New Measurement of the Antiproton-to-Proton Flux Ratio up to 100 GeV in the Cosmic Radiation

Abstract

A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented. The results were obtained with the PAMELA experiment, which was launched into low-Earth orbit on-board the Resurs-DK1 satellite on June 15th 2006. During 500 days of data collection a total of about 1000 antiprotons have been identified, including 100 above an energy of 20 GeV. The high-energy results are a tenfold improvement in statistics with respect to all previously published data. The data follow the trend expected from secondary production calculations and significantly constrain contributions from exotic sources, e.g., dark matter particle annihilations.

Cosmic ray anomalies from the MSSM?

“…These sets are the most recent, cover the largest range of energies and have the smallest quoted errors. 6 As noted above, B/C provides quite a sensitive constraint on the ratio (L/D 0xx ), but cannot separately constrain either L or D 0xx . This degeneracy can be broken by measuring the abundance of unstable radioactive nuclei relative to their stable isotopic counterparts, i.e., flux ratios such as 10 Be/ 9 Be, which are referred to as "radio-clocks."…”

“…The Fermi Gamma Ray Space Telescope (FERMI) reports [5] a slightly stiffer electron spectrum than expected, but with no dramatic features. These are countered by observations of the anti-proton fraction (ratio ofp to p) by PAMELA [6] and various gamma ray measurements by FERMI ( [7][8][9];preliminary results for a larger range of energies were presented in [10]) which reveal no unexpected characteristics.…”

“…6 The PAMELA Collaboration have also recently made a measurement of B/C (see e.g., [80]) but this is…”

“…Figure 6:p/p spectra for all 524 astrophysical models with no SUSY contributions (grey curves). Also shown is thep/p spectrum for the benchmark model (red curve), along with the PAMELAp/p data [6].…”

“…Errors for the FERMI-LAT data set are derived from [5] by adding statistical and systematic errors in quadrature while those for the PAMELA data sets are purely statistical, as quoted by the collaboration in [4] and [6]. The contributions to individual experimental bins from the theory spectra obtained from GALPROP/DarkSUSY are determined by numerically integrating the curves over the relevant bin.…”