The experimental and theoretical situation regarding mesonic and non-mesonic decays of light hypernuclei is reviewed. Although some models give reasonable results for pionic decays as well as the total weak decay rate, no existing approach explains, even qualitatively, the observed spin-isospin dependence of AN->NN non-mesonic weak decays.
Invited Talk Xlth European Conference on Few-Body PhysicsFontevraud, France August 31 -September 5, 1987
DISCLAIMERThis report was prepared as an accounl of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of Iheir employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Abstract The experimental and theoretical situation regarding mesonic and non-mesonic decays of light hypernuclei is reviewed. Although some models give reasonable results for pionic decays as well as the total weak decay rate, no existing approach explains, even qualitatively, the observed spin-isospin dependence of AN -< NN non-mesonic weak decays.
IntroductionIt has long been realized that light hypernuclei oiler a unique laboratory for the study of the non-mesonic weak decay process AN-• NN. The light systems j\H, ^H, j^He and ^He provide nuclear cores of different spin and isospin, so that one can derive information on the characteristic spin-isospin dependence of AN->NN conversion. For light systems, the pionic decay modes (A -» pir~, ra7r°) are comparable in rate to the non-mesonic modes, whereas for heavier systems (A > 12) the latter are dominant (due to strong Pauli blocking effects for the low momentum recoiling nudeon in mesonic decay). Existing calculations for the decay widths use simplified wave functions for the 3, 4, and 5-body hypernuclear systems. In view of the large experimental uncertainties, the use of more sophisticated wave functions has not been necessary. However, this situation could change in the future if more precise data become available.We first review briefly the experimental situation; new data on ^He are availablefrom an experiment at Brookhaven. We consider the implications of the new results for the spin-isospin dependence of the AN -> NN process. Various theoretical approaches to the problem are discussed. Although some of these are consistent with the total weak decay rates of hypernuclei, none are able to account for more interesting features such as the spin...
