Nuclear Internal Pair Creation and Search for a light neutral boson

A significant number of experiments have been carried out over last four decades in search of a light neutral boson.  These efforts have been driven by several anomalous experiemntal results which have been discussed in terms of creation and decay of a light scalar boson.  However, none of these experiments  has succeeded in providing a clear evidence of the creation and subsequent dilepton decay of such a particle.  The experiments have been of varied types, namely, beam-dump, pion decay, nuclear deexcitation,  e+e- scattering etc.  All these measurements have resulted in setting limits on the mass and life time of such a light scalar particle.  In light of this the finding of the most recent measurement by a Hungarian group of the possible creation and decay of a light scalar boson in nuclear decay has generated much interest and needs minute scrutiny. In the first part of this talk we will discuss the physics of nuclear internal pair decay and the associated techniques for analysing such measurements followed by a discussion of the Hungarian result. The internal pair creation of excited nuclear states also provide the opportunity to study nuclear giant resonances, in particular the Giant Monopole resonance that tells us about nuclear matter compressibility. In the second part of the talk we will discuss a large pair (di-lepton) spectrometer, arguably the largest and most powerful of all such instruments, that was designed and built in Stony Brook Univ. many years ago and used for finding di-lepton decay of Giant Monopole states in hot rotating nuclei.