studies of the sensitivity to point-like sources for a flexible-tower geometries for km3net

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


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


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


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


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.


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


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


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


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)


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


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



RXJ1713.7-3946 SNR -39.46 2.040.04stat 0.2 syst 21.30.5stat 4.2 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)


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


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


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°


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

studies of the sensitivity to point-like sources for a flexible-tower geometries for km3net

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