1. Transversal calibration of Geiger Cells
Wire chamber electronics  ADC & TDC
Drift_time(ns) = (TDCmax – TDC(anode) × 20)
The drift time is also known as the anode time, ta
TDCFAST_MIN < TDCFAST < TDCFAST_MIN
TDCFAST_MAX = 307
TDCFAST_MIN = 220
Range of TDCFAST_MIN needs calibrating to ensure we are measuring as many Geiger hits as possible
Optimized value somewhere between 0 and 220
How to actually use TDC and get something physical out of it i.e. how to get the distance measurements to the anode from the drift time (which comes from these TDC’s)
V, I. Tretyak, Prague, Nov 24-26, 2004
Idea: if the value of TDCFAST_MIN decreases, the TDC_FAST distribution (aka TDCanode) is biased to lower values and from the above equation, the drift time increases, thereby increasing the distance travelled by the electron, and the effective size of the Geiger cell. As TDCFAST_MIN increases, the drift time decreases.

2. Geiger Cell Layout More layers Layer 3 Layer 2 Layer 1 e- Source Foil
But in actuality…

3. Geiger Cell Layout More layers Really an ‘octagonal’ structure:
Should really overlap
Layer 3
Layer 2
Layer 1
That’s one cell on its own that is hexagonal, the composite structure can be a little more complicated with overlapping e-
Source Foil
But software not sensitive to size of Geiger cells – it just knows TDC values…

4. Geiger Cell Layout More layers
TDC_FAST_MIN = 220  Too low and you MISS events
Layer 3
Layer 2
Layer 1
As far as the software is concerned, the geiger cells are circles, with a radius dictated by the value of TDC_FAST_MIN e-
Source Foil
Track detected by 2 cells (shaded)

5. Geiger Cell Layout More layers
TDC_FAST_MIN = 0  Too high and you DOUBLE COUNT events
Layer 3
Layer 2
Layer 1 e-
Source Foil
Track detected by 5 cells (shaded)

6. Number of events originating from layer N.
- Includes everything (1 tracks, 2 tracks, etc events)
- Just one cut (on energy)
Observations:
- More events are detected early on
Kink (in between layers 4 and 5) due to high levels of radon background
Therefore:
USE PHASE 2 DATA TO ELIMINATE BACKGROUND (ALS0 VICTOR’S SUGGESTION)
USE HIGH ENERGY ELECTRONS > 2MeV
Betabeta_2533: Nov 05
Betabeta_4376: Sep 03
Phase 1 data
Phase 2 data
TDCFAST_MIN = 220
Phase 1 data known for having more background than phase 2 data

7. Number of HIGH ENERGY events originating from layer N.
Still a peak
Probably best to initially focus on first block of geiger cells (layers 1-4)
Next: just vary TDCFAST_MIN for all layers (equally) and see what impact it has
on the total number of tracks detected per run (this is layer independent):

8. Variation of the mean number of tracks with TDCFAST_MIN
Phase 1
For each and every event look at the mean number of tracks per event
First observation (see last few pages): you expect the number of n-track events to decrease, peaking at ~ 1, so this mean of ~ 1.2 makes sense
This mean is increasing with –TDCFAST_MIN (past 1) so we have more 2,3,4 … track events being registered( thus pushing the mean to higher values)
Also expect more 1 track events to pull back the mean but there are more events with 1 track so overall mean will be higher than 1
These tiny fluctuations not due to random error caused by reconstruction phase
TDC
FAST_MIN
280
260
240
220
200
180
160
140
120
100 80 60 40 20 %
(220)
64.7
87.7
96.8
100.0
100.8
101.4
101.8
102.0
102.3
102.5
102.7
102.8
102.9

9. However, these numbers should not be used to calibrate TDCFAST_MIN as it looks at all events (no cuts) i.e. it looks at everything that NEMO can through at it and averages this mess – which isn’t wise!
This is just to give an indication as to what varying TDCFAST_MIN can do

10. Variation of number of selected events (past cuts) with TDCFAST_MIN
Phase 1
Although this is the number of selected events, the cuts ensure that this is equal to the number of tracks (no averaging nonsense now)
CUTS APPLIED
NOW FINALLY APPLY SOME CUTS
Nscin = 1
Ntra = 1
Emin = 2MeV
Charge < 0
Assoc
- Distribution going in the right direction, but not really flattening off (too many fluctuations)
- Doesn’t appear to give us the necessary precision to calibrate TDCFAST_MIN
This graph is much more meaningful as it doesn’t average over everything, instead just what we need.

11. Origin of tracks: in terms of layer
CUTS APPLIED
Phase 1
__ Total
__ Layer 1
__ Layer 2
__ Layer 3
__ Layer 4
__ Layer 5
__ Layer 6
Note: there are no events that originate from the 7th, 8th and 9th layers (such events are not relevant to NEMO)

12. Close up: CUTS APPLIED Phase 1 Layer 1 Layer 2 Layer 3 Layer 4 Layer 5

13. Variation of number of selected events (past cuts) with TDCFAST_MIN
Phase 2
CUTS APPLIED

14. Origin of tracks: in terms of layer
CUTS APPLIED
Phase 2

15. Close up: CUTS APPLIED Phase 2
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
NOTE: if TDC value > 220 (i.e. smaller distance), it should have fewer events (but not always – it depends on how low you make it)
If TDC value < 220 (i.e. greater distance, it need not have more events but MUST NOT have fewer)

16. Variation of the number of ‘geiger cells hits’ with TDCFAST_MIN
CUTS APPLIED
Variation of the number of ‘geiger cells hits’ with TDCFAST_MIN
Phase 2
__ all hits
__ non associated hits
__ hits associated with first track

17. Summary and what next: - NEMO’s current TDC calibration good
- Can expect a 3% increase in number of tracks (globally)
- Do not want to calibrate all layers (too much background in between gaps?)
Repeat for
(i) crossing electron
(ii) change TDC_FAST_MIN for each layer