Lifetime of theΛ0Hyperon

Abstract

A precision measurement of the A 0 lifetime has been made in a helium bubble chamber. An exposure to a stopping K~ beam yielded 2239 A°'s, with a mean momentum of ~250 MeV/c, which satisfied rigorous selection criteria designed to minimize biases. The mean lifetime was found to be r = (2.36±0.06)X10~1 0 sec.

Progress report on few-body hypernuclei

“…in good agreement with τ exp ( 4 Λ H)=193±25 ps, τ exp ( 4 Λ He)=250±19 ps, as measured at KEK [28] and confirmed for 4 Λ He at BNL [29]. A special feature of the 4 Λ H-4 Λ He mirror hypernuclei is the particularly strong charge symmetry breaking (CSB) reflected in their spectra, as shown in Fig.…”

“…2 3 Λ H lifetime Measurements of the 3 Λ H lifetime in emulsion or bubble-chamber experiments during the 1960s and early 1970s gave conflicting and puzzling results. Particularly troubling appeared a conference report by Block et al claiming a lifetime of τ( 3 Λ H)=(95 +19 −15 ) ps [3], to be compared with a free Λ lifetime τ Λ =(236±6) ps [4] measured in the same He bubble chamber (BC). However, the He BC experiment [5] concluding that era, coauthored by the same Block, reported a value of τ( 3 Λ H)=(246 +62 −41 ) ps, in agreement with a Λ lifetime of (263±2) ps.…”

“…Λ OPE CSB (central plus tensor) contribution to the splitting of the 4 Λ H-4 Λ He mirror g.s. levels roughly agrees with the observed value ∆B J=0…”

Recent progress on few-body hypernuclei

“…Do we understand this value in simple terms? A back-of-the-envelope estimate gives the following approximate expressions for 4 Λ H (Z=1) and 4 Λ He (Z=2) decay rates relative to the free Λ decay:…”

“…Particularly meaningful tests of hyperon-nucleon and hyperon-hyperon strong-interaction models are possible in light Λ and ΛΛ hypernuclei, A ≤ 6, which the topics reviewed below are concerned with. ) ps [3], to be compared with a free Λ lifetime τ Λ =(236±6) ps [4] measured in the same He bubble chamber (BC). However, the He BC experiment [5] concluding that era, coauthored by the same Block, reported a value of τ( 3Λ H)=(246 +62 −41 ) ps, in agreement with a Λ lifetime of (263±2) ps.…”