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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

20 years of cosmic muons research performed in IFIN-HH

During the last two decades a modern direction in particle physics research has been developed in IFIN-HH Bucharest, Romania. The history started with the WILLI detector built in IFIN-HH Bucharest in collaboration with KIT Karlsruhe (formerly Forschungszentrum Karlsruhe). The detector was designed for measurements of the low energy muon charge ratio (< 1GeV) based on a delayed coincidence method, measuring the decay time of the muons stopped in the detector: the positive muons decay freely, but the negative muons are captured in the atom thus creating muonic atoms and decay depending on the nature of the host atom. In a first configuration, the WILLI detector was placed in a fixed position for measuring vertical muons. Further WILLI has been transformed in a rotatable device which allows directional measurements of muon charge ratio and muon flux. The results exhibit a pronounced azimuthal asymmetry (East-West effect) due to the different in fluence of the geomagnetic field on the trajectories of positive and negative muons in air. In parallel, flux measurement, taking into account muon events with nergies > 0.4GeV, show a diurnal modulation of the muon flux. The analysis of the muon events for energies < 0.6GeV reveals an aperiodic variation of the muon flux. A new detection system performing coincidence measurements between the WILLI calorimeter and a small array of 12 scintillators plates has been installed in IFIN-HH starting from the autumn of 2010. The aim of the system is to investigate muon charge ratio from individual EAS by using the mini-array as trigger for the WILLI calorimeter. Such experimental studies could provide detailed information on hadronic interaction models and primary cosmic ray composition at energies around 10{sup 15}eV. Simulation studies and preliminary experimental tests, regarding the performances of the mini-array, have been performed using H and Fe primaries, with energies in a range 10{sup 13}eV - 10{sup 15}eV. The results show detailed effects of the direction of EAS incidence relative to the geomagnetic field, depending, in particular, of the primary mass. Based on the results, we can say that WILLI-EAS experiment could be used for testing the hadronic interaction models. Measurements of the high energy muon flux in underground of the salt mine from Slanic Prahova, Romania was performed using a new mobile detector developed in IFIN-HH, Bucharest. Consisting of 2 scintillator plates measuring in coincidence, the detector is installed on a van which facilitates measurements on different positions at surface or in underground. The detector was used to measure muon fluxes in different locations at surface or in underground. The detector was used to measure muon fluxes at different sites of Romania and in the underground of the salt mines from Slanic Prahova, Romania where IFIN-HH has a modern underground laboratory. New methods for the detection of cosmic ray muons are investigated in our institute based on scintillator techniques using optical fiber and MPPC photodyodes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

On the possibility to discriminate the mass of the primary cosmic ray using the muon arrival times from extensive air showers: Application for Pierre Auger Observatory

In this paper we study the possibility to discriminate the mass of the primary cosmic ray by observing the muon arrival times in ground detectors. We analyzed extensive air showers (EAS) induced by proton and iron nuclei with the same energy 8 Multiplication-Sign 10{sup 17} eV simulated with CORSIKA, and analyzed the muon arrival times at ground measured by the infill array detectors of the Pierre Auger Observatory (PAO). From the arrival times of the core and of the muons the atmospheric depth of muon generation locus is evaluated. The results suggest a potential mass discrimination on the basis of muon arrival times and of the reconstructed atmospheric depth of muon production. An analysis of a larger set of CORSIKA simulations carried out for primary energies above 10{sup 18} eV is in progress.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

First detection of high-energy astrophysical neutrinos with IceCube

The IceCube detector at the South Pole is the world’s largest neutrino telescope, instrumenting a cubic kilometre of deep clear ice. Completed in late 2010, the detector has recorded the arrival directions and energies of tens of thousands of neutrinos – mostly those produced when cosmic rays collide with the Earth’s atmosphere. Here, we report on the first observation of high-energy neutrinos from beyond the Earth’s atmosphere, identified using a novel method to strongly suppress atmospheric neutrinos coming downward into the detector from the southern sky, leaving a sample of neutrinos highly likely to be of astrophysical origin.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

SUPERDIFFUSIVE SHOCK ACCELERATION

The theory of diffusive shock acceleration is extended to the case of superdiffusive transport, i.e., when the mean square deviation grows proportionally to t{sup {alpha}}, with {alpha} > 1. Superdiffusion can be described by a statistical process called Levy random walk, in which the propagator is not a Gaussian but it exhibits power-law tails. By using the propagator appropriate for Levy random walk, it is found that the indices of energy spectra of particles are harder than those obtained where a normal diffusion is envisaged, with the spectral index decreasing with the increase of {alpha}. A new scaling for the acceleration time is also found, allowing substantially shorter times than in the case of normal diffusion. Within this framework we can explain a number of observations of flat spectra in various astrophysical and heliospheric contexts, for instance, for the Crab Nebula and the termination shock of the solar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ANISOTROPY OF TeV COSMIC RAYS AND OUTER HELIOSPHERIC BOUNDARIES

Cosmic rays in the energy range from about tens of GeV to several hundreds of TeV are observed on Earth, with an energy-dependent anisotropy of order 0.01%-0.1% and a consistent topology that appears to significantly change at higher energy. The nearest and most recent galactic cosmic-ray sources might stochastically dominate the observation and possibly explain a change in orientation of the anisotropy as a function of energy. However, the diffusion approximation is not able to explain its non-dipolar structure and, in particular, the significant contribution of small angular scale features. Particle propagation within the mean free path in the local interstellar medium might have a major role in determining the properties of galactic cosmic rays, such as their arrival distribution. In particular, scattering on perturbations induced in the local interstellar magnetic field by the heliosphere wake may cause a re-distribution of anisotropic cosmic rays below about 100 TeV toward the direction of the elongated heliotail and of the local interstellar magnetic field in the outer heliosphere. Such scattering processes are considered responsible for the observed TeV cosmic-ray global anisotropy and its fine angular structure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CENTAURUS A AS A POINT SOURCE OF ULTRAHIGH ENERGY COSMIC RAYS

We probe the possibility that Centaurus A (Cen A) is a point source of ultrahigh energy cosmic rays (UHECRs) observed by Pierre Auger Observatory (PAO), through the statistical analysis of the arrival direction distribution. For this purpose, we set up the Cen A dominance model for the UHECR sources, in which Cen A contributes the fraction f {sub C} of the whole UHECR with energy above 5.5 Multiplication-Sign 10{sup 19} eV and the isotropic background contributes the remaining 1 - f {sub C} fraction. The effect of the intergalactic magnetic fields on the bending of the trajectory of Cen A originated UHECRs is parameterized by the Gaussian smearing angle {theta} {sub s}. For the statistical analysis, we adopted the correlational angular distance distribution (CADD) for the reduction of the arrival direction distribution and the Kuiper test to compare the observed and the expected CADDs. We identify the excess of UHECRs in the Cen A direction and fit the CADD of the observed PAO data by varying two parameters f {sub C} and {theta} {sub s} of the Cen A dominance model. The best-fit parameter values are f {sub C} Almost-Equal-To 0.1 (the corresponding Cen A fraction observed at PAO is f {sub C,PAO} Almost-Equal-To 0.15, that is, about 10 out of 69 UHECRs) and {theta} {sub s} = 5 Degree-Sign with the maximum likelihood L {sub max} = 0.29. This result supports the existence of a point source smeared by the intergalactic magnetic fields in the direction of Cen A. If Cen A is actually the source responsible for the observed excess of UHECRs, the rms deflection angle of the excess UHECRs implies the order of 10 nG intergalactic magnetic field in the vicinity of Cen A.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ENERGETIC PARTICLE DIFFUSION IN CRITICALLY BALANCED TURBULENCE

Observations and modeling suggest that the fluctuations in magnetized plasmas exhibit scale-dependent anisotropy, with more energy in the fluctuations perpendicular to the mean magnetic field than in the parallel fluctuations and the anisotropy increasing at smaller scales. The scale dependence of the anisotropy has not been studied in full-orbit simulations of particle transport in turbulent plasmas so far. In this paper, we construct a model of critically balanced turbulence, as suggested by Goldreich and Sridhar, and calculate energetic particle spatial diffusion coefficients using full-orbit simulations. The model uses an enveloped turbulence approach, where each two-dimensional wave mode with wavenumber k is packed into envelopes of length L following the critical balance condition, L{proportional_to}k {sup -2/3} , with the wave mode parameters changing between envelopes. Using full-orbit particle simulations, we find that both the parallel and perpendicular diffusion coefficients increase by a factor of two, compared to previous models with scale-independent anisotropy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

OBSERVATION OF COSMIC-RAY ANISOTROPY WITH THE ICETOP AIR SHOWER ARRAY

We report on the observation of anisotropy in the arrival direction distribution of cosmic rays at PeV energies. The analysis is based on data taken between 2009 and 2012 with the IceTop air shower array at the south pole. IceTop, an integral part of the IceCube detector, is sensitive to cosmic rays between 100 TeV and 1 EeV. With the current size of the IceTop data set, searches for anisotropy at the 10{sup -3} level can, for the first time, be extended to PeV energies. We divide the data set into two parts with median energies of 400 TeV and 2 PeV, respectively. In the low energy band, we observe a strong deficit with an angular size of about 30 Degree-Sign and an amplitude of (- 1.58 {+-} 0.46{sub stat} {+-} 0.52{sub sys}) Multiplication-Sign 10{sup -3} at a location consistent with previous observations of cosmic rays with the IceCube neutrino detector. The study of the high energy band shows that the anisotropy persists to PeV energies and increases in amplitude to (- 3.11 {+-} 0.38{sub stat} {+-} 0.96{sub sys}) Multiplication-Sign 10{sup -3}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

MODELING THE MOLECULAR COMPOSITION IN AN ACTIVE GALACTIC NUCLEUS DISK

We use a high-temperature chemical network to derive the molecular abundances in axisymmetric accretion disk models around active galactic nuclei (AGNs) within 100 pc using simple radial and vertical density and temperature distributions motivated by more detailed physical models. We explore the effects of X-ray irradiation and cosmic-ray ionization on the spatial distribution of the molecular abundances of CO, CN, CS, HCN, HCO{sup +}, HC{sub 3}N, C{sub 2}H, and c-C{sub 3}H{sub 2} using a variety of plausible disk structures. These simple models have molecular regions with an X-ray-dominated region layer, a midplane without the strong influence of X-rays, and a high-temperature region in the inner portion with moderate X-ray flux where families of polyynes (C{sub n}H{sub 2}) and cyanopolyynes can be enhanced. For the high midplane density disks we explore, we find that cosmic rays produced by supernovae do not significantly affect the regions unless the star formation efficiency significantly exceeds that of the Milky Way. We highlight molecular abundance observations and ratios that may distinguish among theoretical models of the density distribution in AGN disks. Finally, we assess the importance of the shock crossing time and the accretion time relative to the formation time for various chemical species. Vertical column densities are tabulated for a number of molecular species at both the characteristic shock crossing time and steady state. Although we do not attempt to fit any particular system or set of observations, we discuss our models and results in the context of the nearby AGN NGC 1068.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Lateral distribution of radio emission and its dependence on air shower longitudinal development

The lateral distribution function (LDF) of radio emission from an extensive air shower is considered as the basic signature sensitive to the shower longitudinal development and, as a consequence, to the mass of a primary cosmic ray's particle that initiated a given shower. The peculiarities in the LDF's structure as well as their sensitivity to the height of shower maximum are investigated and explained.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Interpretation of AMS-02 electrons and positrons data

We perform a combined analysis of the recent AMS-02 data on electrons, positrons, electrons plus positrons and positron fraction, in a self-consistent framework where we realize a theoretical modeling of all the astrophysical components that can contribute to the observed fluxes in the whole energy range. The primary electron contribution is modeled through the sum of an average flux from distant sources and the fluxes from the local supernova remnants in the Green catalog. The secondary electron and positron fluxes originate from interactions on the interstellar medium of primary cosmic rays, for which we derive a novel determination by using AMS-02 proton and helium data. Primary positrons and electrons from pulsar wind nebulae in the ATNF catalog are included and studied in terms of their most significant (while loosely known) properties and under different assumptions (average contribution from the whole catalog, single dominant pulsar, a few dominant pulsars). We obtain a remarkable agreement between our various modeling and the AMS-02 data for all types of analysis, demonstrating that the whole AMS-02 leptonic data admit a self-consistent interpretation in terms of astrophysical contributions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

DETECTION OF OH{sup +} IN TRANSLUCENT INTERSTELLAR CLOUDS: NEW ELECTRONIC TRANSITIONS AND PROBING THE PRIMARY COSMIC RAY IONIZATION RATE

We present the detection of rotationally resolved electronic transitions in the OH{sup +} A{sup 3}Π–X{sup 3}Σ{sup −} (0, 0) and (1, 0) bands toward CD-32 4348, HD 63804, HD 78344, and HD 80077. These four translucent clouds have been studied in a recent Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph observational run. In total, seven absorption features of OH{sup +} are detected, and six of them are identified here for the first time, providing a precise tool to trace OH{sup +} in translucent interstellar clouds. An improved set of line positions and oscillator strengths is compiled to support our data interpretation. A dedicated analysis of the observed features in individual targets yields an accurate determination of OH{sup +} column densities. The results are applied to estimate the primary cosmic ray ionization rate in the investigated translucent clouds, which yields a typical value of ∼1.0 × 10{sup −16} s{sup −1}. In addition, following this work, two of the new interstellar features recently reported by Bhatt and Cami, at ∼3572.65 and 3346.96 Å, can be identified as OH{sup +} absorption lines now.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Contribution from cosmological scalar perturbations to the angular velocity spectrum of extragalactic sources

The possibility of the influence of adiabatic scalar perturbations on the angular velocity spectrum of extragalactic sources is considered. The multipole expansion coefficients of the angular velocity field in terms of vector spherical harmonics are calculated. We show that there is no contribution from adiabatic perturbations to the angular spectrum for a spatially flat Universe at the dusty stage, while there is a contribution only to the electric multiple coefficients at the stage of {Lambda}-term domination. The cases of long-wavelength and short-wavelength perturbations are considered separately. The relationship between the multipole angular velocity spectrum and the primordial scalar perturbation spectrum is discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

High-energy cosmic ray muons in the Earth's atmosphere

We present the calculations of the atmospheric muon fluxes at energies 10-10{sup 7} GeV based on a numerical-analytical method for solving the hadron-nucleus cascade equations. It allows the non-power-law behavior of the primary cosmic ray (PCR) spectrum, the violation of Feynman scaling, and the growth of the total inelastic cross sections for hadron-nucleus collisions with increasing energy to be taken into account. The calculations have been performed for a wide class of hadron-nucleus interaction models using directly the PCR measurements made in the ATIC-2 and GAMMA experiments and the parameterizations of the primary spectrum based on a set of experiments. We study the dependence of atmospheric muon flux characteristics on the hadronic interaction model and the influence of uncertainties in the PCR spectrum and composition on the muon flux at sea level. Comparison of the calculated muon energy spectra at sea level with the data from a large number of experiments shows that the cross sections for hadron-nucleus interactions introduce the greatest uncertainty in the energy region that does not include the knee in the primary spectrum.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Mass composition of 10{sup 17}- to 10{sup 18}-eV primary cosmic rays according to data on the lateral distribution of radio emission from extensive air showers

Experimental data obtained for the lateral distribution of radio emission from extensive air showers (EAS) at the array of Moscow State University (30-34 MHz) and the LOPES array (40-80 MHz) were comparedwith the results of calculations performed within amicroscopic approach based on aMonte Carlo simulation of EAS (CORSIKA code). The same experimental data were used to reconstruct the distribution of the depth of the EAS maximum at cosmic-ray energies in the range of 1017-1018 eV. The energy dependence of the depth of the EAS maximum was constructed for the case of data from the LOPES array, and the mass composition of cosmic rays was estimated for this case. From the resulting dependences, it follows that the mass composition shows a trend toward becoming lighter in the energy range being considered.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗