115 research outputs found
Semileptonic B to D decays at nonzero recoil with 2+1 flavors of improved staggered quarks
The Fermilab Lattice-MILC collaboration is completing a comprehensive program
of heavy-light physics on the MILC (2+1)-flavor asqtad ensembles with lattice
spacings as small as 0.045 fm and light-to-strange-quark mass ratios as low as
1/20. We use the Fermilab interpretation of the clover action for heavy valence
quarks and the asqtad action for light valence quarks. The central goal of the
program is to provide ever more exacting tests of the unitarity of the CKM
matrix. We give a progress report on one part of the program, namely the
analysis of the semileptonic decay B to D at both zero and nonzero recoil.
Although final results are not presented, we discuss improvements in the
analysis methods, the statistical errors, and the parameter coverage that we
expect will lead to a significant reduction in the final error for |V_cb| from
this decay channel.Comment: 7 pages, 3 figures, LATTICE 2011 conferenc
Charmed meson decay constants in three-flavor lattice QCD
We present the first lattice QCD calculation with realistic sea quark content
of the D^+ meson decay constant f_{D^+}. We use the MILC Collaboration's
publicly available ensembles of lattice gauge fields, which have a quark sea
with two flavors (up and down) much lighter than a third (strange). We obtain
f_{D^+} = 201 +/- 3 +/- 17 MeV, where the errors are statistical and a
combination of systematic errors. We also obtain f_{D_s} = 249 +/- 3 +/- 16 MeV
for the D_s meson.Comment: note added on recent CLEO measurement; PRL versio
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Techniques of the FLASH Thin Target Experiment
The fluorescence yield in air is reported for wavelength and pressure ranges of interest to ultra-high energy cosmic ray detectors. A 28.5 GeV electron beam was used to excite the fluorescence. Central to the approach was the system calibration, using Rayleigh scattering of a nitrogen laser beam. In atmospheric pressure dry air, at 304 K the yield is 20.8 {+-} 1.6 photons per MeV
The Central Laser Facility at the Pierre Auger Observatory
The Central Laser Facility is located near the middle of the Pierre Auger
Observatory in Argentina. It features a UV laser and optics that direct a beam
of calibrated pulsed light into the sky. Light scattered from this beam
produces tracks in the Auger optical detectors which normally record nitrogen
fluorescence tracks from cosmic ray air showers. The Central Laser Facility
provides a "test beam" to investigate properties of the atmosphere and the
fluorescence detectors. The laser can send light via optical fiber
simultaneously to the nearest surface detector tank for hybrid timing analyses.
We describe the facility and show some examples of its many uses.Comment: 4 pages, 5 figures, submitted to 29th ICRC Pune Indi
Deep Underground Science and Engineering Lab: S1 Dark Matter Working Group
A study of the current status of WIMP dark matter searches has been made in
the context of scientific and technical planning for a Deep Underground Science
and Engineering Laboratory (DUSEL) in the U.S. The table of contents follows:
1. Overview
2. WIMP Dark Matter: Cosmology, Astrophysics, and Particle Physics
3. Direct Detection of WIMPs
4. Indirect Detection of WIMPs
5. Dark Matter Candidates and New Physics in the Laboratory
6. Synergies with Other Sub-Fields
7. Direct Detection Experiments: Status and Future Prospects
8. Infrastructure
9. International Context
10. Summary and Outlook
11. AcknowledgmentsComment: Final working group report of 17 Feb 2007 updated to address reviewer
comments (Latex, 32 pages
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A General Theorem Relating the Bulk Topological Number to Edge States in Two-dimensional Insulators
We prove a general theorem on the relation between the bulk topological quantum number and the edge states in two dimensional insulators. It is shown that whenever there is a topological order in bulk, characterized by a non-vanishing Chern number, even if it is defined for a non-conserved quantity such as spin in the case of the spin Hall effect, one can always infer the existence of gapless edge states under certain twisted boundary conditions that allow tunneling between edges. This relation is robust against disorder and interactions, and it provides a unified topological classification of both the quantum (charge) Hall effect and the quantum spin Hall effect. In addition, it reconciles the apparent conflict between the stability of bulk topological order and the instability of gapless edge states in systems with open boundaries (as known happening in the spin Hall case). The consequences of time reversal invariance for bulk topological order and edge state dynamics are further studied in the present framework
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