Christopher G. Tully - Observing the Big Bang with Relic Neutrinos

The Universe has expanded by a factor of over one billion between the present-day and the early thermal epoch known as the neutrino decoupling. We observe markers that track the dynamics of this expansion in many forms: the recession of galaxies (Hubble Expansion), the dim afterglow of the hot plasma epoch (Cosmic Microwave Background) and the abundances of light elements (Big Bang Nucleosynthesis). The epoch of neutrino decoupling produced a fourth pillar of confirmation – the Cosmic Neutrino Background (CNB). In our current understanding, the CNB was created in the first second after elementary particles spontaneously filled the void of the early Universe. These early universe relics have cooled under the expansion of the Universe and are sensed indirectly through the action of their diminishing thermal velocities on large-scale structure formation. Recent experimental advances open up new opportunities to directly detect the CNB through the process of neutrino capture on tritium, an achievement which would profoundly confront and extend the sensitivity of precision cosmology data. PTOLEMY, an experiment at the Gran Sasso National Laboratory in Italy, is a novel method of 2D target surfaces, fabricated from graphene, that forms a basis for a large-scale relic neutrino detector. Recent PTOLEMY publications [1,2] describe the underlying technique for achieving CNB sensitivity and redefines the future direction of neutrino mass measurements. The discussion of PTOLEMY focusses on experimental challenges, recent developments and the path forward to discovery sensitivity.

References

[1] M.G. Betti et al., "A Design for an Electromagnetic Filter for Precision Energy Measurements at the Tritium Endpoint”, Progress in Particle and Nuclear Physics, 106, (2019) 120-131, https://doi.org/10.1016/j.ppnp.2019.02.004

[2] M.G. Betti et al., "Neutrino physics with the PTOLEMY project”, Journal of Cosmology and Astroparticle Physics, 07, (2019) 047, https://doi.org/10.1088/1475-7516/2019/07/047