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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. Sensitivity to point-like sources. - PowerPoint PPT Presentation
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R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Studies of the sensitivity to point-like sources for a flexible-tower geometries for
KM3NeT
R. Coniglione C. Distefano and P. SapienzaIstituto Nazionale di Fisica Nucleare- Laboratori Nazionali del Sud
for the KM3NeT consortium
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
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
Detector lay-out
Number of structures -> 127 towers - hexagonNumber of storeys/structure -> 20PMT -> 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 -> 40mDistance between towers -> 180m
Geometry parameters
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
ANTARES codes modified for km3 detectors + modifications for large detectorParticles generators generator (all flavours), CC+NC interaction. In simulation: + & CC- atmospheric neutrinos: several prescriptions in the code; prompt taken into account.
In simulation: Bartol + RQPM-high prescription- Muon generation with MUPAGE: No atmospheric muons in these simulationsDetector response- Detector geometry- Light generation and propagation in water ->absorption and scattering taken into
account. Simulation input abs=70 m@450nmandscat= 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
input 47kHz and ±1s time windowTrack reconstruction- Based on PDF maximization - Trigger based on local coincidences to reject hits due to optical background
The Monte Carlo codes&
inputs
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Sensitivity calculation
The binned method is used -> Feldman and Cousins approach with the minimization of the Model Rejection Factor -> cuts on track reconstruction quality,nhit (related to the muon energy),Rbin (radius of the cone around the source).
s
bkgss N
NMRF 90
90
ddEd
EAN bkgseffbkgs
,, ,
Sensitivity depends on:• Neutrino spectrum & source extension• Effective neutrino area -> detector response• Source declination -> visibility• Oservation years
How to identify few events from source amongst large number of background events ? -> statistical approachesTwo 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.
90 is 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.
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Il numero di eventi di segnale e di fondo si calcola a partire dall’area efficace:
),()()(),(),( EPNEEVEA EarthAefficaceefficace
gengen
recefficace V
ENENEV ),(
),(),(
Neutrino cross section
nucleons per unit volume
Earth Absorption
Angle between neutrino and muons gen
Median of the angle distribution between the generated and reconstructed muon
Effective neutrino area
Effective area
X
N
QC applied
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Source spectrum for point-like sources
source spectrum E- normalized atE dN/dE = 10-8 cm-2 GeV-1 s-1
Expected in an angular bin of 1° around a source with =-60°
Energy range of interest 3TeV-100TeV
In order to reject atmospheric neutrino background cuts on , Nhit, Rbin
Lambda distribution
Nhit distribution
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Sensitivity to point like sources as a function of observation years
KM3NeT = 60° spectrum E-2
Ratio with respect to 1 year of observation time
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
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Sensitivity to point-like sources as a function of the number of towers
E-2 neutrino flux =-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
From Aharens et al. Astr. Phys. (2004) – binned method
Average value of sensitivity fromR. Abbasi et al. Astro-ph (2009)
Sensitivity to point like source as a function of the source declination for three years of observation time
Black lines IceCube sensitivityRed lines KM3NeT sensitivity From R. Abbasi et al.
Astro-ph (2009) scaled – unbinned method
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
Neutrino spectrum E-2
name type (degree)
Spectral index
GammaFlux
TeV-1 cm-2 s-1 @1 TeV
H1303-631 UID - 63.11 2.440.05stat 0.2 syst 4.30.3stat 1.3 syst
RCW86 SNR -62.29 2.510.1stat 2.710.35stat
H1427-608 UID - 60.51 2.160.14stat 0.2 syst 1.30.4stat 0.3 syst
H0852-463RXJ0852-4622
Vela juniorSNR - 46.20 2.10.1stat 0.2 syst 212stat 6 syst
H1626-490 UID - 49.05 2.180.12stat 0.2 syst 4.90.9stat 1 syst
H1702-420 UID - 42.04 2.070.08stat 0.2 syst 9.11.1stat 1.8 syst
H1708-410 UID - 41.04 2.460.08stat 0.2 syst 2.70.3stat 0.5 syst
RXJ1713.7-3946 SNR -39.46 2.040.04stat 0.2 syst 21.30.5stat 4.2 syst
H1731-347 UID - 34.43 2.260.1stat 0.2 syst 6.10.8stat 1.2 syst
H1841-055 UID - 5.3 2.410.08stat 0.2 syst 12.81.3stat 2.6 syst
H1857+026 UID +2.6 2.390.08stat 0.2 syst 6.10.7stat 1.2 syst
H1858+020 UID +2.6 2.170.12stat 0.2 syst 0.60.1stat 0.1 syst
Cas A SNR +58 2.50.4stat 0.1 syst 0.600.12stat 0.12 syst
Source list from F. Aharonian et al. Rep. Prog. Phys. (2008)
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Sensitivity for 3 years of observation timeNeutrino spectrum E-2
Flat behaviour of sensitivity vs declination for a large region of sin. Not to ascribe only to the visibility effect
Visibility correction
Sens(=0°,T=3year) = sens(=-60°,T)
T is the fraction of time below the horizon
Sensitivity vs declination behaviour analysis
KM3NeT =60° corrected for the visibility KM3NeT sensitivity
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Mediterranean Sea latitude 36°
-80-70
-60-50
=-40-30
-20
-10
0 +20+40 +50
Above the horizon Below the horizon
Near the horizon the effect of Earth absorption is reduced for high energy neutrinos
Sensitivity vs declination Phi versus theta as a function of declination
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
Effective neutrino area for point-like sources (theta <96°)No quality cuts applied
= 0°= -20° = -60°
Values scaled for the visibility
Balance between Earth absorption and visibility effects
Sensitivity vs declination Effective neutrino areas as a function of declination
For E>30 TeV effect of Earth absorbtion visible
log10 E (GeV)log10 E (GeV)
Aef
f (m
2 )
Aef
f (m
2 )
= 0°= -20° = -60°
R. Coniglione, VLVnT09, Athens 13.16 october ‘09
General behaviourGeneral behaviour of sensitivity to point like sources has of sensitivity to point like sources hasbeen studied for KM3NeT detectorbeen studied for KM3NeT detector• Sub-linear increase of sensitivitySub-linear increase of sensitivity with the number of detector with the number of detector
towerstowers• Saturation effect with the number of observation yearsSaturation effect with the number of observation years• Shows a flat behavior with a very large acceptance (>3Shows a flat behavior with a very large acceptance (>3) in ) in
source declination -> balance between visibility and Earth source declination -> balance between visibility and Earth absorption -> dependence on the site latitude absorption -> dependence on the site latitude
KM3NeTKM3NeT sensitivity estimated with the binned method sensitivity estimated with the binned methodImprovement on sensitivity for point-like sources expected Improvement on sensitivity for point-like sources expected with unbinned method and exploitation of energy infowith unbinned method and exploitation of energy info