755 research outputs found
A Self-Consistent Model for Positronium Formation from Helium Atoms
The differential and total cross sections for electron capture by positrons
from helium atoms are calculated using a first-order distorted wave theory
satisfying the Coulomb boundary conditions. In this formalism a parametric
potential is used to describe the electron screening in a consistent and
realistic manner. The present procedure is self consistent because (i) it
satisfies the correct boundary conditions and post-prior symmetry, and (ii) the
potential and the electron binding energies appearing in the transition
amplitude are consistent with the wave functions describing the collision
system. The results are compared with the other theories and with the available
experimental measurements. At the considered range of collision energies, the
results agree reasonably well with recent experiments and theories.
[Note: This paper will be published on volume 42 of the Brazilian Journal of
Physics
Measurement of the branching fraction and CP content for the decay B(0) -> D(*+)D(*-)
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APS.We report a measurement of the branching fraction of the decay B0βD*+D*- and of the CP-odd component of its final state using the BABAR detector. With data corresponding to an integrated luminosity of 20.4ββfb-1 collected at the Ξ₯(4S) resonance during 1999β2000, we have reconstructed 38 candidate signal events in the mode B0βD*+D*- with an estimated background of 6.2Β±0.5 events. From these events, we determine the branching fraction to be B(B0βD*+D*-)=[8.3Β±1.6(stat)Β±1.2(syst)]Γ10-4. The measured CP-odd fraction of the final state is 0.22Β±0.18(stat)Β±0.03(syst).This work is supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the A.P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Measurement of D-s(+) and D-s(*+) production in B meson decays and from continuum e(+)e(-) annihilation at βs=10.6 GeV
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APSNew measurements of Ds+ and Ds*+ meson production rates from B decays and from qqΜ
continuum events near the Ξ₯(4S) resonance are presented. Using 20.8 fb-1 of data on the Ξ₯(4S) resonance and 2.6 fb-1 off-resonance, we find the inclusive branching fractions B(BβDs+X)=(10.93Β±0.19Β±0.58Β±2.73)% and B(BβDs*+X)=(7.9Β±0.8Β±0.7Β±2.0)%, where the first error is statistical, the second is systematic, and the third is due to the Ds+βΟΟ+ branching fraction uncertainty. The production cross sections Ο(e+e-βDs+X)ΓB(Ds+βΟΟ+)=7.55Β±0.20Β±0.34pb and Ο(e+e-βDs*Β±X)ΓB(Ds+βΟΟ+)=5.8Β±0.7Β±0.5pb are measured at center-of-mass energies about 40 MeV below the Ξ₯(4S) mass. The branching fractions Ξ£B(BβDs(*)+D(*))=(5.07Β±0.14Β±0.30Β±1.27)% and Ξ£B(BβDs*+D(*))=(4.1Β±0.2Β±0.4Β±1.0)% are determined from the Ds(*)+ momentum spectra. The mass difference m(Ds+)-m(D+)=98.4Β±0.1Β±0.3MeV/c2 is also measured.This work was supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the Swiss NSF, A. P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Search for rare quark-annihilation decays, B --> Ds(*) Phi
We report on searches for B- --> Ds- Phi and B- --> Ds*- Phi. In the context
of the Standard Model, these decays are expected to be highly suppressed since
they proceed through annihilation of the b and u-bar quarks in the B- meson.
Our results are based on 234 million Upsilon(4S) --> B Bbar decays collected
with the BABAR detector at SLAC. We find no evidence for these decays, and we
set Bayesian 90% confidence level upper limits on the branching fractions BF(B-
--> Ds- Phi) Ds*- Phi)<1.2x10^(-5). These results
are consistent with Standard Model expectations.Comment: 8 pages, 3 postscript figues, submitted to Phys. Rev. D (Rapid
Communications
Aging and Error Processing: Age Related Increase in the Variability of the Error-Negativity Is Not Accompanied by Increase in Response Variability
Background: Several studies report an amplitude reduction of the error negativity (Ne or ERN), an event-related potential occurring after erroneous responses, in older participants. In earlier studies it was shown that the Ne can be explained by a single independent component. In the present study we aimed to investigate whether the Ne reduction usually found in older subjects is due to an altered component structure, i.e., a true alteration in response monitoring in older subjects. Methodology/Principal Findings: Two age groups conducted two tasks with different stimulus response mappings and task difficulty. Both groups received fully balanced speed or accuracy instructions and an individually adapted deadline in both tasks. Event-related potentials, Independent Component analysis of EEG-data and between trial variability of the Ne were combined with analysis of error rates, coefficients of variation of RT-data and ex-Gaussian fittings to reaction times. The Ne was examined by means of ICA and PCA, yielding a prominent independent component on error trials, the Ne-IC. The Ne-IC was smaller in the older than the younger subjects for both speed and accuracy instructions. Also, the Ne-IC contributed to a much lesser extent to the Ne in older than in younger subjects. RT distribution parameters were not related to Ne/ERP-variability. Conclusions/Significance: The results show a genuine reduction as well as a different component structure of the Ne in older compared to young subjects. This reduction is not reflected in behaviour, apart from a general slowing of olde
Effects of the cannabinoid CB1 receptor antagonist rimonabant on distinct measures of impulsive behavior in rats
Rationale Pathological impulsivity is a prominent feature in several psychiatric disorders, but detailed understanding of the specific
neuronal processes underlying impulsive behavior is as yet lacking.
Objectives As recent findings have suggested involvement of the brain cannabinoid system in impulsivity, the present study aimed at further
elucidating the role of cannabinoid CB1 receptor activation in distinct measures of impulsive behavior.
Materials and methods The effects of the selective cannabinoid CB1 receptor antagonist, rimonabant (SR141716A) and agonist WIN55,212-2 were tested in various measures of impulsive behavior,
namely, inhibitory control in a five-choice serial reaction time task (5-CSRTT), impulsive choice in a delayed reward paradigm,
and response inhibition in a stop-signal paradigm.
Results In the 5-CSRTT, SR141716A dose-dependently improved inhibitory control by decreasing the number of premature responses. Furthermore,
SR141716A slightly improved attentional function, increased correct response latency, but did not affect other parameters.
The CB1 receptor agonist WIN55,212-2 did not change inhibitory control in the 5-CSRTT and only increased response latencies and errors
of omissions. Coadministration of WIN55,212-2 prevented the effects of SR141716A on inhibitory control in the 5-CSRTT. Impulsive
choice and response inhibition were not affected by SR141716A at any dose, whereas WIN55,212-2 slightly impaired response
inhibition but did not change impulsive choice.
Conclusions The present data suggest that particularly the endocannabinoid system seems involved in some measures of impulsivity and provides
further evidence for the existence of distinct forms of impulsivity that can be pharmacologically dissociated
Mitochondria can orchestrate sex differences in cell fate of vascular smooth muscle cells from rats
Author Correction: Cross-ancestry genome-wide association analysis of corneal thickness strengthens link between complex and Mendelian eye diseases
Emmanuelle Souzeau, who contributed to analysis of data, was inadvertently omitted from the author list in the originally published version of this Article. This has now been corrected in both the PDF and HTML versions of the Article
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