SETUP OF SCINTILLATORS WITH Mtec IN PLACE

Posted to elog by Glen Marshall, 17 Oct 2004:
http://midtwist.triumf.ca:8081/EL/041017.306?exp=twist

This is a belated record of setting up the Mtec, M, and PU scintillators.

The Mtec HV is set at 1600V. The response is different from August since I
added a 50 ohm terminator in the anode clip connector of the PMT base, which
changes the gain vs HV but also makes the pulse shape nicer. 1600V with a 30
mV discriminator seems to work for the PACT adc pulse height measurement,
for muons and pions up to 50 MeV/c, with little efficiency for positrons.
Mtec is 1/16" scintillator (about 1.5 mm), which will completely stop
surface muons. Only the TEC, a 0.005" (0.125 mm) mylar vacuum window, and
some very thin (0.025 mm?) wrapping slow the muons before they enter Mtec,
so it measures several MeV, thus the big difference with positron signals.
We have seen evidence that for pions which stop in Mtec, at the right
momentum, two pulse heights are clear, one of which I think includes some
energy from the muon after the pion decays (early decays still within the
PACT gate).

Recall that Mtec uses the M1 scintillator signal cable, so M1 was initially
left off. I put nominal voltage (previous elogs, paper on rack next to
LeCroy HV supply) on M2 and all four PU scintillators, looking for signals
on the scope but not doing any other tweaking. However, M2 gave no signal.
This needs to be checked.

I think the M2 problem is with the base or PMT; could not see any noise
whatsoever at nominal HV. I swapped cables to M1, which did show noise
signals as it should, so it is not cables or HV channel.

To allow the time difference of Mtec and M to be estimated, I left the M2
signal cable attached to M1, and M1 HV on, so that the M2 TDC has been
recording M1, whose time difference with the M1 TDC (which is now Mtec)
should tell us the difference. Have not looked at the TDC histograms, though.

Main issue: M2 problem needs to be fixed. If necessary, we may have to steal
a base/PMT from the DS scintillator system, and make up something else for DS.