Illuminating Dark Matter and Primordial Black Holes with Interstellar Antiprotons

Interstellar antiproton fluxes can arise from dark matter annihilating ordecaying into quarks or gluons that subsequently fragment into antiprotons.Evaporation of primordial black holes also can produce a significant antiprotoncosmic-ray flux. Since the background of secondary antiprotons from spallationhas an interstellar energy spectrum that peaks at $\sim 2\gev$ and fallsrapidly for energies below this, low-energy measurements of cosmic antiprotonsare useful in the search for exotic antiproton sources. However, measurement ofthe flux near the earth is challenged by significant uncertainties from theeffects of the solar wind. We suggest evading this problem and more effectivelyprobing dark-matter signals by placing an antiproton spectrometer aboard aninterstellar probe currently under discussion. We address the experimentalchallenges of a light, low-power-consuming detector, and present an initialdesign of such an instrument. This experimental effort could significantlyincrease our ability to detect, and have confidence in, a signal of exotic,nonstandard antiproton sources. Furthermore, solar modulation effects in theheliosphere would be better quantified and understood by comparing results toinverse modulated data derived from existing balloon and space-based detectorsnear the earth.Comment: 18 pages, 3 figure