CEA DSM Irfu

Physics Simulations for KM3NeT

Giulia Vannonirepresenting the KM3NeT Consortium

(CEA Saclay, Irfu)

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CEA DSM Irfu

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.

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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

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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

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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

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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

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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)

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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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CEA DSM Irfu

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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CEA DSM Irfu

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]

CEA DSM Irfu

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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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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