Production of heavy hypernuclei in the p+Bi reaction and determination of their lifetime for fission induced by Λ decay

P Kulessa,A Strzałkowski,B Kamys,M Matoba,H.R Koch,O.W.B Schult,W Borgs,H Hodde,M Hartmann,D Prasuhn,H Ohm,W Cassing,K Pysz,R Maier,I Zychor,L Jarczyk,Z Rudy

doi:10.1016/s0370-2693(98)00397-9

Abstract

Abstract The production of Λ hypernuclei was studied in proton reactions with Bi nuclei and the lifetime of the produced heavy hypernuclei was measured by the observation of delayed fission using the recoil shadow method. The measurements were performed at 1.9 GeV proton energy whereas the background was determined at 1.0 GeV. From the distribution of the fission fragments in the shadow region the lifetime τ=[161±7( statist. )±14( system. )] ps was obtained and from a comparison of counting rates of prompt and delayed fission fragments the production cross section of hot Λ hypernuclei was determined to be (350±140) μ b.

Highlights

The lifetime of a L particle bound in hypernuclei differs from that in free space due to the following effects: Ø the mesonic decay of the L particle is strongly inhibited due to the small available phase space of the decay products ŽPauli blocking
The investigation of the decay of heavy hypernuclei, which proceeds only due to weak interaction, may shed some light on the problem of weak interactions of baryons in nuclear matter
Kulessa et al.r Physics Letters B 427 (1998) 403–408 surements of their lifetime the recoil shadow method w1x in which the fragments from delayed fission Žinduced by L decay. are detected in a detector region screened against prompt fission fragments by some diaphragm

Summary

Introduction

The lifetime of a L particle bound in hypernuclei differs from that in free space due to the following effects: Ø the mesonic decay of the L particle is strongly inhibited due to the small available phase space of the decay products ŽPauli blocking.,. The protons from the COSY facility produced hypernuclei in collisions with a U target w7x and the lifetime for delayed fission was determined from the distribution of fission fragments detected in the shadow region of two position sensitive multiwire proportional chambers.

Results

Conclusion