Particle astrophysics with high energy neutrinos

[1] Fast neutrons are generated naturally at the land surface by energetic cosmic rays. These “background” neutrons respond strongly to the presence of water at or near the land surface and represent a hitherto elusive intermediate spatial scale of observation that is ideal for land surface studies and modeling. Soil moisture, snow, and biomass each have a distinct influence on the spectrum, height profile, and directional intensity of neutron fluxes above the ground, suggesting that different sources of water at the land surface can be distinguished with neutron data alone. Measurements can be taken at fixed sites for long-term monitoring or in a moving vehicle for mapping over large areas. We anticipate applications in many previously problematic contexts, including saline environments, wetlands and peat bogs, rocky soils, the active layer of permafrost, and water and snow intercepted by vegetation, as well as calibration and validation of data from spaceborne sensors.

/pdf/nature-s-neutron-probe-land-surface-hydrology-at-an-elusive-46ehhpxnwh.pdf

Nature's neutron probe: Land surface hydrology at an elusive scale with cosmic rays

The topic of this review is the particle astrophysics of high energy neutrinos. High energy is defined as $E_{\nu} > 100$~MeV. Main topics include: -- atmospheric neutrinos and muons from $\pi$, $K$ and charm decay. They probe uncharted territory in neutrino oscillations and constitute both the background and calibration of high energy neutrino telescopes, -- sources of high energy neutrino beams: the galactic plane, the sun, X-ray binaries, supernova remnants and interactions of extra-galactic cosmic rays with background photons, -- an extensive review of the mechanisms by which active galaxies may produce high energy particle beams, -- high energy neutrino signatures of cold dark matter and, -- a brief review of detection techniques (water and ice Cherenkov detectors, surface detectors, radio- and acoustic detectors, horizontal airshower arrays) and the instruments under construction.

Particle Physics with High Energy Neutrinos

Results are presented of a harmonic analysis of the large-scale cosmic-ray (CR) anisotropy as observed by the Milagro observatory. We show a two-dimensional display of the sidereal anisotropy projections in right ascension (R.A.) generated by the fitting of three harmonics to 18 separate declination bands. The Milagro observatory is a water Cherenkov detector located in the Jemez mountains near Los Alamos, New Mexico. With a high duty cycle and large field of view, Milagro is an excellent instrument for measuring this anisotropy with high sensitivity at TeV energies. The analysis is conducted using a seven-year data sample consisting of more than 95 billion events, the largest such data set in existence. We observe an anisotropy with a magnitude around 0.1% for CRs with a median energy of 6 TeV. The dominant feature is a deficit region of depth (2.49 ± 0.02 stat. ± 0.09 sys.) ×10–3 in the direction of the Galactic north pole centered at 189 deg R.A. We observe a steady increase in the magnitude of the signal over seven years.

/pdf/the-large-scale-cosmic-ray-anisotropy-as-observed-with-1zh1vyrnpl.pdf

The large-scale cosmic-ray anisotropy as observed with milagro

In an attempt to understand the source and propagation of galactic cosmic rays we have employed the Modified Weighted Slab technique along with recent values of the relevant cross sections to compute primary to secondary ratios including B/C and Sub-Fe/Fe for different galactic propagation models. The models that we have considered are the disk-halo diffusion model, the dynamical halo wind model, the turbulent diffusion model and a model with minimal reacceleration. The modified weighted slab technique will be briefly discussed and a more detailed description of the models will be given. We will also discuss the impact that the various models have on the problem of anisotropy at high energy and discuss what properties of a particular model bear on this issue.

http://arxiv.org/pdf/astro-ph/0007293.pdf

The Modified Weighted Slab Technique: Models and Results

The radial intensity gradients near the ecliptic plane for galactic cosmic ray He (180-450 MeV/nucleon), H (130-220 MeV), and the integral counting rate of ions >70 MeV are studied using the Pioneer 10/11, Voyager 2, and IMP 6, 7, and 8 observing network over the 1972.25-1996.0 time period at heliocentric distances extending to 64 AU. These gradients display complex temporal and spatial changes that are dominated by the 11-year solar activity cycle but with the 22-year heliomagnetic cycle also having an important role. The data are well ordered out to ∼55 AU using a radial dependence of the intensity gradient g r of the form G 0 r α , where r is the heliocentric distance in astronomical units (AU). With this representation it becomes possible to estimate g r as a function of r at a given time or as a function of time at a given radial distance. Over successive solar minima these values of g r decrease rapidly with increasing heliocentric distance, and for He at 50 AU are 3 times larger in 1987 than in 1977, in general agreement with the expected effects of particle gradient and curvature drifts in the large-scale interplanetary magnetic field. Near solar maximum the gradients increase significantly over their solar minimum values, with a greatly reduced radial dependence for He, while for H, g r increases with increasing r. The radial gradients of the integral rate of ions >70 MeV show a much smaller temporal and spatial variation.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JA01871

Radial intensity gradients of galactic cosmic rays (1972–1995) in the heliosphere

Extensive air showers (EAS) with median primary energy (E
 m) of (1013÷1015) eV have been observed since 1970 at Mt. Norikura (2770 m above sea level; geographic latitude 36.1°N, longitude 137.6°E) in order to study a cosmic-ray sidereal daily variation of galactic origin. We report here a summary of the observed results. EAS shows a significant sidereal diurnal variation with an amplitude (0.060±0.003)% and a phase (0.8±0.3) h sidereal local time forE
 m≈1.5·1013eV. Sidereal semi- and tridiurnal variations also are statistically significant. These variations are proved to be of galactic origin by a method which uses the difference of two directional (eastward and westward) air shower observations. It is found that these variations are subject, as predicted by Nagashimaet al., to the annual variation due to the heliomagnetospheric modulation of the galactic anisotropy, which dominates in the rigidity region ≈1012V, and further that the annual variation changes its phase due to the polarity reversal of the polar magnetic field of the Sun, which occurs at the period of the maximum solar activity. This indicates that the anisotropy is produced by the charged cosmic rays, contrary to the expectation from the γ-ray origin hypothesis suggested by Alexeenko and Navara. With the increase ofE
 m, the anisotropy seems to be reduced as we have not been able to detect any significant sidereal variation in EAS withE
 m≈2·1014eV. This seems contradictory to the conventional conclusion that the energy spectrum of the anisotropy is flat or slightly increases with energy.

/pdf/galactic-cosmic-ray-anisotropy-and-its-modulation-in-the-9iwyy8rxzv.pdf

Galactic cosmic-ray anisotropy and its modulation in the heliomagnetosphere inferred from air shower observation at Mt. Norikura

We have analyzed the yearly averaged sidereal daily variations in the count rates of 44 underground muon telescopes by fitting Gaussian functions to the data. These functions represent the Loss-cone (LC) and Tail-in (TI) anisotropies of the recent sidereal anisotropies model proposed by Nagashima et al. (1). The underground muon telescopes cover the median rigidity range 143 GV-1400 GV and almost entire celestial sphere. From the Gaussian amplitudes and positions we have confirmed that the TI anisotropy is more prominent in the southern hemisphere with its reference axis located at declination (δ)≈14 °S, and right ascension (α)≈4.7 sidereal hours. The TI anisotropy is asymmetric about its reference axis and the observed time of maximum intensity depends on the viewing latitude of the underground muon telescopes. We have used the parameters of the Gaussian fits to devise an empirical model of the sidereal anisotropies. We present these results and discuss the TI anisotropy in relation to the model heliosph...

Gaussian analysis of two hemisphere observations of galactic cosmic ray sidereal anisotropies

By using the two-hemisphere network of underground muon telescopes we have examined the average sidereal daily variations in the count rates recorded by 48-component muon telescopes. The telescopes respond to primary cosmic rays with rigidities between ∼140 and 1700 GV and view almost the entire celestial sphere. We have modeled the data by using Gaussian functions, and we have related the Gaussian parameters to the recent tail-in and loss cone anisotropy model proposed by Nagashima et al. [1995a, b] to explain the sidereal daily variations. We have used the model parameters to derive the rigidity and latitude spectra of the galactic anisotropies and find them to be qualitatively in agreement with Nagashima et al.'s predictions. The results indicate, however, that the tail-in anisotropy is asymmetric about its reference axis, whereas the loss cone anisotropy is more symmetric. We show that these characteristics of the galactic anisotropies may explain the north–south asymmetry observed in the amplitude of the sidereal diurnal variation derived from Fourier analysis techniques.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JA02520

Preliminary analysis of two‐hemisphere observations of sidereal anisotropies of galactic cosmic rays

The Cosmic Ray Radial and Latitudinal Intensity Gradients in the Inner and Outer Heliosphere 1996-2001.3

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