Photon detector (CsI(Tl) calorimeter)The photon calorimeter, a highly segmented assembly of 768 CsI(Tl) crystals, covers 75% of the total solid angle. There are 12 holes for outgoing charged particles and 2 holes for the beam entrance and exit.
we have now concluded that we can in principle reuse the PIN readout system in E246. For the energy measurement and pile-up rejection, a FADC is proposed instead of a peakhold ADC as used in E246. The maximum acceptable rate is then determined by the dynamic range of the charge- sensitive preampli er which is estimated to be 30-40 kHz; this should be sufficient for the E36 experiment. The timing information from the FADC is good enough to apply module clustering for the gamma event. The FADC system is very powerful for the separation of pulse pileup. The full width of the output signal from the main shaping ampli er in E246 was about 10 μs including a tail component. The peak position of a FADC pulse is located at tp≈ 3.5 μs from the start of a signal. The decomposition of a pileup signal should be easy than as in the case for the APD readout investigated for E06 without any degradation of the energy resolution for the rst as well as the second pulse. The energy resolution of this readout system was estimated to be 14% (FWHM) for 1.27 MeV γ-ray. The incoherent equivalent noise level for four CsI(Tl) modules (typical cluster size) is expected to be 220 keV. Thus, the energy threshold for the internal bremsstrahlung photon detection of the radiative Ke2 decay will be able to reduced down to 1 MeV. This results in an improved performance for E36 in which we need the detection of bremsstrahlung photons with an energy as low as possible.