PAMELA Experiment Research Articles

Boron isotopes in the PAMELA experiment

In this work, a new analysis of the isotopic composition of boron nuclei (B) in galactic cosmic rays (GCR) in the range of rigidities of 1–5 GV (nuclear energies 0.1–1.5 GeV/nucleon) was carried out using data from the PAMELA space experiment 2006–2014 on the rigidity of detected nuclei and their velocity (time-of-flight analysis and ionization losses in the instrument’s multilayer calorimeter). The new results of the PAMELA experiment expand the energy range of previous measurements, are consistent with the few existing data, and indicate deviations of the B isotope ratios from the GALPROP simulation data for the GCR, similar to the deviations for the Li and Be isotopes in the PAMELA data, which can be interpreted as evidence of observation against the background of the GCR the contribution of several local sources from explosions of nearby (hundreds of parsec) supernovae.

Semi-empirical model of galactic cosmic ray spectrum

The galactic cosmic rays are high-energy particles that reach us from all directions of the vast universe. Their transport in the interplanetary medium is well described by the transport equation, first derived by Parker in 1965. An approximate solution of the cosmic ray transport equation for 1 AU is used to construct a simplified, semi-empirical model of the cosmic ray spectrum. The model parameters are obtained by fitting the proton spectra of the PAMELA experiment. The values of the model parameters are presented for the period 2006-2014, which includes the solar minimum between cycles 23 and 24 and the maximum phase of cycle 24. Our analysis shows that the proposed semi-empirical model agrees approximately well with the force-field approximation to the cosmic ray transport equation.

Preliminary results of the search for helium nuclei in solar energetic events measured in the PAMELA experiment

We presented the preliminary results of the search for helium nuclei in solar energetic events measured in the PAMELA experiment in the rigidity range from 0.1 to 1 GV from 2006 to 2014. We constructed selection criteria for helium nuclei and estimated their efficiency. The spectra are approximated using a simple power-law function and functional form based on Ellison-Ramaty, consisting of a power-law spectrum modulated by an exponential.

Preliminary Results from the Search for Helium Nuclei in Solar Energetic Events Measured in the PAMELA Experiment

Preliminary Results from the Search for Helium Nuclei in Solar Energetic Events Measured in the PAMELA Experiment

Charge–Sign Dependence of Cosmic Ray Modulation from the PAMELA Experiment

Charge–Sign Dependence of Cosmic Ray Modulation from the PAMELA Experiment

Charge-sign dependence of cosmic-ray modulation by the PAMELA experiment

To study the solar modulation of cosmic-ray fluxes below 1 GeV, machine learning methods allowed obtaining the flux ratios of positrons and electrons with energies from 100 to 500 MeV, and the fluxes of electrons and protons with 1–1.7 GV rigidities from the PAMELA experiment for 2006–2016. The observed features of the data obtained and its comparison with the AMS-02 experimental data enable researching the charge-sign dependence of the modulation around the solar minimum in 2009 and the maximum in 2015.

Scalar dark matter with Z3 symmetry in the type-II seesaw mechanism

We study a simple complex scalar singlet dark matter (DM) model with ${Z}_{3}$ symmetry in the framework of the type-II seesaw mechanism. We use the model to explain the excess of electron-positron flux measured by the AMS-02, DAMPE, and Fermi-LAT Collaborations, which is encouraged by the decay of the triplets produced from dark matter annihilations in the Galactic halo. We focus on the nondegenerate case in which the mass of DM is larger than that of the triplets' and deliberately alleviates the leptophilic properties of the DM, so that the semiannihilation effects are enhanced. With the guarantee of ${Z}_{3}$ symmetry, by fitting the antiproton spectrum observed in the PAMELA and AMS experiments, we find that the DM cubic terms and the couplings between DM and the Higgs boson are strongly constrained, leading to the semiannihilation cross-section fraction less than 11% when DM mass is given at 2 TeV.

Study of Forbush Decrease Recovery Times by the Payload for Antimatter Matter Exploration and Light-Nuclei Astrophysics (PAMELA) Experiment

Study of Forbush Decrease Recovery Times by the Payload for Antimatter Matter Exploration and Light-Nuclei Astrophysics (PAMELA) Experiment

Helium Fluxes Measured by the PAMELA Experiment from the Minimum to the Maximum Solar Activity for Solar Cycle 24

Abstract Time-dependent energy spectra of galactic cosmic rays (GCRs) carry fundamental information regarding their origin and propagation. When observed at the Earth, these spectra are significantly affected by the solar wind and the embedded solar magnetic field that permeates the heliosphere, changing significantly over an 11 yr solar cycle. Energy spectra of GCRs measured during different epochs of solar activity provide crucial information for a thorough understanding of solar and heliospheric phenomena. The PAMELA experiment collected data for almost 10 years (2006 June 15–2016 January 23), including the minimum phase of solar cycle 23 and the maximum phase of solar cycle 24. In this paper, we present new spectra for helium nuclei measured by the PAMELA instrument from 2010 January to 2014 September over a three-Carrington-rotation time basis. These data are compared to the PAMELA spectra measured during the previous solar minimum, providing a picture of the time dependence of the helium-nuclei fluxes over a nearly full solar cycle. Time and rigidity dependencies are observed in the proton-to-helium flux ratios. The force-field approximation of the solar modulation was used to relate these dependencies to the shapes of the local interstellar proton and helium-nuclei spectra.

Monte Carlo simulation of CRAND protons trapped at low Earth orbits

The Cosmic Ray Albedo Neutron Decay (CRAND) is believed to be the principal mechanism for the formation of inner proton radiation belt -- at least for relatively higher energy particles. We implement this mechanism in a Monte Carlo simulation procedure to calculate the trapped proton radiation at the low Earth orbits, through event-by-event interaction of the cosmic ray particles in the Earth's atmosphere and their transportation in the magnetosphere. We consider the generation of protons from subsequent decay of the secondary neutrons from the cosmic ray interaction in the atmosphere and their transport (and/or trapping) in the geomagnetic field. We address the computational challenges for this type of calculations and develop an optimized algorithm to minimize the computation time. We consider a full 3D description of the Earth's atmospheric and magnetic-field configurations using the latest available models. We present the spatial and phase-space distribution of the trapped protons considering the adiabatic invariants and other parameters at the low Earth orbits. We compare the simulation results with the trapped proton flux measurements made by PAMELA experiment at low Earth orbit and explain certain features observed by the measurement.

Light Nuclei Identification in Cosmic Rays in the PAMELA Experiment by Multiple Measurements of Energy Loss along the Particle Track

Light Nuclei Identification in Cosmic Rays in the PAMELA Experiment by Multiple Measurements of Energy Loss along the Particle Track

Amplitude and Temporal Characteristics of 27-Day Variations in the Galactic Cosmic Ray Flux, Measured during the PAMELA Experiment between 2006 and 2016

Amplitude and Temporal Characteristics of 27-Day Variations in the Galactic Cosmic Ray Flux, Measured during the PAMELA Experiment between 2006 and 2016

Energy Dependence of the Main Characteristics of Forbush Decreases, Obtained by the PAMELA Experiment

Energy Dependence of the Main Characteristics of Forbush Decreases, Obtained by the PAMELA Experiment

Influence of the temperature of the photosphere and deeper layers of the Sun on the spectra of gamma quanta with energies above 511 keV during solar flares

Gamma-ray quanta, which occur during solar flares due to the interaction of accelerated protons with the photosphere and deeper layers of the sun, enter interplanetary space from a thickness of several tens of g/cm2. In the presented work, gamma quanta with energies of more than 511 keV are considered. This makes it possible to exclude from consideration the dependence of the probability of ortho- and parapositronium formation on the temperature and density of the solar matter. And also do not consider the probability of annihilation by two or 3 gamma quanta. Thus, the reactions of thermal neutrons remain dependent on the temperature. As the ambient temperature increases, the average number of elastic neutron scattering before capture increases. This leads to a more likely penetration of neutrons to a greater depth or their departure into the interplanetary space. The high temperature of the Sun below the photosphere may be one of the reasons for the absence of the 2.223 MeV line in solar flares with registered protons in the PAMELA and AMS2 experiments. Using the GEANT4 package, the spectra of gamma-quanta arising in nuclear interactions are calculated. The temperature-dependent features of the gamma-ray spectra are discussed.

East–West Proton Flux Anisotropy Observed with the PAMELA Mission

Abstract We present a study of the east–west anisotropy of trapped-proton fluxes in low-Earth orbit based on the measurements of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) experiment. The differential intensities of eastward- and westward-traveling protons detected in the South Atlantic Anomaly region were estimated as a function of equatorial pitch angle and drift shell, for six energy bins between 80 MeV and 2 GeV. We found that, as a consequence of the strong atmospheric gradient coupled with the large gyroradius in this energy range, the intensities of eastward fluxes exceed those of westward fluxes by a factor of ∼10–20. However, the reported directional asymmetry also depends on the sign of the local flux gradient, resulting in more intense westward fluxes beyond the radial distances where the inner belt peaks. PAMELA observations can be used to improve the description of the near-Earth radiation environment at lowest altitudes and highest trapping energies, where current theoretical and empirical models are affected by the largest uncertainties.

Observations of Forbush Decreases of Cosmic-Ray Electrons and Positrons with the Dark Matter Particle Explorer

Abstract The Forbush decrease (FD) represents the rapid decrease of the intensities of charged particles accompanied with the coronal mass ejections or high-speed streams from coronal holes. It has been mainly explored with the ground-based neutron monitor network, which indirectly measures the integrated intensities of all species of cosmic rays by counting secondary neutrons produced from interaction between atmospheric atoms and cosmic rays. The space-based experiments can resolve the species of particles but the energy ranges are limited by the relatively small acceptances except for the most abundant particles like protons and helium. Therefore, the FD of cosmic-ray electrons and positrons have just been investigated by the PAMELA experiment in the low-energy range (<5 GeV) with limited statistics. In this paper, we study the FD event that occurred in 2017 September with the electron and positron data recorded by the Dark Matter Particle Explorer. The evolution of the FDs from 2 GeV to 20 GeV with a time resolution of 6 hr are given. We observe two solar energetic particle events in the time profile of the intensity of cosmic rays, the earlier, and weaker, one has not been shown in the neutron monitor data. Furthermore, both the amplitude and recovery time of fluxes of electrons and positrons show clear energy dependence, which is important in probing the disturbances of the interplanetary environment by the coronal mass ejections.

Spectra of Electrons and Positrons with Energies above 50 MeV, According to Data from the PAMELA Experiment

Spectra of Electrons and Positrons with Energies above 50 MeV, According to Data from the PAMELA Experiment

Using Data from a Ground-Based Network of Detectors and the PAMELA and AMS-02 Experiments to Compare Long-Term Variations in the Cosmic Ray Flux

Using Data from a Ground-Based Network of Detectors and the PAMELA and AMS-02 Experiments to Compare Long-Term Variations in the Cosmic Ray Flux

Solar-cycle Variations of South Atlantic Anomaly Proton Intensities Measured with the PAMELA Mission

Abstract We present a study of the solar-cycle variations of >80 MeV proton flux intensities in the lower edge of the inner radiation belt, based on the measurements of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission. The analyzed data sample covers an ∼8 yr interval from 2006 July to 2014 September, thus spanning from the decaying phase of the 23rd solar cycle to the maximum of the 24th cycle. We explored the intensity temporal variations as a function of drift shell and proton energy, also providing an explicit investigation of the solar modulation effects at different equatorial pitch angles. PAMELA observations offer new important constraints for the modeling of low-altitude particle radiation environment at the highest trapping energies.

Numerical modeling of cosmic rays in the heliosphere: Analysis of proton data from AMS-02 and PAMELA

Galactic cosmic rays (CRs) inside the heliosphere are affected by solar modulation. To investigate this phenomenon and its underlying physical mechanisms, we have performed a data-driven analysis of the temporal dependence of the CR proton flux over the solar cycle. The modulation effect was modeled by means of stochastic simulations of cosmic particles in the heliosphere. The model were constrained using measurements of CR protons made by AMS-02 and PAMELA experiments on monthly basis from 2006 to 2017. With a global statistical analysis of these data, we have determined the key model parameters governing CR diffusion, its dependence on the particle rigidity, and its evolution over the solar cycle. Our results span over epochs of solar minimum, solar maximum, as well as epochs with magnetic reversal and opposite polarities. Along with the evolution of the CR transport parameters, we study their relationship with solar activity proxies and interplanetary parameters. We find that the rigidity dependence of the parallel mean free path of CR diffusion shows a remarkable time dependence, indicating a long-term variability in the interplanetary turbulence that interchanges across different regimes over the solar cycle. The evolution of the diffusion parameters show a delayed correlation with solar activity proxies, reflecting the dynamics of the heliospheric plasma, and distinct dependencies for opposite states of magnetic polarity, reflecting the influence of charge-sign dependent drift in the CR modulation.