PAMELA spectrum of electrons and positrons of cosmic rays in the energy range of 0.05–1.2 TeV

A proprietary method is used to process measurement data from a high-energy particle (protons, electrons, and positrons with Е ≥ 50 GeV) spectrometer in a near-Earth orbit. The data from three detector systems are used: a tracker in a constant magnetic field (TRK), a calorimeter (CAL), and a neutron detector (ND). A relatively simple and efficient way of isolating electrons and positrons from the total charged particle flux entering the PAMELA spectrometer is proposed. A technique for determining the energy of isolated primary particles and retrieving their energy spectra is described. The composite electron and positron spectrum (below, the total electron and positron flux is referred to simply as the electron flux) for energies up to 1.5 TeV is presented.     

Energy scale calibration of the KEDR tagging system

The KEDR detector tagging system is a symmetric focusing magnetic spectrometer of small-angle electrons born in the interaction region of the VEPP-4M collider. Using this system, which is designed for studying the two-photon processes, the scattered electrons and positrons energy is measured with a resolution of ΔE/E₀= 0.03–0.6% where E₀ is the beam energy. Two different methods are employed for calibrating the tagging system energy scale: the first one involves the electron/positron tagging by the energy of the singlebremsstrahlung photon measured in the BGO calorimeter, and the second one is based on the determination of the recoil electrons spectrum edge in the Compton backscattering of monochromatic laser radiation. The technical implementation and the present status of the calibration system are discussed in this paper.     

Measurement of the azimuthal anisotropy coefficient <Emphasis Type="Italic">v</Emphasis><Subscript>2</Subscript> for the emission of α particles in nucleus-nucleus collisions at energies 1.88–10.6 GeV/nucleon

The azimuthal anisotropy of the emission of α particles in collisions of the ²²Ne, ²⁴Mg, ⁵⁶Fe, and ¹⁹⁷Au nuclei with photoemulsion nuclei has been measured at projectile energies E_pr = 1.88–10.6 GeV/nucleon. The results are compared with similar measurements for protons. It has been found that the ratio of the azimuthal anisotropy coefficients v₂ for α particles and protons is equal to 6 ± 2 at low energies E_pr ≈ 2 GeV/nucleon, whereas these coefficients coincide with each other for energies E_pr ≥ 4 GeV/nucleon. This difference may indicate that, at low projectile energies, α particles are formed predominantly at the early stage of a collective flow. Formation of α particles for E_pr ≥ 4 GeV/nucleon likely occurs at the stage of nuclear matter scattering.     

Calibration procedure of the Δ<Emphasis Type="Italic">E</Emphasis>–<Emphasis Type="Italic">E</Emphasis> detectors for <Emphasis Type="Italic">dp</Emphasis> breakup investigation at nuclotron

Calibration procedure of ΔE ? E detectors used in dp breakup reaction measurement in the framework of DSS project is discussed. Time information from all PMTs along with amplitude information and known energy values of pp quasi elastic reaction are used to find calibration coefficients for ΔE and E detectors. Calibration coefficients are used to recover deposited particle energies. ΔE vs. E plots, energies and missing mass spectra are compared with geant4 Monte Carlo simulation. Missing mass for particular physical configuration is calculated as a test of the calibration procedure quality.     

Energy spectra of secondary particles in γ families and their sensitivity to the spectrum of primary cosmic rays

Spectra of secondary particles (γ-rays) in γ-families detected in the X-ray chambers in the Pamirs (H = 600 g cm^?2) have been analyzed. These γ-ray spectra show a bend at the energy E* _γ ≈ (ΣE _γ )^min, where (ΣE _γ )^min is the lowest total energy of γ-rays in the families above which γ-families were selected. The bend is not related to the knee in the spectrum of primary particles; it is due to the use of the ΣE _γ selection criterion. The E _γ spectrum slope is sensitive to the spectrum of the primary cosmic rays in the region E _γ ≥ (ΣE _γ )^min.     

A Method for Estimation of the Parameters of the Primary Particle of an Extensive Air Shower by a High-Altitude Detector

A method for estimation of the parameters of the primary particle of an extensive air shower (EAS) by a high-altitude detector complex is described. This method was developed as part of the Pamir-XXI project. The results may be useful for other high-altitude projects and the EAS method in general. The specific configurations of optical detectors for Cherenkov EAS radiation and charged-particle detectors, the methods for data processing, and the attainable accuracy of reconstruction of parameters of primary particles (energy, direction, mass/type) are presented. The results primarily cover optical detectors that are suitable for studying EASs from primary nuclei in the range of energies E⁰ = 100 TeV–100 PeV and showers from primary γ-quanta with energies of E_γ ≥ 30 TeV. Grids of charged-particle detectors designed to determine the EAS direction and energy in the E⁰ = 1 PeV–1 EeV range are also considered. The obtained accuracy estimates are the upper limits of the actual experimental accuracies.     

Features of the Mechanism of Formation of the Radiation Belt of High-Energy Electrons and Positrons

New results of the PAMELA experiment revealed significant difference in the electron and positrons flux and fraction between trapped particles of the radiation belt and quasitrapped particles. A decrease in the ratio of the electron-to-positron fluxes both with increasing altitude and with decreasing energy was observed for the inner radiation belt, but this does not fit in currently used models. The residual atmosphere density in the trapping region for L ~ 1.15?1.2 is estimated on the basis of calculations of trapped-particle trajectories in the Earth’s magnetosphere. It is shown that processes leading to the energy loss for trapped electrons and positrons in the interactions with residual-atmosphere atoms play an important role in the formation of fluxes of these particles, but these processes cannot cause the reduction of the positron fraction in the total flux at energies below some 100 MeV. The role of the process of δ-electron production in the formation of the belt of trapped electrons and positrons is considered. Allowance for this process makes it possible to explain the above reduction at least partly.     

Investigation of excitation of Ag atoms in internal conversion of γ rays

Excitation of Ag atoms in the internal conversion of γ rays due to the E3 transition in ^109m Ag has been measured on an anti-Compton spectrometer and a multidimensional-coincidence spectrometer with GeSi(Li) detectors. The probability of double ionization of the K shell is determined to be P _KK =(2.5 ± 0.2) × 10^?4. It is shown that the direct process is dominant in excitation of Ag atoms.     

Observations of Trapped Electrons and Positrons with E > 50 MeV in the Inner Radiation Belt by the PAMELA Magnetic Spectrometer

Geomagnetically trapped electrons and positrons with energy above 50 MeV were observed in PAMELA experiment on board Resurs DK satellite. The instrument consists of magnetic spectrometer, imaging electromagnetic calorimeter, time-of-flight system, anticoincidence and neutron detectors that provide unique particle identification and background rejection. PAMELA was collecting data since June 2006 till January 2016. The satellite orbit with initial altitude 350–600 km and inclination 70° crosses the inner radiation belt in South Atlantic Anomaly at L-shell ∼1.2. The trapped electrons and positrons were selected on the basis of a trajectory simulation in the Earth magnetic field. Features of the energy spectra of electrons and positrons at low energies are analyzed.

     

Large transverse momenta in the stratospheric STRANA superfamily

A unique γ-hadron cosmic-ray superfamily with E ₀ > 10¹⁶ eV has been detected in the stratosphere. This is the only analyzed event with such a high energy, unattainable for accelerators. This event exhibits alignment of the most energetic particles and very large transverse momenta (>2.5 GeV/c).     

The spectrum of cosmic-ray particles and their origin

An analysis of all the direct measurements of the spectrum for all cosmic-ray particles over the energy range 0.1–10 TeV reveals an anomaly in the spectrum in the form of a step if the spectrum is represented as E^βI₀(E). The pattern of the anomaly unequivocally implies a proton spectrum with a knee at energy close to 1 TeV. The qualitative difference between the spectra of protons and nuclei with Z≥2 (the latter have a purely power-law spectrum over a wide energy range) leads us to conclude that the acceleration conditions for protons and nuclei are different. We consider the process characteristic only of protons that may be responsible for the emergence of a knee in the proton spectrum.     

Hardware-Software Complex for Measurement of Energy and Angular Distributions of Charged Particles Formed in Nuclear Reactions

A hardware-software complex for measurement of energy and angular distributions of charged particles formed in nuclear reactions is presented. Hardware and software structures of the complex, the basic set of the modular nuclear-physical apparatus of a multichannel detecting system on the basis of ΔE–E telescopes of silicon detectors, and the hardware of experimental data collection, storage, and processing are presented and described.     

Inelastische Positronenstreuung am Atomkern

The ratio of the total and differential cross section for the inelastic positron-nucleus scattering (ē, N)-process to the total (γ, N) -cross section is derived in Born approximation for electric and magnetic dipole transitions. The result agrees with that obtained for the (e, N)-processes. Using the relativistic Coulomb Eigenfunctions for the continuous spectrum of the positrons, the Coulomb correction, the effect of screening and that of finite nuclear size agree with the (e, N)-process, when the annihilation of positrons with atomic electrons is neglected, and for positron energiesE _1,2 ⁺ >10 MeV. The effect of finite nuclear size is only calculated in Born approximation. ForE _1,2 ⁺ ≦2 MeV only the Coulomb correction differs from that obtained for the (e, N)-process. In the angular distribution for the (ē, N)-process there should be no interference of positron waves scattered by different multipoles, where the inelastic scattered positrons are detected. Numerical calculations have been carried out for nuclei withZ=6.29 and 82 and scattering angles ?=1°, 132°, 160° and 180° of the positron. This theory can be compared with the experiments in progress by W.C.Barber et al. using positrons for the inelastic scattering process at nuclei. The two-and three-virtual quanta-exchange effect in the (ē, N)-cross section is below 1.3% for positron energies between 10≦E ₁ ⁺ ≦300 MeV, and decreases rapidly for higher energies. This theory is also valied for inelastic scattering processes with positiveμ-mesons at nuclei; one has only to change the mass in the following equations.     

Study of characteristics of an electromagnetic calorimeter based on PbWO<Subscript>4</Subscript> crystals

Characteristics of a prototype of the electromagnetic calorimeter based on PbWO₄ scintillation crystals were studied. Measurements were performed using the electron beam of the DESY synchrotron in the range of 1–6 GeV. The energy resolution of the prototype was σ/E = 2.4%/E ⊕ 3.9% / √E ⊕ 1.2%.     

Ein experimenteller Beitrag zu der durch langsame Primärelektronen ausgelösten Sekundärelektronenemission

The energy distribution of secondary electrons emitted from a highly degassed polycristalline Pt surface was investigated as a function of low energy (V _p ) primary electrons 5<V _p <150eV. The measurements were carried out in an UHV of better than 10^?10 mm Hg. The dependence of the numberN _S ^(Ev) of secondary electrons of a fixed energyE _v (3<E _v <12eV) on the energyV _p of the primaries (=isochromates) is studied. A lot of observations can be detected:

1. I.
   The exit depth of true secondary electrons is strongly dependent of their energy.     
   
   

Elektron-Photon-Kaskaden in Blei

A Monte-Carlo program has been used for the calculation of electron-photon cascade showers in lead. Bremsstrahlung, electron-electron scattering, multiple scattering, ionization loss, pair creation, Compton effect, and photoelectric effect are taken into account, with empirically corrected values for the cross-sections of these processes. Electrons are followed down toE _e =1,5 MeV and photons toE _γ =0,25. After a comparison of the Monte-Carlo results with available experimental data, the following distributions for electrons and photons are presented for primary electrons incident on lead with energiesE ₀=100, 200, 400 and 1000 MeV and depthst ranging from 0,5 to 25X ₀:

1. 1.
   Number of particles as function of deptht for various cut-off energiesE betweenE _e (orE _γ resp.) up toE=0,9·E ₀. Interpolation formulas are given for the height and position of the maxima of the distributions mentioned before.     
   
   

Production of Heavy Helium <Superscript>5</Superscript>Hе in the Absorption of Stopped Pions by <Superscript>10,11</Superscript>B Nuclei

Helium ⁵Hе states are sought in missing-mass (MM) spectra from reactions of the absorption of stopped pions: ¹⁰В(π^?, dt)Х and ¹¹В(π^?, tt)Х. The experiment is conducted using the LANL accelerator equipped with a two-arm semiconductor charged-particle spectrometer. The parameters of the ground state agree with the literature data. The best fit for the first excited level is obtained at E_r = 1.8(5) MeV and Γ = 4.7(7) MeV. Neither of the two reactions produce statistically significant evidence for the presence of highly excited (E_x ≥ 20 MeV) states of ⁵Hе.     

Quantum mechanical equations of motion of particles and spin in polarized media

Quantum mechanical equations of motion are obtained for particles and spin in media with polarized electrons in the presence of external fields. The motion of electrons and their spins is governed by the exchange interaction, while the motion of positrons and their spin is governed by the annihilation interaction. For particles with spin S ≥ 1, second-order terms in spin are taken into account. The equations obtained can be applied to describe the motion of particles and spin both in magnetic and nonmagnetic media.     

Effect of secondary electrons on the yield of electron-stimulated desorption of neutral atoms under differently localized core-level excitations in a substrate

This paper reports on the results of a comparative analysis of the changes in the electron-stimulated desorption (ESD) yield of neutral particles from layers of alkali metal and Ba atoms deposited on the surface of a metal atop an oxygen (O/W, O/Mo) or germanium (Ge/W) film as a function of the incident electron beam energy E. The atomic yield q(E) is compared with the ionization cross sections of the core levels whose ionization potentials coincide with the ESD yield thresholds of the atoms. Three types of dependences q(E) are discussed, and the role of the secondary electrons generated in the electron-bombarded substrate for each type of the dependence of the ESD yield on E is elucidated. The analysis is based on the experimental studies performed by the authors in the recent years, starting from 1991. It is shown that the actual type of dependence q(E) is determined both by the actual localization of the atom excited by the electron beam and by the extent of localization of the core excitation resulting in ESD.