Transcript Document

Physics Simulations for
KM3NeT
Giulia Vannoni
representing the KM3NeT Consortium
(CEA Saclay, Irfu)
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Optimisation Parameter Space
Optical Modules
Requirements, based on 1 km3
detector:
Detection units
Angular res. ≤ 0.1 @ E  30 TeV
corresponds to an overall single
photon time resolution < 2ns.
Site
(depth,
water properties)
Layout
Reconstruction
Future step in
the optimisation
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Seabed Layout
km3 instrumented volume  100 – 200 DUs
Sharp corners worsen the reconstruction capability.
1 km
Cube
Uneven behaviour in different energy ranges (optimised below 1
TeV and above 100 TeV) for some of the different detector
designs under study.
Ring
Chosen as common layout for optimisation and comparison of
different detector options.
Adopted in the following
Hexagon
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Optical Modules
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.
31x3” PMTs (35% Q.E.) housed in
a single 17” sphere.
Time coincidences between hits in
neighbouring PMTs of the same
OM.
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Detection Units
Towers with bars and 6
OMs per storey (based
on NEMO design).
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Strings with grouped OMs
(based on Antares
design).
Strings with single
OMs hosting
multiPMTs
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Monte Carlo Info
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.
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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: Da ≤ 0.1 at 30 TeV. (Da : 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)
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DU Density Optimisation
Antares-like design: point-like source (E-2) sensitivity as a function of DU distance.
 20 × 30m
91 lines
 20 × 45m
 30 × 30m
154 lines
optimum: Dl ≈ 130±20m
independent of number and
composition of strings.
optimum string density:
80-100 per km2
Optimum distance slightly changed by water properties.
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DU Density Optimisation
Tower design: response as a function of DU distance.
Muon angular resolution and neutrino effective area: quality cut applied (~0.1 at
30 TeV)
130_20_30_08
180_20_50_10
bar length
storey distance
Ratio 180/130
DU distance
no. storeys per tower
(fixed)
Optimum reached around DU
distance 150  180 m and
storey distance 30  50 m.
log10En (GeV)
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“Bar Effect”
Tower design, 100 GeV < Em <1 TeV
Muon hits on 2 towers
Muon hits on 1 tower
15 m bar
q – qrec
j – jrec
q – qrec
j – jrec
1 m bar
q–qrec <3°  40% j–jrec <3°  19%
q–qrec <3°  31% j–jrec <3°  4%
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q–qrec <3°  39% j–jrec <3°  25%
q–qrec <3°  37% j–jrec <3°  15%
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“Bar Effect”
Concept: 3D structure on single DU.
Two adjacent storeys in tower design.
90
Larger distances on single storey for Antareslike design.
From single OM to pairs on a single arm to
preserve time coincidences.
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“Bar Effect”
Illustration on Antares-like design:
storey radius [m]
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.
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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
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Point Source Limit
For this plot: 127 towers, 6m bars, 180m distance, 20 storeys at 40m, 6x8” OMs.
90% C.L. exclusion limit, spectrum E-2
Antares, 1 yr, unbinned
IceCube80, 1 yr,
binned (Aharens et
al., 2004)
1 yr, binned
IceCube80, 1 yr,
unbinned (Abbasi
et al., 2009)
3 yr, binned
sind
Galactic 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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