Slides from talk by Chris Tully at the Opening New Windows to the Universe forum at Brookhaven National Labs on 2021-11-03: PTOLEMY: Relic Neutrino Detection New developments since this post was originally created: Cosmologist Sunny Vagnozzi shares some updated info on the PTOLEMY project status in a short thread here. He also mentions that he is collaborating on a paper about PTOLEMY with Stefano Gariazzo that will soon (as of March 2020) be posted on the arXiv. -—

This is about paper 1902.05508, posted to the arXiv on 2/14/2019.

I was mostly unfamiliar with this groundbreaking project so this new paper provided a reading-up opportunity, leading to these general overview notes. I added the bolding for emphasis.

The PTOLEMY project¹ aims to directly detect relic neutrinos from the cosmic neutrino background (CNB or CνB), along with a impressive broader set of capabilities or opportunities^2a. The project is described as the “the first of its kind and the only one^2b conceived that can look directly at the image of the Universe encoded in neutrino background produced in the first second after the Big Bang”.³ (pg2) Achieving the project's goal “would profoundly confront and extend the sensitivity of precision cosmology data.”(pg5) This paper addresses the theoretical aspects of the project, its physics goals, and an outline of the project's scope of work to be done in the next three years. An earlier paper 1808.01892 gives more details on three phases of the project: proof-of-principle demonstrator, scalable prototype realization and tests, and full detector construction.

The technology is based on neutrino capture on beta decaying nuclei (NCB)⁵, with tritium (³H) determined as the best choice. The capture results in a tiny boost of energy to the electrons emitted in tritium decay, so there'll be a peak in the electron spectrum above the β-decay endpoint⁴. The planned target is ∼100g of tritium atomically bound to a radio-pure graphene substrate (they refer to it as “tritiated graphene”). They expect ∼10 CνB capture events per year, depending on the mass hierarchy and the Dirac versus Majorana nature of the neutrinos; the rate is half as large for non-relativistic Dirac neutrinos^2a. The anticipated energy resolution is ∼0.05eV, “an order of magnitude beyond the original target and the highest resolution of any calorimeter.” [source]