691 research outputs found
Subcentimeter depth resolution using a single-photon counting time-of-flight laser ranging system at 1550 nm wavelength
We demonstrate subcentimeter depth profiling at a stand off distance of 330m using a time-of-flight approach based on time-correlated single-photon counting. For the first time to our knowledge, the photon-counting time-of-flight technique was demonstrated at a wavelength of 1550nm using a superconducting nanowire single-photon detector. The performance achieved suggests that a system using superconducting detectors has the potential for low-light-level and eye-safe operation. The system’s instrumental response was 70ps full width at half-maximum, which meant that 1cm surface-to-surface resolution could be achieved by locating the centroids of each return signal. A depth resolution of 4mm was achieved by employing an optimized signal-processing algorithm based on a reversible jump Markov chain Monte Carlo method
Fast tracking of hidden objects with single-pixel detectors
A fast tracking system is demonstrated that is based on single laser illumination and a few single-pixel single photon avalanche diode (SPAD) detectors that improves on the previous tracking of non-line-of-sight motion by a factor of 300 in laser power. With an average illumination power of only 2 mW, a 15 cm ×15 cm object located up to 2.5 m away is tracked whilst outside of the direct line-of-sight and moving at approximately 6 cm/s
Ge-on-Si single-photon avalanche diode detectors: design, modeling, fabrication, and characterization at wavelengths 1310 and 1550 nm
The design, modeling, fabrication, and characterization of single-photon avalanche diode detectors with an epitaxial Ge absorption region grown directly on Si are presented. At 100 K, a single-photon detection efficiency of 4% at 1310 nm wavelength was measured with a dark count rate of ~ 6 megacounts/s, resulting in the lowest reported noise-equivalent power for a Ge-on-Si single-photon avalanche diode detector (1×10-14 WHz-1/2). The first report of 1550 nm wavelength detection efficiency measurements with such a device is presented. A jitter of 300 ps was measured, and preliminary tests on after-pulsing showed only a small increase (a factor of 2) in the normalized dark count rate when the gating frequency was increased from 1 kHz to 1 MHz. These initial results suggest that optimized devices integrated on Si substrates could potentially provide performance comparable to or better than that of many commercially available discrete technologies
Rotational and vibrational spectra of quantum rings
One can confine the two-dimensional electron gas in semiconductor
heterostructures electrostatically or by etching techniques such that a small
electron island is formed. These man-made ``artificial atoms'' provide the
experimental realization of a text-book example of many-particle physics: a
finite number of quantum particles in a trap. Much effort was spent on making
such "quantum dots" smaller and going from the mesoscopic to the quantum
regime. Far-reaching analogies to the physics of atoms, nuclei or metal
clusters were obvious from the very beginning: The concepts of shell structure
and Hund's rules were found to apply -- just as in real atoms! In this Letter,
we report the discovery that electrons confined in ring-shaped quantum dots
form rather rigid molecules with antiferromagnetic order in the ground state.
This can be seen best from an analysis of the rotational and vibrational
excitations
Magneto-transport in periodic and quasiperiodic arrays of mesoscopic rings
We study theoretically the transmission properties of serially connected
mesoscopic rings threaded by a magnetic flux. Within a tight-binding formalism
we derive exact analytical results for the transmission through periodic and
quasiperiodic Fibonacci arrays of rings of two different sizes. The role played
by the number of scatterers in each arm of the ring is analyzed in some detail.
The behavior of the transmission coefficient at a particular value of the
energy of the incident electron is studied as a function of the magnetic flux
(and vice versa) for both the periodic and quasiperiodic arrays of rings having
different number of atoms in the arms. We find interesting resonance properties
at specific values of the flux, as well as a power-law decay in the
transmission coefficient as the number of rings increases, when the magnetic
field is switched off. For the quasiperiodic Fibonacci sequence we discuss
various features of the transmission characteristics as functions of energy and
flux, including one special case where, at a special value of the energy and in
the absence of any magnetic field, the transmittivity changes periodically as a
function of the system size.Comment: 9 pages with 7 .eps figures included, submitted to PR
Global Search for New Physics with 2.0/fb at CDF
Data collected in Run II of the Fermilab Tevatron are searched for
indications of new electroweak-scale physics. Rather than focusing on
particular new physics scenarios, CDF data are analyzed for discrepancies with
the standard model prediction. A model-independent approach (Vista) considers
gross features of the data, and is sensitive to new large cross-section
physics. Further sensitivity to new physics is provided by two additional
algorithms: a Bump Hunter searches invariant mass distributions for "bumps"
that could indicate resonant production of new particles; and the Sleuth
procedure scans for data excesses at large summed transverse momentum. This
combined global search for new physics in 2.0/fb of ppbar collisions at
sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D
Rapid Communication
Observation of Orbitally Excited B_s Mesons
We report the first observation of two narrow resonances consistent with
states of orbitally excited (L=1) B_s mesons using 1 fb^{-1} of ppbar
collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the
Fermilab Tevatron. We use two-body decays into K^- and B^+ mesons reconstructed
as B^+ \to J/\psi K^+, J/\psi \to \mu^+ \mu^- or B^+ \to \bar{D}^0 \pi^+,
\bar{D}^0 \to K^+ \pi^-. We deduce the masses of the two states to be m(B_{s1})
= 5829.4 +- 0.7 MeV/c^2 and m(B_{s2}^*) = 5839.7 +- 0.7 MeV/c^2.Comment: Version accepted and published by Phys. Rev. Let
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
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