x 10(-6), and A(CP)(B+-->phiK+)= -0.07+/-0.17(stat)+0.03 / -0.02(syst). Both decays are governed in the standard model by second order (penguin) b-->s(-)ss amplitudes.

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