**Physics Laboratory** School of Science and Technology Hellenic Open University Apostolos Tsirigotis Simulation Studies of km3 Architectures KM3NeT Collaboration Meeting 16-18 April 2007, Pylos, Greece The project is co-funded by the European Social Fund & National Resources EPEAEK-II (PYTHAGORAS)

**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

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

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

**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 • For the simulation of the neutrino interaction events PYTHIA is used • All the interactions and transportations of the secondary particles are simulated (Multiple track simulation) • Fast simulation techniques and EM shower parameterization • Optical Noise and PMT response simulation • Visualization of detector components, particle tracks and hits

**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 • Χ2fit without taking into account the charge (number of photons) • Kalman Filter • (novel application in this area)

**MultiPMT Optical Module (NIKHEF Design)** 20 x 3” PMTs (Photonis XP53X2) in each 17” Optical Module Outside view Inside View Single PMT Rate (dark current + K40) ~ 4kHz 120 Hz Double coincidence rate per OM (20 ns window) 6 Noise Hits per 6μsec window (9600 MultiPMT OMs in a KM3 Grid)

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

**Input** Trigger Time (ns)

**IceCube Geometry: 9600 OMs looking up & down in a hexagonal** grid. 80 Strings, 60 storeys each. 17m between storeys 125 meters

**Nestor Geometry with 37 Towers in a hexagonal formation.** Each tower has 21 floors 120 meters in diameter, with 50 meters between floors. 7 Storeys per floor 2 MultiPMT OMs per Storey, one looking down the other up 10878 Optical Modules Nestor Geometry with 19 Towers in a hexagonal formation. Each tower has 21 floors 120 meters in diameter, with 50 meters between floors. 13 Storeys per floor 2 MultiPMT OMs per Storey, one looking down the other up 10374 Optical Modules y(m) y(m) 300m 200m x(m) x(m)

**Prefit and Filtering Efficiency (1 TeV Muons, isotropic** flux, IceCube Geometry, 9600 OMs) Events with number of hits (noise+signal) >4 Events passing the prefit criteria Noise Noise Signal Signal Number of Active OMs Number of Active OMs Percentage of noise hits after filtering Events passing the prefit criteria after background filtering Noise Signal Number of Active OMs percentage

**Prefit Resolution** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) Space angle difference (degrees) σ = 0.47 degrees Zenith angle difference (degrees)

**Fit Resolution** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) σ=0.085 degrees σ = 0.07 degrees Azimuth angle difference (degrees) Zenith angle difference (degrees)

**Fit Resolution** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) median 0.1 degrees Space angle difference (degrees)

**Goodness of fit** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) σ = 1.05 theta pool (θsim – θrec)/σrecv σ = 1.01 phi pool (φsim – φrec)/σrec

**Goodness of fit** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) Χ2probability cut

**Resolution Estimation** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) Number of active OMs in one subdetector • Divide the detector in 2 identical sub detectors • Reconstruct the muon separately for each sub detector • Compare the 2 reconstructed track directions Number of active OMs in whole detector

**Resolution Estimation** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) σ=0.14 degrees Zenith angle difference between the 2 reconstructed directions (degrees) Space angle difference between the 2 reconstructed directions (degrees)

**Resolution Estimation** (1 TeV Muons, isotropic flux, IceCube Geometry, 9600 OMs) σ=0.094 degrees σ=0.07 degrees Zenith angle difference of subdetectors (degrees) Zenith angle difference of whole detector (degrees)

**Comparison of three different Geometries** Atmospheric (CC) neutrino events (1-10TeV) Space angle difference between neutrino and muon track median 0.7 degrees 1 TeV muon neutrino degrees median 0.3 degrees 5 TeV muon neutrino degrees

**Comparison of three different Geometries** Atmospheric (CC) neutrino events (1-10TeV) Reconstruction Efficiency Muon Energy (GeV) IceCube Geometry (Only Down looking OMs) IceCube Geometry (Up-Down looking OMs) Nestor Geometry (Up Down looking OMs) All three geometries have the same resolution (~0.07 degrees in zenith angle)

**Comparison of 4 different Detectors** Atmospheric (CC) neutrino events (100GeV-10TeV) Nestor Sparse Geometry (Up Down looking OMs) Muon effective area (m2) IceCube Geometry (Up-Down looking OMs) Nestor Dense Geometry (Up Down looking OMs) IceCube Geometry (Only Down looking OMs) Neutrino Energy (GeV)