# The Neutron Mean Life and Big Bang Nucleosynthesis

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## Abstract

**:**

## 1. Introduction

## 2. Standard BBN

## 3. Abundance Sensitivities to ${\mathbf{\tau}}_{\mathbf{n}}$

## 4. BBN ‘Predictions’ of ${\mathbf{\tau}}_{\mathbf{n}}$

## 5. Summary and Outlook

- New neutron lifetime measurements are planned. These include (a) both an upgrade magneto-gravitational trap experiment UCN$\tau $+, and (b) an upgraded pulsed beam experiment, Beam Lifetime 3 (BL3) [68]. These can shed new light on and perhaps resolve the ${\tau}_{n}$ puzzle.
- The next generation CMB measurements from CMB-S4 will significantly improve both the determination of ${Y}_{p}$ and ${N}_{\nu}$ from the CMB [66]. Improved ${\tau}_{n}$ measurements will be important for BBN to fully exploit these results, particularly ${N}_{\nu}$.
- The ongoing effort to improve astronomical ${Y}_{p}$ determinations continues. As we have discussed here and elsewhere [19], reaching the ambitious goal of ${\sigma}_{\mathrm{obs}}\left({Y}_{p}\right)=0.001$ would open a new window on new physics generally and ${\tau}_{n}$ in particular, approaching a precision near that of the present experimental discrepancy.

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Notes

1 | The arrows at the top of the figure correspond to typical baryon densities taken from mass-to-light ratios typical of the solar neighborhood, the central parts of galaxies, hot gas, and binaries and small groups of galaxies (BSG). At the time, it was not clear what object was truly representative of the cosmological average. |

2 | For more information about the construction and use of ideograms, see any issue of the Review of Particle Properties or the Review of Particle Physics. |

3 | In fact, we assume $\Lambda $CDM, so that in addition to these Standard Model particles and interactions, there is (1) a nonzero cosmological constant $\Lambda $ which will be negligible during BBN, and (2) cold dark matter which we take to be so weakly interacting as to have no effect on BBN. These assumptions can be relaxed; see reviews in refs. [45,46,47]. |

4 | Including the in-beam measurement would further increase the dispersion requiring a scale factor of 2.2. |

## References

- Walker, T.P.; Steigman, G.; Schramm, D.N.; Olive, K.A.; Kang, H.S. Primordial nucleosynthesis redux. Astrophys. J.
**1991**, 376, 51–69. [Google Scholar] [CrossRef] - Olive, K.A.; Steigman, G.; Walker, T.P. Primordial nucleosynthesis: Theory and observations. Phys. Rept.
**2000**, 333, 389–407. [Google Scholar] [CrossRef] [Green Version] - Fields, B.D.; Olive, K.A. Big bang nucleosynthesis. Nucl. Phys.
**2006**, 777, 208–225. [Google Scholar] [CrossRef] [Green Version] - Fields, B.D.; Molaro, P.; Sarkar, S. Big-Bang Nucleosynthesis. Chin. Phys. C
**2014**, 38, 339–344. [Google Scholar] [CrossRef] [Green Version] - Steigman, G. Primordial Nucleosynthesis in the Precision Cosmology Era. Ann. Rev. Nucl. Part. Sci.
**2007**, 57, 463–491. [Google Scholar] [CrossRef] [Green Version] - Iocco, F.; Mangano, G.; Miele, G.; Pisanti, O.; Serpico, P.D. Primordial Nucleosynthesis: From precision cosmology to fundamental physics. Phys. Rep.
**2009**, 472, 1–76. [Google Scholar] [CrossRef] [Green Version] - Pitrou, C.; Coc, A.; Uzan, J.P.; Vangioni, E. Precision big bang nucleosynthesis with improved Helium-4 predictions. Phys. Rep.
**2018**, 754, 1–66. [Google Scholar] [CrossRef] [Green Version] - Cyburt, R.H.; Fields, B.D.; Olive, K.A.; Yeh, T.-H. Big Bang Nucleosynthesis: 2015. Rev. Mod. Phys.
**2016**, 88, 015004. [Google Scholar] [CrossRef] [Green Version] - Fields, B.D.; Olive, K.A.; Yeh, T.H.; Young, C. Big-Bang Nucleosynthesis after Planck. J. Cosmol. Astropart. Phys.
**2020**, 3, 010. [Google Scholar] [CrossRef] [Green Version] - Particle Data Group; Workman, R.L.; Burkert, V.D.; Crede, V.; Klempt, E.; Thoma, U.; Tiator, L.; Agashe, K.; Aielli, G.; Allanach, B.C.; et al. Review of Particle Physics. Prog. Theor. Exp. Phys.
**2022**, 2022, 083C01. [Google Scholar] - Aghanim, N.; Akrami, Y.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Barreiro, R.B.; Bartolo, N.; Basak, S.; Battye, R. Planck 2018 results. VI. Cosmological parameters. Astron. Astrophys.
**2020**, 641, A6. [Google Scholar] - Janot, P.; Jadach, S. Improved Bhabha cross section at LEP and the number of light neutrino species. Phys. Lett. B
**2020**, 803, 135319. [Google Scholar] [CrossRef] - Olive, K.A.; Schramm, D.N.; Steigman, G.; Turner, M.S.; Yang, J.M. Big Bang Nucleosynthesis as a Probe of Cosmology and Particle Physics. Astrophys. J.
**1981**, 246, 557. [Google Scholar] [CrossRef] - Yang, J.M.; Turner, M.S.; Steigman, G.; Schramm, D.N.; Olive, K.A. Primordial Nucleosynthesis: A Critical Comparison of Theory and Observation. Astrophys. J.
**1984**, 281, 493–511. [Google Scholar] [CrossRef] - Ellis, J.R.; Olive, K.A. Constraints on Light Particles From Stellar Evolution. Nucl. Phys. B
**1983**, 223, 252–268. [Google Scholar] [CrossRef] [Green Version] - Christensen, C.J.; Nielsen, A.; Bahnsen, A.; Brown, W.K.; Rustad, B.M. Free-Neutron Beta-Decay Half-Life. Phys. Rev. D
**1972**, 5, 1628–1640. [Google Scholar] [CrossRef] - Bondarenko, L.N.; Kurguzov, V.V.; Prokofev, Y.A.; Rogov, E.V.; Spivak, P.E. Measurement of the Neutron Half Time. Pisma Zh. Eksp. Teor. Fiz.
**1978**, 28, 328–333. [Google Scholar] - Byrne, J.; Morse, J.; Smith, K.F.; Shaikh, F.; Green, K.; Greene, G.L. A New Measurement of the Neutron Lifetime. Phys. Lett. B
**1980**, 92, 274–278. [Google Scholar] [CrossRef] - Yeh, T.H.; Shelton, J.; Olive, K.A.; Fields, B.D. Probing physics beyond the standard model: Limits from BBN and the CMB independently and combined. J. Cosmol. Astropart. Phys.
**2022**, 10, 046. [Google Scholar] [CrossRef] - Baltrusaitis, R.M.; Becker, J.; Blaylock, G.; Brown, J.S.; Bunnell, K.; Burnett, T.; Cassell, R.; Coffman, D.; Cook, V.; Coward, D.H.; et al. [Particle Data Group]. Decays of the J/ψ into Two Pseudoscalar Mesons. Phys. Lett. B
**1982**, 111, 1–294. [Google Scholar] - Kosvintsev, Y.Y.; Kushnir, Y.A.; Morozov, V.I.; Terekhov, G.I. Application of Ultracold Neutrons for Neutron Lifetime Measurement. JETP Lett.
**1980**, 31, 236. (In Russian) [Google Scholar] - Wilkinson, D.H. The neutron lifetime. Prog. Part. Nucl. Phys.
**1981**, 6, 325–332. [Google Scholar] [CrossRef] - Tanabashi, M.; Hagiwara, K.; Hikasa, K.; Nakamura, K.; Sumino, Y.; Takahashi, F.; Tanaka, J.; Agashe, K.; Aielli, G.; Amsler, C.; et al. Review of Particle Properties. Particle Data Group. Rev. Mod. Phys.
**1984**, 56, S1–S304. [Google Scholar] - Mampe, W.; Ageron, P.; Bates, C.; Pendlebury, J.M.; Steyerl, A. Neutron Lifetime Measured With Stored Ultracold Neutrons. Phys. Rev. Lett.
**1989**, 63, 593–596. [Google Scholar] [CrossRef] [Green Version] - Olive, K.A.; Schramm, D.N.; Steigman, G.; Walker, T.P. Big Bang Nucleosynthesis Revisited. Phys. Lett. B
**1990**, 236, 454–460. [Google Scholar] [CrossRef] [Green Version] - Yeh, T.H.; Olive, K.A.; Fields, B.D. The impact of new d(p,γ)3 rates on Big Bang Nucleosynthesis. J. Cosmol. Astropart. Phys.
**2021**, 3, 046. [Google Scholar] [CrossRef] - Hagiwara, K. Review of Particle Physics. Phys. Rev. D
**2002**, 66, 010001. [Google Scholar] [CrossRef] [Green Version] - Arzumanov, S.; Bondarenko, L.; Chernavsky, S.; Fomin, A.; Morozov, V.; Panin, Y.; Drexel, W.; Schreckenbach, K.; Geltenbort, P.; Pendlebury, J. Neutron life time value measured by storing ultracold neutrons with detection of inelastically scattered neutrons. Phys. Lett. B
**2000**, 483, 15–22. [Google Scholar] [CrossRef] - Cyburt, R.H.; Fields, B.D.; Olive, K.A. The NACRE Thermonuclear Reaction Compilation and Big Bang Nucleosynthesis. New Astron.
**1996**, 6, 215. [Google Scholar] [CrossRef] [Green Version] - Spergel, D.N.; Verde, L.; Peiris, H.V.; Komatsu, E.; Nolta, M.R.; Bennett, C.L.; Halpern, M.; Hinshaw, G.; Jarosik, N.; Kogut, A.; et al. First year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Determination of cosmological parameters. Astrophys. J. Suppl.
**2003**, 148, 175–194. [Google Scholar] [CrossRef] [Green Version] - Cyburt, R.H.; Fields, B.D.; Olive, K.A. Primordial nucleosynthesis with CMB inputs: Probing the early universe and light element astrophysics. Astropart. Phys.
**2002**, 17, 87–100. [Google Scholar] [CrossRef] [Green Version] - Serebrov, A.; Varlamov, V.; Kharitonov, A.; Fomin, A.; Pokotilovski, Y.; Geltenbort, P.; Butterworth, J.; Krasnoschekova, I.; Lasakov, M.; Tal’daev, R.; et al. Measurement of the neutron lifetime using a gravitational trap and a low-temperature Fomblin coating. Phys. Lett. B
**2005**, 605, 72–78. [Google Scholar] [CrossRef] [Green Version] - Mathews, G.J.; Kajino, T.; Shima, T. Big Bang nucleosynthesis with a new neutron lifetime. Phys. Rev. D
**2005**, 71, 021302. [Google Scholar] [CrossRef] [Green Version] - Beringer, J.; Arguin, J.F.; Barnett, R.M.; Copic, K.; Dahl, O.; Groom, D.E.; Lin, C.J.; Lys, J.; Murayama, H.; Wohl, C.G.; et al. [Particle Data Group]. Review of Particle Physics (RPP). Phys. Rev. D
**2012**, 86, 010001. [Google Scholar] [CrossRef] [Green Version] - Wietfeldt, F.E.; Greene, G.L. Colloquium: The neutron lifetime. Rev. Mod. Phys.
**2011**, 83, 1173–1192. [Google Scholar] [CrossRef] [Green Version] - Pichlmaier, A.; Varlamov, V.; Schreckenbach, K.; Geltenbort, P. Neutron lifetime measurement with the UCN trap-in-trap MAMBO II. Phys. Lett. B
**2010**, 693, 221–226. [Google Scholar] [CrossRef] - Steyerl, A.; Pendlebury, J.M.; Kaufman, C.; Malik, S.S.; Desai, A.M. Quasielastic scattering in the interaction of ultracold neutrons with a liquid wall and application in a reanalysis of the Mambo I neutron-lifetime experiment. Phys. Rev. C
**2012**, 85, 065503. [Google Scholar] [CrossRef] - Arzumanov, S.; Bondarenko, L.; Chernyavsky, S.; Geltenbort, P.; Morozov, V.; Nesvizhevsky, V.V.; Panin, Y.; Strepetov, A. A measurement of the neutron lifetime using the method of storage of ultracold neutrons and detection of inelastically up-scattered neutrons. Phys. Lett. B
**2015**, 745, 79–89. [Google Scholar] [CrossRef] [Green Version] - Serebrov, A.P.; Kolomensky, E.A.; Fomin, A.K.; Krasnoshchekova, I.A.; Vassiljev, A.V.; Prudnikov, D.M.; Shoka, I.V.; Chechkin, A.V.; Chaikovskiy, M.E.; Varlamov, V.E.; et al. Neutron lifetime measurements with a large gravitational trap for ultracold neutrons. Phys. Rev. C
**2018**, 97, 055503. [Google Scholar] [CrossRef] [Green Version] - Pattie, R.W., Jr.; Callahan, N.B.; Cude-Woods, C.; Adamek, E.R.; Broussard, L.J.; Clayton, S.M.; Currie, S.A.; Dees, E.B.; Ding, X.; Engel, E.M.; et al. Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection. Science
**2018**, 360, 627–632. [Google Scholar] [CrossRef] [Green Version] - Ezhov, V.F.; Andreev, A.Z.; Ban, G.; Bazarov, B.A.; Geltenbort, P.; Glushkov, A.G.; Knyazkov, V.A.; Kovrizhnykh, N.A.; Krygin, G.B.; Naviliat-Cuncic, O.; et al. Measurement of the neutron lifetime with ultra-cold neutrons stored in a magneto-gravitational trap. JETP Lett.
**2018**, 107, 671–675. [Google Scholar] [CrossRef] [Green Version] - Gonzalez, F.M.; Fries, E.M.; Cude-Woods, C.; Bailey, T.; Blatnik, M.; Broussard, L.J.; Callahan, N.B.; Choi, J.H.; Clayton, S.M.; Currie, S.A.; et al. Improved neutron lifetime measurement with UCNτ. Phys. Rev. Lett.
**2021**, 127, 162501. [Google Scholar] [CrossRef] [PubMed] - Yue, A.T.; Dewey, M.S.; Gilliam, D.M.; Greene, G.L.; Laptev, A.B.; Nico, J.S.; Snow, W.M.; Wietfeldt, F.E. Improved Determination of the Neutron Lifetime. Phys. Rev. Lett.
**2013**, 111, 222501. [Google Scholar] [CrossRef] [PubMed] [Green Version] - Czarnecki, A.; Marciano, W.J.; Sirlin, A. Neutron Lifetime and Axial Coupling Connection. Phys. Rev. Lett.
**2018**, 120, 202002. [Google Scholar] [CrossRef] [PubMed] [Green Version] - Pospelov, M.; Pradler, J. Big Bang Nucleosynthesis as a Probe of New Physics. Ann. Rev. Nucl. Part. Sci.
**2010**, 60, 539–568. [Google Scholar] [CrossRef] [Green Version] - Jedamzik, K.; Pospelov, M. Big Bang Nucleosynthesis and Particle Dark Matter. New J. Phys.
**2009**, 11, 105028. [Google Scholar] [CrossRef] - Malaney, R.A.; Mathews, G.J. Probing the early universe: A Review of primordial nucleosynthesis beyond the standard Big Bang. Phys. Rept.
**1993**, 229, 145–219. [Google Scholar] [CrossRef] - Bernstein, J.; Brown, L.S.; Feinberg, G. Cosmological Helium Production Simplified. Rev. Mod. Phys.
**1989**, 61, 25. [Google Scholar] [CrossRef] [Green Version] - Mukhanov, V.F. Nucleosynthesis without a computer. Int. J. Theor. Phys.
**2004**, 43, 669. [Google Scholar] [CrossRef] [Green Version] - Froustey, J.; Pitrou, C. Incomplete neutrino decoupling effect on big bang nucleosynthesis. Phys. Rev. D
**2020**, 101, 043524. [Google Scholar] [CrossRef] [Green Version] - Aver, E.; Berg, D.A.; Olive, K.A.; Pogge, R.W.; Salzer, J.J.; Skillman, E.D. Improving helium abundance determinations with Leo P as a case study. J. Cosmol. Astropart. Phys.
**2021**, 3, 027. [Google Scholar] [CrossRef] - Aver, E.; Berg, D.A.; Hirschauer, A.S.; Olive, K.A.; Pogge, R.W.; Rogers, N.S.J.; Salzer, J.J.; Skillman, E.D. A comprehensive chemical abundance analysis of the extremely metal poor Leoncino Dwarf galaxy (AGC 198691). Mon. Not. R. Astron. Soc.
**2021**, 510, 373–382. [Google Scholar] [CrossRef] - Pettini, M.; Cooke, R. A new, precise measurement of the primordial abundance of Deuterium. Mon. Not. R. Astron. Soc.
**2012**, 425, 2477–2486. [Google Scholar] [CrossRef] [Green Version] - Cooke, R.; Pettini, M.; Jorgenson, R.A.; Murphy, M.T.; Steidel, C.C. Precision measures of the primordial abundance of deuterium. Astrophys. J.
**2014**, 781, 31. [Google Scholar] [CrossRef] - Riemer-Sørensen, S.; Webb, J.K.; Crighton, N.; Dumont, V.; Ali, K.; Kotuš, S.; Bainbridge, M.; Murphy, M.T.; Carswell, R. A robust deuterium abundance; Re-measurement of the z = 3.256 absorption system towards the quasar PKS1937-1009. Mon. Not. R. Astron. Soc.
**2015**, 447, 2925–2936. [Google Scholar] [CrossRef] [Green Version] - Balashev, S.A.; Zavarygin, E.O.; Ivanchik, A.V.; Telikova, K.N.; Varshalovich, D.A. The primordial deuterium abundance: SubDLA system at z
_{abs}= 2.437 towards the QSO J 1444+2919. Mon. Not. R. Astron. Soc.**2016**, 458, 2188–2198. [Google Scholar] [CrossRef] [Green Version] - Cooke, R.J.; Pettini, M.; Nollett, K.M.; Jorgenson, R. The primordial deuterium abundance of the most metal-poor damped Lyα system. Astrophys. J.
**2016**, 830, 148. [Google Scholar] [CrossRef] [Green Version] - Riemer-Sørensen, S.; Kotuš, S.; Webb, J.K.; Ali, K.; Dumont, V.; Murphy, M.T.; Carswell, R.F. A precise deuterium abundance: Remeasurement of the z = 3.572 absorption system towards the quasar PKS1937?101. Mon. Not. R. Astron. Soc.
**2017**, 468, 3239–3250. [Google Scholar] [CrossRef] - Zavarygin, E.O.; Webb, J.K.; Dumont, V.; Riemer-Sørensen, S. The primordial deuterium abundance at z
_{abs}= 2.504 from a high signal-to-noise spectrum of Q1009 + 2956. Mon. Not. R. Astron. Soc.**2018**, 477, 5536–5553. [Google Scholar] [CrossRef] [Green Version] - Cooke, R.J.; Pettini, M.; Steidel, C.C. One Percent Determination of the Primordial Deuterium Abundance. Astrophys. J.
**2018**, 855, 102. [Google Scholar] [CrossRef] [Green Version] - Cyburt, R.H.; Fields, B.D.; Olive, K.A. An Update on the big bang nucleosynthesis prediction for Li-7: The problem worsens. J. Cosmol. Astropart. Phys.
**2008**, 11, 012. [Google Scholar] [CrossRef] [Green Version] - Fields, B.D.; Olive, K.A. Implications of the non-observation of
^{6}Li in halo stars for the primordial^{7}Li problem. J. Cosmol. Astropart. Phys.**2022**, 10, 078. [Google Scholar] [CrossRef] - Ryan, S.G.; Beers, T.C.; Olive, K.A.; Fields, B.D.; Norris, J.E. Primordial Lithium and Big Bang Nucleosynthesis. Astrophys. J.
**2000**, 530, L57. [Google Scholar] [CrossRef] [Green Version] - Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H.-G.; Behara, N.T.; Hernandez, J.I.G.; Steffen, M.; Cayrel, R.; Freytag, B.; Van’t Veer, C. et al. The metal-poor end of the Spite plateau. 1: Stellar parameters, metallicities and lithium abundances. Astron. Astrophys.
**2010**, 522, A26. [Google Scholar] [CrossRef] [Green Version] - Salvati, L.; Pagano, L.; Consiglio, R.; Melchiorri, A. Cosmological constraints on the neutron lifetime. J. Cosmol. Astropart. Phys.
**2016**, 3, 055. [Google Scholar] [CrossRef] [Green Version] - Abazajian, K.N.; Adshead, P.; Ahmed, Z.; Allen, S.W.; Alonso, D.; Arnold, K.S.; Baccigalupi, C.; Bartlett, J.G.; Battaglia, N.; Benson, B.A.; et al. CMB-S4 Science Book, First Edition. arXiv
**2016**, arXiv:1610.02743. [Google Scholar] - Wilson, J.T.; Lawrence, D.J.; Peplowski, P.N.; Eke, V.R.; Kegerreis, J.A. Measurement of the free neutron lifetime using the neutron spectrometer on NASA’s Lunar Prospector mission. Phys. Rev. C
**2021**, 104, 045501. [Google Scholar] [CrossRef] - Wietfeldt, F.E.; Biswas, R.; Caylor, J.; Crawford, B.; Dewey, M.S.; Fomin, N.; Greene, G.L.; Haddock, C.C.; Hoogerheide, S.F.; Mumm, H.P.; et al. Comments on Systematic Effects in the NIST Beam Neutron Lifetime Experiment. arXiv
**2022**, arXiv:2209.15049. [Google Scholar]

**Figure 1.**The helium mass fraction as a function of the baryon-to-photon ratio for three choices of ${N}_{\nu}=2,3$, and 4 and three choices of ${\tau}_{1/2}$ with ${N}_{\nu}=3$. Figure circa 1981 from ref. [13].

**Figure 2.**The average mean lifetime of the neutron as compiled by the Review of Particle Properties/Physics. Please note that the uncertainty in the mean life for more recent measurements is smaller than the symbol showing the mean.

**Figure 3.**Ideograms for neutron lifetime measurements. (

**a**) Ideogram for the seven measurements contributing to the PDG average neutron mean life in 2012; (

**b**) Ideogram for the eight measurements contributing to the PDG average neutron mean life in 2022.

**Figure 4.**Time evolution of the light element abundances during BBN. Please note that time (upper axis) increases to the right, and so the temperature is shown to decrease to the right.

**Figure 5.**The helium mass fraction as a function of the baryon-to-photon ratio for three choices of ${N}_{\nu}=2,3$, and 4 and for a spread in values of ${\tau}_{1/2}$ up to $\pm 3\sigma $ about the mean with ${N}_{\nu}=3$.

**Figure 6.**The sensitivity of the ${}^{4}\mathrm{He}$ abundance to the neutron mean lifetime, assuming a Gaussian distribution for ${\tau}_{n}$ with mean and uncertainty given by Equation (2). In addition to the peak of the likelihood, denoted by a star, we show the 1, 2, and 3$\sigma $ contours.

**Figure 8.**Light element abundance likelihood functions. Shown are the likelihoods for each of the light nuclides: (

**a**) the ${}^{4}\mathrm{He}$ mass fraction, ${Y}_{p}$, (

**b**) D/H, (

**c**) ${}^{3}\mathrm{He}$/H, and (

**d**) ${}^{7}\mathrm{Li}$. The solid-lined, dark-shaded (purple) curves are the BBN+CMB predictions, based on Planck inputs as discussed in the text. The dashed-lined, light-shaded (yellow) curves show astronomical measurements of the primordial abundances, for all but ${}^{3}\mathrm{He}$ where reliable primordial abundance measures do not exist. For ${}^{4}\mathrm{He}$, the dotted-lined, medium-shaded (cyan) curve shows the independent CMB determination of ${}^{4}\mathrm{He}$.

**Figure 10.**Comparison of the current and potential future BBN predicted likelihood function for ${\tau}_{n}$ with the experimental likelihood. The solid blue curve shows the current BBN prediction, which is tightened to the green dashed curve if the uncertainty in the helium mass fraction can be reduced to ${\sigma}_{\mathrm{obs}}\left({Y}_{p}\right)=0.001$. For comparison, the red dot-dashed curve shows the experimental value for ${\tau}_{n}$ represented by a Gaussian. The distribution represented by the ideogram is shown by the thin cyan solid curve.

**Table 1.**Neutron mean life and uncertainty (in s) as reported by the review of Particle Properties and Review of Particle Physics.

Year | ${\mathit{\tau}}_{\mathit{n}}$ | ${\mathit{\sigma}}_{{\mathit{\tau}}_{\mathit{n}}}$ | Year | ${\mathit{\tau}}_{\mathit{n}}$ | ${\mathit{\sigma}}_{{\mathit{\tau}}_{\mathit{n}}}$ | Year | ${\mathit{\tau}}_{\mathit{n}}$ | ${\mathit{\sigma}}_{{\mathit{\tau}}_{\mathit{n}}}$ |
---|---|---|---|---|---|---|---|---|

1959 | 1013 | ±26 | 1967 | 935 | ±14 | 1972 | 918 | ±14 |

1980 | 937 | ±18 | 1982 | 925 | ±11 | 1984 | 898 | ±16 |

1988 | 896 | ±10 | 1990 | 888.6 | ±3.5 | 1992 | 889.1 | ±2.1 |

1994 | 887.0 | ±2.0 | 1998 | 886.7 | ±1.9 | 2002 | 885.7 | ±0.8 |

2012 | 880.1 | ±1.1 | 2014 | 880.3 | ±1.1 | 2016 | 880.2 | ±1.0 |

2020 | 879.4 | ±0.6 | 2022 | 878.4 | ±0.5 |

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Yeh, T.-H.; Olive, K.A.; Fields, B.D.
The Neutron Mean Life and Big Bang Nucleosynthesis. *Universe* **2023**, *9*, 183.
https://doi.org/10.3390/universe9040183

**AMA Style**

Yeh T-H, Olive KA, Fields BD.
The Neutron Mean Life and Big Bang Nucleosynthesis. *Universe*. 2023; 9(4):183.
https://doi.org/10.3390/universe9040183

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Yeh, Tsung-Han, Keith A. Olive, and Brian D. Fields.
2023. "The Neutron Mean Life and Big Bang Nucleosynthesis" *Universe* 9, no. 4: 183.
https://doi.org/10.3390/universe9040183