arXiv subjects

Paolo Desiati

Publications and source records attributed to Paolo Desiati.

33 records · Page 2Linked to original sources

arXiv2019

Experimental biases on the heliospheric contribution to the observed TeV cosmic ray anisotropy

The arrival direction distribution of cosmic ray particles observed on Earth is shaped by the cumulative effects of their galactic source locations and of trajectory bending in the turbulent interstellar magnetic field. Coherent magnetic structures are expected to disrupt particle trajectories and their observed distribution, as well. The heliosphere, the large magnetic bubble generated by the sweeping effect of solar wind on the local interstellar plasma, strongly affects the TeV cosmic ray particles detected on Earth. By unfolding the heliospheric influence on the observed anisotropy, it is possible to determine the pitch angle distribution of cosmic rays in the interstellar medium. This information makes it possible to study in detail the global diffusion properties of TeV cosmic rays in the Galaxy. However, observational blindness to key features of the cosmic ray arrival direction distribution may lead to biases in the determination of the heliospheric influence and of the interstellar CR distribution. Any inference of galactic TeV CR diffusion properties must carefully account for local propagation phenomena and observational limitations.

astro-ph.HE↗

arXiv2016

A New Maximum-Likelihood Technique for Reconstructing Cosmic-Ray Anisotropy at All Angular Scales

The arrival directions of TeV-PeV cosmic rays show weak but significant anisotropies with relative intensities at the level of one per mille. Due to the smallness of the anisotropies, quantitative studies require careful disentanglement of detector effects from the observation. We discuss an iterative maximum-likelihood reconstruction that simultaneously fits cosmic ray anisotropies and detector acceptance. The method does not rely on detector simulations and provides an optimal anisotropy reconstruction for ground-based cosmic ray observatories located in the middle latitudes. It is particularly well suited to the recovery of the dipole anisotropy, which is a crucial observable for the study of cosmic ray diffusion in our Galaxy. We also provide general analysis methods for recovering large- and small-scale anisotropies that take into account systematic effects of the observation by ground-based detectors.

astro-ph.HE↗

arXiv2014

The Transport of Cosmic Rays Across Magnetic Fieldlines

The long residence times and small anisotropies of cosmic rays suggest that they are well confined and well scattered by the Galactic magnetic field. Due to the disklike shape of the confinement volume, transport in the vertical direction, perpendicular to the mean Galactic magnetic field, is key to cosmic ray escape. It has long been recognized that this vertical transport depends both on the vertical component of the fieldlines themselves and on the extent to which the cosmic rays are tied to the fieldlines. In this paper we use magnetic fields with very simple spatial and temporal structure to isolate some important features of cross fieldline transport. We show that even simple magnetic nonuniformities combined with pitch angle scattering can enhance cross fieldline transport by several orders of magnitude, while pitch angle scattering is unnecessary for enhanced transport if the field is chaotic. Nevertheless, perpendicular transport is much less than parallel transport in all the cases we study. We apply the results to confinement of cosmic rays in the Fermi Bubbles.

astro-ph.HE↗

arXiv2013

Observation of TeV-PeV cosmic ray anisotropy with IceCube, IceTop and AMANDA

The study of cosmic ray anisotropy in the TeV-PeV energy range could provide clues about the origin and propagation of cosmic rays in our galactic neighborhood. Because the observed anisotropy is very small, below the per-mille level, large event volumes are needed in order to characterize it in sufficient detail. Over the last six years, the IceCube Observatory has collected 150 billion cosmic ray induced muon events. This large data sample made it possible to detect anisotropies in the southern hemisphere, down to the 10$^{-5}$ level, at primary energies in excess of 10 TeV. The observed anisotropy is not a simple dipole, but it can be described as composed of multipole components of the spherical harmonic expansion, to about 10$^{\circ}$. A change in topological structure of the cosmic ray arrival distribution is observed above 100 TeV. Data collected with the air shower array IceTop above 300 TeV confirm the observations up to the PeV energy scale. Moreover, the addition of data collected with the AMANDA neutrino telescope, which operated between 2000 and 2007, has enabled us to search for time variability in the observed TeV anisotropy.

astro-ph.HE↗

arXiv2013

Influence of hadronic interaction models and the cosmic ray spectrum on the high energy atmospheric muon and neutrino flux

The recent observations of muon charge ratio up to about 10 TeV and of atmospheric neutrinos up to energies of about 400 TeV has triggered a renewed interest into the high-energy interaction models and cosmic ray primary composition. A reviewed calculation of lepton spectra produced in cosmic-ray induced extensive air showers is carried out with a primary cosmic-ray spectrum that fits the latest direct measurements below the knee. In order to achieve this, we used a full Monte Carlo method to derive the inclusive differential spectra (yields) of muons, muon neutrinos and electron neutrinos at the surface for energies between 80 GeV and hundreds of PeV. The air shower simulator {\sc corsika} 6.990 was used for showering and propagation of the secondary particles through the atmosphere, employing the established high-energy hadronic interaction models {\sc sibyll} 2.1, {\sc qgsjet-01} and {\sc qgsjet-ii 03}. We show that the performance of the interaction models allows makes it possible to predict the spectra within experimental uncertainties, while {\sc sibyll} generally yields a higher flux at the surface than the qgsjet models. The calculation of the flavor and charge ratios has lead to inconsistent results, mainly influenced by the different representations of the K/$π$ ratio within the models. Furthermore, we could quantify systematic uncertainties of atmospheric muon- and neutrino fluxes, associated to the models of the primary cosmic-ray spectrum and the interaction models. For most recent parametrizations of the cosmic-ray primary spectrum, atmospheric muons can be determined with an uncertainty smaller than $^{+15}_{-13}$% of the average flux. Uncertainties of the muon- and electron neutrino fluxes can be calculated within an average error of $^{+32}_{-22}$% and $^{+25}_{-19}$%, respectively.

astro-ph.HE↗

arXiv2012

IceCube Observatory: Neutrinos and the Origin of Cosmic Rays

The completed IceCube Observatory, the first km^3 neutrino telescope, is already providing the most stringent limits on the flux of high energy cosmic neutrinos from point-like and diffuse galactic and extra-galactic sources. The non-detection of extra-terrestrial neutrinos has important consequences on the origin of the cosmic rays. Here the current status of astrophysical neutrino searches, and of the observation of a persistent cosmic ray anisotropy above 100 TeV, are reviewed.

astro-ph.HE↗

arXiv2012

Beaming neutrino and antineutrinos across the Earth to disentangle neutrino mixing parameters

A MINOS result seemed to hint a different anti-neutrino mass splitting and mixing angle with respect to the neutrino ones, offering a hint for a CPT violation in lepton sector. However more recent MINOS data reduced the neutrino-antineutrino differences leading to a narrow discrepancy almost compatible with no CPT violation, hard to be disentangled. Moreover last a few years of OPERA activity on tau appearance is still un-probed (one unique event). Both flavor muon-tau mixing, tau appearance and eventual CPT violation disentanglement need more tools to be enhanced. Atmospheric muon neutrino spectra and anisotropy in Deep Core at ten-tens GeV (yet unpublished) may test the muon-tau conversion but they can hardly reveal such last tiny MINOS CPT asymmetry. We show how the longest baseline neutrino oscillation available, crossing most of the Earth diameter, within an OPERA-like experiment from CERN (or FERMILAB) to ICECUBE-Deep Core neutrino detector at 21 GeV energy, may at best disentangle even last tiny CPT violation (within 6 sigma a year) while testing at highest rate tau-antitau appearance. We propose the muon neutrino disappearance or (for any CPT violation) the partial anti-muon appearance at the longest distances. Such a tuned detection experiment may lead to a clear and strong signature of tau or anti-tau generation (even within its neutral current noise background events): nearly one antitau or two tau a day. The tau appearance signal is above (or within) 10 sigma a year, even for 1% OPERA-like experiment. Peculiar configurations for theta_13 angle test and hierarchy neutrino mass test may also be addressed by a Deep Core-PINGU array detector observing electron neutrino shower at 6 GeV neutrino energy windows.

hep-ph↗

arXiv2010

Large Scale Cosmic Ray Anisotropy With IceCube

We report on a study of the anisotropy in the arrival direction of cosmic rays with a median energy per Cosmic Ray (CR) particle of ~ 14 TeV using data from the IceCube detector. IceCube is a neutrino observatory at the geographical South Pole, when completed it will comprise 80 strings plus 6 additional strings for the low energy array Deep Core. The strings are deployed in the deep ice between 1,450 and 2,450 meters depth, each string containing 60 optical sensors. The data used in this analysis were collected from April 2007 to March 2008 with 22 deployed strings. The data contain ~ 4.3 billion downward going muon events. A two-dimensional skymap is presented with an evidence of 0.06% large scale anisotropy. The energy dependence of this anisotropy at median energies per CR particle of 12 TeV and 126 TeV is also presented in this work. This anisotropy could arise from a number of possible effects; it could further enhance the understanding of the structure of the galactic magnetic field and possible cosmic ray sources.

astro-ph.HE↗

arXiv2010

Neutrino Astrophysics and Galactic Cosmic Ray Anisotropy in IceCube

The IceCube Observatory is a kilometer-cube neutrino telescope under construction at the South Pole and planned to be completed in early 2011. When completed it will consist of 5,160 Digital Optical Modules (DOMs) which detect Cherenkov radiation from the charged particles produced in neutrino interactions and by cosmic ray initiated atmospheric showers. IceCube construction is currently 90% complete. A selection of the most recent scientific results are shown here. The measurement of the anisotropy in arrival direction of galactic cosmic rays will also be presented and discussed.

astro-ph.IM↗

arXiv2010

Seasonal variation of atmospheric leptons as a probe of charm

The intensity of TeV atmospheric muons and neutrinos depends on the temperature in the stratosphere. We show that the energy-dependence in the 100 TeV range of the correlation with temperature is sensitive to the fraction of muons and neutrinos from decay of charmed hadrons. We discuss the prospects for using the temperature effect as observed in gigaton neutrino detectors to measure the charm contribution.

astro-ph.HE↗

arXiv2010

Atmospheric Variations as observed by IceCube

We have measured the correlation of rates in IceCube with long and short term variations in the South Pole atmosphere. The yearly temperature variation in the middle stratosphere (30-60 hPa) is highly correlated with the high energy muon rate observed deep in the ice, and causes a +/-10% seasonal modulation in the event rate. The counting rates of the surface detectors, which are due to secondary particles of relatively low energy (muons, electrons and photons), have a negative correlation with temperatures in the lower layers of the stratosphere (40-80 hPa), and are modulated at a level of +/-5%. The region of the atmosphere between pressure levels 20-120 hPa, where the first cosmic ray interactions occur and the produced pions/kaons interact or decay to muons, is the Antarctic ozone layer. The anticorrelation between surface and deep ice trigger rates reflects the properties of pion/kaon decay and interaction as the density of the stratospheric ozone layer changes. Therefore, IceCube closely probes the ozone hole dynamics, and the temporal behavior of the stratospheric temperatures.

astro-ph.HE↗

arXiv2008

Neutrino Astronomy with the IceCube Observatory and Implications for Astroparticle Physics

The IceCube Observatory is a km^3 neutrino telescope currently under construction at the geographic South Pole. It will comprise 4800 optical sensors deployed on 80 vertical strings between 1450 and 2450 meters under the ice surface. Currently IceCube is operational and recording data with 40 strings (i.e. 2400 optical sensors). The IceCube Observatory will collect an unprecedented number of high energy neutrinos that will allow us to pursue studies of the atmospheric neutrino flux, and to search for extraterrestrial sources of neutrinos, whether point-like or unresolved. IceCube results will have an important impact on neutrino astrophysics, especially if combined with observations done with other cosmic messengers, such as gamma rays or ultra high energy cosmic rays. They may also reveal clues on the origin of cosmic rays at ultra high energies. Here we report results from AMANDA and the most recent results from the first 22 strings of IceCube.

astro-ph↗

arXiv2006

IceCube : Toward a km^3 Neutrino Telescope

Since the end of the 2005-2006 austral summer, the IceCube detector consists of an array of 9 strings, deployed between 1450 m and 2450 m of depth and containing 540 digital optical sensors and 16 IceTop surface stations with 64 sensors. With the integrated AMANDA-II experiment this is the world's largest neutrino telescope in operation. The construction status of IceCube is presented along with an update on physics performance study for the detection of high energy neutrinos. The potential of the full km^3-scale telescope in the search for astrophysical sources is also addressed.

astro-ph↗

arXiv2006

Neutrino Astronomy at the South Pole: latest Results from AMANDA-II

AMANDA-II is the largest neutrino telescope collecting data at the moment, and its main goal is to search for sources of high energy extra-terrestrial neutrinos. The detection of such sources could give non-controversial evidence for the acceleration of charged hadrons in cosmic objects like Supernova Remnants, Micro-quasars, Active Galactic Nuclei or Gamma Ray Bursts. No significant excess has been found in searching for neutrinos from both point-like and non-localized sources. However AMANDA-II has significantly improved analysis techniques for better signal-to-noise optimization. The km$^3$-scale IceCube telescope will enlarge the observable energy range and improve the sensitivities of high energy neutrino searches due to its 30 times larger effective area.

astro-ph↗

arXiv2003

Neutrino Astronomy at the South Pole: Status of the AMANDA Experiment

AMANDA (Antarctic Muon And Neutrino Detector Array) is a neutrino telescope built under the southern polar icecap, and its scope is exploring the possibility to detect high energy cosmic neutrinos generated by powerful celestial objects where acceleration mechanisms can bring protons up to 10^20 eV. We describe the achievements and results from the AMANDA-B10 prototype and the preliminary results from the current AMANDA-II detector showing a dramatic increase in sensitivity. An outlook on IceCube will be given.

astro-ph↗