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.

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

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…

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)

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)

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

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):

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

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

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.

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)

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

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

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

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)

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

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