Spiking is a useful approach to improve the accuracy of regional or national calibrations when they are used to predict at local scales. To do this, a small subset of local samples (spiking subset) ...is added to recalibrate the initial calibration. If the spiking subset is small in comparison with the size of the initial calibration set, then it could have little noticeable effect and a small improvement can be expected. For these reasons, we hypothesized that the accuracy of the spiked calibrations can be improved when the spiking subset is extra‐weighted. We also hypothesized that the spiking subset selection and the initial calibration size could affect the accuracy of the recalibrated models. To test these hypotheses, we evaluated different strategies to select the best spiking subset, with and without extra‐weighting, to spike three different‐sized initial calibrations. These calibrations were used to predict the soil organic carbon (SOC) content in samples from four target sites. Our results confirmed that spiking improved the prediction accuracy of the initial calibrations, with any differences depending on the spiking subset used. The best results were obtained when the spiking subset contained local samples evenly distributed in the spectral space, regardless of the initial calibration's characteristics. The accuracy was improved significantly when the spiking subset was extra‐weighted. For medium‐ and large‐sized initial calibrations, the improvement from extra‐weighting was larger than that caused by the increase in spiking subset size. Similar accuracies were obtained using small‐ and large‐sized calibrations, suggesting that incipient spectral libraries could be useful if the spiking subset is properly selected and extra‐weighted. When small‐sized spiking subsets were used, the predictions were more accurate than those obtained with ‘geographically‐local’ models. Overall, our results indicate that we can minimize the efforts needed to use near‐infrared (NIR) spectroscopy effectively for SOC assessment at local scales.
Astroparticle experiments have provided a long list of achievements both for particle physics and astrophysics. Many of these experiments require to be protected from the background produced by ...cosmic rays in the atmosphere. The main options for such protection are to build detectors deep under ground (mines, tunnels) or in the deep sea or Antarctic ice. In this proceeding we review the main results shown in the RICAP 2013 conference related with these kind of experiments and the prospects for the future.
Neutrino telescopes have a wide scientific scope. One of their main goals is the detection of dark matter, for which they have specific advantages. Neutrino telescopes offer the possibility of ...looking at several kinds of sources, not all of them available to other indirect searches. In this work we provide an overview of the results obtained by the ANTARES neutrino telescope, which has been taking data for almost ten years. One of the most interesting ones is the Sun, since a detection of high energy neutrinos from it would be a very clean indication of dark matter, given that no significant astrophysical backgrounds are expected, contrary to other indirect searches. Moreover, the limits from neutrino telescopes for spin-dependent cross section are the most restrictive ones. Another interesting source is the Galactic Centre, for which ANTARES has a better visibility than IceCube, due to its geographical location. This search gives limits on the annihilation cross section. Other dark matter searches carried out in ANTARES include the Earth and dwarf galaxies.
Results and prospects of dark matter searches with ANTARES Zornoza, J.D.; Lambard, G.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2014, Letnik:
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Dark matter is one of the most important scientific goals for neutrino telescopes. These instruments have particular advantages with respect to other experimental approaches. Compared to direct ...searches, the sensitivity of neutrino telescopes to probe the spin-dependent cross-section of WIMP-proton is unsurpassed. On the other hand, neutrino telescopes can look for dark matter in the Sun, so a potential signal would be a strong indication of dark matter, contrary to the case of other indirect searches like gammas or cosmic rays, where more conventional astrophysical interpretations are very hard to rule out. We present here the results of a binned search for neutralino annihilation in the Sun using data gathered by the ANTARES neutrino telescope during 2007–2008. These results include limits on the neutrino and muon flux and on the spin-dependent and spin-independent cross-section of the WIMP-proton scattering.
ANTARES is the first neutrino telescope in the sea. It consists of a three-dimensional array of 885 photomultipliers to collect the Cherenkov light induced by relativistic muons produced in CC ...interactions of high energy neutrinos. One of the main scientific goals of the experiment is the search for dark matter. We present here the analysis of data taken during 2007 and 2008 to look for a WIMP signal in the Sun. WIMPs are one of the most popular scenarios to explain the dark matter content of the Universe. They would accumulate in massive objects like the Sun or the Galactic Center and their self-annihilation would produce (directly or indirectly) high energy neutrinos detectable by neutrino telescopes. Contrary to other indirect searches (like with gamma rays or positrons), the search for neutrinos in the Sun is free from other astrophysical contributions, so the interpretation of a potential signal in terms of dark matter is much more robust.
A search for cosmic neutrino sources using the data collected with the ANTARES neutrino telescope between early 2007 and the end of 2015 is performed. For the first time, all neutrino ...interactions-charged- and neutral-current interactions of all flavors-are considered in a search for point-like sources with the ANTARES detector. In previous analyses, only muon neutrino charged-current interactions were used. This is achieved by using a novel reconstruction algorithm for shower-like events in addition to the standard muon track reconstruction. The shower channel contributes about 23% of all signal events for an E−2 energy spectrum. No significant excess over background is found. The most signal-like cluster of events is located at (α,δ)=(343.8°,23.5°) with a significance of 1.9σ. The neutrino flux sensitivity of the search is about E2dΦ/dE=6×10−9 GeV cm−2 s−1 for declinations from −90° up to −42°, and below 10−8 GeV cm−2 s−1 for declinations up to 5°. The directions of 106 source candidates and 13 muon track events from the IceCube high-energy sample events are investigated for a possible neutrino signal and upper limits on the signal flux are determined.
A search for cosmic neutrino sources using six years of data collected by the ANTARES neutrino telescope has been performed. Clusters of muon neutrinos over the expected atmospheric background have ...been looked for. No clear signal has been found. The most signal-like accumulation of events is located at equatorial coordinates R.A. = -46degrees.8 and decl. = -64degrees.9 and corresponds to a 2.2sigma background fluctuation. In addition, upper limits on the flux normalization of an E super(-2) muon neutrino energy spectrum have been set for 50 pre-selected astrophysical objects. Finally, motivated by an accumulation of seven events relatively close to the Galactic Center in the recently reported neutrino sample of the IceCube telescope, a search for point sources in a broad region around this accumulation has been carried out. No indication of a neutrino signal has been found in the ANTARES data and upper limits on the flux normalization of an E super(-2) energy spectrum of neutrinos from point sources in that region have been set. The 90% confidence level upper limits on the muon neutrino flux normalization vary between 3.5 and 5.1 X 10 super(-8) GeV cm super(-2) s super(-1), depending on the exact location of the source.
A search for a diffuse flux of astrophysical muon neutrinos, using data collected by the ANTARES neutrino telescope is presented. A (0.83×2π) sr sky was monitored for a total of 334 days of ...equivalent live time. The searched signal corresponds to an excess of events, produced by astrophysical sources, over the expected atmospheric neutrino background. The observed number of events is found compatible with the background expectation. Assuming an E−2 flux spectrum, a 90% c.l. upper limit on the diffuse νμ flux of E2Φ90%=5.3×10−8 GeVcm−2s−1sr−1 in the energy range 20 TeV–2.5 PeV is obtained. Other signal models with different energy spectra are also tested and some rejected.
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