261 research outputs found
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
The taming of an impossible child: a standardized all-in approach to the phylogeny of Hymenoptera using public database sequences
<p>Abstract</p> <p>Background</p> <p>Enormous molecular sequence data have been accumulated over the past several years and are still exponentially growing with the use of faster and cheaper sequencing techniques. There is high and widespread interest in using these data for phylogenetic analyses. However, the amount of data that one can retrieve from public sequence repositories is virtually impossible to tame without dedicated software that automates processes. Here we present a novel bioinformatics pipeline for downloading, formatting, filtering and analyzing public sequence data deposited in GenBank. It combines some well-established programs with numerous newly developed software tools (available at <url>http://software.zfmk.de/</url>).</p> <p>Results</p> <p>We used the bioinformatics pipeline to investigate the phylogeny of the megadiverse insect order Hymenoptera (sawflies, bees, wasps and ants) by retrieving and processing more than 120,000 sequences and by selecting subsets under the criteria of compositional homogeneity and defined levels of density and overlap. Tree reconstruction was done with a partitioned maximum likelihood analysis from a supermatrix with more than 80,000 sites and more than 1,100 species. In the inferred tree, consistent with previous studies, "Symphyta" is paraphyletic. Within Apocrita, our analysis suggests a topology of Stephanoidea + (Ichneumonoidea + (Proctotrupomorpha + (Evanioidea + Aculeata))). Despite the huge amount of data, we identified several persistent problems in the Hymenoptera tree. Data coverage is still extremely low, and additional data have to be collected to reliably infer the phylogeny of Hymenoptera.</p> <p>Conclusions</p> <p>While we applied our bioinformatics pipeline to Hymenoptera, we designed the approach to be as general as possible. With this pipeline, it is possible to produce phylogenetic trees for any taxonomic group and to monitor new data and tree robustness in a taxon of interest. It therefore has great potential to meet the challenges of the phylogenomic era and to deepen our understanding of the tree of life.</p
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.
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
Solar axion search with the CAST experiment
The CAST (CERN Axion Solar Telescope) experiment is searching for solar
axions by their conversion into photons inside the magnet pipe of an LHC
dipole. The analysis of the data recorded during the first phase of the
experiment with vacuum in the magnet pipes has resulted in the most restrictive
experimental limit on the coupling constant of axions to photons. In the second
phase, CAST is operating with a buffer gas inside the magnet pipes in order to
extent the sensitivity of the experiment to higher axion masses. We will
present the first results on the data taking as well as the
system upgrades that have been operated in the last year in order to adapt the
experiment for the data taking. Expected sensitivities on the
coupling constant of axions to photons will be given for the recent run just started in March 2008.Comment: Proceedings of the ICHEP 2008 conferenc
The X-ray Telescope of CAST
The Cern Axion Solar Telescope (CAST) is in operation and taking data since
2003. The main objective of the CAST experiment is to search for a hypothetical
pseudoscalar boson, the axion, which might be produced in the core of the sun.
The basic physics process CAST is based on is the time inverted Primakoff
effect, by which an axion can be converted into a detectable photon in an
external electromagnetic field. The resulting X-ray photons are expected to be
thermally distributed between 1 and 7 keV. The most sensitive detector system
of CAST is a pn-CCD detector combined with a Wolter I type X-ray mirror system.
With the X-ray telescope of CAST a background reduction of more than 2 orders
off magnitude is achieved, such that for the first time the axion photon
coupling constant g_agg can be probed beyond the best astrophysical constraints
g_agg < 1 x 10^-10 GeV^-1.Comment: 19 pages, 25 figures and images, replaced by the revised version
accepted for publication in New Journal of Physic
Search for solar axion emission from 7Li and D(p,gamma)3He nuclear decays with the CAST gamma-ray calorimeter
We present the results of a search for a high-energy axion emission signal
from 7Li (0.478 MeV) and D(p,gamma)3He (5.5 MeV) nuclear transitions using a
low-background gamma-ray calorimeter during Phase I of the CAST experiment.
These so-called "hadronic axions" could provide a solution to the long-standing
strong-CP problem and can be emitted from the solar core from nuclear M1
transitions. This is the first such search for high-energy pseudoscalar bosons
with couplings to nucleons conducted using a helioscope approach. No excess
signal above background was found.Comment: 20 pages, 8 figures, final version to be published in JCA
Search for low Energy solar Axions with CAST
We have started the development of a detector system, sensitive to single
photons in the eV energy range, to be suitably coupled to one of the CAST
magnet ports. This system should open to CAST a window on possible detection of
low energy Axion Like Particles emitted by the sun. Preliminary tests have
involved a cooled photomultiplier tube coupled to the CAST magnet via a
Galileian telescope and a switched 40 m long optical fiber. This system has
reached the limit background level of the detector alone in ideal conditions,
and two solar tracking runs have been performed with it at CAST. Such a
measurement has never been done before with an axion helioscope. We will
present results from these runs and briefly discuss future detector
developments.Comment: Paper submitted to the proceedings of the "4th Patras Workshop on
Axions, WIMPs and WISPs", DESY, Hamburg Site - Germany, 18-21 June 2008.
Author affiliations are reported on the title page of the paper. In version
2: 1 affiliation change, 3 references adde
Fast photon detection for the COMPASS RICH detector
The COMPASS experiment at the SPS accelerator at CERN uses a large scale Ring
Imaging CHerenkov detector (RICH) to identify pions, kaons and protons in a
wide momentum range. For the data taking in 2006, the COMPASS RICH has been
upgraded in the central photon detection area (25% of the surface) with a new
technology to detect Cherenkov photons at very high count rates of several 10^6
per second and channel and a new dead-time free read-out system, which allows
trigger rates up to 100 kHz. The Cherenkov photons are detected by an array of
576 visible and ultra-violet sensitive multi-anode photomultipliers with 16
channels each. The upgraded detector showed an excellent performance during the
2006 data taking.Comment: Proceeding of the IPRD06 conference (Siena, Okt. 06
Fast Photon Detection for Particle Identification with COMPASS RICH-1
Particle identification at high rates is an important challenge for many
current and future high-energy physics experiments. The upgrade of the COMPASS
RICH-1 detector requires a new technique for Cherenkov photon detection at
count rates of several per channel in the central detector region, and a
read-out system allowing for trigger rates of up to 100 kHz. To cope with these
requirements, the photon detectors in the central region have been replaced
with the detection system described in this paper. In the peripheral regions,
the existing multi-wire proportional chambers with CsI photocathode are now
read out via a new system employing APV pre-amplifiers and flash ADC chips. The
new detection system consists of multi-anode photomultiplier tubes (MAPMT) and
fast read-out electronics based on the MAD4 discriminator and the F1-TDC chip.
The RICH-1 is in operation in its upgraded version for the 2006 CERN SPS run.
We present the photon detection design, constructive aspects and the first
Cherenkov light in the detector.Comment: Proceedings of the Imaging 2006 conference, Stockholm, Sweden, 27-30
June 2006, 5 pages, 6 figures, to appear in NIM A; corrected typo in caption
of Fig.
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