Astroparticle Physics


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Astronomie, Physik
Elsevier - JOURNALS DEPARTMENT Saunders/Mosby/Harcourt Health
0927-6505
monatlich
Englisch
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Astroparticle Physics publishes experimental and theoretical research papers in the interacting fields of Cosmic Ray Physics, Astronomy and Astrophysics, Cosmology and Particle Physics focusing on new developments in the following areas: High-energy cosmic-ray physics and astrophysics; Particle cosmology; Particle astrophysics; Related astrophysics: supernova, AGN, cosmic abundances, dark matter etc.; High-energy, VHE and UHE gamma-ray astronomy; High- and low-energy neutrino astronomy; Instrumentation and detector developments related to the above-mentioned fields.
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Atmospheric neutrinos and the knee of the cosmic ray spectrum
The nature of the knee in the all-particle spectrum of cosmic rays remains subject of much investigation, especially in the aftermath of recent measurements claiming the detection of a knee-like feature in the spectrum of the light component of cosmic rays at energy  ∼ 700 TeV, at odds with the standard picture in which the knee in the all-particle spectrum is dominated by light cosmic rays. Here we investigate the implications of this and other scenarios in terms of the measured flux of atmospheric neutrinos. In particular we discuss the possibility that the spectrum of atmospheric neutrinos in the region  ≳ 50 TeV may provide information about the different models for the mass composition in the knee region. We investigate the dependence of the predicted atmospheric neutrino flux on the shape of the light cosmic ray spectra and on the interaction models describing the development of showers in the atmosphere. The implications of all these factors for the identification of the onset of an astrophysical neutrino component are discussed.
Dual MeV gamma-ray and dark matter observatory - GRAMS Project
GRAMS (Gamma-Ray and AntiMatter Survey) is a novel project that can simultaneously target both astrophysical observations with MeV gamma rays and an indirect dark matter search with antimatter. The GRAMS instrument is designed with a cost-effective, large-scale LArTPC (Liquid Argon Time Projection Chamber) detector surrounded by plastic scintillators. The astrophysical observations at MeV energies have not yet been well-explored (the so-called “MeV-gap”) and GRAMS can improve the sensitivity by more than an order of magnitude compared to previous experiments. While primarily focusing on MeV gamma-ray observations, GRAMS is also optimized for cosmic ray antimatter surveys to indirectly search for dark matter. In particular, low-energy antideuterons will provide an essentially background-free dark matter signature. GRAMS will be a next generation experiment beyond the current GAPS (General AntiParticle Spectrometer) project for antimatter survey.
V-shaped cherenkov images of magnetically-separated gamma-rays
Cherenkov Telescope Array (CTA) is an upcoming instrument that will start a new generation of atmospheric Cherenkov telescopes. CTA is expected not only to provide an unprecedented sensitivity in the tens of GeV to hundreds of TeV range, but also to considerably improve the systematic uncertainties of the measurements. We study the images registered by Cherenkov telescopes from low energy gamma rays with its first interaction in the upper parts of the atmosphere. The images show a characteristic separation due to the deflection of the first
e

e
+
pair in the Geomagnetic Field. We evaluate the performance of the standard stereoscopic analysis for such events. We derive also a novel method for energy estimation of V-shaped events based purely on geometrical properties of the image. We investigate the potential of combining the classical energy estimation and the novel method for independent validation of the systematic shifts in the energy scale of Cherenkov telescopes and discuss the limitations of such analysis.
On the sensitivity of present direct detection experiments to WIMP–quark and WIMP–gluon effective interactions: A systematic assessment and new model–independent approaches
Assuming for Weakly Interacting Massive Particles (WIMPs) a Maxwellian velocity distribution in the Galaxy we provide an assessment of the sensitivity of existing Dark Matter (DM) direct detection (DD) experiments to operators up to dimension 7 of the relativistic effective field theory describing dark matter interactions with quarks and gluons. In particular we focus on a systematic approach, including an extensive set of experiments and large number of couplings, both exceeding for completeness similar analyses in the literature. The relativistic effective theory requires to fix one coupling for each quark flavor, so in principle for each different combination the bounds should be recalculated starting from direct detection experimental data. To address this problem we propose an approximate model–independent procedure that allows to directly calculate the bounds for any combination of couplings in terms of model–independent limits on the Wilson coefficients of the non–relativistic theory expressed in terms of the WIMP mass and of the neutron–to–proton coupling ratio cn
/cp
. We test the result of the approximate procedure against that of a full calculation, and discuss its possible pitfalls and limitations. We also provide a simple interpolating interface in Python that allows to apply our method quantitatively.
Revisiting Ryskin’s model of cosmic acceleration
Cosmic backreaction as an additional source of the expansion of the universe has been a debate topic since the discovery of cosmic acceleration. The major concern is whether the self interaction of small-scale nonlinear structures would source gravity on very large scales. Gregory Ryskin argued against the additional inclusion of gravitational interaction energy of astronomical objects, whose masses are mostly inferred from gravitational effects and hence should already contain all sources with long-range gravity forces. Ryskin proposed that the backreaction contribution to the energy momentum tensor comes instead from the rest of the universe beyond the observable patch. Ryskin’s model solves the fine-tuning problem and is in good agreement with the Hubble diagram of Type Ia supernovae. In this article we revisit Ryskin’s model and show that it is inconsistent with at least one of the following statements: (i) the universe is matter-dominated at low redshift (z ≲ 2); (ii) the universe is radiation-dominated at sufficiently high redshift; (iii) matter density fluctuations are tiny (

10

4
) at the recombination epoch.
The Astrophysical Multimessenger Observatory Network (AMON): Performance and science program
The Astrophysical Multimessenger Observatory Network (AMON) has been built with the purpose of enabling near real-time coincidence searches using data from leading multimessenger observatories and astronomical facilities. Its mission is to evoke discovery of multimessenger astrophysical sources, exploit these sources for purposes of astrophysics and fundamental physics, and explore multimessenger datasets for evidence of multimessenger source population AMON aims to promote the advancement of multimessenger astrophysics by allowing its participants to study the most energetic phenomena in the universe and to help answer some of the outstanding enigmas in astrophysics, fundamental physics, and cosmology. The main strength of AMON is its ability to combine and analyze sub-threshold data from different facilities. Such data cannot generally be used stand-alone to identify astrophysical sources. The analyses algorithms used by AMON can identify statistically significant coincidence candidates of multimessenger events, leading to the distribution of AMON alerts used by partner observatories for real-time follow-up that may identify and, potentially, confirm the reality of the multimessenger association. We present the science motivation, partner observatories, implementation and summary of the current status of the AMON project.
Neutron and muon-induced background studies for the AMoRE double-beta decay experiment
AMoRE (Advanced Mo-based Rare process Experiment) is an experiment to search a neutrinoless double-beta decay of 100Mo in molybdate crystals. The neutron and muon-induced backgrounds are crucial to obtain the zero-background level (
<
10

5
counts/(keV · kg · yr)) for the AMoRE-II experiment, which is the second phase of the AMoRE project, planned to run at YEMI underground laboratory. To evaluate the effects of neutron and muon-induced backgrounds, we performed Geant4 Monte Carlo simulations and studied a shielding strategy for the AMORE-II experiment. Neutron-induced backgrounds were also included in the study. In this paper, we estimated the background level in the presence of possible shielding structures, which meet the background requirement for the AMoRE-II experiment.
A muon-based observable for a photon search at 30–300 PeV
The observation of an ultra-high energy photon component of the cosmic radiation is one of the open problems in Astroparticle Physics. The stringent theoretical and experimental upper limits to the photon flux above 100 TeV make the search of a weak photon signal in the vast hadronic cosmic ray background a challenging task. At these energies, photon primaries entering the atmosphere develop an extensive air shower which is driven by electromagnetic processes with a poor muon component. The muon content of the air showers is one of the most promising observables that could lead to the best possible discrimination between photons and hadronic cosmic rays. In this article, we define a parameter capable of quantifying the muon component while reducing the fluctuations due to the unknown lateral distribution of muons. We explain the different features of this observable using simulated air showers between 30 and 300 PeV. We show that a merit factor of 5 in the separation between photon and proton primaries and a photon signal efficiency of at least  ∼ 92% while rejecting 99.97% of the proton-initiated showers can be reached in the mentioned energy range of interest. This separation power can be achieved provided the shower features, specially the primary energy, are reconstructed sufficiently precise and without significant biases.
Model-independent search for neutrino sources with the ANTARES neutrino telescope
A novel method to analyse the spatial distribution of neutrino candidates recorded with the ANTARES neutrino telescope is introduced, searching for an excess of neutrinos in a region of arbitrary size and shape from any direction in the sky. Techniques originating from the domains of machine learning, pattern recognition and image processing are used to purify the sample of neutrino candidates and for the analysis of the obtained skymap. In contrast to a dedicated search for a specific neutrino emission model, this approach is sensitive to a wide range of possible morphologies of potential sources of high-energy neutrino emission. The application of these methods to ANTARES data yields a large-scale excess with a post-trial significance of 2.5σ. Applied to public data from IceCube in its IC40 configuration, an excess consistent with the results from ANTARES is observed with a post-trial significance of 2.1σ.
Influence of non-spherical dust grains on the growing of astrophysical dusty plasma waves with (r, q) distribution function
The influence of dust rotation on the growing of dust-ion acoustic surface waves is investigated in a sharply bounded astrophysical dusty plasma containing the non-spherical dust grains and non-thermal electrons whose velocity distribution function takes the form of the generalized (r, q) distribution function, where r and q are the two spectral indices for the generalized distribution function. We assume that the angular frequency of the rotating non-spherical dust grains is close to the wave frequency to derive the resonant growth rate of the surface wave. The result shows that the surface wave becomes more unstable as the rotation frequency is increasing. If the rotation frequency is too low, the instability disappears in the domain of high wave numbers. We also have found that growth rate decreases as the moment of inertia of the rotating dust grains increases in astrophysical non-thermal plasmas.
A search for solar axion induced signals with COSINE-100
We present results from a search for solar axions with the COSINE-100 experiment. We find no evidence of solar axion events from a data-set of 6,303.9 kg · days exposure and set a 90% confidence level upper limit on the axion-electron coupling, gae
, of 1.70
×
10

11
for an axion mass less than 1 keV/c2. This limit excludes QCD axions heavier than 0.59 eV/c2 in the DFSZ model and 168.1 eV/c2 in the KSVZ model.
Radio Morphing: towards a fast computation of the radio signal from air showers
Over the last years, radio detection has matured to become a competitive method for the detection of air showers. Arrays of thousands of antennas are now envisioned for the detection of cosmic rays of ultra high energy or neutrinos of astrophysical origin. The data exploitation of such detectors requires to run massive air-shower simulations to evaluate the radio signal at each antenna position. In order to reduce the associated computational cost, we have developed a semi-analytical method for the computation of the emitted radio signal called Radio Morphing. The method consists in computing the radio signal of any air-shower at any location from the simulation of one single reference shower at given positions by (i) a scaling of the electric-field amplitude of this reference shower, (ii) an isometry on the simulated positions and (iii) an interpolation of the radio pulse at the desired position. This technique enables one to compute electric field time traces with characteristics very similar to those obtained with standard computation methods, but with computation times reduced by several orders of magnitude. In this paper, we present this novel tool, explain its methodology, and discuss its limitations. Furthermore, we validate the method on a typical event set for the future GRAND experiment showing that the calculated peak amplitudes are consistent with the results from ZHAireS simulations with a mean offset of
+
8.5
% and a standard deviation of 27.2% in this specific case. This overestimation of the signal strength by Radio Morphing arises mainly from the choice of the underlying reference shower.
Prediction and detection potential of fusion neutrinos from nearby stars
The calculated shapes of neutrino spectra and fluxes from the most prominent stellar sources of neutrinos within 12 parsec of the Sun are shown. The flux of neutrinos reaching Earth from these stars is calculated from numerical stellar models fitting the observational calibrations, obtained from photometric and asteroseimologic studies found in the literature. The possibility and shortcomings for a potential detection (in terms of the extremely low neutrino flux, the possible level of the neutrino background introduced by unspecified stellar sources within 12 parsec and the expected event rate) is discussed.
Estimation of radio emission from neutrino induced showers in rock salt above 1018 eV
Emission of electromagnetic waves from high energy particle showers is a powerful tool that can be used to detect the most elusive cosmic neutrinos of astrophysical or cosmogenic origin. We present here simulations of showers with a primary energy in the range
10
18

10
21
eV initiated by νe, νμ
and ντ
neutrinos. A medium that is both dense and transparent in the low radio frequencies part of the electromagnetic spectrum, like rock salt, is used as active medium where the shower develops. The calculation of the radio signal was performed by approximating the shower with a current density using the longitudinal profile of the charge excess, for estimation at low frequencies, below 500 MHz.
The aim of this work is to give estimates of the amplitude of the signal induced by νe, νμ
and ντ
neutrinos.
Radio detection of cosmic rays in [1.7–3.7] MHz: The EXTASIS experiment
Since 2003, significant efforts have been devoted to the understanding of the radio emission of extensive air showers above 20 MHz. Despite some studies led until the early nineties, the band available below 20 MHz has remained unused for 20 years. However, it has been claimed by some pioneering experiments that extensive air showers emit a strong electric field in this band and that there is evidence of a large increase of the radio pulse amplitude with decreasing frequencies. The EXTASIS experiment, located within the Nançay Radioastronomy Observatory and supported by the scintillator array and the autonomous radio stations of the CODALEMA experiment, aims to re-investigate the low-frequency band, and especially to study the so-called ”sudden death” contribution, the expected electric field radiated by the shower front when hitting ground level. In this work, we present the instrumental setup of the EXTASIS experiment composed of 7 low-frequency antennas operating in [1.7–3.7] MHz and covering approximately 1 km2. We report the observation of 18 air showers detected in coincidence in the three instruments, and estimate a detection threshold of 23 ± 4 µV from comparisons with detailed SELFAS3 simulations. We also report a strong correlation of the low-frequency signal observation with the atmospheric electric field.
Fast localization of coalescing binaries with a heterogeneous network of advanced gravitational wave detectors
We present the expected performance regarding fast sky localization of coalescing binaries with a network of three gravitational wave detectors having heterogeneous sensitivities, such as the LIGO-Virgo network. A hierarchical approach can be used in order to make an effective use of information from the least sensitive detector. In this approach, the presence of an event seen in coincidence in the two more sensitive detectors triggers a focused search in the data of the third, less sensitive, detector with a lower signal-to-noise ratio (SNR) threshold. We investigate the benefit for sky localization that can be expected in such an approach, using simulated data and signals. We find that as the sensitivity of Virgo approaches one third of the LIGO sensitivity, the accuracy and precision of the localization can be improved by about a factor 3 when Virgo data are searched with an SNR threshold around 3.5.
Search for WIMP-129Xe inelastic scattering with particle identification in XMASS-I
A search for Weakly Interacting Massive Particles (WIMPs) was conducted with the single-phase liquid-xenon detector XMASS through inelastic scattering in which 129Xe nuclei were excited, using an exposure (327 kg × 800.0 days) 48 times larger than that of our previous study. The inelastic excitation sensitivity was improved by detailed evaluation of background, event classification based on scintillation timing that distinguished γ-rays and β-rays, and simultaneous fitting of the energy spectra of γ-like and β-like samples. No evidence of a WIMP signal was found. Thus, we set the upper limits of the inelastic channel cross section at 90% confidence level, for example,
4.1
×
10

39
cm
2
for a 200 GeV/c
2 WIMP. This result provides the most stringent limits on the SD WIMP-neutron interaction and is better by a factor of 7.7 at 200 GeV/c
2 than the existing experimental limit.
Determination of cosmic-ray primary mass on an event-by-event basis using radio detection
We present a new methodology to discriminate between light and heavy ultra-high energy cosmic-ray primaries on an event-by-event basis using information from the radio detection of extensive air showers at MHz frequencies. Similarly to other methods to determine primary cosmic ray composition, the one presented here is based on comparisons between detected radio signals and Monte Carlo simulations for multiple primary cosmic ray compositions. Unlike other methods that first reconstruct the depth of maximum shower development X
max to relate it to the nature of the primaries, we instead infer the cosmic-ray composition directly. The method is most effective in the case of inclined showers that arrive at large zenith angles with respect to the vertical to the ground, where methods based on the determination of X
max lose accuracy. We show that a discrimination efficiency between 65% and 80% can be reached for zenith angles θ ≳ 60∘, even when typical uncertainties in radio detection are taken into account, including shower energy uncertainty. Our methodology could in principle be applied in large and sparse radio arrays, designed with the large radio footprint of inclined showers in mind, to significantly increase the statistics of ultra-high energy cosmic-ray composition studies.
Slow liquid scintillator candidates for MeV-scale neutrino experiments
Slow liquid scintillator Cherenkov detectors have been proposed as part of several future neutrino experiments because they can provide both directionality and energy measurements. This feature is expected to enhance the sensitivities for MeV-scale neutrino physics, including solar physics, the search for supernova relic neutrino, and the study of geo-sciences. In this study, the characteristics of a slow liquid scintillator were investigated, along with the light yields and decay time constants for various combinations of linear alkylbenzene (LAB), 2,5-diphenyloxazole (PPO), and 1,4-bis (2-methylstyryl)-benzene (bis-MSB). The results of our study indicated that LAB with 0.07 g/L of PPO and 13 mg/L of bis-MSB was the best candidate for an effective separation between Cherenkov and scintillation lights with a reasonably high light yield.
On the possibilities of high-energy neutrino production in the jets of microquasar SS433 in light of new observational data
Microquasar SS433 is composed by a supergiant star that feeds mass through a supercritical accretion disk to a  ∼10 M
⊙ black hole. The latter launches two oppositely directed jets that precess with a period of 162 days. The system has been detected at different spatial scales in frequencies ranging from radio to gamma rays, and has long been considered as a potential neutrino source which has been observed by AMANDA in the past, and later IceCube, leading to more restrictive upper bounds on the neutrino flux. In this work, we explore the possibilities that neutrinos could be produced in the jets of this source at levels consistent, or at least, not incompatible with any current data on electromagnetic emission available. In order to do so, we consider the injection of both electrons and protons at different positions in the jets, and we compute their broadband photon emission by synchrotron and interactions with ambient photons and matter. After correcting the high energy photon flux by the effect of γγ and γN absorption, we obtain the surviving flux that arrive on Earth and compare it with observational data by gamma-ray detectors. The flux of high energy neutrinos is consistently computed and we find that if they are eventually detected with IceCube, production must take place at the inner jets, where gamma-ray absorption is important, in order to avoid current VHE constraints form HESS and MAGIC. Additionally, we find that if the flux of 25 TeV gamma-rays recently detected with HAWC and which corresponds to the jet termination region were produced mainly by pp interactions, this would lead to a too faint neutrino flux that is beyond the reach of IceCube in its present configuration.
Atmospheric monitoring and inter-calibration of the telescope optical throughput efficiencies using the trigger rates of the Cherenkov Telescope Array
We discuss a calibration method for imaging atmospheric Cherenkov telescope arrays, based on the detection of cosmic rays. The focus lies on the monitoring of transmission of Cherenkov light in the atmosphere and on the relative calibration of telescope optical throughput efficiencies. We present an approach that addresses both issues by surveying and comparing trigger rates of telescopes in a stereoscopic configuration. A Monte Carlo feasibility study was conducted to explore dependencies of stereo trigger rates on the array layout and observing conditions of the Cherenkov Telescope Array (CTA). Analytical expressions for most of these dependencies have been found and implemented in an extension of the method of the Cherenkov Transparency Coefficient (CTC). In the investigated examples, the resolution of the method for the atmospheric and array calibration has been shown to be 4% and 4–7%, respectively.
A novel method for atmospheric correction of cosmic-ray data based on principal component analysis
A new method for atmospheric correction of cosmic ray data is designed. It’s fully empirical, based on the principal component analysis. The method requires knowledge of the pressure and the temperature profile of the atmosphere. It’s applicable to all muon detectors. The method is tested on muon data from two detectors in Belgrade cosmic ray station, one located on the ground level and the other at the depth of 25 mwe. Correction reduces variance by 64.5% in ground level detector data and 38.1% in underground data. At the same time, the amplitude of the annual variation is reduced by 86.0% at ground level and 54.9% underground. With the same data sets the presented method performs better than the integral correction method.
Present and projected sensitivities of Dark Matter direct detection experiments to effective WIMP-nucleus couplings
Assuming for Weakly Interacting Massive Particles (WIMPs) a Maxwellian velocity distribution in the Galaxy we explore in a systematic way the relative sensitivity of an extensive set of existing and projected Dark Matter (DM) direct detection experiments to each of the 14 couplings that parameterize the most general non-relativistic (NR) effective Hamiltonian allowed by Galilean invariance for a contact interaction driving the elastic scattering off nuclei of WIMPs of spin 1/2. We perform our analysis in terms of two free parameters: the WIMP mass mχ
and the ratio between the WIMP-neutron and the WIMP-proton couplings cn
/cp
. We include the modified signal spectral shape due to non–standard interactions when it is needed in the determination of the bound, such as in the case of background subtraction or of the application of the optimal–interval method. For each coupling, in the mχ
–cn
/cp
plane we provide contour plots of the most stringent 90% C.L. bound on the WIMP–nucleon cross section and show the experiment providing it. We also introduce NRDD_constraints, a simple interpolating code written in Python that allows to obtain the numerical value of the bound as a function of the WIMP mass mχ
and of the coupling ratio cn
/cp
for each NR coupling. We find that 9 experiments out of the 14 present Dark Matter searches considered in our analysis provide the most stringent bound on some of the effective couplings for a given choice of (mχ, cn
/cp
): this is evidence of the complementarity of different target nuclei and/or different combinations of count-rates and energy thresholds when the search of DM is extended to a wide range of possible interactions.
VERITAS Detection of LS 5039 and HESS J1825-137
With 8 hours of observations, VERITAS confirms the detection of two very high energy gamma-ray sources. The gamma-ray binary LS 5039 is detected with a statistical significance of 8.8σ. The measured flux above 1 TeV is
(
2.5
±
0.4
)
×
10

12
cm

2
s

1
near inferior conjunction and
(
7.8
±
2.8
)
×
10

13
cm

2
s

1
near superior conjunction. The pulsar wind nebula HESS J1825-137 is detected with a statistical significance of 6.7σ and a measured flux above 1 TeV of
(
3.9
±
0.8
)
×
10

12
cm

2
s

1
.
Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data
Many Galactic sources of gamma rays, such as supernova remnants, are expected to produce neutrinos with a typical energy cutoff well below 100 TeV. For the IceCube Neutrino Observatory located at the South Pole, the southern sky, containing the inner part of the Galactic plane and the Galactic Center, is a particularly challenging region at these energies, because of the large background of atmospheric muons. In this paper, we present recent advancements in data selection strategies for track-like muon neutrino events with energies below 100 TeV from the southern sky. The strategies utilize the outer detector regions as veto and features of the signal pattern to reduce the background of atmospheric muons to a level which, for the first time, allows IceCube searching for point-like sources of neutrinos in the southern sky at energies between 100 GeV and several TeV in the muon neutrino charged current channel. No significant clustering of neutrinos above background expectation was observed in four years of data recorded with the completed IceCube detector. Upper limits on the neutrino flux for a number of spectral hypotheses are reported for a list of astrophysical objects in the southern hemisphere.
Revisiting the TeV detection prospects for radio galaxies
Radio galaxies host relativistic jets oriented away from our line of sight, making them challenging targets for Very High Energy (VHE, E > 100 GeV) γ-ray detectors. Indeed, out of  ∼ 100 extragalactic sources detected at E > 100 GeV, only six are radio galaxies, while the great majority are blazars hosting aligned jets. The new Cherenkov Telescope Array (CTA) will provide order-of-magnitude improvements in sensitivity and spectral resolution with respect to the present generation of ground-based γ-ray observatories, opening new frontiers for high-energy studies of radio galaxies. In a previous paper, we studied the detection prospects of misaligned jets with the CTA for a sample of sources from the Third Fermi-LAT catalog (3FGL). In this work, we complement this study taking advantage of the expanded sample from the Fourth Fermi-LAT catalog (4FGL), which includes roughly double the number of sources. We simulate CTA observations of 41 γ-ray radio galaxies, extrapolating their Fermi-LAT spectrum into the TeV energy range assuming different spectral shapes. We predict that the CTA will detect eleven new TeV radio galaxies with an observational campaign of 50 hours per source, under the realistic assumption of a spectral cutoff at 0.5 TeV. This would increase the sample of VHE radio galaxies by a factor of three, and result in the first detection of FR II radio galaxies at these energies. By simulating CTA observations with 5 hours exposure, we predict that two Fermi-LAT radio galaxies should already be well within reach of current TeV observatories. Finally we have investigated the prospects for a CTA detection of extended VHE emission from the lobe-dominated FR I Fornax A, and predict that such a detection will be possible for integration times  ≳ 50 hours. We conclude that, in line with our previous findings, the CTA will significantly impact our understanding of misaligned jets at TeV energies, allowing us to perform population studies, as well as a comparison between the two main radio galaxy subclasses for the first time in this energy band.
Measurement of the Gamma Ray Background in the Davis Cavern at the Sanford Underground Research Facility
Abstract
Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from γ-rays emitted by 40K and the 238U and 232Th decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4,850-foot level. In order to characterise the cavern background, in-situ γ-ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0–3300 keV) varied from 596 Hz to 1355 Hz for unshielded measurements, corresponding to a total flux from the cavern walls of 1.9 ± 0.4 γ cm

2
s

1
. The resulting activity in the walls of the cavern can be characterised as 220 ± 60 Bq/kg of 40K, 29 ± 15 Bq/kg of 238U, and 13 ± 3 Bq/kg of 232Th.
Study of cosmogenic radionuclides in the COSINE-100 NaI(Tl) detectors
COSINE-100 is a direct detection dark matter search experiment that uses a 106 kg array of eight NaI(Tl) crystals that are kept underground at the Yangyang Underground Laboratory to avoid cosmogenic activation of radioisotopes by cosmic rays. Even though the cosmogenic activity is declining with time, there are still significant background rates from the remnant nuclides. In this paper, we report measurements of cosmogenic isotope contaminations with less than one year half-lives that are based on extrapolations of the time dependent activities of their characteristic energy peaks to activity rates at the time the crystals were deployed underground. For longer-lived 109Cd (
T
1
/
2
=
1.27
y) and 22Na (
T
1
/
2
=
2.6
y), we investigate time correlations and coincidence events due to several emissions. The inferred sea-level production rates are compared with calculations based on the ACTIVIA and MENDL-2 model calculations and experimental data. The results from different approaches are in reasonable agreement with each other. For 3H, which has a long, 12.3 year half-life, we evaluated the activity levels and the exposure times that are in reasonable agreement with the time period estimated for each crystal’s exposure.
Vanishing vacuum energy
The vacuum energy problem arises because quantum fields fluctuate even at the absolute zero of temperature. These “zero-point” (
T
=
0
) vacuum fluctuations have non-zero energy. Since in general relativity all types of energy generate the space-time curvature, vacuum energy must enter the Einstein field equation as a source term. Here we find that vacuum energy is zero if and only if the vacuum equation of state embodies relativistic invariance.
On the parametrization of the distributions of depth of shower maximum of ultra-high energy extensive air showers
The distribution of depth in which a cosmic ray air shower reaches its maximum number of particles (X
max) is studied and parametrized. Three functions are studied for proton, carbon, silicon, and iron primary particles with energies ranging from 1017 eV to 1020 eV for three hadronic interaction models: EPOS-LHC, QGSJetII.04, and Sibyll2.3c. The function which best describes the X
maxdistribution of a mixed composition is also studied. A very large number of simulated showers and a detailed analysis procedure are used to guarantee negligible effects of undersampling and of fitting in the final results. For the first time, a comparison of several functions is presented under the same assumption with the intention of selecting within them the best functional form to describe the X
maxdistribution. The Generalized Gumbel distribution is shown to be the best option among the options for a general description of all cases. The Log-normal distribution is also a good choice for some cases while the Exponentially Modified Gaussian distribution has shown to be the worst choice in almost all cases studied. All three functions are parametrized as a function of energy and primary mass.
Imprint of a Steep Equation of State in the growth of structure
We study the cosmological properties of a dynamical of dark energy (DE) component determined by a Steep Equation of State (SEoS)
w
(
z
)
=
w
0
+
w
i
(
z
/
z
T
)
q
1
+
(
z
/
z
T
)
q
. The SEoS has a transition at zT
between two pivotal values (wi, w
0) which can be taken as an early time and present day values of w and the steepness is given by q. We describe the impact of this dynamical DE at background and perturbative level. The steepness of the transition has a better cosmological fit than a conventional CPL model with
w
=
w
0
+
w
a
(
1

a
)
. Furthermore, we analyze the impact of steepness of the transition in the growth of matter perturbations and structure formation. This is manifest in the linear matter power spectrum, P(k), the logarithmic growth function, fσ
8(z), and the differential mass function
d
n
/
d
log
M
(
z
=
0
)
. The differences in these last three quantities is at a percent-level using the same cosmological baseline parameters in our SEoS and a ΛCDM model. However, we find an increase in the power spectrum, producing a bump at k ≈ kT
with kT
 ≡ aTH(aT
) the mode associated to the time of the steep transition (
a
T
=
1
/
(
1
+
z
T
)
). Different dynamics of DE lead to a different amount of DM at present time which has an impact in Power Spectrum and accordingly in structure formation.
Corrigendum to ‘Measurement of the neutron background at the Canfranc Underground Laboratory LSC’ [Astroparticle Physics 42 (2013) 1–6]
Author(s): D. Jordan, J.L. Tain, A. Algora, J. Agramunt, C. Domingo-Pardo, M.B. Gomez-Hornillos, R. Caballero-Folch, G. Cortés, D. Cano-Ott, E. Mendoza, I. Bandac, A. Bettini, L.M. Fraile, C. Domingo
Calibration of the LOFAR low-band antennas using the Galaxy and a model of the signal chain
The LOw-Frequency ARray (LOFAR) is used to make precise measurements of radio emission from extensive air showers, yielding information about the primary cosmic ray. Interpreting the measured data requires an absolute and frequency-dependent calibration of the LOFAR system response. This is particularly important for spectral analyses, because the shape of the detected signal holds information about the shower development. We revisit the calibration of the LOFAR antennas in the range of
30

80
MHz. Using the Galactic emission and a detailed model of the LOFAR signal chain, we find an improved calibration that provides an absolute energy scale and allows for the study of frequency dependent features in measured signals. With the new calibration, systematic uncertainties of 13% are reached, and comparisons of the spectral shape of calibrated data with simulations show promising agreement.
Autonomous radio detection of air showers with the TREND50 antenna array
TREND50 is a radio detection setup of 50 self-triggered antennas working in the 50-100 MHz frequency range and deployed in a radio-quiet valley of the Tianshan mountains (China). TREND50 achieved its goal: the autonomous radiodetection and identification of air showers. Thanks to a dedicated offline selection algorithm, 564 air shower candidates were indeed selected out of 7 · 108 transient radio signals recorded during the 314 live days of data taken during the first two years of operation of this setup (2011 and 2012). This event rate, as well as the distribution of the candidate directions of arrival, is consistent with what is expected from cosmic-ray-induced air showers according to simulations, assuming an additional  ∼ 20% contamination of the final sample by background events. This result is obtained at the cost of a reduced air shower detection efficiency, estimated to be  ∼ 3%. This low efficiency is mostly due to the large amount of dead time of the setup. This result paves the way for the GRANDProto35 experiment, the first stage of the GRAND project.
Constraints on the diffuse photon flux with energies above 1018 eV using the surface detector of the Telescope Array experiment
We present the results of the search for ultra-high-energy photons with nine years of data from the Telescope Array surface detector. A multivariate classifier is built upon 16 reconstructed parameters of the extensive air shower. These parameters are related to the curvature and the width of the shower front, the steepness of the lateral distribution function, and the timing parameters of the waveforms sensitive to the shower muon content. A total number of two photon candidates found in the search is fully compatible with the expected background. The 95% CL limits on the diffuse flux of the photons with energies greater than 1018.0, 1018.5, 1019.0, 1019.5 and 1020.0 eV are set at the level of 0.067, 0.012, 0.0036, 0.0013,
0.0013
km

2
yr

1
sr

1
correspondingly.
Deep learning techniques applied to the physics of extensive air showers
Deep neural networks are a powerful technique that have found ample applications in several branches of physics. In this work, we apply deep neural networks to a specific problem of cosmic ray physics: the estimation of the muon content of extensive air showers when measured at the ground. As a working case, we explore the performance of a deep neural network applied to large sets of simulated signals recorded for the water-Cherenkov detectors of the Surface Detector of the Pierre Auger Observatory. The inner structure of the neural network is optimized through the use of genetic algorithms. To obtain a prediction of the recorded muon signal in each individual detector, we train neural networks with a mixed sample of simulated events that contain light, intermediate and heavy nuclei. When true and predicted signals are compared at detector level, the primary values of the Pearson correlation coefficients are above 95%. The relative errors of the predicted muon signals are below 10% and do not depend on the event energy, zenith angle, total signal size, distance range or the hadronic model used to generate the events.
Zenith angle dependence of the cosmic ray rate as measured with Imaging air-Cherenkov Telescopes
The rate of extensive air-showers observed with imaging air-Cherenkov telescopes is zenith angle dependent. This effect originates from the increasing geometrical distance of the observed shower to the telescope with increasing zenith distance. This paper investigates how this alters the observed image and how this affects the trigger rate as a function of zenith angle. The discussed effects include the change of Cherenkov light yield, of absorption in the atmosphere, of photon density at the aperture and of the image size at the focal plane of the telescope. Based on a simple model for the atmosphere and well-known first principles on the development of extensive air-showers, the zenith angle dependence is expressed analytically. The assumption that most light is emitted from the shower core and mathematical approximations allow to derive an analytical expression describing the zenith angle dependence well with only three free parameters which are directly linked with the underlying physics. This suggests further investigations about how these fit parameters are linked to the properties of the atmosphere and the instrument. Using data published by the First G-APD Cherenkov Telescope, a good match of the fit functions with the data is obtained. For the trigger rate of cosmic rays, the obtained parameters are consistent with the naive expectation.
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