The Cosmic-Ray antiproton flux between 3 and 49 GeV

TL;DR

CAPRICE98 delivers a high-energy measurement of the cosmic-ray antiproton flux from 3 to 49 GeV using a balloon-borne magnetic spectrometer with a Gas RICH, ToF, drift chambers, and a silicon-tungsten calorimeter. The analysis identifies 31 antiprotons and shows that the observed spectrum and the antiproton-to-proton ratio are consistent with secondary production in the Galaxy, although a primary component cannot be excluded due to two events at the highest energies. The work carefully quantifies backgrounds, efficiencies, and corrections (payload, atmosphere, and geomagnetic transmission) and demonstrates consistency with prior measurements and secondary-production models, while setting the stage for higher-statistics experiments. These results constrain propagation and solar-modulation effects and have implications for exotic sources such as dark matter annihilation, motivating missions like PAMELA and AMS for improved high-energy antiproton measurements.

Abstract

We report on a new measurement of the cosmic ray antiproton spectrum. The data were collected by the balloon-borne experiment CAPRICE98 which was flown on 28-29 May 1998 from Fort Sumner, New Mexico, USA. The experiment used the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas Ring Imaging Cherenkov (RICH) detector, a time-of-flight system, a tracking device consisting of drift chambers and a superconducting magnet and a silicon-tungsten calorimeter. The RICH detector was the first ever flown capable of mass-resolving charge-one particles at energies above 5 GeV. A total of 31 antiprotons with rigidities between 4 and 50 GV at the spectrometer were identified with small backgrounds from other particles. The absolute antiproton energy spectrum was determined in the kinetic energy region at the top of the atmosphere between 3.2 and 49.1 GeV. We found that the observed antiproton spectrum and the antiproton-to-proton ratio are consistent with a pure secondary origin. However, a primary component may not be excluded.