Carla Distefano for the NEMO Collaboration

C.Distefano KM3NET ‘Physics and Simulation (WP2)’ Oct 24 – 25, 2006

LNS

NEMO sensitivity to point sources

Carla Distefanofor the NEMO Collaboration

KM3NET ‘Physics and Simulation (WP2)’ Oct 24 – 25, 2006


LNSOutline of the talk

• Estimate of the NEMO detector sensitivity

• Simulation of the km3 neutrino telescope

• Event selection criteria

• Results

• Physics cases

• Microquasars

• SNR RXJ1713.7-3946

• Estimate of the NEMO detector sensitivity

• Simulation of the km3 neutrino telescope

• Event selection criteria

• Results

• Physics cases

• Microquasars

• SNR RXJ1713.7-3946


LNSDetector sensitivity to muon neutrino fluxes

We compute the detector sensitivity to muon neutrinos from point-like sources:

minimum muon neutrino flux detectable with respect to the background.

90% c.l.

Calculation of the sensitivity spectrum:

- we simulate the expected background b (atm. and ) and we estimate the 90% c.l.

sensitivity in counts <90(b)> (Feldman & Cousins);

- we simulate a reference source spectrum

(d/d)0 which produces ns counts;

- we calculate the sensitivity spectrum as:

- we apply the event selection in order to minimize the sensitivity.

Feldman & Cousins define the sensitivity as the average upper limits for no true signal. It is the maximum number of events that can be excluded at a given confidence level.

90

90 0

( )

s

d b d

d n d


LNSSimulated NEMO-km3 detector

Simulated Detector Geometry:

• square array of 81 NEMO towers

• 140 m between each tower

• 18 floors for each tower

• vertical distance 40 m

• storey length 20 m

• 4 PMTs for each storey

• 5832 PMTs

• Depth = 3500 m (Capo Passero site)

PMT location

and

orientation

(PMT=10”)

DETECTOR LAY-OUTThe ANTARES code gentra v1r2

has been used to generate the

detector geometry file.


LNSSimulation of point-like neutrino sources

We use the ANTARES code genhen v6r2 to simulate Ngen=6·109 interacting neutrinos in the

energy range 102÷108 GeV with a generation spectral index X=1.

Source declination: = - 60˚

- 24 hours of diurnal visibility

- large up-going angular range covered by the source (24 – 84)

Code km3 v2r1 is used to simulate the passage of muons inside the detector and to generate

the PMT hits using the photon tables with the absorption length profile measured in the Capo

Passero site.

Code modk40 v4r8 is used to add optical background hits with a rate of 30 kHz on 10” PMTs.

Code recov4r4km3 is used to reconstruct the events:

Trigger for prefit: at least 3 hits with charge higher than 3.5 p.e. or in concidence

Work in progress: test different trigger conditions (charge hit threshold; triple coincidence

included in recov4r5km3 ), test reco version recov4r6km3


LNSSimulation of point-like neutrino sources

2,GeV

0

/ GeV cm sd

d

Nrec 5.1·105 reconstructed events

Source declination: = - 60˚

- 24 hours of diurnal visibility

- large up-going angular range covered by

the source (24 – 84)

detectable (>100 GeV)

reconstructed

The generated neutrino events are

weighted to a reference spectrum with

a power-law shape


LNS

We

igh

ted

Ev

en

ts

Simulation of atmospheric neutrino background

We use the ANTARES event generation code genhen v6r2 (weighted generation);

We simulated a power law interacting neutrino spectrum:

X=2 for 102 GeV < < 108 GeV ;

Ngen= 7·109 interacting neutrinos

4 isotropic angular distribution

The atmospheric neutrino events are

weighted to the Bartol + RQPM (highest

prediction) flux

Nrec 5·105 reconstructed events

Bartol+RQPM

1 year

NBartol+RQPM 4·104 expected events/year

Events at the detector


LNSSimulation of atmospheric muon background

The events are generated at the detector, applying a weighted generation technique. We

simulate a broken power law spectrum (compromise between the requirement of high statistics

and CPU time consumption):

The atmospheric muon events are weighted to the

Okada parameterization (Okada, 1994), taking into

account the depth of the NEMO Capo Passero site

(3500 m) and the flux variation inside the detector

sensitive height (~ 900 m):

X=1 for < 1 TeV; Ngen= 3·107 events

X=3 for > 1 TeV; Ngen= 2.5·107 events

Nrec 3.8·106 reconstructed events

NOkada 4·108 expected events/year

tgen 4 days

We

igh

ted

Ev

en

ts

Okada1 year


We

igh

ted

Ev

en

ts

Okada1 year



LNS

We

igh

ted

Co

un

ts

Atmospheric muon background for a point-like source

• Reconstructed events have a RA

flat distribution.

• We can project the full sample of

reconstructed events in a few

degrees bin RA, centered in the

source position.

• We get statistics of atmospheric

muons corresponding to a time of

years for each source declination.

mis-reconstructed atm. muons

=-60° exp. events/year

Atm. (1°) 1.1

Atm. (1°) 2.6·103

• The statistics of generated events corresponds to a few days.


LNSEvent selection criteria

• quality cut:

The used reconstruction algorithm is a robust track fitting procedure based on a maximization

likelihood method. The reconstruction may give more than one possible solutions:

> cut - log(L)/NDOF+0.1(Ncomp-1)

(see ANTARES documentation)

log(L)/NDOF log-likelihood per degrees of freedom

Ncomp number of compatible solutions (within 1)

• energy cut:

Nfit>Nfitmin Nfit number of hits in the reconstructed event

• angular cuts:

- rejection of down-going tracks

rec<

max rec reconstructed event direction

- choice of the search bin size

r<rmin r angular distance from source position


LNSOptimization of the event selection

The optimal values of cut, Nfitmin,

max and rmin are chosen optimizing the

detector sensitivity:

Different possible combination of the parameters cut, Nfitmin,

max and rmin are

tested among:

cut= 7.19.0, step=0.1

Nfitmin=6 50, step=1

max < source

max (source upper transit), step=1 deg

rmin=0.1 1 deg, step=0.1

90

90 0

( )

s

d b d

d n d


LNSSensitivity for a point-like ( = -60˚) neutrino source (3 years)

Search bin:

NEMO 0.5˚

IceCube 1˚

=2

IceCube sensitivity values from

Ahrens et al. Astrop. Phys. 20 (2004) 507

(d/d)90 is expressed in GeV-1/cm2 sNeutrino energy range:102 - 108 GeV

C.Distefano CRIS 2006 – Catania May 29 – June 2

LNSEvent detection for a point-like ( = -60˚) neutrino source

Energy spectra of detectable, reconstructed and selected neutrino events (3 years) neutrino energy range 102-108 GeV

detectable (>100 GeV)

reconstructed

selected

C.Distefano CRIS 2006 – Catania May 29 – June 2


=1

=1.5

=2

=2.5

Detector sensitivity as a function of the search bin radius

For all spectra indices the sensitivity doesn’t vary significantly

in the range 0.3°<rbin<0.6°



Detector sensitivity as a function of

the high energy neutrino cut-off max

Hard spectrum sources: the detector

sensitivity is better and gets better if

the spectrum extends to VHE.

Soft spectrum sources: the detector

sensitivity doesn’t vary much with max.


LNSSensitivity for a point-like neutrino source (3 years)

=2

Diurnal visibility:

Time per day spent by the source

below the Astronomical Horizon

with respect to the latitude of the

Capo Passero site.

The detector sensitivity gets worse

with increasing declination due to the

decrease of the diurnal visibility.

Equatorial coordinates

Detector sensitivity as a function of the source declination

<cut> = -7.3 no selection in Nfit

<rbin> = 0.5° max = 90°-101°


LNSGalactic Microquasars

• Galactic X-ray binary systems which exhibit relativistic radio jets;

• persistent or bursting;

• about 20 identified microquasars;

• not extremely powerful sources but close to the Earth;

• good sources to investigate astrophysical relativistic jets (AGN, GRB);

• jet composition;

• possible TeV neutrino sources.


LNSDetector sensitivity (1 year data taking)

The sensitivity is calculated for a

- neutrino spectrum with = 2

and = 1-100 TeV.

Sensitivity vs. declination

Average sensitivity:

~510-11 erg/cm2 s

search bin radius 0.5°-1°


LNSMicroquasar neutrinos: selected events (1 year)

Steady microquasars

Neutrino fluxes predicted by Distefano et al., 2002

Microquasars SS433 and GX339-4:

NEMO could detect neutrinos in 1 year of data taking or strongly

constrain source physical parameters (acceleration efficiency,

energy content …)

Average number of selected

events from source Nµm and

of background Nµb in 1 year

observation time.


LNSMicroquasar neutrinos: selected events

Improvement considering time correlation with

source bursts (multi-messenger analysis):

Nb~10-3 events per burst

Cumulative analysis of considered bursts:

Nm=2.55.0 events N

b<0.1 events

Bursting microquasarsWe assume that transient sources cause 1 burst per year: N

m calculated for 1 burst, Nb

calculated in 1 year.

Improvement integrating over more bursts per

microquasar (mandatory knowledge of the duty cycle):

GRS 1915+105 and GRO J1655-40 may show more

than 1 burst per year;

Cir X-1 periodic bursts (T~17 days ~1.5 evt/year).

Neutrino fluxes predicted by Distefano et al., 2002

no significant spectral variation =2.1-2.2 -evidence of DSA of protons ?

energy spectrum and morphology

RXJ1713.7-3946 is a TeV source !

HESS 2004 data: preliminary !

=2.1-2.2 with a curvature cutoff (?)at high energies

From F. Aharonian, VLVnT2


LNSSNR: RX J1713.7-3946

Aharonian et al. Nature 432, 75, 2004

Expected neutrino flux:

Alvarez-Muñiz & Halzen (ApJ 576, L33, 2002):

d/d ~ 4 ·10-8 -2 cm-2 s-1 GeV-1

max = 10 TeV

Costantini & Vissani (Astrop. Phys. 23, 477, 2005):

d/d ~ 3 ·10-8 -2.2 cm-2 s-1 GeV-1

= 50 GeV1 PeVKappes et al. (ApJ submitted):

d/d ~ - exp(-(

cut)1/2)

=15.52 10-12 cm-2 s-1 TeV-1 =1.72 cut= 1.35 TeV

Kistler & Beacom (Phys. ReV. D74, 063007, 2006):

d/d ~ - exp(-

cut)

=15.0 10-12 cm-2 s-1 TeV-1 =2.19 cut= 50 TeV


LNSSNR: RX J1713.7-3946

(d/d)90 is expressed in cm-2 s-1 GeV-1Ns: source events; N

b: bkg events.

Expected neutrino events in 3 years of data taking:

Simulations were conducted assuming point-like source

The source is extended with a diameter of 1.3°

The effect of source extension is under study

Carla Distefano for the NEMO Collaboration

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