69 research outputs found
Violation of Quasineutrality in Semiconductor Transport: The Dember Effect
Exact solution of the linearized equations for steady-state transport in
semiconductors yields two modes that vary exponentially in space, one involving
screening (without entropy production) and one involving diffusion and
recombination (with entropy production). Neither mode is quasineutral. For
constant surface photoexcitation with generation of electrons and holes, the
steady-state response is a linear combination of these modes, subject to global
electroneutrality. The resultant charge separation produces a voltage
difference across the sample (the Dember effect)
Search for Solar Axions Using Fe-57
We have made a search for Fe-57 gamma rays of energy 14.4 keV induced by
resonant absorption of monochromatic solar axions, as proposed by Moriyama. The
proposed axions are suggested to be emitted from the Sun, in M1 transitions
between the first, thermally excited state and the ground state of Fe-57. An
upper limit on hadronic axion mass of 745 eV is obtained at the 95% confidence
level, it being assumed that z=0.56 and S=0.5.Comment: 4 pages, latex, revtex source, 1 postscript figure included, Title
revised, some references added and expanded discussion. Version accepted by
Phys. Lett.
Search for solar axions using Li-7
We describe a novel approach to the search for solar, near-monochromatic
hadronic axions, the latter being suggested to be created in the solar core
during M1 transitions between the first excited level of Li-7, at 478 keV, and
the ground state. As a result of Doppler broadening, in principle these axions
can be detected via resonant absorption by the same nuclide on the Earth.
Excited nuclei of Li-7 are produced in the solar interior by Be-7 electron
capture and thus the axions are accompanied by emission of Be-7 solar neutrinos
of energy 384 keV. An experiment was made which has yielded an upper limit on
hadronic axion mass of 32 keV at the 95% confidence level.Comment: revtex, 4 pages with 2 figures, title revised, minor changes, matches
version to appear in Phys. Rev.
Recent searches for solar axions and large extra dimensions
We analyze the data from two recent experiments designed to search for solar
axions within the context of multidimensional theories of the Kaluza-Klein
type. In these experiments, axions were supposed to be emitted from the solar
core, in M1 transitions between the first excited state and the ground state of
57Fe and 7Li. Because of the high multiplicity of axionic Kaluza-Klein states
which couple with the strength of ordinary QCD axions, we obtain much more
stringent experimental limits on the four-dimensional Peccei-Quinn breaking
scale f_{PQ}, compared with the solar QCD axion limit. Specifically, for the
57Fe experiment, f_{PQ}>1x10^6 GeV in theories with two extra dimensions and a
higher-dimensional gravitational scale M_H of order 100 TeV, and f_{PQ}>1x10^6
GeV in theories with three extra dimensions and M_H of order 1 TeV (to be
compared with the QCD axion limit, f_{PQ}>8x10^3 GeV). For the 7Li experiment,
f_{PQ}>1.4x10^5 GeV and 3.4x10^5 GeV, respectively (to be compared with the QCD
axion limit, f_{PQ}>1.9x10^2 GeV). It is an interesting feature of our results
that, in most cases, the obtained limit on f_{PQ} cannot be coupled with the
mass of the axion, which is essentially set by the (common) radius of the extra
dimensions.Comment: 4 pages, revtex 4, minor changes, version accepted by PR
Prospects for the CERN Axion Solar Telescope Sensitivity to 14.4 keV Axions
The CERN Axion Solar Telescope (CAST) is searching for solar axions using the
9.0 T strong and 9.26 m long transverse magnetic field of a twin aperture LHC
test magnet, where axions could be converted into X-rays via reverse Primakoff
process. Here we explore the potential of CAST to search for 14.4 keV axions
that could be emitted from the Sun in M1 nuclear transition between the first,
thermally excited state, and the ground state of 57Fe nuclide. Calculations of
the expected signals, with respect to the axion-photon coupling, axion-nucleon
coupling and axion mass, are presented in comparison with the experimental
sensitivity.Comment: 4 pages, 1 figure. Submitted to Nucl. Instr. and Meth.
New solar axion search in CAST with He filling
The CERN Axion Solar Telescope (CAST) searches for conversion in
the 9 T magnetic field of a refurbished LHC test magnet that can be directed
toward the Sun. Two parallel magnet bores can be filled with helium of
adjustable pressure to match the X-ray refractive mass to the axion
search mass . After the vacuum phase (2003--2004), which is optimal for
eV, we used He in 2005--2007 to cover the mass range of
0.02--0.39 eV and He in 2009--2011 to scan from 0.39--1.17 eV. After
improving the detectors and shielding, we returned to He in 2012 to
investigate a narrow range around 0.2 eV ("candidate setting" of our
earlier search) and 0.39--0.42 eV, the upper axion mass range reachable with
He, to "cross the axion line" for the KSVZ model. We have improved the
limit on the axion-photon coupling to (95% C.L.), depending on the pressure settings. Since 2013, we
have returned to vacuum and aim for a significant increase in sensitivity.Comment: CAST Collaboration 6 pages 3 figure
Hunting up low-mass bosons from the Sun using HPGe detector
In this experiment we aim to look for keV-mass bosons emitted from the Sun,
by looking at a process analogous to the photoelectric/Compton effect inside
the HPGe detector. Their coupling to both electrons and nucleons is assumed.
For masses above 25 keV, the mass dependence of our limit on the
scalar-electron coupling reveals a constraint which proves stronger than that
obtained recently and based on the very good agreement between the measured and
predicted solar neutrino flux from the ^{8}B reaction. On the other hand, the
mass dependence of our limit on the scalar-proton/electron coupling together
entails a limit on a possible Yukawa addition to the gravitational inverse
square low. Such a constraint on the Yukawa interactions proves much stronger
than that derived from the latest AFM Casimir force measurement.Comment: elsarticle style, 4 eps figures, 4 pages, minor corrections, some
clarifications added, to appear in Phys. Lett.
Results and perspectives of the solar axion search with the CAST experiment
The status of the solar axion search with the CERN Axion Solar Telescope
(CAST) will be presented. Recent results obtained by the use of He as a
buffer gas has allowed us to extend our sensitivity to higher axion masses than
our previous measurements with He. With about 1 h of data taking at each of
252 different pressure settings we have scanned the axion mass range 0.39 eV 0.64 eV. From the absence of an excess of x rays when the
magnet was pointing to the Sun we set a typical upper limit on the axion-photon
coupling of g GeV at 95% C.L., the
exact value depending on the pressure setting. CAST published results represent
the best experimental limit on the photon couplings to axions and other similar
exotic particles dubbed WISPs (Weakly Interacting Slim Particles) in the
considered mass range and for the first time the limit enters the region
favored by QCD axion models. Preliminary sensitivities for axion masses up to
1.16 eV will also be shown reaching mean upper limits on the axion-photon
coupling of g GeV at 95% C.L.
Expected sensibilities for the extension of the CAST program up to 2014 will be
presented. Moreover long term options for a new helioscope experiment will be
evoked.Comment: 4 pages, 2 pages, to appear in the proceedings of the 24th Rencontres
de Blois V2 A few affiliations were not corrected in previous version V3
Author adde
Search for chameleons with CAST
In this work we present a search for (solar) chameleons with the CERN Axion
Solar Telescope (CAST). This novel experimental technique, in the field of dark
energy research, exploits both the chameleon coupling to matter () and to photons () via the Primakoff effect. By reducing
the X-ray detection energy threshold used for axions from 1keV to 400eV
CAST became sensitive to the converted solar chameleon spectrum which peaks
around 600eV. Even though we have not observed any excess above background,
we can provide a 95% C.L. limit for the coupling strength of chameleons to
photons of for .Comment: 8 pages, 12 figure
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
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