6,759 research outputs found

    Double handbag description of proton-antiproton annihilation into a heavy meson pair

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    We propose to describe the process ppˉD0ˉD0 p \bar{p} \,\to\, \bar{D^0} D^0 in a perturbative QCD motivated framework where a double-handbag hard process uduˉdˉcˉc u d \bar u \bar d \to \bar{c} c factorizes from transition distribution amplitudes, which are quasi forward hadronic matrix elements of ΨqΨqΨc\Psi_q \Psi_q \Psi_c operators, where q denotes light quarks and c denotes the heavy quark. We advocate that the charm-quark mass acts as the large scale allowing this factorization. We calculate this process in the simplified framework of the scalar diquark model and present the expected cross sections for the PANDA experiment at GSI-FAIR.Comment: 25 page

    D0ˉD0\bar{D^0} D^0-production in ppˉp\bar{p}-collisions within a double handbag approach

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    We estimate the scattering amplitude of the process ppˉD0ˉD0 p \bar{p} \,\to\, \bar{D^0} D^0 within a double-handbag framework where transition distribution amplitudes, calculated through an overlap representation, factorize from a hard subprocess. This process will be measured in the PˉANDA\bar{\text{P}}\text{ANDA} experiment at GSI-FAIR.Comment: Talk given at the 11th International Conference on Low Energy Antiproton Physics (LEAP2013

    3D shape based reconstruction of experimental data in Diffuse Optical Tomography

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    Diffuse optical tomography (DOT) aims at recovering three-dimensional images of absorption and scattering parameters inside diffusive body based on small number of transmission measurements at the boundary of the body. This image reconstruction problem is known to be an ill-posed inverse problem, which requires use of prior information for successful reconstruction. We present a shape based method for DOT, where we assume a priori that the unknown body consist of disjoint subdomains with different optical properties. We utilize spherical harmonics expansion to parameterize the reconstruction problem with respect to the subdomain boundaries, and introduce a finite element (FEM) based algorithm that uses a novel 3D mesh subdivision technique to describe the mapping from spherical harmonics coefficients to the 3D absorption and scattering distributions inside a unstructured volumetric FEM mesh. We evaluate the shape based method by reconstructing experimental DOT data, from a cylindrical phantom with one inclusion with high absorption and one with high scattering. The reconstruction was monitored, and we found a 87% reduction in the Hausdorff measure between targets and reconstructed inclusions, 96% success in recovering the location of the centers of the inclusions and 87% success in average in the recovery for the volumes

    Feasibility study of an optical radiometer for determining the composition of the Mars atmosphere from shock layer radiation during entry, volume II Final report

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    Optical radiometer feasibility study for determining composition of Mars atmosphere from shock layer radiation during entry - instrumentatio

    Spin relaxation and coherence times for electrons at the Si/SiO2 interface

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    While electron spins in silicon heterostructures make attractive qubits, little is known about the coherence of electrons at the Si/SiO2 interface. We report spin relaxation (T1) and coherence (T2) times for mobile electrons and natural quantum dots at a 28Si/SiO2 interface. Mobile electrons have short T1 and T2 of 0.3 us at 5 K. In line with predictions, confining electrons and cooling increases T1 to 0.8 ms at 350 mK. In contrast, T2 for quantum dots is around 10 us at 350 mK, increasing to 30 us when the dot density is reduced by a factor of two. The quantum dot T2 is shorter than T1, indicating that T2 is not controlled by T1 at 350 mK but is instead limited by an extrinsic mechanism. The evidence suggests that this extrinsic mechanism is an exchange interaction between electrons in neighboring dots.Comment: Extended with more experiments and rewritten. 6 pages, 5 figures, to be submitted to Phys. Rev.

    Sea ice-atmospheric interaction: Application of multispectral satellite data in polar surface energy flux estimates

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    This is the third annual report on: Sea Ice-Atmosphere Interaction - Application of Multispectral Satellite Data in Polar Surface Energy Flux Estimates. The main emphasis during the past year was on: radiative flux estimates from satellite data; intercomparison of satellite and ground-based cloud amounts; radiative cloud forcing; calibration of the Advanced Very High Resolution Radiometer (AVHRR) visible channels and comparison of two satellite derived albedo data sets; and on flux modeling for leads. Major topics covered are arctic clouds and radiation; snow and ice albedo, and leads and modeling

    Transient Nucleation near the Mean-Field Spinodal

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    Nucleation is considered near the pseudospinodal in a one-dimensional ϕ4\phi^4 model with a non-conserved order parameter and long-range interactions. For a sufficiently large system or a system with slow relaxation to metastable equilibrium, there is a non-negligible probability of nucleation occurring before reaching metastable equilibrium. This process is referred to as transient nucleation. The critical droplet is defined to be the configuration of maximum likelihood that is dynamically balanced between the metastable and stable wells. Time-dependent droplet profiles and nucleation rates are derived, and theoretical results are compared to computer simulation. The analysis reveals a distribution of nucleation times with a distinct peak characteristic of a nonstationary nucleation rate. Under the quench conditions employed, transient critical droplets are more compact than the droplets found in metastable equilibrium simulations and theoretical predictions.Comment: 7 Pages, 5 Figure
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