Limits RegistryPUBLIC RECORD
Limits RegistryThe UCNtau experiment at Los Alamos National Laboratory, which traps ultracold neutrons magneto-gravitationally, measured the free neutron lifetime at 877.75 seconds with an uncertainty of about 0.35 seconds (combined statistical and systematic), reported in 2021 — the tightest constraint to date, though it remains in mild tension with lifetimes measured by the competing 'beam method'.
The question, scope, and sources behind this Registry record.
The UCNtau experiment at Los Alamos National Laboratory, which traps ultracold neutrons magneto-gravitationally, measured the free neutron lifetime at 877.75 seconds with an uncertainty of about 0.35 seconds (combined statistical and systematic), reported in 2021 — the tightest constraint to date, though it remains in mild tension with lifetimes measured by the competing 'beam method'.
The smallest experimental uncertainty achieved in measuring the mean lifetime of a free (unbound) neutron before beta decay.
Change a parameter to stress-test whether a proposed result is still inside the published specification. This is an audit aid, not a proof checker.
This record has no editable parameters. Read the formal question and assumptions before challenging it.
Current frontiers derived from accepted Claims.
An observed or demonstrated result; no opposing bound is implied.
The frontier is not sacred
Most progress starts with a disagreement that survives contact with evidence. If you can push the known lower bound up or pull the upper bound down, show us the work.
≥ when you have shown that at least this value is achievable.≤ when you have shown that anything above this value is impossible.No vibes. State the value, define the scope, and link the paper, proof, code, or reproduction that lets another person check it. Editors review every challenge before the public record changes.
Challenge this recordAssertions tied to evidence, attribution, and review.
The frontier as it changed over time.
Only accepted Claims matching the current specification contribute to the displayed bounds. Strict inequalities remain open; contradictory Claims require editorial review.
1 accepted Claim, with 1 linked evidence records.
Permanent ID limitsregistry.com/limits/LR-LONGEST-NEUTRON-LIFETIME-EXPERIMENT
No active verified bounties are linked to this Limit.
View verified bounty tracker ↗No accepted machine-checked reproductions are recorded for this Limit.
Limits Registry. LR-LONGEST-NEUTRON-LIFETIME-EXPERIMENT. Most precise measurement of the free neutron lifetime. 2026.