PAMELA results on the cosmic-ray antiproton flux from 60 MeV to 180 GeV in kinetic energy

The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray antiproton flux and the antiproton-to-proton flux ratio which extends previously published measurements down to 60 MeV and up to 180 GeV in kinetic energy. During 850 days of data acquisition approximately 1500 antiprotons were observed. The measurements are consistent with purely secondary production of antiprotons in the galaxy. More precise secondary production models are required for a complete interpretation of the results.Comment: 11 pages, 3 figures, 1 table. Accepted for publication in Physical Review Letter

Time Dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015

Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field

Cosmic ray electrons and positrons over decade with the PAMELA experiment

The PAMELA experiment has measured cosmic ray particles and antiparticles fluxes at Earth orbit from June 2006 till January 2016 onboard the Resurs-DK1 satellite. Measurements were carried out during the solar minimum of 23 solar cycle with negative polarity A < 0 of heliospheric magnetic field till the beginning of 24 cycle with positive polarity A > 0. In this paper, the results of observations of electron and positron fluxes are presented in wide energy range from several hundreds MeVs till several TeVs These measurements provide important information to study cosmic ray sources and propagation in Galaxy and heliosphere

Unexpected Cyclic Behavior in Cosmic-Ray Protons Observed by PAMELA at 1 au

Protons detected by the PAMELA experiment in the period 2006-2014 have been analyzed in the energy range between 0.40-50 GV to explore possible periodicities besides the well known solar undecennial modulation. An unexpected clear and regular feature has been found at rigidities below 15 GV, with a quasi-periodicity of $\sim$450 days. A possible Jovian origin of this periodicity has been investigated in different ways. The results seem to favor a small but not negligible contribution to cosmic rays from the Jovian magnetosphere, even if other explanations cannot be excluded.Comment: article 4 figures, 1 tabl

Secondary positrons and electrons in near-Earth space in the PAMELA experiment

Fluxes of electrons and positrons with energies above ~100 MeV in the near-Earth space are measured with the PAMELA magnetic spectrometer aboard the Resurs DK-1 satellite launched on June 15, 2006, into a quasipolar orbit with an altitude of 350–600 km and an inclination of 70°. Calculating the trajectories of detected electrons and positrons in the magnetosphere of the Earth allows us to determine their origin and isolate particles produced during interaction between cosmic rays and the residual atmosphere. Spatial distributions of albedo, quasitrapped, and trapped (in the radiation belt) positrons and electrons are presented. The ratio of positron and electron fluxes suggests that the fluxes of trapped particles of the radiation belt and quasitrapped secondary particles have different mechanisms of formation

Evidence of Energy and Charge Sign Dependence of the Recovery Time for the 2006 December Forbush Event Measured by the PAMELA Experiment

New results on the short-term galactic cosmic ray (GCR) intensity variation (Forbush decrease) in December 2006 measured by the PAMELA instrument are presented. Forbush decreases are sudden suppressions of the GCR intensities which are associated with the passage of interplanetary transients such as shocks and interplanetary coronal mass ejections (ICMEs). Most of the past measurements of this phenomenon were carried out with ground-based detectors such as neutron monitors or muon telescopes. These techniques allow only the indirect detection of the overall GCR intensity over an integrated energy range. For the first time, thanks to the unique features of the PAMELA magnetic spectrometer, the Forbush decrease commencing on 2006 December 14, following a CME at the Sun on 2006 December 13 was studied in a wide rigidity range (0.4 - 20 GV) and for different species of GCRs detected directly in space. The daily averaged GCR proton intensity was used to investigate the rigidity dependence of the amplitude and the recovery time of the Forbush decrease. Additionally, for the first time, the temporal variations in the helium and electron intensities during a Forbush decrease were studied. Interestingly, the temporal evolutions of the helium and proton intensities during the Forbush decrease were found in good agreement, while the low rigidity electrons (< 2 GV) displayed a faster recovery. This difference in the electron recovery is interpreted as a charge-sign dependence introduced by drift motions experienced by the GCRs during their propagation through the heliosphere

Solar modulation of cosmic deuteron fluxes in the PAMELA experiment

The preliminary results from measurements of deuteron fluxes in galactic cosmic rays (GCR) in the vicinity of the Earth in 2006–2009 are presented. The results are obtained by analyzing data from the PAMELA experiment aboard the Resurs DK-1 satellite. High-precision detection instruments provided an opportunity to identify GCR deuterons and measure their spectrum in the energy interval of 90–650MeV/nucleon. Spectra averaged over six-month intervals from the summer of 2006 to the summer of 2009 (the solar activity minimum) are presented. The influence of solar modulation on the observed spectrum is clearly seen in the results

Measuring the spectra of high-energy cosmic-ray particles in the PAMELA experiment

The available data on the energy spectra of electrons, protons, and helium nuclei in the high-energy region are fragmentary, a situation made worse by their scarcity. Due to limitations imposed on the use of the magnetic spectrometer in the PAMELA satellite experiment, the calorimeter must be used for measurements performed in the high-energy region. The processing of experimental data accumulated in more than eight years of measurements with the calorimeter, neutron detector, and scintillation counters allows the spectra of high-energy particles to be obtained, greatly expanding our understanding of the nature of primary cosmic rays

PAMELA and electrons RID C-1210-2011

The 15th of June 2006, the PAMELA satellite-borne experiment was launched from the Baikonur cosmodrome and it has been collecting data since July 2006. The apparatus comprises a time-of-flight system, a silicon-microstrip magnetic spectrometer, a silicon-tungsten electromagnetic calorimeter, an anticoincidence system, a shower tail counter scintillator and a neutron detector. The combination of these devices allows precision studies of the charged cosmic radiation to be conducted over a wide energy range (100 MeV-100's GeV) with high statistics. The measurement of the positron to electron fraction and of the electron energy spectrum in order to search for exotic sources, such as dark matter particle annihilations, are within the PAMELA primary scientific goal. (C) 2010 Elsevier B.V. All rights reserved