Ultra- and extremely high energy neutrino astronomy

0.46 MB·English

by  I. Sokalski

INCONTRISULLAFISICA DELLEALTEENERGIE TORINO, APRIL 14-16,2004
Ultra- and Extremely High Energy Neutrino
Astronomy
5 IgorSokalski1)a)
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0 1.IstitutoNazionalediFisicaNucleare/SezionediBari,ViaAmendola173,I-70126Bari,Italy
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n Abstract—Scientificmotivationsforultra-andextremelyhighenergyneutrinoastronomyarecon-
a sidered. Sources and expected fluxes of EHE/UHE neutrinos are briefly discussed. Operating and
J
planned experiments on astrophysical neutrino detection are reviewed focusing on deep underwa-
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ter/iceCherenkovneutrinotelescopes.

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v
1 Introduction
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0 From cosmic ray studies, there is a clear evidence that energies of primary cosmic rays extend up to enormous
1 energiesof more than 1020eV with highestenergy cosmic rays detected by Fly’s Eye (HiRes) collaboration[1,
0 2], Yakutsk air shower array [3] and the AGASA experiment[4]. At the same time, the highest energy cosmic
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rays represent still a terra incognita with respect to the processes powering them. The key question of modern
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astrophysics- namely,Whatis the natureofthe cosmic highenergy world? - hasto be consideredas unsolved.
/
x Thereisnoprobeexceptforneutrinowhichcouldhelpustoanswerthisquestion.Electricallychargedprotonsand
e
heaviernuclei,whosearrivaldirectionisscrambledbygalacticandintergalacticmagneticfields,areabletopoint
-
p backtothesourcesoftheiraccelerationonlyaboveapproximately1–10EeV1).γ-rayskeeptheinitialdirection
e buttheUniverseisnottransparentforthematenergiesaboveTeVrangesincetheyannihilateintoelectron-positron
h
pairsinanencounterwitha2.7Kcosmicmicrowavebackgroundphotonsorwithinfra-redradiation.Forexample,
:
v γ-quantumof 1PeV energycan notreach us evenfromthe Galaxy center(10 kpc). Neutronsare too short-live
i
X particlesandtheyarenotintime tocrossevenourGalaxybeforedecayingif theirenergyisbelowseveralEeV.
Thus, neutrino remainsthe only i) weak interacting; ii) stable; and iii) neutral probe which can reach the Earth
r
a (whereweareabletoobserveit)fromthecosmologicaldistanceskeepingoriginaldirectionandpointingbackto
thesourceofitsorigin,meetingthusthebasicrequirementsofastronomy.
MeV-range neutrino astronomy have been existing for forty years with two neutrino sources identified so far,
namely the Sun and Supernova SN-1987A, which at the moment remain the only two experimentally proved
extraterrestrialneutrinosources. Developmentofultra-andextremelyhighenergy2) neutrinoastronomyisunder
way, being still in its infancy. It started in 1960 with academician Markov’s suggestion to use a natural basins
(lakesor seas) todeploytherea largevolumeneutrinotelescopes[5]. Thelargeinstrumentedvolumeis needed
due to the two basic reasons: firstly, expected fluxes of UHE/EHE neutrinos are very low and, secondly, cross
NC(CC)
section of neutralcurrent(NC) and chargedcurrent(CC) neutrinointeractionsν N −→ ν (l)X (by which
l l
neutrinosaresupposedtobe detected)issmalldespiteits increasewith theneutrinoenergy. Todetectneutrinos
associated with highest energy cosmic rays one needs a kilometer scale detectors. After the first experimental
stepsatthemiddleofthe1970th(theDUMANDproject[6])anddetectionofthefirst’underwater’atmospheric
neutrinoatthemiddleofthe1990th(theBAIKALexperiment[7])experimentalgroupsandcollaborationsmoved
tothe nextstage: creationof detectorswith effectiveareasof0.1 km2 andhigherwith anultimate goalto build
neutrinotelescopeswitheffectivevolumesofonecubickilometer.
a)OnleavefromInstituteforNuclearResearchoftheRussianAcademyofSciences,Moscow,Russia
1)Letusremindtheenergyunitsrelevanttothediscussedtopic: 1GeV= 109eV,1TeV= 1012eV,1PeV= 1015eV,1EeV= 1018eV,
1ZeV=1021eV,correspondingly.
2)Ultrahighenergyrange(UHE)isEν =30TeV–30PeV;extremelyhighenergyrange(EHE)isEν >30PeV,respectively.
Thistalkreviewsthephysicalgoalsandexperimentalstatusforultra-andextremelyhighenergyneutrinoastron-
omyfocusing,firstofall,onoperatingandplanneddeepunderwater/iceCherenkovneutrinotelescopes.
2 Detection Principles and Scientific Goals
Underwater/iceneutrinotelescopes(UNTs)representa3-Darraysofphotomultipliersdeployeddeepinthelake,
oceanorinthepolariceatthedepthof1to4kilometerstoprovidewithashieldagainstthesunandmoonlight
backgroundandbackgroundofatmosphericmuons. DetectionprincipleisbasedonregistrationoftheCherenkov
photonsemittedbychargedleptons(includingthoseemittedbysecondariesproducedalongtheirwayinthewater
or ice and by their decay products)which are generated in CC neutrinointeractions ν N −C→C lX (see Fig. 1).
l
AlsohadronicshowersproducedinNCneutrinointeractionsν N −N→C ν X insideUNTsensitivevolumecanbe
l l
Figure1:NeutrinodetectioninanUNT(schematicview)
detectedbyradiatedCherenkovphotons.PMThittimesandpositionsprovidewithapossibilitytoreconstructthe
trackorshowervertexwhileachargecollectedonPMTanodesallowstoreconstructtheenergy.
Figure2: TwoeventtopologiesinanUNT(schematicview).
Thus,therecanbetwomaineventtopologiesinUNTs(Fig.2):
• trackeventincaseofmuonofanyenergyortau-leptonwithenergyE &2PeV(approximatelyabovethis
τ
energytau-leptonisabletopropagateremarkabledistancebeforedecaythankstotheLorentzfactor);
• shower event in case of electron, tau-lepton with energy E .2PeV and NC interactions of all flavor
τ
neutrinos.
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However,realeventsmay containbothtopologies. TrackofUHE/EHEmuonortau-leptoniscomplementedby
showersproducedbysecondarieswhicharegeneratedinthemuoninteractions:bremsstrahlung,directe+e−-pair
production,photonuclearinteractionsandknock-onelectronproduction.Withsomeprobabilitytheseshowerscan
takethemajorfractionofµ/τ energyandevenalltheenergy(firstofallduetobremsstrahlung).Thus,acombined
topologytrack+showertakesplace. Aswellas,atau-leptontrackwithasubsequentdecaycreatesuchcombined
topology. CC muon neutrino (or tau neutrino if E is in multi-PeV range or higher) interaction within UNT
ντ
sensitivevolumewithanhadronicshowerintheneutrinointeractionvertexandsubsequentchargedleptontrack
alsoproducesacombinedtopologywhichisevenmorecomplexincaseoftau-leptonifitdecaysinsidesensitive
volumeprovidingthus with at least two showers: in neutrinointeractionpointand at the decay point(so called
’doublebang’[8]). On the other hand, at energiesbelow PeV range two showersat the tau neutrinointeraction
vertexandatthetau-leptondecaypointaresoclosetoeachotherthatcannotbeseparatedatreconstruction(also
tau-leptontrackcannotbedistinguished)andthus,suchaneventcanbeconsideredasapureshowerone.
Themaingoalof UHE/EHEneutrinoastronomyis todeterminetheoriginofhighenergycosmicrays. Forthis
itisneededtodetectnaturalfluxofthehighenergyneutrinosmeasuringneutrinoenergy,directionalinformation
andintensity.ExpectedsourcesofUHE/EHEneutrinosareasfollows(moredetailedreviewcanbefound,e.g.,in
[9]):
• steadysourceslike,e.g.,ActiveGalacticNuclei(AGN),SupernovaRemnants(SNR)ormicroquasars;
• transientsourceslikeGammaRayBursts(GBR);
• decayofsuperheavyparticlesortopologicaldefects.
Detection of UHE/EHE neutrinos and identification of their sources would allow to clarify the origination of
UHE/EHE cosmic rays and to understand the processes by which the nature fills the Universe with the highest
energyparticles.
Fitted value of par[2]=Sigma
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2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7
log E (GeV)
10 m gen
Figure3: EnergyresolutionoftheANTARES12-stringdetector(seeSec.4.5)whichisplannedtobedeployed
by2007(takenfrom[10]):sigmaofthedistributionoflog (Erec/Et)versusEt.
10 µ µ µ
Accuracy of energy measurements in UNTs is not too high. Energy reconstruction is based on the increase of
emitted Cherenkovlightdue to muon(τ) catastrophicenergylosses above≈1TeV. Also, amountof Cherenkov
photonsproducedbybothhadronicandelectromagneticshowerismoreorlessproportionaltotheshowerenergy.
But due to stochastic nature of energy losses and due to the fact that an UNT represent a non-dense detector
with PMTs spaced by typically 10-100m, UNTs can not be a good calorimeter: for instance, dispersion of the
log (Erec/Et)distribution(whereEt isthetruemuonenergyandErecisthereconstructedenergy,respectively)
10 µ µ µ µ
isaroundσ ≈0.5atE ∼5TeVandσ ≈0.3forE &100TeVwhichmeansthatthemuonenergyresolutionis
µ µ
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atthelevelof2-3only(seeFig.3). Besides,anadditionalun-avoidederroratneutrinoenergymeasurementcomes
fromthefactthatfractionofenergythatistakenbychargedleptonatneutrinoCCinteractionhasadistributionand
ifneutrinointeractionoccursfarapartUNTsensitivevolumeand,hence,showerenergycannotbereconstructed,
reconstructedchargedleptonenergyisnotagoodestimatorfortheneutrinoenergy.
mmeeddiiaann ooff eerrrroorr
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ee angle m , m
gr rec true
e
n (d 1 angle m rec,(cid:10) n true
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ar r
ul
g 0.5
n
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m
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2 4 6 8
log (E /GeV)
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Figure 4: Angular resolution of the 12-string ANTARES detector versus E (taken from [10]): median of the
ν
distribution of the angle in space between the reconstructed muon track and the true muon track (solid) or the
parentneutrinotrack(dashed).BelowE ≈10TeVthereconstructionerrorisdominatedbyν−µkinematics,at
ν
higherenergiesaccuracyislimitedonlybyPMTTTSandlightscattering.
AngularresolutionfortrackeventsatUHE/EHErangeis,typically,at∼0.1◦–1.0◦level(Fig.4)anditissufficient
forsearchofpoint-likeneutrinosources.
The first main backgroundfor neutrinoevents comesfrom down-goingatmospheric muonsand it is suppressed
by puttingUNT as deeperas possible to providewith a shield of water or ice (each 1 km of water suppressthe
atmosphericmuonbackgroundbyapproximatelyoneorderofmagnitude)andbyselectingofup-goingeventsas
neutrinocandidates.Thesecondbackgroundisduetoatmosphericneutrinos.Thefluxofastrophysicalneutrinosis
expectedtobehavelikeE−2.0whereastheatmosphericneutrinospectrumfallslikeE−3.7,yieldingabettersignal-
ν νatm
to-backgroundratioathigherenergies. Thus,atmosphericneutrinobackgroundcanbesuppressedbysettingthe
off-lineenergythresholdatthelevelE ∼10-100TeV.
thr
Except for deep underwater or ice neutrino detection other techniques are also discussed and used (for more
detailedreviewsee[11]):
• detectionofcoherentCherenkovradiowavesemittedbyelectromagneticshowers[12];
• acousticpulsesgeneratedinmatterheatedbyUHE/EHEcascadesduetoionizationenergylosses[13];
• detectionofneutrinointeractionsbyhorizontalairshowers(bothwithtraditionalEarth-basedlargeextensive
airshowerarrays[14]andwithsatellitespace-baseddetectors[15]).
Such kind of experiments have a high energy thresholds (at EeV energy range) and are aimed to detection of
highestenergyneutrinos.TargetmassesforneutrinointeractionareatthelevelofGiga-tonsandhigherproviding
withopportunitytodetectweakneutrinofluxes.
3 Predicted Fluxes and Bounds
AllthemodelsforgenerationofUHE/EHEparticlescanbedividedroughlybytwomainclasses.
Bottom-up models consider initially low energy particles which are accelerated up to UHE/EHE, typically, by
shockwavespropagatinginaccretiondisksaroundblackholesoralongtheextendedjetsemittedperpendicularly
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to the disk. Neutrino are supposed to be produced in decays of mesons which are generated by interaction of
acceleratedparticles with surroundingmatter or photonfields. Such models predictE−2.0 behaviorof neutrino
ν
spectrum. Bynormalizationoftheneutrinofluxtotheknowncosmicrayfluxonecanobtainanupperboundof
dN/dE ∼5×10−8E−2GeV−1cm−2s−1sr−1(Waxman-Bahcalllimit[16])totheneutrinofluxintegratedover
ν ν
allpossiblesourcesordiffuseneutrinoflux(Fig.5). Moredetailedconsiderationwhichinvolves,inparticular,the
source transparency,leads to boundsat the level between the Waxman-Bahcalllimit and dN/dE ∼ 10−6E−2
ν ν
GeV−1 cm−2 s−1 sr−1 ([17],’MPRobscured’and’MPRtransparent’inFig.5). Thelastfluxvaluemoreorless
correspondstothebestexperimentallimitssetbythemomentondiffuseneutrinoflux.
Figure5: Waxman-Bahcall([16],linemarked’WB’)andMannheim-Protheroe-Rachen([17],linesmarked’MPR
obscured’and’MPRtransparent’)limitsondiffuseneutrinoflux. Atmosphericneutrinofluxisshownattheleft,
aswell(thestripcorrespondstodifferentzenithangles).
Insocalledtop-downscenariosparticlesarenotacceleratedbut,instead,arebornwithhighenergiesindecaysof
super-massiveparticleswhichgenerateUHE/EHEnucleons,γ-raysandneutrinos.
Differentpredictionsforneutrinofluxesgeneratedindifferentsources(see,e.g.,[18])leadtoexpectedfluxatthe
Earthatthelevelof∼100eventyr−1km−2aboveE >10TeV.
ν
4 Underwater/ice Neutrino Projects
TheneutrinotelescopewordmapisshowninFig.6.
4.1 DUMAND
The first project for deep underwater Cherenkov neutrino detection, DUMAND (Deep Underwater Muon and
NeutrinoDetector [6]) existedfromabout1976through1995. The goalwas the constructionof the detector,to
beplacedat4800mdepthinthePacificOceanoffKeaholePointontheBigIslandofHawaii. Manypreliminary
studieswere carried out, fromtechnologyto ocean optics. A prototypeverticalstring of instrumentssuspended
froma special ship was employedto demonstrate the technology,and measure the cosmic ray muon flux in the
deepocean. TheDUMANDhardwarewasdonatedtotheNESTORProjectinGreece(Sec.4.4),andmayyetbe
employed there. Although the DUMAND project was canceled in 1995, it stimulated a lot the developmentof
underwatertechniqueforneutrinodetection.
4.2 Baikal
TheBaikalneutrinodetectoris locatedata depthof 1100m in SiberianLakeBaikal. Theexperimentstartedin
early80th,thefirststationarysingle-stringdetectorsequippedwith12-36PMTswereputinoperationin1984-86.
In1993theBaikalcollaborationwasthefirsttodeploypioneering3-Dunderwaterarrayconsistingof3strings(as
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Figure6:Theneutrinotelescopeworldmap
m
m
30 pe
7 pe
70(71)ns
87(84)ns
4 pe
~5m 45(47)ns
15 pe
9 pe
30(32)ns
43(42)ns
2 pe
22(17)ns o
~15
7 pe
5 pe 0 ns
0 ns
Figure7:ThefirsttwoatmosphericneutrinosdetectedunderwaterintheBaikalexperimentin1994.ThehitPMTs
aremarkedinblack. Numbersgivethemeasuredamplitudes(inphotoelectrons)andmeasured(expected)times
withrespecttothefirsthitchannel.
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Figure8: TheBaikalneutrinotelescopeNT-200(left)anditsplannedupgradeNT-200+(right)
necessaryforfullspatialreconstruction). In1996thefirstatmosphericneutrinosdetectedunderwater(seeFig.7)
werereported[7].
Since19988-stringNT-200detectorequippedwith19215“PMTsistakingdata(Fig.8). Anupgrade(NT-200+)
isunderconstructionanditisplannedtobecompletedby2005. NT-200+willconsistofNT-200surroundedby
3 additionalstrings placed 100m apartand it is optimizedfor diffuse neutrinoflux detection. The currentlimit
ondiffuseneutrinofluxsetbytheBaikalexperimentisdN/dE ∼ 1.3×10−6E−2 GeV−1 cm−2 s−1 sr−1 for
ν ν
energyrange 10TeV≤ E ≤10PeV (assuming E−2 neutrinospectra). Besides, limits on magnetic monopole
ν ν
flux, Q-ball flux, results on search of neutralinosin the core of the Earth, measurementson atmospheric muons
andneutrinoswerereported[19].
4.3 AMANDA/IceCube
The first antarctic detector AMANDA-B10 was put into operation at the beginning of 1997. It consists of 302
PMTsdeployedatadepth1500-2000m. AMANDA(AntarcticMuonandNeutrinoDetectorArray)collaboration
uses 3km thick ice layer at the geographicalSouth Pole. Holesare drilled with hotwater and then stringswith
PMTsarefrozenintotheice.InJanuary2000deploymentofadditional9stringswascompletedandsincethattime
AMANDA-IIdetectorisinoperationwith677PMTsat19strings(seeFig.9).TheuniquefeatureofAMANDAis
thatitcontinuouslyworksincoincidencewithsurfaceairshowerexperimentSPASE[20]whichallowtocalibrate
theangularresolution.GivenaE−2benchmarkneutrinospectralshape,limitsdN/dE ∼1.5×10−6E−2GeV−1
ν ν ν
cm−2 s−1 sr−1 and dN/dE ∼ 0.86×10−6E−2 GeV−1 cm−2 s−1 sr−1 are seton diffuseneutrinoflux in the
ν ν
ranges 1PeV≤ E ≤3EeV and 50TeV≤ E ≤5PeV, respectively [21]. Estimated sensitivity to the point-
ν ν
likeneutrinosourcesisatthelevelofexpectedneutrinofluxesfromAGNsMrk421andMrk501[22],aswellas
frommicroquasarSS433foraspecificmodel[23]. Alsoresultsonatmosphericmuonsandneutrinos,WIMPand
magneticmonopolessearch, searchforsupernovaebursts, primarycosmic raycompositionhavebeenpublished
bytheAMANDAcollaboration[24].
As a nextstep of developmentof the neutrinoobservatoryat the South Pole creationof neutrinotelescope with
instrumentedvolumeof1km3 (IceCube)isforeseen[25]. Itwillconsistof4800PMTsdeployedon80vertical
strings(eachof60PMTs)atthedepthfrom1400mto2400m.Thedistancebetweenstringsis125m,thedistance
betweenPMTsalongthestrings16m.ExistingdetectorAMANDA-IIwillbeintegratedtoIceCube.Fig.10gives
aschematicviewofIceCubeanditspositionwithrespecttoAMANDA-IIandtheairshowerarray. Deployment
operationsattheSouthPolewillbegininlate2004anddetectorwillbecompletedby2010. With45,000atmo-
spheric neutrinosrecordedper year the ultimate sensitivity to an extraterrestrialE−2 neutrinoflux after 3 years
ν
ofdatatakingisdN/dE ∼ 3(10)×10−9E−2 GeV−1 cm−2 s−1 sr−1 (thefirstnumberreferstothe90%limit
ν ν
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Depth
1000 m
200 m
120 m
1150 m
Optical
Module
1500 m
HV divider
(cid:0)(cid:1)(cid:0)(cid:1)
main cable (cid:0)(cid:1)(cid:0)(cid:1)
pressure
housing
PMT
silicon gel
2000 m
light diffuser ball
2350 m
Inner 10 strings:
zoomed in on one
AMANDA-II AMANDA-B10 optical module (OM)
Figure9: The AMANDA detector. The scheme is illustrated by Eiffeltower at the left. Each dotrepresentsan
opticalmodulewithPMT.
Figure10:SchematicviewonthefutureIceCubedetector
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andthesecondonetothe5σ sensitivity). ThisislowercomparedtoWaxman-BahcalandMannheim-Protheroe-
Rachen upper bounds[16, 17] and to the most popular predictions on diffuse neutrino flux which are based on
differentmodels[18].
4.4 NESTOR
NESTOR(NeutrinoExtendedSubmarineTelescopewith OceanographicResearch)[26] willbe deployedin the
MediterraneanSea,nearPylos(Greece)at4kmdepth. Itisplannedtobe’towerbaseddetector’(Fig.11). Each
Figure11:SchematicviewoftheNESTORdetector
tower consists of 12 hexagonal floors spaced by 30m with 6 pairs of up-down looking 15“ PMTs each. The
diameteroftheflooris32m. TheeffectiveareaofthetowerwithrespecttoTeV-rangemuonsisabout0.02km2.
The NESTOR collaborationhas passed througha long phase of site evaluationand technologytests. An 28km
electro-opticalcablewasputontheseafloortoconnectthedetectorandshorestationin2000anditwasrepairedin
2002.InMarch,2003a’prototypefloor’equippedwith12PMTswasdeployed.Over5millionsofmuontriggers
wererecordedduringitsoperation.
4.5 ANTARES
The ANTARES project [27] (Astronomy with a Neutrino Telescope and Abyss environmental RESearch) was
formedin1996.In1996-99anintenseR&Dprogramwasperformed.Thedeploymentandrecoverytechnologies,
electronicsandmechanicalstructuresweredevelopedandtestedwithmorethan30deploymentsofautonomous
strings.Theenvironmentalpropertiesatthedetectorsitewereinvestigated.ANTARESR&Dprogramculminated
with deployment and 8 month operation of a 350m length ’demonstrator string’ (November 1999 - July 2000)
instrumented with 7 PMTs at a depth of 1100m, 40 km off the coast of Marseille. The string was controlled
andreadoutvia37km-longelectro-opticalcableconnectedtotheshorestation. ∼5·104seven-foldcoincidences
fromatmosphericmuonswererecorded. Theangulardistributionofatmosphericmuonswasreproducedandthe
fractionofmulti-muoneventswasfoundtobeinagreementwithexpectation.
After extensive R&D programthe collaborationmovedinto construction of a 12-string detector in the Mediter-
raneanSeaat2400mdepth,∼40kmoff-shoreofLaSeynesurMer,nearToulon(42◦50′N,6◦10′E).Eachstring
will be instrumented with 75 PMTs housed in glass spheres (see Fig. 12). PMTs are grouped in triplets at 25
levelsseparatedby14.5m. 3PMTsineachtripletareorientedat45◦tothenadir.Stringsareseparatedfromeach
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Figure12:SchematicviewoftheANTARES12-stringdetector
otherby∼70m. AllthestringsareconnectedtoaJunctionBox(JB)bymeansofelectro-opticallinkcables. The
JB is connected to the shore station by a 50km length 48-fiber electro-opticalcable. Undersea connectionsare
performedwith a mannedsubmarine. The deploymentof the detectoris plannedfor 2005-2007. The important
milestonesthathavebeenachievedbythecollaborationare:
• theelectro-opticalcableconnectingdetectorandshorestationwasdeployedinOctober2001;
• theindustrialproductionof900OMsstartedinApril2002;
• sinceDecember2002theJBisincommunicationwiththeshorestation;
• in December 2002 and February 2003 the ’prototypeinstrumentation string’ and the ’prototype detection
string’(equippedwith15OMs)weresuccessfullydeployed(recoveredinMayandJuly,2003,respectively);
• inMarch2003bothstringswereconnectedtoJBwiththeNautilemannedsubmarineanddatatakingstarted.
Thesensitivityofthedetectortodiffuseneutrinofluxesachievedbyrejectingthebackgroundwithanenergycutof
E =50GeVallowstoreachWaxman-Bahcalllimitin3years. TheANTARESsensitivityforpoint-likesource
cut
searches (90% C.L.) assuming E−2 differentialν flux is in the range 4÷50·10−16cm−2s−1 (dependingon the
sourcedeclination)after1year,whichgivesarealhopetodetectasignalfromthemostpromisingsources.
ThedeploymentoftheANTARESneutrinotelescopecanbeconsideredasasteptowardthecreationofa1km3
detectorintheMediterraneanSea.
4.6 NEMO
NEMO [28] (NEutrino subMarine Observatory) is an R&D project of the Italian National Institute for Nuclear
Physics(INFN)for1km3neutrinounderwatertelescopetobedeployedinMediterraneanSeanearCapoPassero,
Sicily,atthedepthof3500mwheretransparencyandotherwaterparametersareoptimal.Atthefirststage(1998-
2000)theNEMOcollaborationperformedanintensivesearchprogram(morethan20seacampaigns)todetermine
theoptimalsiteforthefuturedetector.AlsoR&Dprogramonmaterials,PMTsandmechanicalcomponentsofthe
detectorwereperformed. Atthesecondstagewhichstartedin2002,theadvancedR&Dandprototypingisdone.
The laboratorywhich is connectedwith test site of-shoreCatania by28km electro-opticalcable is used for this
purpose.TheoverallnumberofPMTsinNEMOdetectormaylaybetween7000and10000.
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