Carla Distefano for the NEMO Collaboration

C.Distefano Barcelona July 4 – 7, 2006

LNS

Detection of point-like neutrino sources with the NEMO-km3 telescope

THE MULTI-MESSENGER APPROACH TO UNIDENTIFIED GAMMA-RAY SOURCESBarcelona July 4 – 7, 2006

Carla Distefanofor the NEMO Collaboration LNS


LNSOutline of the talk

• The NEMO project

• Simulation of the km3 neutrino telescope performance

• Pointing accuracy

• Sensitivity to point-like neutrino sources

• Physics cases

• Microquasar LS 5039

• SNR RXJ1713.7-3946

• The NEMO project

• Simulation of the km3 neutrino telescope performance

• Pointing accuracy

• Sensitivity to point-like neutrino sources

• Physics cases

• Microquasar LS 5039

• SNR RXJ1713.7-3946


LNSNeutrino telescope projectsBAIKAL, AMANDA: taking dataNESTOR, ANTARES, NEMO R&D: under constructionICECUBE: completion expected in 2010KM3NET – Mediterranean: EU Design Study 2006-2008

AMANDAICECUBE

BAIKAL

ANTARES

2400 m

NESTOR

3800 m

NEMO

3500 m

• In order to obtain the whole sky coverage 2 telescopes must be built

• The Galactic Centre is observable only from the Northern Hemisphere

Small scale detectors and demonstrators

km3 scale telescopes


LNSNEMO

The NEMO Collaboration is dedicating a special effort in:

• search, characterization and monitoring of a deep sea site adequate

for the installation of the Mediterranean km3;

• development of technologies for the km3 (technical solutions chosen

by small scale demonstrators are not directly scalable to a km3).

• test of prototypes in deep sea: NEMO Phase-1 in Catania

• realization of a marine infrastructure for the km3: NEMO Phase-2 in

Capo Passero

The NEMO Collaboration is dedicating a special effort in:

• search, characterization and monitoring of a deep sea site adequate

for the installation of the Mediterranean km3;

• development of technologies for the km3 (technical solutions chosen

by small scale demonstrators are not directly scalable to a km3).

• test of prototypes in deep sea: NEMO Phase-1 in Catania

• realization of a marine infrastructure for the km3: NEMO Phase-2 in

Capo Passero


LNSThe Capo Passero deep sea site

• The average depth is 3500 m, the distance from shore is 100 km.

• It is located in a wide abyssal plateau far from shelf breaks and geologically stable.

• Optical properties of deep sea water are the best measured among investigated sites (absorption length close to optically pure water astro-ph\0603701).

• Optical background is low (~30 kHz on 10’’ PMT at 0.5 s.p.e. threshold) and mainly due to 40K decay since the bioluminescence activity is extremely low.

• Underwater currents are very low (2.5 cm/s) and stable.

After eight years of activity in seeking and monitoring abyssal sites in the

Mediterranean Sea the NEMO Collaboration has selected a site close to Capo

Passero, Sicily (36° 16’ N, 16° 06’ E) .

The site has been proposed to ApPEC on January 2003 as candidate site for the

installation of the km3.


LNSSeawater optical properties in Capo Passero

Average values 2850÷3250 m

• Light Absorption and Attenuation lengths measured in Capo Passero don’t show seasonal dependence.

• Absorption lengths measured in Capo Passero are close to the optically pure sea water data.


LNS

Optical background was measured

in Capo Passero @ 3000 m depth.

Data are consistent with 30 kHz background on

10”PMT at 0.5 s.p.e.

(mainly 40K decay, very few bioluminescence).

Optical data are consistent with biological measurements:

No luminescent bacteria have been observed in Capo Passero

below 2500 m

Optical background in Capo Passero

40K

Baseline rate~ 30 kHz

15

20

25

30

35

0 7 14 21 28 35 42 49

Co

un

tin

g r

ates

(kH

z)

0.0%

0.5%

1.0%

1.5%

2.0% Tim

e abo

ve 200 kHz

Days

30 kHz


LNSFeasibility study for the km3 telescope

• 1 main Junction Box

• 8 10 secondary Junction Boxes

• 60 80 towers

• 140 200 m between each tower

• 16 18 floors for each tower

• 64 72 PMT for each tower

• 4000 6000 PMTs

Parameters to optimize: distances, number of towers, tower height, …

Electro-optical cable from shore

Primary Junction Box

Secondary Junction Boxes

towers

electro-optical cables network

Detector architecture issues

• Reduce the number of structures to

reduce the number of underwater

connections and allow operation with

a ROV;

• Detector modularity.


LNSNEMO Phase-1

300

m

Mini-Tower compacted

Mini-Tower unfurled

15 m

Deployment of JB and mini-tower Sept. 2006

Junction Box

NEMO mini-tower(4 floors, 16 OMs)

TSS FrameDeployedJanuary 2005

• Realization of the key elements of

the km3

• Validation of the technological

solutions proposed

• Installation at 2000 m offshore

Catania (LNS Underwater Test Site)


LNSSimulated NEMO-km3 detector

20 m

40 m

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

- optical background 30 kHz

- optical properties of the

NEMO site of Capo Passero

- ANTARES s/w tools used

PMT location and orientation


LNSDetector pointing accuracy: observation of the Moon shadow

Moon rest frame

Moon disk

Event density

(1 year of data

taking)

Detection of the deficit (The Moon

Shadow) provides a measurement of:

• the detector angular resolution;

• the detector absolute orientation.

The Moon absorbs Cosmic Rays a lack of atmospheric muons is expected.

2659 8deg

0.19 0.02deg

k

2

222 2

12moon

dNk e

d

100 days needed to observe a 3 effect


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.

0s

90

90dd

n)b(

dd


LNSAtmospheric muon and neutrino background

Atmospheric neutrinos:

• upward tracks are good neutrino candidates;

• event direction and energy criteria can be used to

discriminate background from astrophysical signals.

Atmospheric muons:

• down-going muons are several orders of magnitude

more than neutrino-induced muons;

• up-going background events are due to mis-

reconstructed (fake) tracks;

• quality cuts applied to reject mis-reconstructed

tracks.

ANTARES


LNSEvent simulation

exp. events/year

1 7.1·107

1.5 5.7·104

2 163.5

2.5 1.29

Atm. (1°) 1.06

Atm. (1°) 7.9·103

NBartol+RQPM 4·104 expected events/year

NOkada 4·108 expected events/year

Atmospheric neutrinos are generated according to the Bartol + RQPM (highest prediction) flux

Atmospheric muons are generated according to the Okada parameterization, taking into

account the depth of the NEMO Capo Passero site (3500 m) and the flux variation inside the

detector sensitive height (~ 900 m):

Astrophysical neutrinos: source declination: = - 60˚

- 24 hours of diurnal visibility

- large up-going angular range covered by the

source (24 – 84)

Neutrino energy range: 102 - 108 GeV

s cmGeV /10 2GeV,

7

0

dd


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

Neutrino energy range:

102 - 108 GeV

(d/d)90 expressed

in GeV-1/cm2 s



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

Average search bin: <rbin> = 0.5°

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

LNSMicroquasar: LS 5039

HESS observed TeV -rays from LS 5039

Observed gamma-ray spectrum:

(0.25 TeV) = 5.1 0.8·10-12 ph/cm2 s

= 2.12 0.15

Aharonian et al. astro-ph/0508658

Aharonian et al. Science 309, 746, 2005

Neutrino energy flux:

f(0.1 TeV) ~ 10-10 erg/cm2 s

Sensitivity:

f,90 is expressed in erg/cm2 s

Selected events:

Ns: source events;

Nb: bkg events.

Expected neutrino events in 3 years of data taking:


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 PeV

Expected neutrino events in 3 years of data taking: Sensitivity:

(d/d)90 is expressed in

GeV-1/cm2 s

Selected events:

Ns: source events;

Nb: bkg events.


LNSOutlook

The NEMO project:

R&D study for the realization of the Mediterranean km3 neutrino telescope:

Search, characterization and monitoring of an adequate deep sea site;

Development of technologies for the km3 ;

Test of prototypes in deep sea: NEMO Phase-1 in Catania;

Realization of a marine infrastructure for the km3: NEMO Phase-2 in Capo Passero.

Angular Resolution and Pointing Accuracy:

Detection of the Moon shadow in 100 days;

Estimated angular resolution 0.2°;

Absolute pointing can be recovered looking at the Moon Shadow.

Detector Sensitivity to point sources (3 years):

NEMO (=2,102-108 GeV, =-60°) 1.2·10-9 E-2/(GeV cm2 s) search-bin 0.5°

ICECUBE 2.4·10-9 search-bin 1°

Discussed physics cases:

QSO LS 5039 and SNR RXJ1713.7-3946: both sources could be detected in 3 years;

a survey of TeV gamma-ray sources is under analysis.


LNS


LNS

We

igh

ted

Ev

en

ts

Simulation of atmospheric neutrino background

We use the ANTARES event generation code (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 3.7·105 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

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


tgen 4 days

We

igh

ted

Ev

en

ts

Okada1 year


We

igh

ted

Ev

en

ts

Okada1 year



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

Klimushin, Bugaev & Sokalski parameterization (PRD,

64, 014016, 2001), taking into account the depth of the

NEMO Capo Passero site 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


tgen 4 days

1 year


1 year



LNSAtmospheric muon background for a point-like source

• The statistics of generated events

corresponds to a few days.

• Reconstructed events have a RA flat

distribution.

• We can project the full sample of

simulated events in a few degrees bin RA,

centered in the source position.

• We get statistics of atmospheric muons

corresponding to a time of ~1 year for each

microquasar.

Distribution of equatorial coordinates of the reconstructed atmospheric muons.

We

igh

ted

Co

un

tsW

eig

hte

d C

ou

nts


LNS

=1

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

reconstructionselection

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

=2

=1.5

=2.5


LNSEstimate of the detector angular resolution

= 0.19 ± 0.02 deg

Event Selection:

Nhitmin= 20

cut= -7.6

S1year=5.5

median angle of selected events:

estimated angular resolution:

= 0.22 deg

Reconstructed

Selected


LNS

0.2

0.4

0.6

Study of the telescope absolute pointing

We introduce a rotation around the Z axis to simulate a possible systematic error

in the absolute azimuthal orientation of tracks.

(1 year of data taking)

• for 0.2 (expected accuracy), the shadow is still

observable at the Moon position;

• for 0.2 (pessimistic case), systematic errors may be

corrected;

• the presence of possible systematic errors in the absolute

zenithal orientation is still under analysis.

Moon rest frame Moon rest frame

Moon rest frame


LNSThe km3 telescope: a downward looking detector

Neutrino telescopes search for muon tracks induced by neutrino interactions

The downgoing atmospheric flux overcomes by several orders of

magnitude the expected fluxes induced by interactions.

On the other hand, muons cannot

travel in rock or water more than

50 km at any energy

Upgoing and horizontal muon

tracks are neutrino signatures


LNSAtmospheric muon background vs depth

Downgoing muon background is

strongly reduced as a function of

detector installation depth.

Depth >3000 m (1 km rock) is

suggested for detector installation

NEMO

NESTOR

ANTARESAMANDA

Bugaev

BAIKAL


LNSCherenkov track reconstruction

pseudo vertex

j 0 j j cc(t - t ) = l + d tg( )

ANTARES

Cherenkov photons emitted by the

muon track are correlated by the

causality relation:

The track can be reconstructed

during offline analysis of space-

time correlated PMT signals (hits).

Fit yields muon track parameters

(, ) and number of hit PMTs


LNSEvent selection

• 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)

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 positionThe optimal values of cut, Nfitmin, max and rmin are chosen optimizing the detector sensitivity.



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


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

max = 90°-101° <rbin> = 0.5°


LNSMicroquasar: LS 5039

HESS observed TeV -rays from LS 5039

(0.25 TeV) = 5.1 0.8·10-12 ph/cm2 s

= 2.12 0.15

Aharonian et al. astro-ph/0508658

Aharonian et al. Science 309, 746, 2005

f(0.1 TeV) ~ 10-10 erg/cm2 s

f,90 is expressed in erg/cm2 s


Ns: source events; N

b: bkg events.


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 PeV

(d/d)90 is expressed in GeV-1/cm2 sNs: source events; N

b: bkg events.


Documents

Carla Distefano for the NEMO Collaboration