<p>Phys.org's <a href="https://phys.org/news/2021-10-physicists-world-precise-neutron-lifetime.html" rel="nofollow noreferrer">Physicists announce the world's most precise measurement of neutron lifetime</a> discusses the accepted for publication Phys. Rev. Letter <em>Improved neutron lifetime measurement with UCNτ</em> (links in block quote) and says:</p>
<blockquote>
<p>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.</p>
<p>The results from the team, which encompasses scientists from over 10 national labs and universities in the United States and abroad, represent <strong>a more than two-fold improvement</strong> over <a href="https://phys.org/news/2018-05-levitation-yields-neutron-lifetime.html" rel="nofollow noreferrer">previous measurements</a>—with an uncertainty of <strong>less than one-tenth of a percent.</strong></p>
<p>The work is <a href="https://journals.aps.org/prl/accepted/b4074Yc6S6b1c98cc3e829630f8de021af1aba78c" rel="nofollow noreferrer">reported</a> 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 href="https://arxiv.org/pdf/2106.10375.pdf" rel="nofollow noreferrer">A pre-print version of the paper is also available (arXiv)</a>.</p>
</blockquote>
<p>The article begins:</p>
<blockquote>
<p>Introduction.</p>
<p>The decay <span class="math-container">$n \rightarrow p + e^- + \bar{\nu}_e$</span> is the simplest example of nuclear β-decay. The mean neutron
lifetime τn provides a key input for predicting primordial light element abundances <sup>1</sup>.</p>
<p><sup>1</sup><a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.71.021302" rel="nofollow noreferrer">Big Bang Nucleosynthesis with a New Neutron Lifetime</a> (<a href="https://arxiv.org/abs/astro-ph/0408523" rel="nofollow noreferrer">arXiv</a>)</p>
</blockquote>
<p>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.</p>
<p><strong>Question:</strong> How sensitive are early universe abundance calculations to the neutron half-life?</p>
<p>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.</p>
<p>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.</p>

CC BY-SA 4.0
2021-10-13T08:45:42.523Z
3 questions in 3 hours
Was'
CC BY-SA 4.0
2021-10-13T08:47:51.980Z
@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
CC BY-SA 4.0
2021-10-13T10:24:28.753Z
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.
ProfRob
<cosmology><nucleosynthesis><elemental-abundances><neutrons>
How sensitive are early universe abundance calculations to the neutron half-life?
uhoh
# How sensitive are early universe abundance calculations to the neutron half-life?

(Asked by: username_0 on 2021-10-13)

Phys.org's [Physicists announce the world's most precise measurement of neutron lifetime](https://phys.org/news/2021-10-physicists-world-precise-neutron-lifetime.html) 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](https://phys.org/news/2018-05-levitation-yields-neutron-lifetime.html)—with an uncertainty of **less than one-tenth of a percent.**
>
> The work is [reported](https://journals.aps.org/prl/accepted/b4074Yc6S6b1c98cc3e829630f8de021af1aba78c) 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)](https://arxiv.org/pdf/2106.10375.pdf).

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.
>
> 1[Big Bang Nucleosynthesis with a New Neutron Lifetime](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.71.021302) ([arXiv](https://arxiv.org/abs/astro-ph/0408523))

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.

**Tags:** cosmology, nucleosynthesis, elemental-abundances, neutrons

> **Comments:**
> **username_1**: 3 questions in 3 hours  
> **username_0**: @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!  
> **username_2**: 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.  

---

## 0 answers

