Time-projection chamber for the PEN experiment

The PEN collaboration carries out a precision measurement of the π+ → e +ν decay branching ratio at the Paul Scherrer Institute (PSI, Switzerland). A special mini time-projection chamber (mTPC) has been developed for registration of particles in the pion beam. The chamber contains 14 × 10−3 g/cm2 of matter on the particle path. The chamber was successfully used during one-year-long run. Design and characteristics of the mTPC are described.