Abstract

---

"A Precise Measurement of the Pion Beta Decay Rate"

 The PIBETA project at PSI, Switzerland, is a program of 
measurements with the aim of making a precise determination of the
pi+ -> pi0 e+ nu (PIBETA) decay rate, which provides a new 
constraint on the Cabibbo-Kobayashi-Masukawa matrix element Vud.
The PIBETA decay is measured with a stopped pion beam and normalized 
to pi+ -> e+ nu events. The heart of the detector is a 3pi spherical
calorimeter consisting of 240 pure CsI crystals. Details of the design, 
construction and commissioning of the detector are described and 
preliminary results from the 1999 and 2000 data taking are reported.

e-mail contact: hisho@icepp.s.u-tokyo.ac.jp,