Minutes of the forward endcap EMC SeeVogh meeting, 31st of August 2015, 14:00-15:00

Presence:

• Basel: Werner
• Bochum: Claudius, Fritz-Herbert, Miriam, Patrick, Tobias H., Tobias T., Tom, Matthias, Stephan
• Bonn: Christoph
• Groningen: excused
• Uppsala: -
• GSI: -

Discussion of VPTT preamp gain determination:

• Recent Bonn cosmics measurements and last year's Bonn beamtime data give inconsistent results of what gain the preamps should have in order to optimal cover the dynamic range
• If ommitting the origin in the "preamp output vs. deposited energy"-curve linear fit the data become consistent resulting in an preamp output offset of about 80 mV. We judge this as an accidental, unphysical consistence.
• We will check again whether the nonlinearity of the shaper modules used in Bonn requieres an additional correction of the beam time data
• May there also be an effect of 'different pulse shapes' for high and low energetic showers as reported in the past (Myroslav?)
• VPTT preamp production can not be started until we definitely know what gain regime we need for the preamps
• 1.5 kV voltage divider PCBs for all PANDA VPTTs are ready and will be delivered from Basel so we can start mounting them to the tube bases
• Even though we do not know the necessary absolute gain of the VPTT preamps we can already derive form the VPTT gain distribution by what amount the different gain ranges should differ: O(10%)
• This is the same range the tolerance of the gain determining capacitors is stated. However, measurements show, that within a lot the tolerance is less, so building (three) different types of preamps is still forseen. Gain measurements of final preamps will be done anyway...

APD preamps:

• The same uncertainty in gain determination also holds for APD preamps, however, dominating problem here is the susceptibility to oscillation
• We tested different versions (different gain) for susceptibilty to oscillation. Unfortunately we could not see any oscillation, not even on preamps showing this in the past (extreme dependency of the phenomenon on the experimental setup)
• All different preamp versions show ringing (no oscillation) in rising edge of output pulse under certain experimental cicumstences with the typical oscillation frequency of ~250-300 MHz
• In order to go on building a new APD unit we decided for 32 pieces with 1.8 pF gain determinating capacitor to be build by Basel. This is the version a little higher in gain (hence a little more stable) as the one we observed oscillating in the past...

Meeting schedule:

• We decided to skip the next Forward Endcap SeeVogh meeting time slot Monday immediately after the GSI meeting and go on with this series on September 28th without any shifting of time slots.