# How sensitive are early universe abundance calculations to the neutron half-life?

Phys.org's Physicists announce the world's most precise measurement of neutron lifetime discusses the accepted for publication Phys. Rev. Letter Improved neutron lifetime measurement with UCNτ (links in block quote) and says:

An international team of physicists led by researchers at Indiana University Bloomington has announced the world's most precise measurement of the neutron's lifetime.

The results from the team, which encompasses scientists from over 10 national labs and universities in the United States and abroad, represent a more than two-fold improvement over previous measurements—with an uncertainty of less than one-tenth of a percent.

The work is reported in the Oct 13 issue of the journal Physical Review Letters. It was also the subject of a live news briefing at the 2021 Fall Meeting of the American Physical Society Division of Nuclear Physics. A pre-print version of the paper is also available (arXiv).

The article begins:

Introduction.

The decay $$n \rightarrow p + e^- + \bar{\nu}_e$$ is the simplest example of nuclear β-decay. The mean neutron lifetime τn provides a key input for predicting primordial light element abundances 1.

The half-live was already known to better than one part in a thousand, the improvement is now substantially better than a part in a thousand.

Question: How sensitive are early universe abundance calculations to the neutron half-life?

For example, are there some abundances that are much more sensitive than others to the neutron half-life? If for example some processes involve neutrons after 10 half-lives, then the remaining neutrons vary by 10 parts per thousand for a one part per thousand in half-life.

I understand that the neutron half-life measurement is important for several other reasons in particle physics, I'm just asking about the implications for abundances.

• 3 questions in 3 hours
– Was
Oct 13, 2021 at 8:45
• @WalidSiddik I'm an SE addict, I confess! If you search the main meta (or even just Math SE meta) you'll see I'm not the only one!
– uhoh
Oct 13, 2021 at 8:47
• I am surprised the paper does not appear to address this point, since it is listed as one of the motivations for the work. There is a bit of a lever arm, so that the effects on primordial abundance predictions are bigger than 1 part in a thousand. Oct 13, 2021 at 10:24