INFN - Laboratori Nazionali di Frascati, May 1995
From: The Second DAFNE Physics Handbook
Chapter 8: $eta$ Decays
Eds. L. Maiani, G. Pancheri, N. Paver
Supported by the INFN, by the EC under the HCM contract number CHRX-CT920026 and by the authors home institutions.
decays
Departament Física i Enginyeria Nuclear
Universitat Politècnica de Catalunya, E-08034 Barcelona, Spain
cm
The Daphne 
--factory will hopefully represent a clean and copious
source of 
mesons.
Indeed, some 
decays are expected per
year with a clear signal consisting of an 
recoiling against a
monoenergetic photon.
All the 
decays detected so far [1] proceed through
electromagnetic (e.m.) interactions. Some of them, like
, 
, 
, contain external photon(s),
whereas the remaining ones, 
, 
are purely hadronic but
violate G--parity (or isospin symmetry) and are therefore of e.m. origin
too. We present here a survey on these e.m. 
decays. A discussion on
weak decays, with emphasis in C and/or CP violation can be found in
Ref.[2]
Being the 
mass, 
, just above the kaon mass, the
variety of e.m. 
decays represents, in principle, an excellent
laboratory to test
the Chiral Perturbation Theory (ChPT) approach, both in the anomalous and
non--anomalous sectors. The main drawback is played, however, by the
mixing which requires the inclusion of the non Goldstone boson
(a pure 
singlet)
in the ChPT framework. Most of the theoretical predictions
presented assume
ChPT with resonance saturation of the needed counterterms. In some
cases, however, definite ChPT predictions are not available and we present
instead estimates based on phenomenological Vector Meson dominated models.
We give in Section 1 a brief review on the treatment of the
--particle in ChPT. Section 2 is devoted to the anomalous (i.e.
those proceeding through the Wess Zumino term)
decays, whereas the non--anomalous ones are presented in Section 3.