physics simulations for km3net giulia vannoni representing the km3net consortium
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CEA DSM Irfu
Physics Simulations for KM3NeT
Giulia Vannonirepresenting the KM3NeT Consortium
(CEA Saclay, Irfu)
Giulia Vannoni – VLVnT09 1
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Optimisation Parameter Space
Detection units
LayoutSite(depth, water properties)
Reconstruction
Future step in the optimisation
Optical ModulesRequirements, based on 1 km3 detector:
Angular res. ≤ 0.1 @ E 30 TeV
corresponds to an overall single photon time resolution < 2ns.
Giulia Vannoni – VLVnT09 2
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Seabed Layout
Cube
Ring
Hexagon
Sharp corners worsen the reconstruction capability.
Uneven behaviour in different energy ranges (optimised below 1 TeV and above 100 TeV) for some of the different detector designs under study.
Chosen as common layout for optimisation and comparison of different detector options.Adopted in the following
km3 instrumented volume 100 – 200 DUs
1 km
Giulia Vannoni – VLVnT09 3
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31x3” PMTs (35% Q.E.) housed in a single 17” sphere.Time coincidences between hits in neighbouring PMTs of the same OM.
8” PMTs (35% Q.E.) housed in 13” spheres. In order to use time coincidences between hits (for optical background rejection) need to pair OMs.
Optical Modules
Giulia Vannoni – VLVnT09 4
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Towers with bars and 6 OMs per storey (based on
NEMO design).
Strings with single OMs hosting multiPMTs
Strings with grouped OMs (based on Antares
design).
Detection Units
Giulia Vannoni – VLVnT09 5
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Antares Monte Carlo chain, adapted for a km3-scale detector.
Atmospheric muons:
Mupage (MUon PArametric GEnerator) , fast parametric muon simulation (see Becherini et al., 2005).
Single muons and muon bundles.
Neutrinos (upward going):
102 GeV < E < 107 GeV.
Atmospheric: Bartol flux (~ E-3.7) (Agrawal et al., 1996).
Source neutrinos: point source mode in generation code or reweighting of direction.
Reweighting for spectral index.
Reconstruction: pre-fit steps and final likelihood minimisation with PDF tuned on Monte Carlo.
Monte Carlo Info
Giulia Vannoni – VLVnT09 6
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Optimisation Criteria
Note: Optimisation for source search between 1 TeV and 1 PeV.
(DM studies ongoing, not presented here)
Angular resolution
Requirement: ≤ 0.1 at 30 TeV. (median of the angular error between the reconstructed and MC muon track.
Tight quality cuts
or
Point source sensitivity
90% confidence limit (Feldman and Cousins method).
Model Rejection Factor minimisation → optimal cuts: - track quality cut
- search cone
- nhits (energy)
Giulia Vannoni – VLVnT09 7
CEA DSM Irfu Giulia Vannoni – VLVnT09
optimum: l ≈ 130±20m
independent of number and composition of strings.
optimum string density:
80-100 per km2
20 × 30m
20 × 45m
30 × 30m
20 × 30m
20 × 45m
30 × 30m
91 lines
154 lines
DU Density OptimisationAntares-like design: point-like source (E-2) sensitivity as a function of DU distance.
Optimum distance slightly changed by water properties.
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Muon angular resolution and neutrino effective area: quality cut applied (~0.1 at 30 TeV)
DU Density Optimisation
130_20_30_08180_20_50_10
bar length
storey distance
no. storeys per tower(fixed)DU distance
log10E (GeV)
Rati
o
18
0/1
30
Optimum reached around DU
distance 150 180 m and
storey distance 30 50 m.
Tower design: response as a function of DU distance.
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– rec – rec
–rec<3° 19%
–rec<3° 4%
–rec<3° 40%
–rec <3° 31%
Muon hits on 1 towerTower design, 100 GeV < E <1 TeV
“Bar Effect”
– rec – rec
15 m bar
1 m bar
Muon hits on 2 towers
–rec<3° 39%
–rec <3° 37%
–rec <3° 25%
–rec <3° 15%
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“Bar Effect”
Concept: 3D structure on single DU.
Two adjacent storeys in tower design.
Larger distances on single storey for Antares-like design.
From single OM to pairs on a single arm to preserve time coincidences.
90
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sensitivity gain for arms due to better angular resolution.
dependence on spectral index: gain 8% for soft spectrum (E-2.2), 5% for E-1.8 for 3m arms.
“Bar Effect”Illustration on Antares-like design:
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storey radius [m]
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Design DU optimum distance:
130-180 m, depending on details of the design and water properties.
Optimum DU length:
The higher the better (900-1000 m).
- Limited by technical feasibility? (→ preparatory phase)
DU: benefit from extended structure
Tri-dimensional structure with OMs distanced on a barred storey.
OMs:
pairs of OMs or multiPMTs, needed for optical background rejection.
Feasibility studies, prototype testing, cost…→ Preparatory phase
Giulia Vannoni – VLVnT09 13
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90% C.L. exclusion limit, spectrum E-2
Antares, 1 yr, unbinned IceCube80, 1 yr, binned (Aharens et al., 2004)
IceCube80, 1 yr, unbinned (Abbasi et al., 2009)
1 yr, binned
3 yr, binned
Point Source LimitFor this plot: 127 towers, 6m bars, 180m distance, 20 storeys at 40m, 6x8” OMs.
sinGalactic centre
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Diffuse Flux E-2 diffuse flux;
neutrinos and antineutrinos;
cut at 10 above horizon, 1 year;
neutrino energy smearing: resolution 0.5 (log10E)
5×10-9GeVcm-2s-1sr-1
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Numbers of Lines
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