Physics Simulations for KM3NeT Giulia Vannoni representing the KM3NeT Consortium

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Physics Simulations for KM3NeTGiulia
Vannonirepresenting the KM3NeT Consortium
(CEA Saclay, Irfu)
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Optimisation Parameter Space
Optical Modules
Detection units
Requirements, based on 1 km3 detector Angular
res. 0.1? _at_ E ? 30 TeV corresponds to an
overall single photon time resolution lt 2ns.
Layout
Site(depth, water properties)
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
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
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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).
Strings with single OMs hosting multiPMTs
Strings with grouped OMs (based on Antares
design).
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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 lt E lt 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 ? 20 45m ? 30 30m
optimum Dl 13020m 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
no. storeys per tower (fixed)
DU distance
Optimum reached around DU distance 150 ? 180 m
and storey distance 30 ? 50 m.
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Bar Effect
Tower design, 100 GeV lt Em lt1 TeV
Muon hits on 2 towers
Muon hits on 1 tower
15 m bar
q qrec
j jrec
1 m bar
?jjrec? lt3 ? 19 ?jjrec? lt3 ? 4
?qqrec? lt3 ? 40 ?qqrec? lt3 ? 31
?qqrec? lt3 ? 39 ?qqrec? lt3 ? 37
?jjrec? lt3 ? 25 ?jjrec? lt3 ? 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.

90?
From single OM to pairs on a single arm to
preserve time coincidences.
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Bar Effect
Illustration on Antares-like design

• 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.

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Point Source Limit
For this plot 127 towers, 6m bars, 180m
distance, 20 storeys at 40m, 6x8 OMs.
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)

510-9GeVcm-2s-1sr-1
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Numbers of Lines