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First results of a cosmic-ray electron and positron spectrum from 10 GeV to 3 TeV is presented based upon observations with the CALET instrument on the International Space Station starting in October, 2015. Nearly a half million electron and positron events are included in the analysis. CALET is an all-calorimetric instrument with total vertical th...
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The TUS experiment is aimed to study the energy spectrum and arrival direction of Ultra High Energy Cosmic Rays at E ~ 100 EeV from the space orbit by measuring the fluorescence yield of the Extensive Atmospheric Shower in the atmosphere. It is the first orbital telescope designed for such measurements and is taking data since May 19, 2016. The TUS...
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... The calorimetric electron telescope (CALET) is a space experiment installed at the Japanese Experiment Module-Exposed Facility (JEM-EF) on the International Space Station (ISS) for long term observations of cosmic rays and optimized for the measurement of the all-electron spectrum [13]. The first result on the all-electron spectrum by CALET was published in the energy range from 10 GeV to 3 TeV, the first ever significant observation reaching into the TeV region [14]. Subsequently, an updated spectrum was published with a factor ∼2 larger statistics by using more than 2 years of flight data and the full geometrical acceptance in the high-energy region [15]. ...
... The energy of incident electrons is reconstructed using an energy correction function which converts the energy deposit of TASC and IMC into primary energy for each geometrical condition. The absolute energy scale was calibrated and shifted by þ3.5% [14] as a result of a study of the geomagnetic cutoff. Since the full dynamic range calibration [24] was carried out with a scale-free method, its validity holds regardless of the absolute scale uncertainty. ...
Detailed measurements of the spectral structure of cosmic-ray electrons and positrons from 10.6 GeV to 7.5 TeV are presented from over 7 years of observations with the CALorimetric Electron Telescope (CALET) on the International Space Station. The instrument, consisting of a charge detector, an imaging calorimeter, and a total absorption calorimeter with a total depth of 30 radiation lengths at normal incidence and a fine shower imaging capability, is optimized to measure the all-electron spectrum well into the TeV region. Because of the excellent energy resolution (a few percent above 10 GeV) and the outstanding e/p separation (105), CALET provides optimal performance for a detailed search of structures in the energy spectrum. The analysis uses data up to the end of 2022, and the statistics of observed electron candidates has increased more than 3 times since the last publication in 2018. By adopting an updated boosted decision tree analysis, a sufficient proton rejection power up to 7.5 TeV is achieved, with a residual proton contamination less than 10%. The observed energy spectrum becomes gradually harder in the lower energy region from around 30 GeV, consistently with AMS-02, but from 300 to 600 GeV it is considerably softer than the spectra measured by DAMPE and Fermi-LAT. At high energies, the spectrum presents a sharp break around 1 TeV, with a spectral index change from −3.15 to −3.91, and a broken power law fitting the data in the energy range from 30 GeV to 4.8 TeV better than a single power law with 6.9 sigma significance, which is compatible with the DAMPE results. The break is consistent with the expected effects of radiation loss during the propagation from distant sources (except the highest energy bin). We have fitted the spectrum with a model consistent with the positron flux measured by AMS-02 below 1 TeV and interpreted the electron+positron spectrum with possible contributions from pulsars and nearby sources. Above 4.8 TeV, a possible contribution from known nearby supernova remnants, including Vela, is addressed by an event-by-event analysis providing a higher proton-rejection power than a purely statistical analysis.
... Contrary to the positron flux, which has an exponential energy cutoff of about 810 GeV, at the 5σ level the electron flux does not have an energy cutoff below 1.9 TeV (Aguilar et al. 2019a). However, the dropoff around 1 TeV in the total spectrum of positrons and electrons was first reported by the H.E.S.S. Collaboration (Aharonian et al. 2008a(Aharonian et al. , 2009 and validated by the MAGIC (Borla Tridon 2011), VERITAS (Staszak & VERITAS Collaboration 2015) and CALET (Adriani et al. 2017(Adriani et al. , 2018 experiments. The DAMPE experiment also performed a direct measurement of this feature and announced that the break-off was at ∼0.9 TeV (DAMPE Collaboration et al. 2017). ...
... Similar to Figure 2, the spectra of positrons and electrons, their sum from panels (a)-(c), and the ratio of positron to the sum of positrons and electrons in panel (d).The data points are adopted from the AMS-02 and CALET experiments(Adriani et al. 2017(Adriani et al. , 2018Aguilar et al. 2019aAguilar et al. , 2019b. ...
Multi-messenger anomalies, including spectral hardening or excess of nuclei, leptons, ratios of p ¯ / p and B/C, and anisotropic reversal, have been observed in past years. The AMS-02 experiment also revealed different spectral breaks for positrons and electrons at 284 GeV and beyond tera electron volts, respectively. It is natural to ask whether all those anomalies originate from one unified physical scenario. In this work, the spatially dependent propagation (SDP) with a nearby supernova remnant (SNR) source is adopted to reproduce the abovementioned anomalies. There possibly exists a dense molecular cloud (DMC) around SNRs and the secondary particles can be produced by pp collision or fragmentation between the accelerated primary cosmic rays and DMC. As a result, the spectral hardening for primary and secondary particles and ratios of B/C and p ¯ / p can be well reproduced. Due to the energy loss at the source age of 330 kyr, the characteristic spectral break-off for a primary electron is at about 1 TeV as hinted at by the measurements. The secondary positrons and electrons from charged pion take up 5% of energy from their mother particles, so the positron spectrum has a break-off at ∼250 GeV. Therefore, the different spectral breaks for positrons and electrons together with other anomalies can be fulfilled in this unified physical scenario. More interesting is that we also obtain the featured structures as spectral break-offs at 5 TeV for secondary particles of Li, Be, and B, which can be used to verify our model. We hope that those tagged structures can be observed by the new generation of spaceborne experiment HERD in the future.
... CR source distribution Julia Thaler Figure 4: Left: Electron spectra for our models for the four different tolerances in the luminosity approach, both with and without the Fermi sources as well as the density approach model with observed data from different experiments (top to bottom in the legend: [10], [11], [17], [23], [24], [16], [18] Right: Same but for CR protons. Experiments top to bottom: [20], [21], [19], [22]. ...
... However, the qA dependence of the anticorrelation between the GCR intensity and the HCS tilt angle over the solar activity cycle has not been reported yet. In this Letter, we report for the first time the anticorrelations with the HCS tilt angle of the electron and proton count rates simultaneously observed by the Calorimetric Electron Telescope (CALET) [10][11][12][13][14][15][16][17][18][19] onboard the International Space Station over nearly 6 yr between 2015 and 2021. ...
... We apply the following event-selection criteria: (a) off-line trigger condition requiring energy deposits in the bottom two layers of the IMC and the top layer of the TASC to exceed a given set of thresholds, (b) quality cut on the reconstructed track of the incident particle by the Kalman filter method, (c) geometrical condition requiring the reconstructed track to traverse the CHD top layer and the TASC bottom layer, (d) cut on the CHD output to select incident particles with single charge, (e) cut on an energy deposit in all layers of the IMC and the TASC to exclude events passing through the layer without energy deposit, (f) additional cut on the spatial concentration of hit signals in the IMC bottom layer to reduce the proton contamination for the analysis of electron count rates, and (g) cut on the lateral shower development in the TASC top layer for electron and proton discrimination [see the Supplemental Material [21] about the detail of criteria (f) and (g)]. Details of these criteria are provided in [11,14] for the analysis of high-energy electrons, with the important distinction that the analysis here imposes selections on the IMC bottom layer and TASC top layer for electron and proton discrimination given that the low-energy electrons do not penetrate all layers of the TASC. ...
We present the observation of a charge-sign dependent solar modulation of galactic cosmic rays (GCRs) with the Calorimetric Electron Telescope onboard the International Space Station over 6 yr, corresponding to the positive polarity of the solar magnetic field. The observed variation of proton count rate is consistent with the neutron monitor count rate, validating our methods for determining the proton count rate. It is observed by the Calorimetric Electron Telescope that both GCR electron and proton count rates at the same average rigidity vary in anticorrelation with the tilt angle of the heliospheric current sheet, while the amplitude of the variation is significantly larger in the electron count rate than in the proton count rate. We show that this observed charge-sign dependence is reproduced by a numerical “drift model” of the GCR transport in the heliosphere. This is a clear signature of the drift effect on the long-term solar modulation observed with a single detector.
... National Institutes for Quantum and Radiation Science and Technology, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan 39 Nagoya University, Furo, Chikusa, Nagoya 464-8601, Japan 40 College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan We present the results of a direct measurement of the cosmic-ray helium spectrum with the CALET instrument in operation on the International Space Station since 2015. The observation period covered by this analysis spans from October 13, 2015, to April 30, 2022April 30, (2392. ...
... The Calorimetric Electron Telescope (CALET) [35][36][37][38] is a space-based instrument equipped with a thick homogeneous calorimeter, optimized for the measurement of the all-electron spectrum [39,40], yet with excellent capabilities to measure the hadronic component of cosmic rays including proton, light, and heavy nuclei (up to nickel and above) [2,14,41,42] in the energy range up to ∼1 PeV. In this Letter, we present a direct measurement of the cosmicray helium spectrum in kinetic energy E from 40 GeV to 250 TeV with CALET. ...
... The TASC is a homogeneous calorimeter with 12 layers of tightly packed lead-tungstate (PbWO 4 ) logs, providing an energy measurement over a very large dynamic range (more than 6 orders of magnitude) spanning four different gain ranges [44]. A more complete description of the instrument is given in the Supplemental Material of Ref. [39]. ...
We present the results of a direct measurement of the cosmic-ray helium spectrum with the CALET instrument in operation on the International Space Station since 2015. The observation period covered by this analysis spans from October 13, 2015, to April 30, 2022 (2392 days). The very wide dynamic range of CALET allowed for the collection of helium data over a large energy interval, from ∼40 GeV to ∼250 TeV, for the first time with a single instrument in low Earth orbit. The measured spectrum shows evidence of a deviation of the flux from a single power law by more than 8σ with a progressive spectral hardening from a few hundred GeV to a few tens of TeV. This result is consistent with the data reported by space instruments including PAMELA, AMS-02, and DAMPE and balloon instruments including CREAM. At higher energy we report the onset of a softening of the helium spectrum around 30 TeV (total kinetic energy). Though affected by large uncertainties in the highest energy bins, the observation of a flux reduction turns out to be consistent with the most recent results of DAMPE. A double broken power law is found to fit simultaneously both spectral features: the hardening (at lower energy) and the softening (at higher energy). A measurement of the proton to helium flux ratio in the energy range from 60 GeV/n to about 60 TeV/n is also presented, using the CALET proton flux recently updated with higher statistics.
... This method is developed for the derivation of the electron flux and is designed to exploit the larger spread and slower development of proton showers due to penetrating secondary pions. 13 Charge zero -In order to select events consistent with zero primary charge, cuts are made on the energy deposits in CHD and upper IMC layers. These requirements are designed to veto charged particle events effectively. ...
... where the unit of FðT e Þ is given in ðm 2 s sr MeVÞ −1 and the kinetic energy of the CR electrons (T e ) is in MeV. The above fit is consistent with Fermi-LAT [34][35][36][37], AMS-02 [38], PAMELA [39,40], and Voyager [41,42] local interstellar spectrum data, to within an accuracy of 5%. ...
The recoil threshold of direct detection (DD) experiments limits the mass range of dark matter (DM) particles that can be detected, with most DD experiments being blind to sub-MeV DM particles. However, these light DM particles can be boosted to very high energies via collisions with energetic cosmic ray electrons. This allows dark matter particles to induce detectable recoil in the target of direct detection experiments. We derive constraints on a scattering cross section of DM and an electron, using XENONnT and Super-Kamiokande data. Vector and scalar mediators are considered in the heavy and light regimes. We discuss the importance of including energy-dependent cross sections (due to the specific Lorentz structure of the vertex) in our analysis and show that the bounds can be significantly different than the results obtained assuming a constant energy-independent cross section, often assumed in the literature for simplicity. Our bounds are also compared with other astrophysical and cosmological constraints.
... The PAMELA satellite experiment [77] released an abundance of the positron in the CR energy range of 15 − 100GeV. Also the results of a CR electron-positron spectrum, between 10GeV and 3TeV, have been reported based upon observations with CALET [78]. The DAMPE collaboration [79,80] has been presented a measurements of the electron-positron spectrum in the energy range 25 GeV to 4.6TeV. ...
Inspired by the recently new measurement of (g − 2)μ at FermiLab and reported upper bound for electron-dark matter (DM) recoil by the XENON1T collaboration, we revisited phenomenology of a light MeV scale vector dark matter in a leptophilic extension of standard model while a new spinor field plays the role of mediator. A viable parameter space is considered to discuss the possibility of light dark matter relic density as well as anomalous magnetic moment of the muon. We study DM-electron direct detection and cosmological bounds on the parameters space of the model. It is shown that although new bound of (g − 2)μ anomaly greatly confines the parametric space of the model, the thermal light dark matter can exist for \(\mathrm {M_{DM}} \sim 10^{-1}-10^{1} \text {GeV}\).
... Therefore, it is challenging to precisely measure the spectrum of electrons. Currently, the best measurements of the electron and/or positron spectra come from space (or balloon) direct detection experiments, including the magnetic spectrometers and imaging calorimeters [5][6][7][8][9][10][11][12]. The ground-based atmospheric imaging Cherenkov telescope arrays also tried to measure the total electron plus positron spectra to higher energies, which, however, are subject to large systematic uncertainties [13][14][15][16]. ...
Galactic cosmic rays are mostly made up of energetic nuclei, with less than $1\%$ of electrons (and positrons). Precise measurement of the electron and positron component requires a very efficient method to reject the nuclei background, mainly protons. In this work, we develop an unsupervised machine learning method to identify electrons and positrons from cosmic ray protons for the Dark Matter Particle Explorer (DAMPE) experiment. Compared with the supervised learning method used in the DAMPE experiment, this unsupervised method relies solely on real data except for the background estimation process. As a result, it could effectively reduce the uncertainties from simulations. For three energy ranges of electrons and positrons, 80--128 GeV, 350--700 GeV, and 2--5 TeV, the residual background fractions in the electron sample are found to be about (0.45 $\pm$ 0.02)$\%$, (0.52 $\pm$ 0.04)$\%$, and (10.55 $\pm$ 1.80)$\%$, and the background rejection power is about (6.21 $\pm$ 0.03) $\times$ $10^4$, (9.03 $\pm$ 0.05) $\times$ $10^4$, and (3.06 $\pm$ 0.32) $\times$ $10^4$, respectively. This method gives a higher background rejection power in all energy ranges than the traditional morphological parameterization method and reaches comparable background rejection performance compared with supervised machine learning~methods.
... Therefore, it is challenging to precisely measure the spectrum of electrons. Currently, the best measurements of the electron and/or positron spectra come from space (or balloon) direct detection experiments, including the magnetic spectrometers and imaging calorimeters [5][6][7][8][9][10][11][12]. The ground-based atmospheric imaging Cherenkov telescope arrays also tried to measure the total electron plus positron spectra to higher energies, which, however, are subject to large systematic uncertainties [13][14][15][16]. ...
Galactic cosmic rays are mostly made up of energetic nuclei, with less than 1% of electrons (and positrons). Precise measurement of the electron and positron component requires a very efficient method to reject the nuclei background, mainly protons. In this work, we develop an unsupervised machine learning method to identify electrons and positrons from cosmic ray protons for the Dark Matter Particle Explorer (DAMPE) experiment. Compared with the supervised learning method used in the DAMPE experiment, this unsupervised method relies solely on real data except for the background estimation process. As a result, it could effectively reduce the uncertainties from simulations. For three energy ranges of electrons and positrons, 80–128 GeV, 350–700 GeV, and 2–5 TeV, the residual background fractions in the electron sample are found to be about (0.45 ± 0.02)%, (0.52 ± 0.04)%, and (10.55 ± 1.80)%, and the background rejection power is about (6.21 ± 0.03) ×104, (9.03 ± 0.05) ×104, and (3.06 ± 0.32) ×104, respectively. This method gives a higher background rejection power in all energy ranges than the traditional morphological parameterization method and reaches comparable background rejection performance compared with supervised machine learning methods.
