It is now possible to measure fle discriminator thresholds for muons and charge injection signals using diagnostic information
for charge injection the special timing is needed: tack delay=70 (nominal tack delay for charge injection = 104)
for muons:
as diagnostic information contains only OR of all discriminayors in a layer, special setup is needed to measure thersholds of individual discriminators
we can measure threshold in either X-layers or Y-layers
to measure threshold in X-layers:
fle discriminators are enabled for all crystals in Y layers
fle discriminators are enabled for 4 crystal per layer in X layers; there 3 possible sets:
crystals 0,3,6,9
crystals 1,4,7,10
crystals 2,5,8,11
for such setup it is possible to select muons using the signals from crystals in other layers to be sure, that only one crystal could produce the discriminator signal in the layer being measured
Some results:
fle discriminator efficiency vs muon signal for crystal=7, side=0, layer=1 for 3 different threshold settings
thresholds are significantly (2-3 times) higher than was requested as input to the online algorithm defining thershold settings
fle discriminator efficiency vs charge injection signal for crystal=7, side=0, layer=1 for 3 different threshold settings
thresholds are closer to what was expected, but still different - the problem of the online discriminator threshold characterization algorithm
not understood yet
the distribution of the ratio of fle discriminator thresholds (muons to charge injection) for 16 crystal ends
different fast shaper discriminator threshold for muons and charge injection could be explained by different pulse shape in this two cases: for shorter pulse (charge injection) the fast shaper output is higher, so the threshold is reached at smaller signal at slow shaper
ratio muons/ci is ~1.7 for higher threshold settings, but increases to ~2,2 for lowest threshold setting
not understood yet
conlcusion:
fle discriminator settings we used so far (called "4 MeV" or "9 MeV") in reality mean ~10 MeV and ~25 MeV and not acceptable for low energy tests like cosmic muons and Van de Graaf generated photons - we have to use lower setting (called "2 MeV"), which in fact means 5 MeV
the correction of nonlinearity produced by crosstalk from output of fle discriminator is different for muons and charge injection
correction function obtained form charge injection should be scaled according to thershold ratio of muons to charge injection
the online algorithm of fledac characterization and threshold setting should be improved
we need a procedure for threshold measurement to be implemented as a new calibration algorithm
