Precision Measurement of Cosmic-Ray Antiproton Spectrum

TL;DR

The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation.

Abstract

The energy spectrum of cosmic-ray antiprotons has been measured in the range 0.18 to 3.56 GeV, based on 458 antiprotons collected by BESS in recent solar-minimum period. We have detected for the first time a distinctive peak at 2 GeV of antiprotons originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS flights toward the solar maximum will help us to study the solar modulation and the propagation in detail and to search for primary antiproton components.

Figures (4)

• Figure 1: Cross-sectional view of the BESS spectrometer in its 1997 configuration. Overlayed is one of the $\bar{p}$ events.
• Figure 2: The identification of $\bar{p}$ events. The solid lines define the $\bar{p}$ mass band used for the spectrum measurement.
• Figure 3: BESS '95+'97 (solar minimum) antiproton fluxes at the top of the atmosphere together with previous data. The error-bars represent the quadratic sums of the statistical and systematic errors. The curves are recent calculations of the secondary $\bar{p}$ spectra for the solar minimum period.
• Figure 4: BESS '95+'97 $\bar{p}/p$ flux ratios with previous data [9] and the theoretical calculations.