An Extra Positron Problem

Astrolunch is a weekly talk here at the Department of Physics and Astronomy where speakers give talks on a topic outside of their usual expertise. This week’s Astrolunch talk was by Lucy Wilcock, a PhD student studying star formation here at Cardiff University. She overveiwed a recent paper in Nature, covering some results from PAMeLA and the problem with having too many positrons.

The primary research goal of PAMeLA (Payload for Anti-Matter Exploration and Light-nuclei Astrophysics) is to study the antimatter component of cosmic ray radiation. Antiparticles account for a small fraction of cosmic rays. Where the bulk of them originated is not known. It could be that they are produced in interactions between cosmic rays and atoms in the interstellar medium, (this is called a secondary source). They could also be produced in some sort of astrophysical phenomena like in pulsars, microquasars or through dark matter annihilation, which would all be primary sources.

This report outlines a measurement of the positron fraction in the energy range 1.5–100 GeV. In this range they find numbers of positrons that are inconsistent with secondary sources. So could it be that positrons are really being created in an astrophysical object (.e.g  a pulsar or microquasar) or by dark matter annihilation?

Download the PDF of this talk. Read original article on Nature.