New detection technologies for ultra-high energy cosmic rays and neutrinos

Even with an accumulated data set from an integrated six years of lifetime from the Auger experiment, no point sources of charged cosmic rays have be identified at the highest energies. Significantly increased apertures such as promised by the JEMEUSO mission will be required to identify these sources from the cosmic ray signatures themselves. However, in employing water-cherenkov surface detectors as well as fluorescence telescopes, Auger has demonstrated the power provided by the hybrid technology approach. New detection technologies thus provide a valuable tool, in particular for the study of systematic effects. Over the past decade, in particular radio detection of cosmic ray air-showers has become a viable future detection technology to enhance and complement existing air-shower experiments. Following the proof-of-principle provided by the Lopes experiment, this technology is now being pursued in all major air-shower detectors. In the MHz regime, the radio signal is dominated by geomagnetic emission from the electrons deflected in the earth magnetic field, with secondary contributions from a global charge excess. As the majority of the energy in the shower is carried by these electron and the radio signal traverses the atmosphere basically unattenuated, this approach not only promises superior energy resolution but may also provide an independent handle on the longitudinal shower development and hence the primary composition. Theoretical signal predictions provided by detailed Monte-Carlo simulations as well as analytic shower parametrizations are in good agreement with measurements provided by the AERA and Codalema experiments. Recent efforts also include studies of the radio emission in the GHz regime, where the ambient noise is significantly reduced, yet the emission mechanism in this regime has not been firmly established yet. As neutrinos are not deflected in the intergalactic magnetic fields, the detection of neutrino-induced cascades in dense media provides another promising approachfor the identification of the sources of cosmic rays. The low event rates and large required target volumes limit the experimental methods to far-ranging signatures .from the cascade, such as acoustic emission from the quasi-instantaneous energy deposit or Cherenkov emission from the charged particles in the cascade. Searching for optical Cherenkov photons in a cubic-kilometer of Antarctic ice, the IceCube experiment has recently found an excess of high-energy neutrinos in the TeV-PeV range.Yet its effective volume is too small to detect the GZK flux predicted from interaction of the highest-energy cosmic rays with the ambient cosmic microwave background. Seeking to increase the observed target volume, radio observations of the rim of the moon have energy thresholds well beyond the EeV scale and thus are more likely to find interactions of charged cosmic rays than GZK neutrinos. The currently best sensitivity to this flux is provided from searches for GHz radio emission of neutrino-induced cascades in the antarctic ice from the ANITA ballon experiment. While no high-energy neutrinos have been found, a geomagnetic emission component from air-shower

Differential limit on the extremely-high-energy cosmic neutrino flux in the presence of astrophysical background from nine years of IceCube data

We report a quasi-differential upper limit on the extremely-high-energy (EHE) neutrino flux above $5\times 10^{6}$ GeV based on an analysis of nine years of IceCube data. The astrophysical neutrino flux measured by IceCube extends to PeV energies, and it is a background flux when searching for an independent signal flux at higher energies, such as the cosmogenic neutrino signal. We have developed a new method to place robust limits on the EHE neutrino flux in the presence of an astrophysical background, whose spectrum has yet to be understood with high precision at PeV energies. A distinct event with a deposited energy above $10^{6}$ GeV was found in the new two-year sample, in addition to the one event previously found in the seven-year EHE neutrino search. These two events represent a neutrino flux that is incompatible with predictions for a cosmogenic neutrino flux and are considered to be an astrophysical background in the current study. The obtained limit is the most stringent to date in the energy range between $5 \times 10^{6}$ and $5 \times 10^{10}$ GeV. This result constrains neutrino models predicting a three-flavor neutrino flux of $E_\nu^2\phi_{\nu_e+\nu_\mu+\nu_\tau}\simeq2\times 10^{-8}\ {\rm GeV}/{\rm cm}^2\ \sec\ {\rm sr}$at$10^9\ {\rm GeV}$. A significant part of the parameter-space for EHE neutrino production scenarios assuming a proton-dominated composition of ultra-high-energy cosmic rays is excluded.Comment: The version accepted for publication in Physical Review

Functional Changes in the Snail Statocyst System Elicited by Microgravity

BACKGROUND: The mollusk statocyst is a mechanosensing organ detecting the animal's orientation with respect to gravity. This system has clear similarities to its vertebrate counterparts: a weight-lending mass, an epithelial layer containing small supporting cells and the large sensory hair cells, and an output eliciting compensatory body reflexes to perturbations. METHODOLOGY/PRINCIPAL FINDINGS: In terrestrial gastropod snail we studied the impact of 16- (Foton M-2) and 12-day (Foton M-3) exposure to microgravity in unmanned orbital missions on: (i) the whole animal behavior (Helix lucorum L.), (ii) the statoreceptor responses to tilt in an isolated neural preparation (Helix lucorum L.), and (iii) the differential expression of the Helix pedal peptide (HPep) and the tetrapeptide FMRFamide genes in neural structures (Helix aspersa L.). Experiments were performed 13-42 hours after return to Earth. Latency of body re-orientation to sudden 90° head-down pitch was significantly reduced in postflight snails indicating an enhanced negative gravitaxis response. Statoreceptor responses to tilt in postflight snails were independent of motion direction, in contrast to a directional preference observed in control animals. Positive relation between tilt velocity and firing rate was observed in both control and postflight snails, but the response magnitude was significantly larger in postflight snails indicating an enhanced sensitivity to acceleration. A significant increase in mRNA expression of the gene encoding HPep, a peptide linked to ciliary beating, in statoreceptors was observed in postflight snails; no differential expression of the gene encoding FMRFamide, a possible neurotransmission modulator, was observed. CONCLUSIONS/SIGNIFICANCE: Upregulation of statocyst function in snails following microgravity exposure parallels that observed in vertebrates suggesting fundamental principles underlie gravi-sensing and the organism's ability to adapt to gravity changes. This simple animal model offers the possibility to describe general subcellular mechanisms of nervous system's response to conditions on Earth and in space

In-situ estimation of ice crystal properties at the South Pole using LED calibration data from the IceCube Neutrino Observatory

The IceCube Neutrino Observatory instruments about 1 km3 of deep, glacial ice at the geographic South Pole using 5160 photomultipliers to detect Cherenkov light emitted by charged relativistic particles. A unexpected light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow direction of the ice. Birefringent light propagation has been examined as a possible explanation for this effect. The predictions of a first-principles birefringence model developed for this purpose, in particular curved light trajectories resulting from asymmetric diffusion, provide a qualitatively good match to the main features of the data. This in turn allows us to deduce ice crystal properties. Since the wavelength of the detected light is short compared to the crystal size, these crystal properties do not only include the crystal orientation fabric, but also the average crystal size and shape, as a function of depth. By adding small empirical corrections to this first-principles model, a quantitatively accurate description of the optical properties of the IceCube glacial ice is obtained. In this paper, we present the experimental signature of ice optical anisotropy observed in IceCube LED calibration data, the theory and parametrization of the birefringence effect, the fitting procedures of these parameterizations to experimental data as well as the inferred crystal properties.</p