Goals of shift:
- analyze runs taken by Pete and Tavi during evening and night shifts;
- come up with a strategy for improving the TOF efficiencies;
- move the 4 working small paddles to the next group of test TOFs;
Effort:
- I analyzed runs 1584 and 1585 taken overnight - for 3 out of 4 positions
we did not get enough counts to measure anything (not only in the TOFs,
but also not even in the corresponding "sandwitch");
- for LTOF1 the "efficiency" was ridiculously low - 70% (we know from
previous analysis by Chi and myself that the number should be at least
91%);
- John suggested to raise the voltage on LTOF1, just to see if it is a
question of raising the HV;
- Raising voltages by 200 V on the LTOF#1 improved the "efficiency" - from
70% I saw earlier for overnight runs 1484 and 1485 to 85% for run 1589.
It is obviously not a voltage issue (or not only). 200 volts should make
it go through the ceiling!!
- I went back to analyzing runs 1584, 1585 (no change in voltage): I put
ADC cuts on the small paddle corresponding to LTOF#1 and the efficiency
was between 95-98%, depending on cut.
It is obvious we are getting a lot of accidentals with this method, due to
noise in the small paddles' and start counter's PMTs.
- Next I raised the thresholds on all of the small paddles to 41 mV and to
31 mV on the start counter; I left all others at 20 mV.
- I took run 1591; result: only 60 counts in the start counter (after
cutting on good events (TDC in between 0 and 4000). My conclusion was that
I raised the thresold too much on the start counter so I went back to 20
mV;
- I took runs 1592 and 1593. The second one just because I could not
believe the first: still very few events in the start counter, making it
impossible to see anything in the LTOF1 because of the required
coincidence! I DID NOT UNDERSTAND THIS!
- Before leaving, I suggested Pete to lower the thresholds again for the
small paddles, just to find the starting point again, and my theory was
that maybe by raising thresholds on the small paddles I was cutting slower
electrons, creating a timing problem (with the start counter)??? It was
past the end of the shift when I got to this "uncertain conclusion" so I
did not have time to investigate this further...
- Depending on what Pete finds by lowering the small paddles' thresholds
back to 20, he needs to decide how to best go about placing software cuts
that make sense, as it seems that we cannot get to 99% only by raising
voltages and playing with thresholds...
Conclusions:
- This will a long process, the setup does not allow for testing
all the TOFs (first one and last 2 TOFs are never reached by anything that
can be caught in the "sandwitch"); we can do probably a couple TOFs at a
time.
- I would say if we can demonstrate a few of them are over 95% with
meaningful software cuts, that's as good as it will ever get!
The DTF setup was much easier to handle and it took Pete and me more than
a month to get to 99%.
- Once we get around 95% with meaningful software cuts (without relying on
ADCs which are hard to distinguish) then we can raise the voltages on the
test TOFs to see if that improves it (with the same meaningful software
cuts).
Adrian
-------------------------------
Adrian Sindile
Research Assistant
Nuclear Physics Group
University of New Hampshire
phone: (603)862-1691
FAX: (603)862-2998
email: asindile@alberti.unh.edu
http://einstein.unh.edu/~adrian/
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:28 EST