We report on anomalously long duration (2 ms) count rate bursts following the impact of cosmic ray showers near a 7.62 cm x⊘7.62 cm LaBr3 scintillation detector at the High Altitude Water Cherenkov ...array in Mexico, previously described by Stenkin et al. (2001), and termed “neutron bursts.” The largest burst produced 198 counts within 2 ms in our LaBr3 detector. We simulate the neutron burst albedo flux (that is, secondary emissions from an extensive air shower core impacting the ground), and show that (1) the characteristic spectra and count rates are well explained by neutron absorption in the ground and (2) any cosmic ray secondary that produces neutrons, either through hadron inelastic collisions, or photoneutron production by gamma‐rays, produces the same characteristic spectra. This implies that other natural phenomena that produce downward beams of gamma‐rays, like Terrestrial gamma ray flashes, should produce a similar “neutron burst” signature from the photoneutron reactions occurring in the soil.
Plain Language Summary
When very large cosmic ray showers (CRS) impact the ground, neutrons are produced in the soil that will rattle around until they become captured by soil particles and release energetic gamma‐rays. This produces a slow explosion of particles emanating from the ground following a CRS impact, and is termed a 'neutron burst'. We present recent observations of neutron bursts from a hand held sized gamma‐ray detector at the High Altitude Water Cherenkov (HAWC) array in Mexico, that exhibit interesting spectral features (the presence of positron annihilation), and an interesting time structure (hundreds of counts within a few ms). Our simulations indicate that Terrestrial gamma‐ray flashes (TGFs, bursts of gamma‐rays associated with lightning) should also produce these neutron bursts. An implication of this work is that existing deployments of ground based TGF instruments, comprised of small gamma‐ray detectors, can additionally be used to observe signatures of large cosmic ray showers on clear days.
Key Points
We report on fairweather count rate bursts with 2 ms duration following the impact of a large cosmic ray shower near a small scintillation detector at HAWC
Simulations show that the spectra and decay time can be produced by either hadronic interactions, or photoneutron reactions from gamma‐rays
These results imply that downward TGFs could produce a similar delayed neutron signature in the soil near ground based detectors
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain ...unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera-electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray-emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.
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Here, a measurement with high statistics of the differential energy spectrum of light elements in cosmic rays, in particular, of primary H plus He nuclei, is reported. The spectrum is presented in ...the energy range from 6 to 158 TeV per nucleus. Data was collected with the High Altitude Water Cherenkov (HAWC) Observatory between June 2015 and June 2019. The analysis was based on a Bayesian unfolding procedure, which was applied on a subsample of vertical HAWC data that was enriched to 82% of events induced by light nuclei. To achieve the mass separation, a cut on the lateral age of air shower data was set guided by predictions of CORSIKA/QGSJET-II-04 simulations. The measured spectrum is consistent with a broken power-law spectrum and shows a kneelike feature at around E = 24.0$^{+3.6}_{-3.1}$ TeV , with a spectral index γ = -2.51 ± 0.02 before the break and with γ = -2.83 ± 0.02 above it. The feature has a statistical significance of 4.1σ. Within systematic uncertainties, the significance of the spectral break is 0.8σ.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Abstract
In this work, we show the results of a comparative analysis of different reconstruction methods of shower cores produced by Cosmic Rays (CR’s) in a layer of Resistive Plate Chambers (RPC’s) ...that is under consideration for MATHUSLA (Massive Timing Hodoscope for Ultra-Stable neutraL pArticles). The analysis was performed with Monte Carlo simulations. Extensive air showers were simulated with CORSIKA using the GEISHA and QGSJET-II-04 hadronic interaction models for primary protons and iron nuclei in the energy range from 10 TeV to 100 PeV and zenith angles:
θ ≤
20
°
. The detector response was simulated with a simplified Python-based program. The location of the shower core was found using the center of mass of the deposited charge distribution, the maximum of the charge distribution, a fit with an exponential function to the projected distributions on the
X
and
Y
horizontal directions of the 2D charge distributions, and fits with an exponential and a Nishimura-Kamata-Greisen (NKG) lateral functions to the 3D charge distributions of the RPC. We found that the fits of the
X
and
Y
projections with an exponential function and the fits with a NKG function to the 3D signal distributions have a better performance than the other methods.
We test the predictions of hadronic interaction models regarding the depth of maximum of air-shower profiles, X max , and ground-particle signals in water-Cherenkov detectors at 1000 m from the ...shower core, S ( 1000 ) , using the data from the fluorescence and surface detectors of the Pierre Auger Observatory. The test consists of fitting the measured two-dimensional ( S ( 1000 ) , X max ) distributions using templates for simulated air showers produced with hadronic interaction models pos-, et--04, 2.3d and leaving the scales of predicted X max and the signals from hadronic component at ground as free-fit parameters. The method relies on the assumption that the mass composition remains the same at all zenith angles, while the longitudinal shower development and attenuation of ground signal depend on the mass composition in a correlated way. The analysis was applied to 2239 events detected by both the fluorescence and surface detectors of the Pierre Auger Observatory with energies between 10 18.5 eV to 10 19.0 eV and zenith angles below 60°. We found, that within the assumptions of the method, the best description of the data is achieved if the predictions of the hadronic interaction models are shifted to deeper X max values and larger hadronic signals at all zenith angles. Given the magnitude of the shifts and the data sample size, the statistical significance of the improvement of data description using the modifications considered in the paper is larger than 5 σ even for any linear combination of experimental systematic uncertainties. Published by the American Physical Society 2024
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We present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed ...for energies above $5 \cdot 10^{18}$ eV, i.e.~the region of the all-particle spectrum above the so-called "ankle" feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated through a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies, hard spectra and heavy chemical composition. We also show that uncertainties about physical quantities relevant to UHECR propagation and shower development have a non-negligible impact on the fit results.
We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered ...simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the ‘ankle’ at lg(E/eV)=18.5–19.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A>4. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavored as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► IceCube DeepCore lowers the neutrino energy threshold in IceCube to as low as 10GeV. ► The surrounding IceCube detector is an active veto against cosmic ray muons. ► IceCube DeepCore uses higher ...quantum efficiency PMTs in very clear ice. ► IceCube DeepCore has a module density 5× higher than the rest of IceCube.
The IceCube neutrino observatory in operation at the South Pole, Antarctica, comprises three distinct components: a large buried array for ultrahigh energy neutrino detection, a surface air shower array, and a new buried component called DeepCore. DeepCore was designed to lower the IceCube neutrino energy threshold by over an order of magnitude, to energies as low as about 10GeV. DeepCore is situated primarily 2100m below the surface of the icecap at the South Pole, at the bottom center of the existing IceCube array, and began taking physics data in May 2010. Its location takes advantage of the exceptionally clear ice at those depths and allows it to use the surrounding IceCube detector as a highly efficient active veto against the principal background of downward-going muons produced in cosmic-ray air showers. DeepCore has a module density roughly five times higher than that of the standard IceCube array, and uses photomultiplier tubes with a new photocathode featuring a quantum efficiency about 35% higher than standard IceCube PMTs. Taken together, these features of DeepCore will increase IceCube’s sensitivity to neutrinos from WIMP dark matter annihilations, atmospheric neutrino oscillations, galactic supernova neutrinos, and point sources of neutrinos in the northern and southern skies. In this paper we describe the design and initial performance of DeepCore.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Neutrinos with energies above 1017 eV are detectable with the Surface Detector Array of the Pierre Auger Observatory. The identification is efficiently performed for neutrinos of all flavors ...interacting in the atmosphere at large zenith angles, as well as for Earth-skimming τ neutrinos with nearly tangential trajectories relative to the Earth. No neutrino candidates were found in ∼14.7 years of data taken up to 31 August 2018. This leads to restrictive upper bounds on their flux. The 90% C.L. single-flavor limit to the diffuse flux of ultra-high-energy neutrinos with an Eν−2 spectrum in the energy range 1.0×1017eV–2.5×1019eV is E2dNν/dEν<4.4×10−9GeVcm−2s−1sr−1, placing strong constraints on several models of neutrino production at EeV energies and on the properties of the sources of ultra-high-energy cosmic rays.
The unexpectedly high flux of cosmic-ray positrons detected at Earth may originate from nearby astrophysical sources, dark matter, or unknown processes of cosmic-ray secondary production. We report ...the detection, using the High-Altitude Water Cherenkov Observatory (HAWC), of extended tera–electron volt gamma-ray emission coincident with the locations of two nearby middle-aged pulsars (Geminga and PSR B0656+14). The HAWC observations demonstrate that these pulsars are indeed local sources of accelerated leptons, but the measured tera–electron volt emission profile constrains the diffusion of particles away from these sources to be much slower than previously assumed. We demonstrate that the leptons emitted by these objects are therefore unlikely to be the origin of the excess positrons, which may have a more exotic origin.
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