High-energy Atmospheric Muons Research Articles

Calculation of the Flux and Charge Ratio of High-Energy Atmospheric Muons at Sea Level*

Calculation of the Flux and Charge Ratio of High-Energy Atmospheric Muons at Sea Level*

ESTIMACIÓN DEL FLUJO DE MUONES EN EL LABORATORIO SUBTERRÁNEO ANDES

The ANDES Underground Laboratory is being planned and designed to be one of the largest and most shielded laboratories in the Southern Hemisphere, which will be located in the Andes Range, in the area of the current Paso AguaNegra that connects the provinces of San Juan (Argentina) and Elqui (Chile). The diversity of experiments that are being planned, including experiments for the direct and indirect search of dark matter and neutrino precision physics, requires a precise knowledge of the flux of high-energy atmospheric muons within the laboratory. These are produced during the interaction of astroparticles with energies between 1012and 1018eV denominated of high and ultra-high energy with the Earth’s atmosphere. In the high-energy component, muons with energies of tens of TeV can be found, capable of passing through thousands of meters of rock. Previous estimates made from reasonable assumptions about the type of rock expected in the area showed that the expected muon flux was compatible with other underground laboratories at an equivalent depth. In this work, extensive atmospheric showers flux simulations were performed at the laboratory site. Afterwards, there was a selection of those muons with sufficient energy to reach the laboratory-based on their angle of incidence and the height at which they enter the mountain. Then a transfer function was modeled using the new geological studies currently available that allow us to have a detailed model of the rock distribution inside the mountain. Finally, the interaction of these muons with the different types of rock was calculated numerically along their way to the laboratory using the continuous slowdown approximation, thus obtaining that the expected muon flux within the laboratory is 1,47±0,02 day−1m−2sr−1

Simulated Annealing for volcano muography

Muography or muon radiography is a non-invasive emerging image technology relying on high energy atmospheric muons, which complements other standard geophysical tools to understand the Earth’s subsurface.This work discusses a geophysical inversion methodology for volcanic muography, based on the Simulated Annealing algorithm, using a semi-empirical model of the muon flux to reach the volcano topography and a framework for the energy loss of muons in rock.The Metropolis-Simulated-Annealing algorithm starts from an “observed” muon flux and obtains the best associated inner density distribution function inside a syntetic model of the Cerro Machín Volcano (Tolima-Colombia). The estimated initial density model was obtained with GEOMODELER, adapted to the volcano topography. We improved this model by including rock densities from samples taken from the crater, the dome and the areas associated with fumaroles.In this paper we determined the minimum muon energy (a function of the arrival direction) needed to cross the volcanic building, the emerging integrated flux of muons, and the density profile inside a model of Cerro Machin. The present inversion correctly reconstructed the density differences inside the Machín, within a 1% error concerning our initial simulation model, giving a remarkable density contrast between the volcanic duct, the encasing rock and the fumaroles area.

Bayesian joint muographic and gravimetric inversion applied to volcanoes

SUMMARY Gravimetry is a technique widely used to image the structure of the Earth. However, inversions are ill-posed and the imaging power of the technique rapidly decreases with depth. To overcome this limitation, muography, a new imaging technique relying on high energy atmospheric muons, has recently been developed. Because muography only provides integrated densities above the detector from a limited number of observation points, inversions are also ill-posed. Previous studies have shown that joint muographic and gravimetric inversions better reconstruct the 3-D density structure of volcanic edifices than independent density inversions. These studies address the ill-posedness of the joint problem by regularizing the solution with respect to a prior density model. However, the obtained solutions depend on some hyperparameters, which are either determined relative to a single test case or rely on ad-hoc parameters. This can lead to inaccurate retrieved models, sometimes associated with artefacts linked to the muon data acquisition. In this study, we use a synthetic example based on the Puy de Dôme volcano to determine a robust method to obtain the resulting model closest to the synthetic model and devoid of acquisition artefacts. We choose a Bayesian approach to include an a priori density model and a smoothing by a Gaussian spatial correlation function relying on two hyperparameters: an a priori density standard deviation and an isotropic spatial correlation length. This approach has the advantage to provide a posteriori standard deviations on the resulting densities. Using our synthetic volcano, we investigate the most reliable criterion to determine the hyperparameters. Our results suggest that k-fold Cross-Validation Sum of Squares and the Leave One Out methods are more robust criteria than the classically used L-curves. The determined hyperparameters allow to overcome the artefacts linked to the data acquisition geometry, even when only a limited number of muon telescopes is available. We also illustrate the behaviour of the inversion in case of offsets in the a priori density or in the data and show that they lead to recognizable structures that help identify them.

High-energy atmospheric muon flux calculations in comparison with recent measurements

Recently the atmospheric muon spectra at high energies were reconstructed for two ranges of zenith angles, basing on the events collected with the IceCube detector. These measurements reach high energies at which the contribution to atmospheric muon fluxes from decays of short-lived hadrons is expected. Latest IceCube measurements of the high-energy atmospheric muon spectrum indicate the presence of prompt muon component at energies above 500 TeV.

Search for neutrino point sources with the IceCube Neutrino Observatory

The IceCube Neutrino Observatory is a kilometer-scale detector located at the South Pole. The full detector comprises 5,160 photomultipliers (PMTs) deployed among 86 strings from 1.5–2.5 km deep within the ice. The constructing phase started in the austral summer of 2004 and ended in December 2010 with the deployment of the last 7 strings that make up the full detector. In this proceeding we present the results of the time integrated and time dependent point source searches corresponding to the years from April 2008 to May 2010 with two different configurations of the IceCube detector (40 and 59 strings). In the northern sky the IceCube neutrino telescope is sensitive to point sources of neutrinos with E−2 spectra mainly in the TeV–PeV energy range. In the opposite hemisphere, due to the higher contamination of high-energy atmospheric muons, the detector is most sensitive to sources with harder spectra, which produce high fluxes of PeV to EeV energies. The combined sensitivity is about a factor ∼2.5 better than the previous 1-year limit. An overview of the sensitivity and discovery potential for the time integrated searches over three years of IceCube, from April 2008 to May 2011, is also shown.

Towards a muon radiography of the Puy de Dôme

Abstract. High-energy (above a few hundred GeV) atmospheric muons are a natural probe for geophysical studies. They can travel through kilometres of rock allowing for a radiography of the density distribution within large structures, like mountains or volcanoes. A collaboration between volcanologists, astroparticle and particle physicists, Tomuvol was formed in 2009 to study tomographic muon imaging of volcanoes with high-resolution, large-scale tracking detectors. We report on two campaigns of measurements at the flank of the Puy de Dôme using glass resistive plate chambers (GRPCs) developed for particle physics, within the CALICE collaboration.

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. Using these results the differential flux and the flavor ratios of leptons were calculated. The air shower simulator CORSIKA 6.990 was used for showering and propagation of the secondary particles through the atmosphere, employing the established high energy hadronic interaction models SIBYLL 2.1, QGSJet-01 and QGSJet-II-03. We show that the performance of the interaction models allows makes it possible to predict the spectra within experimental uncertainties, while 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. The influence of the knee of cosmic rays is reflected in the secondary spectra at energies between 100 and 200 TeV. 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. See the published paper [1].

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. Using these results the differential flux and the flavor ratios of leptons were calculated. The air shower simulator CORSIKA 6.990 was used for showering and propagation of the secondary particles through the atmosphere, employing the established high energy hadronic interaction models SIBYLL 2.1, QGSJet-01 and QGSJet-II-03. We show that the performance of the interaction models allows makes it possible to predict the spectra within experimental uncertainties, while 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. The influence of the knee of cosmic rays is reflected in the secondary spectra at energies between 100 and 200 TeV. 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. See the published paper [1].

Atmospheric Muons as IceCube Signal

Muons of energies above 1 TeV produced in cosmic ray induced air showers account for the vast majority of events in IceCube. Its enormous size compared to previous volume detectors translates into an unprecedented amount of statistics for high-energy atmospheric muons. This offers a wide range of opportunities for original cosmic ray and particle physics.

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 have 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. Using these results, the differential flux and the flavor ratios of leptons were calculated. The air shower simulator CORSIKA 6.990 was used for showering and propagation of the secondary particles through the atmosphere, employing the established high-energy hadronic interaction models SIBYLL 2.1, QGSJet-01 and QGSJet-II-03. We show that the performance of the interaction models makes it possible to predict the spectra within experimental uncertainties, while 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 $K/\ensuremath{\pi}$ ratio within the models. The influence of the knee of cosmic rays is reflected in the secondary spectra at energies between 100 and 200 TeV. 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 $\genfrac{}{}{0}{}{+15}{\ensuremath{-}13}%$ of the average flux. Uncertainties of the muon and electron neutrino fluxes can be calculated within an average error of $\genfrac{}{}{0}{}{+32}{\ensuremath{-}22}%$ and $\genfrac{}{}{0}{}{+25}{\ensuremath{-}19}%$, respectively.

A new interpretation of the high energy atmospheric muon charge ratio

We present a review of past measurements of the vertical atmospheric muon charge ratio above 1 TeV. In particular we focus on the latest OPERA data which confirm with a higher statistical significance a drop of the charge ratio above ∼3 TeV. We attempt to interpret the result in terms of possible physical mechanisms that could manifest itself in this energy region.

Density imaging of volcanos with atmospheric muons

Their long range in matter renders high-energy atmospheric muons a unique probe for geophysical explorations, permitting the cartography of density distributions which can reveal spatial and possibly also temporal variations in extended geological structures. A Collaboration between volcanologists and (astro-)particle physicists, TOMUVOL, was formed in 2009 to study tomographic muon imaging of volcanos with high-resolution tracking detectors. Here we discuss preparatory work towards muon tomography as well as the first flux measurements taken at the Puy de Dôme, an inactive lava dome volcano in the Massif Central.

TIME-INTEGRATED SEARCHES FOR POINT-LIKE SOURCES OF NEUTRINOS WITH THE 40-STRING IceCube DETECTOR

We present the results of time-integrated searches for astrophysical neutrino sources in both the northern and southern skies. Data were collected using the partially completed IceCube detector in the 40-string configuration recorded between 2008 April 5 and 2009 May 20, totaling 375.5 days livetime. An unbinned maximum likelihood ratio method is used to search for astrophysical signals. The data sample contains 36,900 events: 14,121 from the northern sky, mostly muons induced by atmospheric neutrinos, and 22,779 from the southern sky, mostly high-energy atmospheric muons. The analysis includes searches for individual point sources and stacked searches for sources in a common class, sometimes including a spatial extent. While this analysis is sensitive to TeV–PeV energy neutrinos in the northern sky, it is primarily sensitive to neutrinos with energy greater than about 1 PeV in the southern sky. No evidence for a signal is found in any of the searches. Limits are set for neutrino fluxes from astrophysical sources over the entire sky and compared to predictions. The sensitivity is at least a factor of two better than previous searches (depending on declination), with 90% confidence level muon neutrino flux upper limits being between E2dΦ/dE ∼ 2–200 × 10−12 TeV cm−2 s−1 in the northern sky and between 3–700 × 10−12 TeV cm−2 s−1 in the southern sky. The stacked source searches provide the best limits to specific source classes. The full IceCube detector is expected to improve the sensitivity to dΦ/dE∝E−2 sources by another factor of two in the first year of operation.

THE BAIKAL NEUTRINO TELESCOPE — RESULTS AND PLANS

New results from the Baikal neutrino telescope NT200, based on the first 5 years of operation (1998–2003), are presented. We derive an all-flavor limit on the diffuse flux of astrophysical neutrinos between 20 TeV and 50 PeV, extract an enlarged sample of high energy muon neutrino events, and obtain limits on the flux of high energy atmospheric muons. In 2005, the upgraded telescope NT200+ will be commissioned: 3 additional distant strings with only 12 photo-multipliers each will rise the effective volume to 20 Mton at 10 PeV for this largest running neutrino telescope in the Northern hemisphere.

MONOLITH: A MASSIVE MAGNETIZED TRACKING CALORIMETER FOR THE STUDY OF ATMOSPHERIC NEUTRINO OSCILLATIONS

MONOLITH is a proposed massive (34 kton) magnetized tracking calorimeter at the Gran Sasso laboratory in Italy, optimized for the detection of high energy atmospheric muon neutrinos. The main goal is to establish (or reject) the neutrino oscillation hypothesis through an explicit observation of the full first oscillation swing. The Δm2 sensitivity range for this measurement comfortably covers the complete Super-Kamiokande allowed region. Other measurements include studies of matter effects and the up/down ratio of NC events, the study of cosmic ray muons in the multi-TeV range, and auxiliary measurements from the CERN to Gran Sasso neutrino beam.

Charm production and high energy atmospheric muon and neutrino fluxes

Production of muons and neutrinos in cosmic ray interactions with the atmosphere has been investigated with Monte Carlo models for hadronic interactions. The resulting conventional muon and neutrino fluxes (from π and K decays) agree well with earlier calculations, whereas our prompt fluxes from charm decays are significantly lower than earlier estimates. Charm production is mainly considered as a well defined perturbative QCD process, but we also investigate a hypothetical non-perturbative intrinsic charm component in the proton. The lower charm rate implies better prospects for detecting very high energy neutrinos from cosmic sources.