40,269 research outputs found
LArGe: Background suppression using liquid argon (LAr) scintillation for 0 decay search with enriched germanium (Ge) detectors
Measurements with a bare p-type high purity germanium diode (HPGe) submerged
in a 19 kg liquid argon (LAr) scintillation detector at MPIK Heidelberg are
reported. The liquid argon--germanium system (LArGe) is operated as a 4
anti-Compton spectrometer to suppress backgrounds in the HPGe. This R&D is
carried out in the framework of the GERDA experiment which searches for
0 decays with HPGe detectors enriched in Ge. The goal of
this work is to develop a novel method to discriminate backgrounds in
0 search which would ultimately allow to investigate the
effective neutrino mass free of background events down to the inverse mass
hierarchy scale. Other applications in low-background counting are expected.Comment: 3 pages, 6 figures, conference proceedings of the 10th Topical
Seminar on Innovative Particle and Radiation Detectors (IPRD06) 1 - 5 October
2006 Siena, Ital
Experimental realization of a measurement conditional unitary operation at single photon level and application to detector characterization
Our last experimental results on the realization of a measurement-conditional
unitary operation at single photon level are presented. This gate operates by
rotating by the polarization of a photon produced by means of Type-II
Parametric Down Conversion conditional to a polarization measurement on the
correlated photon. We then propose a new scheme for measuring the quantum
efficiency of a single photon detection apparatus by using this set-up. We
present experimental results obtained with this scheme compared with {\it
traditional} biphoton calibration. Our results show the interesting
potentiality of the suggested scheme.Comment: to appear in Proc. of SPIE meeting, Denver august 200
A Simple UV-Completion of QED in 5D
We construct a Lifshitz-like version of five-dimensional (5D) QED which is UV
- completed and reduces at low energies to ordinary 5D QED. The UV quantum
behaviour of this theory is very smooth. In particular, the gauge coupling
constant is finite at all energy scales and at all orders in perturbation
theory. We study the IR properties of this theory, when compactified on a
circle, and compare the one-loop energy dependence of the coupling in the
Lifshitz theory with that coming from the standard 5D QED effective field
theory. The range of validity of the 5D effective field theory is found to
agree with the more conservative version of Naive Dimensional Analysis.Comment: 24 pages, 7 figures; v2: Minor improvements, matches journal versio
Establishing the nature of companion candidates to X-ray emitting late B-type stars
The most favored interpretation for the detection of X-ray emission from late
B-type stars is that these stars have a yet undiscovered late-type companion
(or an unbound nearby late-type star) that produces the X-rays. Several faint
IR objects at (sub)-arcsecond separation from B-type stars have been uncovered
in our earlier adaptive optics imaging observations, and some of them have been
followed up with the high spatial resolution of the Chandra X-ray observatory,
pinpointing the X-ray emitter. However, firm conclusions on their nature
requires a search for spectroscopic signatures of youth. Here we report on our
recent ISAAC observations carried out in low resolution spectroscopic mode.
Equivalent widths have been used to obtain information on spectral types of the
companions. All eight X-ray emitting systems with late B-type primaries studied
contain dwarf like companions with spectral types later than A7. The only
system in the sample where the companion turns out to be of early spectral type
is not an X-ray source. These results are consistent with the assumption that
the observed X-ray emission from late B-type stars is produced by an active
pre-main sequence companion star.Comment: 6 pages, 2 figures, 3 tables, accepted for publication in MNRA
Critical behavior in ultra-strong-coupled oscillators
We investigate the strong coupling regime of a linear - coupled
harmonic oscillator system, by performing a direct diagonalization of the
hamiltonian. It is shown that the - coupled hamiltonian can be
equivalently described by a Mach-Zehnder-type interferometer with a quadratic
unitary operation in each of its arms. We show a sharp transition of the
unitary operation from an elliptical phase rotator to an elliptical squeezer as
the coupling gets stronger, which leads to the continuous generation of
entanglement, even for a significantly thermal state, in the ultra-strong
coupled regime. It is also shown that this critical regime cannot be achieved
by a classical Hookian coupling. Finally, the effect of a finite-temperature
environment is analyzed, showing that entanglement can still be generated from
a thermal state in the ultra-strong coupled regime, but is destroyed rapidly
Progressive Transient Photon Beams
In this work we introduce a novel algorithm for transient rendering in
participating media. Our method is consistent, robust, and is able to generate
animations of time-resolved light transport featuring complex caustic light
paths in media. We base our method on the observation that the spatial
continuity provides an increased coverage of the temporal domain, and
generalize photon beams to transient-state. We extend the beam steady-state
radiance estimates to include the temporal domain. Then, we develop a
progressive version of spatio-temporal density estimations, that converges to
the correct solution with finite memory requirements by iteratively averaging
several realizations of independent renders with a progressively reduced kernel
bandwidth. We derive the optimal convergence rates accounting for space and
time kernels, and demonstrate our method against previous consistent transient
rendering methods for participating media
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