Studies of the sensitivity to point-like sources for a flexible-tower geometries for KM3NeT

1. Studies of the sensitivity to point-like sources for a flexible-tower geometries for KM3NeT R. Coniglione C. Distefano and P. Sapienza Istituto Nazionale di Fisica Nucleare- Laboratori Nazionali del Sud for the KM3NeT consortium R. Coniglione, VLVnT09, Athens 13.16 october ‘09

2. Sensitivity to point-like sources • The main physics objective of the KM3NeT consortium is the detection of high energy neutrino fluxes from point-like sources. • Optimization work has been performed since the 2006 in order to find the best detector geometry which is a compromise between performance, technical feasibility and cost. The preferred geometry is based on three-dimensional structures. • Results based on MonteCarlo simulation of the sensitivity to point-like source will be presented. • as a function of source declination • as a function of the number of structures • as a function of the observation years R. Coniglione, VLVnT09, Athens 13.16 october ‘09

3. Detector lay-out Geometry parameters Number of structures -> 127 towers - hexagon Number of storeys/structure -> 20 PMT -> 8” 35%QE Number of PMT/floor -> 6 (2 at bar edges down-horizontally looking) + 2 at the center of the bar down-looking at 45° Distance between floors -> 40m Distance between towers -> 180m R. Coniglione, VLVnT09, Athens 13.16 october ‘09

4. The Monte Carlo codes&inputs • ANTARES codes modified for km3 detectors + modifications for large detector • Particles generators • n generator (all flavours), CC+NC interaction. In simulation: nm + nm & CC • atmospheric neutrinos: several prescriptions in the code; prompt n taken into account. In simulation: Bartol + RQPM-high prescription • Muon generation with MUPAGE: No atmospheric muons in these simulations • Detector response • Detector geometry • Light generation and propagation in water ->absorption and scattering taken into account. Simulation input labs=70 m@450nmand lscat= 50 m@450nm • PMT response (photocade area & quantum efficiency + angular acceptance + total efficiency… ) in the simulation 8-inch PMT with 35%QE • optical background randomly distributed around the event time window. Simulation input47kHz and ±1ms time window • Track reconstruction • Based on PDF maximization • Trigger based on local coincidences to reject hits due to optical background R. Coniglione, VLVnT09, Athens 13.16 october ‘09

5. Sensitivity calculation How to identify few events from source amongst large number of background events ? -> statistical approaches Two methods: Binned – analyze the fluctuations on the number of events detected inside a cone. The search of an excess due to events from a source is performed assuming Poisson distribution Unbinned – the expected density distributions of signal and background are described by statistical functions and a likelihood is maximized. The binned method is used -> Feldman and Cousins approach with the minimization of the Model Rejection Factor -> cuts on L (track reconstruction quality),nhit (related to the muon energy),Rbin (radius of the cone around the source). m90is the average maximum limit of background fluctuation at 90% of confidence level observed after hypothetical repetition of an experiment with an expected background and no true signal. • Sensitivity depends on: • Neutrino spectrum & source extension • Effective neutrino area -> detector response • Source declination -> visibility • Oservation years R. Coniglione, VLVnT09, Athens 13.16 october ‘09

6. Effective area m N nm q X Il numero di eventi di segnale e di fondo si calcola a partire dall’area efficace: Earth Absorption Neutrino cross section nucleons per unit volume Median of the angle distribution between the generated and reconstructed muon Effective neutrino area QC applied Angle between neutrino and muons DWn-mgen R. Coniglione, VLVnT09, Athens 13.16 october ‘09

7. Source spectrum for point-like sources Expected n in an angular bin of 1° around a source with d=-60° source spectrum E-a normalized at Ea dN/dE = 10-8 cm-2 GeVa-1 s-1 Energy range of interest 3TeV-100TeV In order to reject atmospheric neutrino background cuts on L, Nhit, Rbin Lambda distribution Nhit distribution R. Coniglione, VLVnT09, Athens 13.16 october ‘09

8. Sensitivity to point like sources as a function of observation years Improvement in sensitivity decreases with the increasing of the observation time After 3 years is reduced by a factor 2.5 with respect to one year KM3NeT d = 60° spectrum  E-2 Ratio with respect to 1 year of observation time R. Coniglione, VLVnT09, Athens 13.16 october ‘09

9. Sensitivity to point-like sources as a function of the number of towers E-2 neutrino flux d=-60° 1 year of observation To improve the sensitivity by 20% from 127 towers to 168 towers (32% more towers) R. Coniglione, VLVnT09, Athens 13.16 october ‘09

10. Sensitivity to point like source as a function of the source declination for three years of observation time Neutrino spectrum E-2 From Aharens et al. Astr. Phys. (2004) – binned method Black lines IceCube sensitivity Red lines KM3NeT sensitivity From R. Abbasi et al. Astro-ph (2009) scaled – unbinned method Average value of sensitivity from R. Abbasi et al. Astro-ph (2009)  Observed Galactic source (SNR, unidentified, microquasar) declination - From F. Aharonian et al. Rep. Prog. Phys. (2008) and MILAGRO sources from Abdo et al. Astrophys. Jour. 658 L33-L36 (2007)  Galactic center declination R. Coniglione, VLVnT09, Athens 13.16 october ‘09

11. Source list from F. Aharonian et al. Rep. Prog. Phys. (2008)

12. Sensitivity vs declination behaviour analysis Sensitivity for 3 years of observation time Neutrino spectrum E-2 Visibility correction Sens(d=0°,T=3year) = sens(d=-60°,DT) DT is the fraction of time below the horizon KM3NeT d=60° corrected for the visibility KM3NeT sensitivity Flat behaviour of sensitivity vs declination for a large region of sind. Not to ascribe only to the visibility effect R. Coniglione, VLVnT09, Athens 13.16 october ‘09

13. Sensitivity vs declination Phi versus theta as a function of declination Below the horizon Mediterranean Sea latitude 36° Above the horizon Near the horizon the effect of Earth absorption is reduced for high energy neutrinos +50 +40 0 +20 -10 -20 -30 d=-40 -50 -60 -70 -80 R. Coniglione, VLVnT09, Athens 13.16 october ‘09

14. Sensitivity vs declination Effective neutrino areas as a function of declination Effective neutrino area for point-like sources (theta <96°) No quality cuts applied Values scaled for the visibility For E>30 TeV effect of Earth absorbtion visible Aeffn (m2) Aeffn (m2) • d = +40° • d = +20° • d = 0° • = -20° • = -60° • d = +40° • d = +20° • d = 0° • = -20° • = -60° log10 En (GeV) log10 En (GeV) Balance between Earth absorption and visibility effects R. Coniglione, VLVnT09, Athens 13.16 october ‘09

15. General behaviour of sensitivity to point like sources has • been studied for KM3NeT detector • Sub-linear increase of sensitivitywith the number of detector towers • Saturation effect with the number of observation years • Shows a flat behavior with a very large acceptance (>3p) in source declination -> balance between visibility and Earth absorption -> dependence on the site latitude KM3NeT sensitivity estimated with the binned method Improvement on sensitivity for point-like sources expected with unbinned method and exploitation of energy info R. Coniglione, VLVnT09, Athens 13.16 october ‘09