Updated: 8 Nov 1994
- The whole detector system has been designed, including the cosmic veto
house and the air conditioning. The
mechanical structure for the CsI
calorimeter is currently being manufactured.
- More than 30 CsI modules for the calorimeter have been tested and meet our
specifications. EMI photomultiplier tubes with UV-transparent windows
have been selected and ordered for the readout of the pure CsI detectors.
Specialized PMT voltage dividers have been designed, built and tested
with the EMI tubes in beam, and have met our requirements regarding peak
linearity and rate-dependent gain stability.
- Specialized trigger modules have been designed, built and tested in beam.
The original triggering scheme has been demonstrated to satisfy our
requirements. 90 % of the electronics modules are already at PSI and
ready for assembly.
- An active target with 77 fibers 3x3 mm each has been built and
successfully tested in-beam. A sensitivity of 30 - 40 ph-e/MeV was
observed with a typical crosstalk of about 10%. The size of the
pion beam spot on the active target is about one centimeter in
- The cylindrical wire chamber 1 is already at PSI and tested
successfully, chamber 2 will be delivered shortly.
- A fast plastic veto counter surrounding the outer wire chamber
consisting of 20 staves read out by 40 PMTs is under construction.
- The CsI response to monoenergetic positrons and gammas has been measured
in several in-beam tests. The observed lineshape is in excellent
agreement with the full Monte Carlo simulation using the CERN GEANT
computer program. See
- Light uniformity of the CsI crystal response to ionizing radiation has
been measured in beam as well as in a dedicated cosmic ray tomography
setup. A wrapping method has been developed which brings the nonunifor-
mity to about 3% over the full crystal length. We are working on a
further reduction of the nonuniformity.
- In the 1994 beamtime, a trigger for pi -> e-nu events has been developed.
An excellent separation of e-nu decay events from the Michel background
was achieved on-line with this trigger.
- During 1995, the detector will be assembled at PSI. The remaining
CsI crystals will arrive during the year, and will be subsequently tested
and integrated in the detector. The detector system is expected to be
completed and assembled by the end of 1995.
- In 1996, the first data of the pion-beta decay will be collected.
To get the statistics required in the first phase (0.5% uncertainty), the
experiment will continue data taking during 1997 and 1998.
S. Ritt, 8 Nov 1994