Cosmic rays, antihelium, and an old navy spotlight

Abstract

Cosmic-ray antideuterium and antihelium have long been suggested as probes of dark matter, as their secondary astrophysical production was thought extremely scarce. But how does one actually predict the secondary flux? Antinuclei are dominantly produced in $pp$ collisions, where laboratory cross section data are lacking. We make a new attempt at tackling this problem by appealing to a scaling law of nuclear coalescence with the physical volume of the hadronic emission region. The same volume is probed by Hanbury Brown--Twiss (HBT) two-particle correlations. We demonstrate the consistency of the scaling law with systems ranging from central and off-axis $AA$ collisions to $pA$ collisions, spanning 3 orders of magnitude in coalescence yield. Extending the volume scaling to the $pp$ system, HBT data allow us to make a new estimate of coalescence that we test against preliminary ALICE $pp$ data. For antihelium the resulting cross section is 1 or 2 orders of magnitude higher than most earlier estimates. The astrophysical secondary flux of antihelium could be within reach of a five-year exposure of AMS02.