Direct Measurements of the Lifetime of Heavy Hypernuclei

TL;DR

This paper presents a direct, high-precision measurement of the lifetime of medium-heavy hypernuclei, confirming the saturation hypothesis and providing new insights into hypernuclear decay processes.

Contribution

It provides the first direct measurement of hypernuclear lifetime across multiple elements, confirming the saturation hypothesis with higher precision than previous studies.

Findings

Measured hypernuclear lifetime agrees with previous Fe-56 data

Results support the saturation hypothesis of hypernuclear lifetime

Disagrees with earlier measurements of certain heavy hypernuclei

Abstract

The lifetime of a Lambda particle embedded in a nucleus (hypernucleus) decreases from that of free Lambda decay due to the opening of the Lambda N to NN weak decay channel. However, it is generally believed that the lifetime of a hypernucleus attains a constant value (saturation) for medium to heavy hypernuclear masses, yet this hypothesis has been difficult to verify. The present paper reports a direct measurement of the lifetime of medium-heavy hypernuclei produced with a photon-beam from Fe, Cu, Ag, and Bi targets. The recoiling hypernuclei were detected by a fission fragment detector using low-pressure multi-wire proportional chambers. The experiment agrees remarkably well with the only previously-measured single-species heavy-hypernucleus lifetime, that of Fe56_Lambda at KEK, and has significantly higher precision. The experiment disagrees with the measured lifetime of an unknown combination of heavy hypernuclei with 180<A<225 and, with a small statistical and systematic uncertainty, strongly favors the expected saturation of the lifetime decrease.