180 research outputs found
Double radiative pion capture on hydrogen and deuterium and the nucleon's pion cloud
We report measurements of double radiative capture in pionic hydrogen and
pionic deuterium. The measurements were performed with the RMC spectrometer at
the TRIUMF cyclotron by recording photon pairs from pion stops in liquid
hydrogen and deuterium targets. We obtained absolute branching ratios of for hydrogen and for deuterium, and
relative branching ratios of double radiative capture to single radiative
capture of for hydrogen
and for
deuterium. For hydrogen, the measured branching ratio and photon energy-angle
distributions are in fair agreement with a reaction mechanism involving the
annihilation of the incident on the cloud of the target proton.
For deuterium, the measured branching ratio and energy-angle distributions are
qualitatively consistent with simple arguments for the expected role of the
spectator neutron. A comparison between our hydrogen and deuterium data and
earlier beryllium and carbon data reveals substantial changes in the relative
branching ratios and the energy-angle distributions and is in agreement with
the expected evolution of the reaction dynamics from an annihilation process in
S-state capture to a bremsstrahlung process in P-state capture. Lastly, we
comment on the relevance of the double radiative process to the investigation
of the charged pion polarizability and the in-medium pion field.Comment: 44 pages, 7 tables, 13 figures, submitted to Phys. Rev.
Near-invariant blur for depth and 2D motion via time-varying light field analysis
Recently, several camera designs have been proposed for either making defocus blur invariant to scene depth or making motion blur invariant to object motion. The benefit of such invariant capture is that no depth or motion estimation is required to remove the resultant spatially uniform blur. So far, the techniques have been studied separately for defocus and motion blur, and object motion has been assumed 1D (e.g., horizontal). This article explores a more general capture method that makes both defocus blur and motion blur nearly invariant to scene depth and in-plane 2D object motion. We formulate the problem as capturing a time-varying light field through a time-varying light field modulator at the lens aperture, and perform 5D (4D light field + 1D time) analysis of all the existing computational cameras for defocus/motion-only deblurring and their hybrids. This leads to a surprising conclusion that focus sweep, previously known as a depth-invariant capture method that moves the plane of focus through a range of scene depth during exposure, is near-optimal both in terms of depth and 2D motion invariance and in terms of high-frequency preservation for certain combinations of depth and motion ranges. Using our prototype camera, we demonstrate joint defocus and motion deblurring for moving scenes with depth variation
Radiative Muon Capture on Hydrogen and the Induced Pseudoscalar Coupling
The first measurement of the elementary process is reported. A photon pair spectrometer was used to measure
the partial branching ratio ( for photons of k >
60 MeV. The value of the weak pseudoscalar coupling constant determined from
the partial branching ratio is , where the first error is the quadrature sum of statistical
and systematic uncertainties and the second error is due to the uncertainty in
, the decay rate of the ortho to para molecule. This
value of g_p is 1.5 times the prediction of PCAC and pion-pole dominance.Comment: 13 pages, RevTeX type, 3 figures (encapsulated postscript), submitted
to Phys. Rev. Let
A search for two body muon decay signals
Lepton family number violation is tested by searching for
decays among the 5.8 positive muon decay events analyzed by the
TWIST collaboration. Limits are set on the production of both massless and
massive bosons. The large angular acceptance of this experiment allows
limits to be placed on anisotropic decays, which can arise
from interactions violating both lepton flavor and parity conservation.
Branching ratio limits of order are obtained for bosons with masses
of 13 - 80 MeV/c and with different decay asymmetries. For bosons with
masses less than 13 MeV/c the asymmetry dependence is much stronger and
the 90% limit on the branching ratio varies up to . This is
the first study that explicitly evaluates the limits for anisotropic two body
muon decays.Comment: 7 pages, 5 figures, 2 tables, accepted by PR
First results from the CERN Axion Solar Telescope (CAST)
Hypothetical axion-like particles with a two-photon interaction would be
produced in the Sun by the Primakoff process. In a laboratory magnetic field
(``axion helioscope'') they would be transformed into X-rays with energies of a
few keV. Using a decommissioned LHC test magnet, CAST has been running for
about 6 months during 2003. The first results from the analysis of these data
are presented here. No signal above background was observed, implying an upper
limit to the axion-photon coupling < 1.16 10^{-10} GeV^-1 at 95% CL for m_a
<~0.02 eV. This limit is comparable to the limit from stellar energy-loss
arguments and considerably more restrictive than any previous experiment in
this axion mass range.Comment: 4 pages, accepted by PRL. Final version after the referees comment
Measurement of the Muon Decay Parameter delta
The muon decay parameter delta has been measured by the TWIST collaboration.
We find delta = 0.74964 +- 0.00066(stat.) +- 0.00112(syst.), consistent with
the Standard Model value of 3/4. This result implies that the product Pmuxi of
the muon polarization in pion decay, Pmu, and the muon decay parameter xi falls
within the 90% confidence interval 0.9960 < Pmuxi < xi < 1.0040. It also has
implications for left-right-symmetric and other extensions of the Standard
Model.Comment: Extended to 5 pages. Referee's comments answere
Precision muon decay measurements and improved constraints on the weak interaction
The TWIST Collaboration has completed its measurement of the three muon decay
parameters \rho, \delta, and P_\mu\xi. This paper describes our determination
of \rho, which governs the shape of the overall momentum spectrum, and \delta,
which controls the momentum dependence of the parity-violating decay asymmetry.
The results are \rho=0.74977\pm 0.00012(stat.)\pm 0.00023(syst.) and \delta =
0.75049\pm 0.00021(stat.)\pm 0.00027(syst.). These are consistent with the
value of 3/4 given for both parameters in the standard model, and each is over
a factor of 10 more precise than the measurements published prior to TWIST. Our
final results on \rho, \delta, and P_\mu\xi have been incorporated into a new
global analysis of all available muon decay data, resulting in improved
model-independent constraints on the possible weak interactions of right-handed
particles.Comment: 19 pages, 10 figure
Search for Dark Matter Axions with CAST-CAPP
The CAST-CAPP axion haloscope, operating at CERN inside the CAST dipole
magnet, has searched for axions in the 19.74 eV to 22.47 eV mass
range. The detection concept follows the Sikivie haloscope principle, where
Dark Matter axions convert into photons within a resonator immersed in a
magnetic field. The CAST-CAPP resonator is an array of four individual
rectangular cavities inserted in a strong dipole magnet, phase-matched to
maximize the detection sensitivity. Here we report on the data acquired for
4124 h from 2019 to 2021. Each cavity is equipped with a fast frequency tuning
mechanism of 10 MHz/min between 4.774 GHz and 5.434 GHz. In the present work,
we exclude axion-photon couplings for virialized galactic axions down to
at the 90% confidence
level. The here implemented phase-matching technique also allows for future
large-scale upgrades.Comment: 24 pages, 5 figures, Published version available with Open Access at
https://www.nature.com/articles/s41467-022-33913-
First results on the search for chameleons with the KWISP detector at CAST
We report on a first measurement with a sensitive opto-mechanical force sensor designed for the direct detection of coupling of real chameleons to matter. These dark energy candidates could be produced in the Sun and stream unimpeded to Earth. The KWISP detector installed on the CAST axion search experiment at CERN looks for tiny displacements of a thin membrane caused by the mechanical effect of solar chameleons. The displacements are detected by a Michelson interferometer with a homodyne readout scheme. The sensor benefits from the focusing action of the ABRIXAS X-ray telescope installed at CAST, which increases the chameleon flux on the membrane. A mechanical chopper placed between the telescope output and the detector modulates the incoming chameleon stream. We present the results of the solar chameleon measurements taken at CAST in July 2017, setting an upper bound on the force acting on the membrane of 80pN at 95% confidence level. The detector is sensitive for direct
coupling to matter 104 = ßm = 108, where the coupling to photons is locally bound to ß¿ = 1011
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