Redesign of the PIBETA Beam Detectors for a New $\pi_{2e}$ Experiment at PSI

PEN, a new experiment aiming to measure the $\pi^+\to e^+\nu$ ($\pi_{2e}$) decay branching ratio with a relative uncertainty of $\sim 5\cdot 10^{-4}$ has begun this year at the Paul Scherrer Institute ring accelerator. A development run with an upgraded PIBETA detector was conducted during the summer of 2006. In this contribution we discuss the design and performance of the new beam detectors: the upstream beam counter, and the active collimator, degrader and target using low-momentum 72-80 MeV/c $\pi^+$ beams. All beam detector waveforms were digitized with a 2 GHz/10 bit Acqiris digitizer.