Digitization in EMC simulation

Dmytro Melnychuk,Soltan Institute for Nuclear Studies,

Warsaw, Poland

General scheme of digitizationPWO Preamplifier/

shaper FADC DigiAPD

● Conversion from deposited energy to photons● Signal conversion in APD● Signal transformation in pre-amplifier/shaper● FADC● Extraction of signal amplitude from FADC output (digital filter or simple parabolic fit)

Design parameters which affect digitization

● Noise (preamplifier + APD)● Photon statistics (photoelectrons per MeV)● Shaping time (integration, differentiation)● Scintillation time constant● FADC frequency

Foreseen but not used at the moment:● Noise dependency on the channel (measured values which will be taken from Condition Data Base (CDB))● Non-uniformity of light production

Values of parameters2 options for read-out electronics:- Quad-preamplifier (developed by Basel group), noise value = 1600 e- at -25 C (0.12 MeV), external shaping = 250 ns- ASIC read-out, noise 4400 e- at -25 C (0.34 MeV), built-in shaping = 100 ns (?)

Other parameters:● APD contribution to noise – excess noise factor F=1.38 at gain M=50, dark current (?)● 400 photoelectrons per MeV at -25 C, QE=70%● 80 MHz FADC● crystal scintillation time 6 ns

Energy resolution dependence on digitization

1) Single gammas with different energies were generated with uniform angular distribution (10, 50, 100, 200, 500, 1000 MeV)

2) Dependence of energy deposited in 1 cluster on parameter of electronics(cluster – group of neighboring crystals) Energy threshold for single crystal = 1MeV

Photon statistic dependenceE=10 MeV E=50 MeV

10 MeV 50 MeVsimple digitization 0.625 3.23noise (0.12 MeV) 0.637 3.30noise (0.12 MeV) +photon statistic

0.71 3.30

RMS (MeV)

Noise dependence

Simpledigitization

0.12 MeV250 ns

(Quad-pream)

0.34 MeV100 ns(ASIC)

10 MeV 0.625 0.711 0.75950MeV 3.23 3.31 3.31100 MeV 4.38 4.54 4.54200 MeV 5.9 5.91 5.91500 MeV 8.7 8.71 8.771000 MeV 16.8 16.7 16.8

RMS (MeV)

Shaping time dependence

0.34 MeV100 ns

0.34 MeV250 ns

10 MeV 0.759 0.72150MeV 3.31 3.30100 MeV 4.54 4.47200 MeV 5.91 5.93500 MeV 8.77 8.721000 MeV 16.8 16.7

RMS (MeV)

Summary1) Energy resolution is sensitive to photon statistic only at lowest energies2) Noise contribution to energy resolution is on the level of 3% and decrease with growth of energy3) Energy resolution does not depend significantly on the shaping time but it a little bit worse for smaller values

To do:● Event mixing● Realistic digi format from DAQ