SciPost Submission Page
Importance of the X ray edge singularity for the detection of relic neutrinos in the PTOLEMY project
by Zhiyang Tan and Vadim Cheianov
Submission summary
| Authors (as registered SciPost users): | Zhiyang Tan |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202310_00021v1 (pdf) |
| Date submitted: | 2023-10-19 14:41 |
| Submitted by: | Tan, Zhiyang |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
Direct detection of relic neutrinos in a beta-decay experiment is an ambitious goal, which has for a long time been beyond the reach of available technology. One of the toughest practical difficulties that such an experiment has to overcome is that it needs to deal with a large amount of radioactive material in such a way as not to compromise the energy resolution required for the separation of useful events from the massive beta-decay background. The PTOLEMY project offers an innovative approach to this problem based on the deposition of radioactive material on graphene. While such an approach is expected to resolve the main difficulty, new challenges arise from the proximity of the beta decayers to a solid state system. In this work, we focus on the effect of the shakeup of the graphene electron system due to a beta-decay event. We calculate the distortion of the relic neutrino peaks resulting from such a shakeup, analyze the impact of the distortion on the visibility of neutrino capture events, and discuss what technological solutions could be used to improve the visibility of neutrino capture events.
Current status:
Reports on this Submission
Strengths
1- the manuscript addresses a topic of great relevance. To dig deeper into the problem of condensed matter effects in the PTOLEMY project is important, and I believe this paper performs a number of step forward.
2- the main intuitive ideas behind the physical effects the authors are describing are presented in a clear way.
3- after pointing out the difficulties related to the detection of relic neutrinos, the authors give semi-concrete recipes on how to mitigate them. This can be of great help to try and identify possible directions to evade the issue.
Weaknesses
1- in more than one point the authors are a bit cavalier about notation, they miss to define quantities and there is a certain number of typos here and there. This makes sometimes reading the paper hard.
2- the discussion about the relevant time scale is a bit vague and, to me, unclear. I think the authors should make an effort to explain it more properly. It is my opinion that this represent probably one of the most important aspects to pin down: what is the relevant time scale that allows one to tell that certain processes are relevant and some others are not? (see "requested changes" for more details.)
Report
In general, I believe this manuscript to be extremely valuable.
It is definitely worth publication, but only after my previous points will be properly addressed.
Requested changes
1- at the beginning of section 2B it is mentioned that this work neglects the recoil of the daughter nucleus. It is unclear to me whether this is done for the sake of simplicity or not. Would the recoil of the final He+ introduce further distortion in the final electronic spectrum?
2- in Eq. (8) the authors introduce the Hamiltonian H_{D-G}. It seems to me that this is the same as the Hamiltonian H_g introduced in Eq. (5). Is this correct? If yes, I would make the notation uniform.
3- the states | ... >_h and | ... >_t in Eq. (16) are not defined. Do they stand for "helium" and "tritium"? It should be explained.
4- is the "i" appearing in the numerator of Eq. (52) an imaginary unit, or a mis-typed index?
5- in Eq. (50) the authors present an estimate of the density of tritium atoms that would allow to neglect disorder effects. I think it would be very useful to compare it with standard graphene density or, even better, to convert to to a mass density. This would allow a more immediate experimental comparison.
6- the various figures are pretty ill-placed. It would be much clearer if they were placed in the same page where they are first mentioned. This way the reader does not have to skim more of the manuscript before getting to them.
7- the only major physical point that confuses me is the following. When discussing the relevance of effects like the hole production in Eq. (7) or the interaction between electrons and impurities (sec. 4B), the authors compare the typical time scale associated to this processes to the inverse energy resolution of the experiment, resorting to the time-energy uncertainty principle. However, I naïvely would have expected the relevant time scale to compare it with to be the formation time of the beta-electron. All processes happening after that are essentially different way of redistributing the energy inside the graphene system which, however, should then be decoupled from the outgoing electron.
I believe this point to be crucial, and I would to understand if the authors have a quantitative way of determining the relevant time scale to be used as benchmark.
As is well known, the time-energy uncertainty principle is always a bit hard to put on firm grounds.