1. Optimization of tower design
R. Coniglione, C. Distefano and P. Sapienza
Istituto Nazionale di Fisica Nucleare- Laboratori Nazionali del Sud
First estimates of sensitivity to point-like sources for different detector lay-out based on tower structures (ONE project)
R. Coniglione, Paris February ‘09

2. Sensitivity calculation
The sensitivity is calculated following the Feldman and Cousins method.
We minimize the average flux limit:
optimizing the following three parameters:
L -> likelihood of reconstructed track
Nfit -> number of hits before the last fit (very rough energy estimator)
Rbin ->search cone radius.
R. Coniglione, Paris February ‘09

3. Codes & simulation inputs
Code > ANTARES codes with Aart strategy modified by LNS
Water -> Labs: ANTARES normalized at 60m or NEMO
Lscat : ANTARES codes
Opt. bkg -> 60 kHz distributed on ± 1 ms window
Trigger -> (local coincidence) OR (high amplitude hit p.e.>2.5p.e.)
Point source -> d = -60° a = -1.8, -2.0, -2.2
atmospheric -> from 102 to 108 GeV and 4p - Bartol flux
m atmospheric -> NO
R. Coniglione, Paris February ‘09

4. Parameters to be optimized
Detector lay-out
Geometry parameters
Number of structures -> 91 towers - hexagon
Number of storeys/structure -> 20
Bar length ->10m
PMT -> 10” 35%QE – Genova fit1 acceptance
Number of PMT/floor -> 6 (2 at bar edges down-horizontally looking) +2 at the center of the bar down-looking at 45°
Parameters to be optimized
Distance between floors -> 30m or 40m
Distance between towers -> 130m, 150m and 180m
Number of PMT/floor > 4 or 6
PMT quantum efficiency -> 23% or 35%
R. Coniglione, Paris February ‘09

5. … as a function of the distance between floors
Sensitivity (GeV s-1 cm-2) to a point like source - 1 year
Spectral index
Distance between towers
Bar length
Distance between floors
Number of floors
-1.8
-2.0
-2.2
150 _ *
150 _ *
*Absorption length ANTARES normalized at 60 m
-1.8
-2.2
Same number of PMT & structures
 ~15% better sensitivity for 40m floor distance
R. Coniglione, Paris February ‘09

6. Source spectrum Source a = -2 Source a = -2.2 Source a = -1.8
Expected n in an angular bin of 1° around a source with d=-60° in one year
x 0.2
Number of expected n / year
Source a = -2
Source a = -2.2
Source a = -1.8
Atmospheric n
source normalized at
E-2 dN/dE = 10-7 cm-2 GeV s-1
R. Coniglione, Paris February ‘09

7. … as a function of the distance between floors
Neutrino effective areas
Distance between towers
Bar length
Distance between floors
Number of floors
quality cuts
150_204010(cut L=-5.8)
150_203010(cut L=-5.5)
150_204010
Ratio
150_203010
*Absorption length ANTARES normalized at 60 m
Same number of PMT & structures
R. Coniglione, Paris February ‘09

8. … as a function of the distance between towers
Bar length
Distance between floors
Number of floors
Neutrino effective areas
quality cuts
 130_ (cut L=-5.8)
 150_ (cut L=-5.8)
 180_ (cut L=-5.2)
Ratio with respect
to 130_204010
ratio
Same number of PMT & structures
*Absorption length NEMO
log10 En (GeV)
R. Coniglione, Paris February ‘09

9. … as a function of the distance between towers
Sensitivity (GeV s-1 cm-2) to a point like source - 1 year
Spectral index
Distance between towers
Bar length
Distance between floors
Number of floors
-1.8
-2.0
-2.2
130 _ *
150 _ *
180 _ *
*Absorption length NEMO
150m better than 130m (~10%)
Very little differences in sensitivity between m
R. Coniglione, Paris February ‘09

10. … as a function of distance between towers considerations for high energy neutrino detection En>100 TeV
High energy effective neutrino areas
No quality cuts applied
En>100 TeV
Distance between towers
Bar length
Distancebetween floors
Number of floors
Aeff (m2)
130_204010
150_204010
180_204010
cos(qn)=[-0.5,0.5] & En>100 TeV
cos(qn)
Aeff (m2)
130_204010
368
150_204010
425
180_204010
483
R. Coniglione, Paris February ‘09

11. … as a function of the number of PMT/floor
Neutrino effective areas
Distance between towers
Bar length
Distance between floors
Number of floors
quality cuts
150_204010
 4 PMT/floor(cut L=-5.8)
 6 PMT/floor(cut L=-5.8)
6 PMT/floor
Ratio
4 PMT/floor
ratio
*Absorption length NEMO
6PMT/floor -> PMTs
4 PMT/floor -> 7280 PMTs
R. Coniglione, Paris February ‘09

12. … as a function of the number of PMT/floor
Sensitivity (GeV s-1 cm-2) to a point like source - 1 year
Spectral index
Distance between towers
Bar length
Distance between floors
Number of floors
-1.8
-2.
-2.2
150_204010*
4 PMT/floor
6 PMT/floor
 Little differences in sensitivity
6 PMT/floor
10” 35% QE
4 PMT/floor
10” 35% QE or
R. Coniglione, Paris February ‘09

13. … as a function of PMT quantum efficiency
Neutrino effective areas
13x13 towers 18floors*
Quality cuts applied
 max 45% /max 23%
 max 35% /max 23%
QE max 23%
 QE max 35%
 QE max 45%
▬ ref det with QE 33%
*See R. Coniglione VLVnT08
R. Coniglione, Paris February ‘09

14. … as a function of PMT quantum efficiency
Sensitivity (GeV s-1 cm-2) to a point like source - 1 year
Distance between towers
Bar length
Distance between floors
Number of floors
Spectral index
-1.8
-2.0
-2.2
180 _ *
35% QE (60kHz)
180_ *
23% QE (40kHz)
Better sensitivity for 35%QE
…but which is the effect of background?
R. Coniglione, Paris February ‘09

15. … effect of the optical background
Sensitivity to point like source a= year
60kHz
45 kHz
0.1 kHz
180_204010
4PMT/floor
(L=-6.2, Nfit=20,
Rbin=0.5)
(L=-9.8, Nfit=22,
(L=-9.8, Nfit=20,
R. Coniglione, Paris February ‘09

16. … one more “exercise” Sensitivity No cuts on Nfit but on En
Sensitivity to point like source a= year
Sensitivity
(GeV cm-2 s-1)
(L=-6.2, Nfit=20,
Rbin=0.5)
(L=-6.1, log10(Ev)=3.5,
Geometry 180_ with 4PMT/floor
No cuts on Nfit but on En
R. Coniglione, Paris February ‘09

17. cost/benefit analysis needed
Summary
Same detector components
Floor distance 30m-40m->better sensitivity (~15%)for 40m
Distance between towers 130m-150m-180m -> slightly better sensitivity at 150m and higher effective areas at high energy
Different number of PMTs or QE PMTs
6/4 PMT/floor ->higher effective areas at low energy but (< 10%) better sensitivity
QE 23% or 35% -> higher effective areas at low energy for 35% QE – sligthly better sensitivity (< 10%)
filtering procedure for background hits rejection to be improved
cost/benefit analysis needed
R. Coniglione, Paris February ‘09

18. Summary
THE END
R. Coniglione, Paris February ‘09