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Apostolos Tsirigotis KM3NeT Design Study: Detector Architecture, Event Filtering and Reconstruction Algorithms XXV Workshop on recent developments in High Energy Physics & Cosmology, 28-31/3/2007,NTUA, Greece The project is co-funded by the European Social Fund & National Resources EPEAEK-II (PYTHAGORAS)

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The Underwater Neutrino Telescope software chain Generation of atmospheric muons and neutrino events Detailed detector simulation (GEANT4) Optical noise and PMT response simulation Prefit & Filtering Algorithms Muon reconstruction

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Event Generation – Flux Parameterization Neutrino Interaction Events Atmospheric Muon Generation (2 Parameterization Models) μ Atmospheric Neutrinos 1 Conventional (no prompt) Model ν ν Cosmic Neutrinos 5 diffuse flux models It is going to be updated Earth

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Event Generation Shadowing of neutrinos by Earth Survival probability Nadir Angle Probability of a ν μ to cross Earth Neutrino Interaction Probability in the active volume of the detector

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Detector Simulation Any detector geometry can be described in a very effective way Use of Geomery Description Markup Language (GDML, version 2.5.0) software package All the relevant physics processes are included in the simulation All the interactions and transportations of the secondary particles are simulated (Multiple track simulation) For the simulation of the neutrino interaction events PYTHIA is used Fast simulation techniques and EM shower parameterization Optical Noise and PMT response simulation Visualization of detector components, particle tracks and hits

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Filtering, Prefit and Reconstruction Algorithms Local (storey) Coincidence Applicable only when there are more than one PMT looking towards the same hemisphere Global clustering (causality) filter 50% Background rejection while all signal hits survive (1km3 Grid & 1 TeV muon) Local clustering (causality) filter 75% Background rejection while 90% of signal hits survive (1km3 Grid & 1 TeV muon) Prefit and Filtering based on clustering of candidate track segments Χ 2 fit without taking into account the charge (number of photons) Kalman Filter (novel application in this area)

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MultiPMT Optical Module (NIKHEF Design) Outside viewInside View 20 x 3 PMTs (Photonis XP53X2) in each 17 Optical Module Single PMT Rate (dark current + K40) ~ 4kHz 120 Hz Double coincidence rate per OM (20 ns window) 3.5 Noise Hits per 6μsec window (4800 MultiPMT OMs in a KM3 Grid)

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Optical Module Readout Use a time-over-threshold (TOT) system (multiple thresholds) Estimation of charge from the time-over-thresholds + multiplicity

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Time (ns) Trigger Input

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125 meters IceCube Geometry: 4800 OMs looking down in a hexagonal grid. 80 Strings, 60 OMs each. 17m between OMs

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Prefit and Filtering Efficiency (1 TeV Muons, uniform flux, IceCube Geometry) Events with number of hits (noise+signal) >4 Number of Active OMs Events passing the clustering criteria Noise Signal Noise Signal Number of Active OMs Signal Noise Number of Active OMs Events passing the clustering criteria after background filtering

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Prefit Resolution Space angle difference (degrees) Zenith angle difference (degrees) σ = 0.47 degrees (1 TeV Muons, uniform flux, IceCube Geometry)

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Fit Resolution(1 TeV Muons, uniform flux, IceCube Geometry) Space angle difference (degrees) Zenith angle difference (degrees) σ = 0.1 degrees

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Fit Resolution(1 TeV Muons, uniform flux, IceCube Geometry) pool (θ sim – θ rec )/σ rec σ = 1.05 Azimuth angle difference (degrees) σ = 0.14 degrees

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Comparison of three different Geometries IceCube Geometry (4800 down looking MultiPMT OMs) IceCube Geometry with 2 MultiPMT OMs per Storey, one looking down the other up Nestor Geometry with 37 Towers in a hexagonal formation. Each tower has 21 floors, with 50 meters between floors. 2 MultiPMT OMs per Storey, one looking down the other up x(m) y(m)

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IceCube Geometry (Down looking OMs) IceCube Geometry (Up- Down looking OMs) Nestor Geometry (Up Down looking OMs) Muon Energy (GeV) Atmospheric (CC) neutrino events (1-10TeV)Comparison of three different Geometries σ=0.11 degrees σ=0.12 degrees Zenith angle difference (degrees)

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Atmospheric (CC) neutrino events (1-10TeV)Comparison of three different Geometries Space angle difference (degrees) Muon Energy (GeV) Reconstruction Efficiency IceCube Geometry (Down looking OMs) IceCube Geometry (Up- Down looking OMs) Nestor Geometry (Up Down looking OMs)

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