2,750 research outputs found
Unitary coupled-channels model for three-mesons decays of heavy mesons
A unitary coupled-channels model is presented for investigating the decays of
heavy mesons and excited meson states into three light pseudoscalar mesons. The
model accounts for the three-mesons final state interactions in the decay
processes, as required by both the three-body and two-body unitarity
conditions. In the absence of the Z-diagram mechanisms that are necessary
consequences of the three-body unitarity, our decay amplitudes are reduced to a
form similar to those used in the so-called isobar-model analysis. We apply our
coupled-channels model to the three-pions decays of a1(1260), pi2(1670),
pi2(2100), and D0 mesons, and show that the Z-diagram mechanisms can contribute
to the calculated Dalitz plot distributions by as much as 30% in magnitudes in
the regions where f0(600), rho(770), and f2(1270) dominate the distributions.
Also, by fitting to the same Dalitz plot distributions, we demonstrate that the
decay amplitudes obtained with the unitary model and the isobar model can be
rather different, particularly in the phase that plays a crucial role in
extracting the CKM CP-violating phase from the data of B meson decays. Our
results indicate that the commonly used isobar model analysis must be extended
to account for the final state interactions required by the three-body
unitarity to reanalyze the three-mesons decays of heavy mesons, thereby
exploring hybrid or exotic mesons, and signatures of physics beyond the
standard model.Comment: 32 pages, 10 figures. Version to appear in PR
Separated structure functions for exclusive K+Lambda and K+Sigma(0) electroproduction at 5.5 GeV measured with CLAS
We report measurements of the exclusive electroproduction of K+Lambda and K+Sigma(0) final states from an unpolarized proton target using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions sigma(U), sigma(LT), sigma(T) T, and sigma(LT\u27) were extracted from the Phi-dependent differential cross sections acquired with a longitudinally polarized 5.499 GeV electron beam. The data span a broad range of momentum transfers Q(2) from 1.4 to 3.9GeV(2), invariant energy W from threshold to 2.6GeV, and nearly the full center-of-mass angular range of the kaon. The separated structure functions provide an unprecedented data sample, which, in conjunction with other meson photo-and electroproduction data, will help to constrain the higher-level analyses being performed to search for missing baryon resonances. DOI: 10.1103/PhysRevC.87.02520
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High-order multiphoton ionization photoelectron spectroscopy of NO
Photoelectron energy angular distributions of NO following three different high-order multiphoton ionization (MPI) schemes have been measured. The 3 + 3 resonantly enhanced multiphoton ionization (REMPI) via the A/sup 2/..sigma../sup +/ (v=O) level yielded a distribution of electron energies corresponding to all accessible vibrational levels (v/sup +/=O-6) of the nascent ion. Angular distributions of electrons corresponding to v/sup +/=O and v/sup +/=3 were significantly different. The 3 + 2 REMPI via the A/sup 2/..sigma../sup +/ (v=1) level produced only one low-energy electron peak (v/sup +/=1). Nonresonant MPI at 532 nm yielded a distribution of electron energies corresponding to both four- and five-photon ionization. Prominent peaks in the five-photon photoelectron spectrum (PES) suggest contributions from near-resonant states at the three-photon level. 4 refs., 3 figs
Neural correlates of children's emotion understanding
This study aimed to develop an EEG paradigm to identify neural correlates of emotion understanding in children. In Experiment 1, children took part in an emotional story task. In Experiment 2, children completed an emotional task and a physical story task Late Positive Potentials (LPP) were demonstrated in response to emotional content in both studies. Together, The study demonstrates the potential value of the LPP as a flexible probe for studying children’s emotion understanding and encourages further work into the specificity versus generality of cognitive processes underpinning the LPP in social information processing
The Effect of Air on Granular Size Separation in a Vibrated Granular Bed
Using high-speed video and magnetic resonance imaging (MRI) we study the
motion of a large sphere in a vertically vibrated bed of smaller grains. As
previously reported we find a non-monotonic density dependence of the rise and
sink time of the large sphere. We find that this density dependence is solely
due to air drag. We investigate in detail how the motion of the intruder sphere
is influenced by size of the background particles, initial vertical position in
the bed, ambient pressure and convection. We explain our results in the
framework of a simple model and find quantitative agreement in key aspects with
numerical simulations to the model equations.Comment: 14 pages, 16 figures, submitted to PRE, corrected typos, slight
change
Coherent control using adaptive learning algorithms
We have constructed an automated learning apparatus to control quantum
systems. By directing intense shaped ultrafast laser pulses into a variety of
samples and using a measurement of the system as a feedback signal, we are able
to reshape the laser pulses to direct the system into a desired state. The
feedback signal is the input to an adaptive learning algorithm. This algorithm
programs a computer-controlled, acousto-optic modulator pulse shaper. The
learning algorithm generates new shaped laser pulses based on the success of
previous pulses in achieving a predetermined goal.Comment: 19 pages (including 14 figures), REVTeX 3.1, updated conten
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Negative ion formation by Rydberg electron transfer: Isotope-dependent rate constants
The formation of negative ions during collisions of rubidium atoms in selected ns and nd Rydberg states with carbon disulfide molecules has been studied for a range of effective principal quantum numbers (10 {le} n* {le} 25). For a narrow range of n* near n* = 17, rate constants for CS{sub 2}{sup {minus}} formation are found to depend upon the isotopic composition of the molecule, producing a negative ion isotope ratio (mass 78 to mass 76, amu) up to 10.5 times larger than the natural abundance ratio of CS{sub 2} isotopes in the reagent. The isotope ratio is found to depend strongly upon the initial quantum state of the Rydberg atom and perhaps upon the collision energy and CS{sub 2} temperature. 32 refs., 5 figs., 1 tab
Age-specific vaccine effectiveness of seasonal 2010/2011 and pandemic influenza A(H1N1) 2009 vaccines in preventing influenza in the United Kingdom
An analysis was undertaken to measure age-specific vaccine effectiveness (VE) of 2010/11 trivalent seasonal influenza vaccine (TIV) and monovalent 2009 pandemic influenza vaccine (PIV) administered in 2009/2010. The test-negative case-control study design was employed based on patients consulting primary care. Overall TIV effectiveness, adjusted for age and month, against confirmed influenza A(H1N1)pdm 2009 infection was 56% (95% CI 42–66); age-specific adjusted VE was 87% (95% CI 45–97) in <5-year-olds and 84% (95% CI 27–97) in 5- to 14-year-olds. Adjusted VE for PIV was only 28% (95% CI x6 to 51) overall and 72% (95% CI 15–91) in <5-year-olds. For confirmed influenza B infection, TIV effectiveness was 57% (95% CI 42–68) and in 5- to 14-year-olds 75% (95% CI 32–91). TIV provided moderate protection against the main circulating strains in 2010/2011, with higher protection in children. PIV administered during the previous season provided residual protection after 1 year, particularly in the <5 years age group
Serologic Cross-Reactivity with Pandemic (H1N1) 2009 Virus in Pigs, Europe
We tested serum samples from pigs infected or vaccinated with European swine influenza viruses (SIVs) in hemagglutination-inhibition assays against pandemic (H1N1) 2009 virus and related North American SIVs. We found more serologic cross-reaction than expected. Data suggest pigs in Europe may have partial immunity to pandemic (H1N1) 2009 virus
Probing the nucleon structure with CLAS
An overview of recent results with CLAS is presented with emphasis on nucleon
resonance studies, nucleon spin structure, and generalized parton
distributions.Comment: Plenary talk presented at NSTAR 2007, Bonn, German
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