2,207 research outputs found
Search for CP-violation in Positronium Decay
CP-violation in the quark sector has been well established over the last
decade, but has not been observed in the lepton sector. We search for
CP-violating decay processes in positronium, using the angular correlation of
(\vec{S}\cdot\vec{k_{1}})(\vec{S}\cdot\vec{k_{1}}\times\vec{k_{2}}), where
\vec{S} is the the positronium spin and \vec{k_{1}}, \vec{k_{2}} are the
directions of the positronium decay photons. To a sensitivity of
2.2\times10^{-3}, no CP-violation has been found, which is at the level of the
CP-violation amplitude in the K meson. A 90% confidence interval of the
CP-violation parameter (C_{CP}) was determined to be -0.0023 < C_{CP} < 0.0049.
This result is a factor 7 more strict than that of the previous experiment
Measurement of Parity Violation in the Early Universe using Gravitational-wave Detectors
A stochastic gravitational-wave background (SGWB) is expected to arise from
the superposition of many independent and unresolved gravitational-wave
signals, of either cosmological or astrophysical origin. Some cosmological
models (characterized, for instance, by a pseudo-scalar inflaton, or by some
modification of gravity) break parity, leading to a polarized SGWB. We present
a new technique to measure this parity violation, which we then apply to the
recent results from LIGO to produce the first upper limit on parity violation
in the SGWB, assuming a generic power-law SGWB spectrum across the LIGO
sensitive frequency region. We also estimate sensitivity to parity violation of
the future generations of gravitational-wave detectors, both for a power-law
spectrum and for a model of axion inflation. This technique offers a new way of
differentiating between the cosmological and astrophysical sources of the
isotropic SGWB, as astrophysical sources are not expected to produce a
polarized SGWB.Comment: 5 pages, 2 figures, 1 tabl
Parametric attosecond pulse amplification far from the ionization threshold from high order harmonic generation in He
Parametric amplification of attosecond coherent pulses around 100 eV at the
single-atom level is demonstrated for the first time by using the 3D
time-dependent Schr{\"o}dinger equation in high-harmonic generation processes
from excited states of He. We present the attosecond dynamics of the
amplification process far from the ionization threshold and resolve the physics
behind it. The amplification of a particular central photon energy requires the
seed XUV pulses to be perfectly synchronized in time with the driving laser
field for stimulated recombination to the He ground state and is only
produced in a few specific laser cycles in agreement with the experimental
measurements. Our simulations show that the amplified photon energy region can
be controlled by varying the peak intensity of the laser field. Our results
pave the way to the realization of compact attosecond pulse intense XUV lasers
with broad applications
An x-ray detector using PIN photodiodes for the axion helioscope
An x-ray detector for a solar axion search was developed. The detector is
operated at 60K in a cryostat of a superconducting magnet. Special care was
paid to microphonic noise immunity and mechanical structure against thermal
contraction. The detector consists of an array of PIN photodiodes and tailor
made preamplifiers. The size of each PIN photodiode is $11\times 11\times 0.5\
{\rm mm^3}$ and 16 pieces are used for the detector. The detector consists of
two parts, the front-end part being operated at a temperature of 60K and the
main part in room temperature. Under these circumstances, the detector achieved
1.0 keV resolution in FWHM, 2.5 keV threshold and 6\times 10^{-5} counts
sec^{-1} keV^{-1} cm^{-2} background level.Comment: 8 pages, 5 figures, submitted to Nucl. Instr. Meth.
Results of a Search for Paraphotons with Intense X-ray Beams at SPring-8
A search for paraphotons, or hidden U(1) gauge bosons, is performed using an
intense X-ray beamline at SPring--8. "Light Shining through a Wall" technique
is used in this search. No excess of events above background is observed. A
stringent constraint is obtained on the photon--paraphoton mixing angle, for .Comment: 10 pages, 4 figure
Direct Observation of the Hyperfine Transition of the Ground State Positronium
We report the first direct measurement of the hyperfine transition of the
ground state positronium. The hyperfine structure between ortho-positronium and
para-positronium is about 203 GHz. We develop a new optical system to
accumulate about 10 kW power using a gyrotron, a mode converter, and a
Fabry-P\'{e}rot cavity. The hyperfine transition has been observed with a
significance of 5.4 standard deviations. The transition probability is measured
to be s for the first time, which
is in good agreement with the theoretical value of
s
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