Biomedical subjects

S Childress

Publications and source records attributed to S Childress.

At least 19 recordsLinked to original sources

PubMed2006

Observation of muon neutrino disappearance with the MINOS detectors in the NuMI neutrino beam.

This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current nu(mu) interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With 1.27 x 10(20) 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336+/-14 events. The data are consistent with nu(mu) disappearance via oscillations with |Delta(m)2/32|=2.74 +0.44/-0.26 x10(-3)eV(2) and sin(2)(2theta(23))>0.87 (68% C.L.).

Journal Article↗

PubMed2004

A determination of the Cabibbo-Kobayashi-Maskawa parameter |V us| using KL decays.

We present a determination of the Cabibbo-Kobayashi-Maskawa parameter |V(us)| based on new measurements of the six largest K(L) branching fractions and semileptonic form factors by the KTeV (E832) experiment at Fermilab. We find |V(us)|=0.2252+/-0.0008(KTeV)+/-0.0021(ext), where the errors are from KTeV measurements and from external sources. We also use the measured branching fractions to determine the CP violation parameter |eta(+-)|=(2.228+/-0.005(KTeV)+/-0.009(ext))x10(-3).

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PubMed2002

Search for the KL-->pi 0 pi 0 e+e- decay in the KTeV experiment.

The recent discovery of a large CP violating asymmetry in KL-->pi+pi-e+e- mode has prompted us to seach for the associated KL-->pi 0 pi 0 e+e- decay mode in the KTeV-E799 experiment at Fermilab. In 2.7 x 10(11) K(L) decays, one candidate event has been observed with an expected background of 0.3 event, resulting in an upper limit for the KL-->pi 0 pi 0 e+e- branching ratio of 6.6 x 10(-9) at the 90% C.L.

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PubMed2002

Radiative decay width measurements of neutral kaon excitations using the primakoff effect.

We use K(L)'s in the 100-200 GeV energy range to produce 147 candidate events of the axial vector pair K1(1270)-K1(1400) in the nuclear Coulomb field of a Pb target and determine the radiative widths Gamma(K1(1400)-->K0+gamma)=280.8+/-23.2(stat)+/-40.4(syst) keV and Gamma(K1(1270)-->K0+gamma)=73.2+/-6.1(stat)+/-28.3(syst) keV. These first measurements appear to be lower than the quark-model predictions. We also place upper limits on the radiative widths for K(*)(1410) and K(*)(2)(1430) and find that the latter is vanishingly small in accord with SU(3) invariance in the naive quark model.

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PubMed2002

Measurement of the K(L) charge asymmetry.

We present a measurement of the charge asymmetry delta(L) in the mode K(L)-->pi(+/-)e(-/+)nu based on 298 x 10(6) analyzed decays. We measure a value of delta(L) = [3322+/-58(stat)+/-47(syst)]x10(-6), in good agreement with previous measurements and 2.4 times more precise than the current best published result. The result is used to place more stringent limits on CPT and DeltaS = DeltaQ violation in the neutral kaon system.

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PubMed2001

First measurement of form factors of the decay Xi(0) --> Sigma(+)e(-)nu macro(e).

We present the first measurement of the form factor ratios g(1)/f(1) (direct axial vector to vector), g(2)/f(1) (second class current), and f(2)/f(1) (weak magnetism) for the decay Xi(0)-->Sigma(+)e(-)nu macro(e) using the KTeV (E799) beam line and detector at Fermilab. From the Sigma(+) polarization measured with the decay Sigma(+)-->p pi(0) and the e(-)-nu; correlation, we measure g(1)/f(1) to be 1.32+/-(0.21)(0.17)(stat)+/-0.05(syst), assuming the SU(3)(f) (flavor) values for g(2)/f(1) and f(2)/f(1). Our results are all consistent with exact SU(3)(f) symmetry.

Journal Article↗

PubMed2001

Branching ratio measurement of the decay K(L) --> e(+)e(-)mu(+)mu(-).

We have collected a 43 event sample of the decay K(L)-->e(+)e(-)mu(+)mu(-) with negligible backgrounds and measured its branching ratio to be (2.62+/-0.40+/-0.17)x10(-9). We see no evidence for CP violation in this decay. In addition, we set the 90% confidence upper limit on the combined branching ratios for the lepton flavor violating decays K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+) at B(K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+))< or =1.23x10(-10), assuming a uniform phase space distribution.

Journal Article↗

PubMed2001

Measurement of the branching ratio and form factor of K(L)-->mu(+)mu(-)gamma.

We report on the analysis of the rare decay K(L)-->mu(+)mu(-)gamma the 1997 data from the KTeV experiment at Fermilab. A total of 9327 candidate events are observed with 2.4% background, representing a factor of 40 increase in statistics over the current world sample. We find that B(K(L)-->mu(+)mu(-)gamma) = (3.62 +/- 0.04(stat) +/- 0.08(syst)) x 10(-7). The form factor parameter alpha(K*) is measured to be alpha(K*) = -0.160(+0.026)(-0.028). In addition, we make the first measurement of the parameter alpha from the D'Ambrosio-Isidori-Portolés form factor, finding alpha = -1.54 +/- 0.10. In that model, this alpha measurement limits the Cabibbo-Kobayashi-Maskawa parameter rho>-0.2.

Journal Article↗

PubMed2001

Measurements of the rare decay K(L) --> e(+)e(-)e(+)e(-).

We observe 441 K(L)-->e(+)e(-)e(+)e(-) candidate events with a background of 4.2 events and measure B(K(L)-->e(+)e(-)e(+)e(-)) = [3.72+/-0.18(stat)+/-0.23(syst)]x10(-8) in the KTeV/E799II experiment at Fermilab. Using the distribution of the angle between the planes of the e(+)e(-) pairs, we measure the CP parameters beta(CP) = -0.23+/-0.09(stat)+/-0.02(syst) and gamma(CP) = -0.09+/-0.09(stat)+/-0.02(syst). We also present the first detailed study of the e(+)e(-) invariant mass spectrum in this decay mode.

Journal Article↗

PubMed2001

Measurement of the branching ratio and asymmetry of the decay Xi degrees -->Sigma degrees gamma.

We have studied the rare weak radiative hyperon decay Xi degrees -->Sigma degrees gamma in the KTeV experiment at Fermilab. We have identified 4045 signal events over a background of 804 events. The dominant Xi degrees -->Lambdapi degrees decay, which was used for normalization, is the only important background source. An analysis of the acceptance of both modes yields a branching ratio of B(Xi degrees -->Sigma degrees gamma)/B(Xi degrees -->Lambdapi degrees ) = (3.34+/-0.05+/-0.09)x10(-3). By analyzing the final state decay distributions, we have also determined that the Sigma degrees emission asymmetry parameter for this decay is alpha(XiSigma) = -0.63+/-0.09.

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PubMed2001

Study of the K(0)(L) --> pi(+)pi(-)gamma Direct Emission Vertex.

We have performed studies of the K(0)(L)-->pi(+)pi(-)gamma direct emission ( DE) and inner Bremsstrahlung ( IB) vertices, based on data collected by KTeV during the 1996 Fermilab fixed target run. We find a(1)/a(2) = -0.737+/-0.034 GeV2 for the DE form-factor parameter in the rho-propagator parametrization, and report on fits of the form factor to linear and quadratic functions as well. We concurrently measure gamma(K(0)(L)-->pi(+)pi(-)gamma,E(*)(gamma)>20 MeV)/gamma(K(0)(L)-->pi(+)pi(-)) = (20.8+/-0.3)x10(-3), and a K(0)(L)-->pi(+)pi(-)gamma DE/(DE+IB) branching ratio of 0.683+/-0.011.

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PubMed2001

Search for the decay KL --> pi(0)e+e-.

We report on a search for the decay KL-->pi(0)e+e- carried out by the KTeV/E799 experiment at Fermilab. This decay is expected to have a significant CP violating contribution and the measurement of its branching ratio could support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or could point to new physics. Two events were observed in the 1997 data with an expected background of 1.06+/-0.41 events, and we set an upper limit B(KL-->pi(0)e+e-)<5.1 x 10(-10) at the 90% confidence level.

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PubMed2000

Flexible filaments in a flowing soap film as a model for one-dimensional flags in a two-dimensional wind.

The dynamics of swimming fish and flapping flags involves a complicated interaction of their deformable shapes with the surrounding fluid flow. Even in the passive case of a flag, the flag exerts forces on the fluid through its own inertia and elastic responses, and is likewise acted on by hydrodynamic pressure and drag. But such couplings are not well understood. Here we study these interactions experimentally, using an analogous system of flexible filaments in flowing soap films. We find that, for a single filament (or 'flag') held at its upstream end and otherwise unconstrained, there are two distinct, stable dynamical states. The first is a stretched-straight state: the filament is immobile and aligned in the flow direction. The existence of this state seems to refute the common belief that a flag is always unstable and will flap. The second is a flapping state: the filament executes a sinuous motion in a manner akin to the flapping of a flag in the wind. We study further the hydrodynamically coupled interaction between two such filaments, and demonstrate the existence of four different dynamical states.

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PubMed2000

Search for the decay K(L) --> pi(0)&mgr;(+)&mgr;(-)

We report on a search for the decay K(L)-->pi(0)&mgr;(+)&mgr;(-) carried out as a part of the KTeV experiment at Fermilab. This decay is expected to have a significant CP violating contribution and a direct measurement will either support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or point to new physics. Two events were observed in the 1997 data with an expected background of 0.87+/-0.15 events, and we set an upper limit B(K(L)-->pi(0)&mgr;(+)&mgr;(-))<3. 8x10(-10) at the 90% confidence level.

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PubMed2000

Search for the weak decay of a lightly bound H0 dibaryon

We present results of a search for a new form of hadronic matter, a six-quark, dibaryon state called the H0, a state predicted to exist in several theoretical models. Analyzing data collected by experiment E799-II at Fermilab, we searched for the decay H0-->Lambdappi(-) and found no candidate events. We place an upper limit on [B(H0-->Lambdappi(-))dsigma(H)/dOmega]/(dsigma(Xi)/dOmega) and, in the context of published models, exclude the region of lightly bound mass states just below the LambdaLambda mass threshold, 2.194<M(H)<2.231 GeV/c(2), with lifetimes from approximately 5x10(-10) sec to approximately 1x10(-3) sec.

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PubMed2000

Observation of CP violation in K(L)-->pi(+)pi(-)e(+)e(-) decays

We report the first observation of a manifestly CP violating effect in the K(L)-->pi(+)pi(-)e(+)e(-) decay mode. A large asymmetry was observed in the distribution of these decays in the CP-odd and T-odd angle straight phi between the decay planes of the e(+)e(-) and pi(+)pi(-) pairs in the K(L) center of mass system. After acceptance corrections, the overall asymmetry is found to be [13.6+/-2. 5(stat)+/-1.2(syst)]%. This is the largest CP-violating effect yet observed when integrating over the entire phase space of a mode and the first such effect observed in an angular variable.

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PubMed1999

Helicopter transport of patients to tertiary care centers after cardiac arrest.

Air transport is commonly used to transfer survivors of cardiac arrest from rural hospitals to large tertiary-care centers, presumably to improve outcome. To examine this issue, a retrospective review of patients stabilized after a cardiac arrest was conducted; 157 transports were reviewed. The mean age of patients was 37.9 +/- 27.8 yrs, with a male to female ratio of 2.2:1. Survivors were significantly older than nonsurvivors. Thirty-one of 69 patients (45%) with primary cardiac disease were discharged alive from the hospital, 75% without neurological sequelae. Only a minority of patients with noncardiac medical illness (7%), electrical injury (33%), suffocation (15%), near-drowning (15%), and inhalation (0%) were discharged alive from the hospital. Outcomes for cardiac arrest in adult patients older than 65 years (32.3% survival) were similar to those for adult patients younger than 65 years (36.2% survival) (P = .887). These results show that survivors of a primary cardiac event have a favorable outcome when transferred by air to tertiary centers when compared with historical controls that were transported by ground. On the other hand, cardiac arrests from noncardiac medical illness, suffocation, near-drowning, and inhalation have a grim prognosis. Prospective studies should clarify the role of air transport in these patients.

Adolescent↗

PubMed1998

Evaluation of visual and instrument shade matching.

STATEMENT OF PROBLEM: Visual color matching to determine shades in dentistry is inconsistent and unreliable. If accurate, instrumental measurement of tooth color would provide objective, quantified data to match natural teeth to clinical shade guides. PURPOSE: This study evaluated and compared the ability of a new computerized colorimeter and a simple visual test to match ceramic shade guide teeth. MATERIAL AND METHODS: Thirty-one (n = 31) observers with normal color vision were allowed unlimited time to match one set of Vita Lumin shade guide teeth to the corresponding shade guide teeth of a second Vita Lumin shade guide. The same test was administered to 14 of the observers several months later to determine within-subject variability. A computerized colorimeter (Colortron II) equipped with a positioning guide was used to measure the middle third of each shade guide tooth. Through a "match tool" present in the computer's software, readings from one shade guide were matched with readings of the other shade guide by using CIELAB measurements and DeltaE values. The mean number of correct matches by the colorimeter and of correct matches in visual test were compared with a 1-tailed t test. Repeatability for both tests was determined with a paired t test. RESULTS: The Colortron II instrument correctly matched 8 of the 16 tabs (50% correct), whereas visual matching by examiners averaged 7. 7 of 16 correct matches (48% correct) (standard deviation 2.7). No statistically significant differences existed between the 2 methods. The colorimeter demonstrated 100% repeatability and the visual test demonstrated fair repeatability (correlation coefficient r =.60). CONCLUSIONS: Shade determination by visual means was inconsistent. Accuracy of a new colorimeter in matching porcelain shade guide teeth was only slightly better.

Ceramics↗