Antiparticles account for a small fraction of cosmic rays and are known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium, which is referred to as a 'secondary source'. Positrons might also originate in objects such as pulsars and microquasars or through dark matter annihilation, which would be 'primary sources'. Previous statistically limited measurements of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron+positron flux at energies between 300 and 600 GeV (ref. 8). Here we report a measurement of the positron fraction in the energy range 1.5-100 GeV. We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources. We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.

Protons and helium nuclei are the most abundant components of the cosmic radiation. Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in our Galaxy. We report precision measurements of the proton and helium spectra in the rigidity range 1 gigavolt to 1.2 teravolts performed by the satellite-borne experiment PAMELA (payload for antimatter matter exploration and light-nuclei astrophysics). We find that the spectral shapes of these two species are different and cannot be described well by a single power law. These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy. More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data

The PAMELA satellite experiment has measured the cosmic-ray positron fraction between 1.5 GeV and 100 GeV. The need to reliably discriminate between the positron signal and proton background has required the development of an ad hoc analysis procedure. In this paper, a method for positron identification is described and its stability and capability to yield a correct background estimate is shown. The analysis includes new experimental data, the application of three different fitting techniques for the background sample and an estimate of systematic uncertainties due to possible inaccuracies in the background selection. The new experimental results confirm both solar modulation effects on cosmic-rays with low rigidities and an anomalous positron abundance above 10 GeV

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.

The differential energy spectrum of galactic cosmic rays near Earth is often parameterized by the force field model with the only time‐dependent parameter, the modulation potential ϕ. Here we present a series of reconstructed monthly values of the modulation potential for the period from July 1936 through December 2009. This works extends our earlier study by employing new data and improving the reconstruction method. The presented series is a composite of three parts. The most reliable part is based on data from the world network of sea level neutron monitors and covers the period since April 1964. The part between February 1951 and March 1964 is based on data from one to two mountain neutron monitors of IGY type and is characterized by larger uncertainties and possible systematic error. The part related to the period before 1951 is based on data from Forbush ground‐based ionization chambers and is characterized by large uncertainties and should be taken with caveats. The reconstructed series has been tested against long‐term data of balloon‐borne measurements of flux of cosmic ray ionizing radiation in the stratosphere performed by the Lebedev Institute since 1957. The comparison shows good agreement since 1964 but suggests that the result before 1964 may contain larger errors in that the NM‐based reconstruction method may underestimate the low energy part of GCR spectrum.