The horizontal axis is in nanoseconds (ns; one billionth of a second), whereas the vertical axis is in picoseconds (ps; one trillionth of a second). The presence of events with negative values is because of the precision of time measurement (123 trillionths of a second). Considering this, the fitted data are represented by the solid line.

Ordinary atomic nuclei comprise protons and neutrons, whereas special atomic nuclei comprise baryons, such as Λ (lambda) and Ξ (xi), which include strange quarks. These are known as hypernuclei. Hypernuclei do not naturally occur; they must be artificially produced using accelerators. These nuclei rapidly decay at approximately 2/10 billionths of a second, and an accurate measurement of this timescale can provide valuable insights into the properties of hypernuclei and the weak nuclear forces responsible for their decay.

We successfully achieved a precise measurement of this extremely short duration using J-PARC’s high-intensity kaon beam. First, the moment of hypernucleus creation was determined based on the time the beam passed through a detector placed just before the target and the velocity of the beam. Next, the particles emitted during the decay of the hypernucleus were detected using an outer detector, and the decay time was determined from the time of passage and the velocity of the emitted particles. The difference between these two corresponds to the lifetime of the hypernucleus. In our experiment, we measured this lifetime with a high precision of 123 trillionths of a second. Moreover, by producing abundant hypernuclei and averaging the measurements, we reduced the lifetime uncertainty to 14 trillionths of a second, even including systematic uncertainties.

This work was supported by JSPS KAKENHI Grant Number JP21H00129.

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