1. Freeze-In and Hole Ice Studies with Flashers
Michelangelo D’Agostino
UC Berkeley
Baton Rouge Collaboration Meeting
April 9, 2006

2. Outline description of the analysis
a first quick-and-dirty look at the data: can we see the freeze-in and transition to hole ice in string 39 data?
comparison to simulation
future work
more “exploration” than “verification”

3. Analysis
for string 39, a set of flasher runs was taken just after deployment, in water, and repeated at various later times
data for DOM’s 4, 12, 18, 19, 36, 40, 42, 48, 54, and 55
two types:
INTRA-TDEP—flash the 6 horizontal and 6 tilted LED’s separately
INTRA-1LED—flash each of the 12 LED’s individually
also wet string flashing to frozen string receiving and vice versa (haven’t looked at these)

4. Analysis
as a first test, let’s look at the average calibrated ATWD waveform in the DOM above the flasher (Chris Wendt’s idea)
for each waveform, feature extract the leading edge
line up all the leading edges in the same bin and take an average of 500
this method throws out any relative timing information, which might also be useful

5. Results
note the scales: many fewer PE’s for horizontal LED’s, as expected
6 Tilted LED’s Only
6 Horizontal LED’s Only
DOM 39-18
Jan. 5 (black) at 4 C vs. Feb. 10 at -25  C (green)

6. Results statistically significant
6 Tilted LED’s Only
6 Horizontal LED’s Only
statistically significant
general trend: fewer PE’s for tilted LED’s and same or more PE’s for horizontal LED’s
DOM 39-18

7. Integrated Charge
variation with depth is an ice properties effect (cf. simulation)
6 Tilted LED’s Only
for all DOM’s but 1, the in ice data shows lower charge, as we could see from the waveforms

8. Integrated Charge 6 Horizontal LED’s Only
less of a clear trend; for quite a few, later data shows more charge

9. Integrated Charge
Is this an effect of hole ice, or of something systematic? Possibly a temperature effect?

10. Single LED DOM 39-19 Horizontal LED’s Vertical LED’s Pair 1 Pair 2

11. Horizontal LED’s
Vertical LED’s
Pair 1
Pair 2
Pair 3
Pair 4
Pair 5
Pair 6
-variation depends on azimuthal angle around the DOM
-vertical and horizontal LED’s at the same azimuth show a similar level of variation between water and ice
-smoking gun: this is not a systematic or temperature effect on the PMT or electronics; it’s a physical difference between the water and the ice

12. Photonics Simulations
hacked photonics to include hole ice scattering around a 12 LED flasher board source
includes the best understanding we have of the fully layered ice
get the bare probability distribution as a function of time (no PMT or waveform simulation); since the data has very many PE, it should be decently close to the PDF
2 sets:
1 with no hole ice scattering
1 with a 30 cm diameter cylinder of 10 cm, 50 cm, and 100 cm effective scattering length hole ice

13. Photonics Simulations
6 Tilted LED’s Only
6 Horizontal LED’s Only
DOM 18
less charge with hole ice
same or more charge with hole ice

14. Photonics Simulations
6 Tilted LED’s Only
hole ice shows less charge
variation with depth like in the data

15. Photonics Simulations
6 Horizontal LED’s Only
hole ice shows same or more charge, quite like the data

16. Interpretations
seems to be a strong case for saying that we can see the freeze-in transition to hole ice: data is consistent with highly scattering hole ice
hole ice has 2 effects:
scatters light out of the tilted LED beams and results in less charge
increases the acceptance of the receiving DOM for the horizontal LED’s resulting in the same or more charge
the hole ice scattering is not azimuthally symmetric

17. Future Work look at waveforms in other DOM’s up and down the string
FADC waveforms?
need full detector Monte Carlo to make more realistic comparisons
the ratio of charge for tilted LED runs to charge for horizontal LED runs varies with the hole ice scattering length in the simulation (i.e. hole ice isotropizes the light output); use this to say something more quantitative

18. Results
6 Tilted LED’s Only
6 Horizontal LED’s Only
Jan. 5 at 5  C (black) vs. Jan. 13 at -21 C (blue) vs.
Feb. 10 at -27  C (green)
DOM 39-12

19. Results
6 Tilted LED’s Only
6 Horizontal LED’s Only
DOM 39-36

20. Results
6 Tilted LED’s Only
6 Horizontal LED’s Only
DOM 39-42

21. Results
6 Tilted LED’s Only
6 Horizontal LED’s Only
DOM 39-48

22. Results
6 Tilted LED’s Only
6 Horizontal LED’s Only
Jan. 5 at 3  C (black) vs. Jan. 13 at -1  C (blue) vs. Feb. 10 at -11  C (green)
DOM 39-54