AN HISTORICAL OVERVIEW OF THE IMPORTANCE OF THE WEAK DECAY OF HYPERNUCLEI Page: 2 of 8
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
An Historical Overview of the Importance of the Weak Decay of
B. F. Gibson a.
aTheoretical Division, Los Alamos, National Laboratory
Los Alamos, NM 87545, U.S.A.
Weak decay of hypernuclei, first cousin to the 0-decay of conventional, nonstrange
nuclei, was initially observed in the 1950s. Pionic decay rates have proven a challenge - to
reconcile nuclear decay rates with that of free A decay. Pauli blocking of the decay nucleon
plays an important role. Nonmesonic decay provides our only practical means of exploring
the four-fermion, strangeness-changing NA -+ NN weak interaction. The NAp vertex
can be investigated in no other way. The large momentum transfer in the nonmesonic
decay process suggests a means to probe short distance aspects of the interaction, possibly
revealing baryon substructure effects. Whether the AI=1/2 rule, which governs free A
decay, also applies to the nonmesonic decay process remains an open question. The free
A does not decay by emission of a 7r+; the 7+ decay of 'He is a puzzle. Finally, the
weak decay of strangeness -2 hypernuclei is an important topic, because the picnic decay
process is central to current efforts to seek and identify AA hypernuclei.
Let me begin by paying tribute to Dick Dalitz and Don Davis. Prof. Dalitz led the
thinking of theorists in this area for many years. Prof. Davis and his collaborators gave
us much of our early data. Without these two gentlemen - as well as others such as our
conference chair - one would not have a field of hypernuclear physics.
In free space the A decays via
A - p +7r- + 38 MeV (64%), A - n + 7r + 41 MeV (36%),
with a lifetime TA = 1/FA = (1/F,- + 1/Fo)-1 = 2.63 x 10-1os. This OS=1 transition
can occur theoretically with a change in isospin of AI = 1/2 or DI = 3/2. An s quark
converts into a u (or d) quark via exchange of a charged W boson. The V-A Hamiltonian
description of the decay can be written as
HV-A = sin BC cos 9COV-A + c.c., OV-A = uy (1 - ys)sd-y'(1 - ys)u , (1)
where 0c is the Cabibbo angle. Such a model implies equal strength for DI = 1/2 and
AI = 3/2 transitions. However, experimentally one finds the AI = 1/2 amplitude to be
*This research was supported by the U.S. Department of Energy under contract W-7405-ENG-36.
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
GIBSON, B. F. AN HISTORICAL OVERVIEW OF THE IMPORTANCE OF THE WEAK DECAY OF HYPERNUCLEI, article, January 9, 2001; Los Alamos, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc722718/m1/2/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.