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Carla Distefano for the NEMO Collaboration

Carla Distefano for the NEMO Collaboration. THE MULTI-MESSENGER APPROACH TO UNIDENTIFIED GAMMA-RAY SOURCES Barcelona July 4 – 7, 2006. LNS. Detection of point-like neutrino sources with the NEMO-km 3 telescope. Outline of the talk. The NEMO project

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Carla Distefano for the NEMO Collaboration

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  1. Carla Distefanofor the NEMO Collaboration THE MULTI-MESSENGER APPROACH TO UNIDENTIFIED GAMMA-RAY SOURCES Barcelona July 4 – 7, 2006 LNS Detection of point-like neutrino sources with the NEMO-km3 telescope

  2. Outline of the talk • The NEMO project • Simulation of the km3 neutrino telescope performance • Pointing accuracy • Sensitivity to point-likeneutrino sources • Physics cases • Microquasar LS 5039 • SNR RXJ1713.7-3946

  3. Neutrino telescope projects 2400m 3800 m NEMO ANTARES NESTOR 3500m BAIKAL, AMANDA:taking data NESTOR, ANTARES, NEMO R&D:under construction ICECUBE: completion expected in 2010 KM3NET – Mediterranean: EU Design Study 2006-2008 Small scale detectors and demonstrators km3 scale telescopes • In order to obtain the whole sky coverage 2 telescopes must be built • The Galactic Centre is observable only from the Northern Hemisphere BAIKAL AMANDA ICECUBE

  4. NEMO • 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

  5. The Capo Passero deep sea site 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. • 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.

  6. Seawater optical properties in Capo Passero Average values 2850÷3250 m • Absorption lengths measured in Capo Passero are close to the optically pure sea water data. • Light Absorption and Attenuation lengths measured in Capo Passero don’t show seasonal dependence.

  7. Optical background in Capo Passero 35 2.0% 30 kHz 30 1.5% Time above 200 kHz Counting rates (kHz) 25 1.0% 20 0.5% 15 0.0% 0 7 14 21 28 35 42 49 Days 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). 40K Optical data are consistent with biological measurements: No luminescent bacteria have been observed in Capo Passero below 2500 m Baseline rate~ 30 kHz

  8. Feasibility study for the km3 telescope Secondary Junction Boxes towers electro-optical cables network Primary Junction Box Electro-optical cable from shore • Detector architecture issues • Reduce the number of structures to • reduce the number of underwater • connections and allow operation with • a ROV; • Detector modularity. • 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 Several layouts under study Parameters to optimize: distances, number of towers, tower height, …

  9. NEMO Phase-1 Mini-Tower unfurled NEMO mini-tower (4 floors, 16 OMs) Deployment of JB and mini-tower Sept. 2006 Junction Box TSS Frame 300 m DeployedJanuary 2005 Mini-Tower compacted • Realization of the key elements of • the km3 • Validation of the technological • solutions proposed • Installation at 2000 m offshore • Catania (LNS Underwater Test Site) 15 m

  10. Simulated 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

  11. Detector pointing accuracy: observation of the Moon shadow Moon rest frame Moon disk The Moon absorbs Cosmic Rays  a lack of atmospheric muons is expected. • Detection of the deficit (TheMoon Shadow) provides a measurement of: • the detector angular resolution; • the detector absolute orientation. Event density (1 year of data taking) 100 days needed to observe a 3 effect

  12. Detector sensitivity to muon neutrino fluxes 90% c.l. We compute the detector sensitivity to muon neutrinos from point-like sources: minimum muon neutrino flux detectable with respect to the background. • Calculation of the sensitivity spectrum: • we simulate the expected backgroundb(atm.  and ) and we estimate the 90% c.l. • sensitivity in counts<90(b)>(Feldman & Cousins); • we simulate a reference source spectrum • (d/d)0which producesnscounts; • 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.

  13. Atmospheric muon and neutrino background ANTARES • 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. • Atmospheric neutrinos: • upward tracks are good neutrino candidates; • event direction and energy criteria can be used to discriminate background from astrophysical signals.

  14. Event simulation Atmospheric neutrinosare generated according to the Bartol + RQPM (highest prediction) flux NBartol+RQPM  4·104 expected events/year Atmospheric muonsare 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): NOkada  4·108 expected events/year 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

  15. Sensitivity for a point-like ( = -60˚) neutrino source (3 years) Neutrino energy range: 102 - 108 GeV (d/d)90 expressed in GeV-1/cm2 s Search bin: NEMO 0.5˚ IceCube 1˚ =2 IceCube sensitivity values from Ahrens et al. Astrop. Phys. 20 (2004) 507

  16. Sensitivity for a point-like ( = -60˚) neutrino source (3 years) 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.

  17. Sensitivity for a point-like neutrino source (3 years) Detector sensitivity as a function of the source declination The detector sensitivity gets worse with increasing declination due to the decrease of the diurnal visibility. =2 Average search bin: <rbin> = 0.5° Diurnal visibility: Time per day spent by the source below the Astronomical Horizon with respect to the latitude of the Capo Passero site. Equatorial coordinates

  18. Microquasar: LS 5039 HESS observed TeV -rays from LS 5039 Aharonian et al. Science 309, 746, 2005 Observed gamma-ray spectrum: (0.25 TeV) = 5.1  0.8·10-12 ph/cm2 s  = 2.12  0.15 Neutrino energy flux: f(0.1 TeV) ~10-10 erg/cm2 s Aharonian et al. astro-ph/0508658 Expected neutrino events in 3 years of data taking: Sensitivity: f,90 is expressed in erg/cm2 s Selected events: Ns: source events; Nb: bkg events.

  19. SNR: RX J1713.7-3946 Expected neutrino flux: Alvarez-Muñiz & Halzen (ApJ 576, L33, 2002): dn/dn~ 4 ·10-8n-2 cm-2 s-1 GeV-1 nmax = 10 TeV Costantini & Vissani (Astrop. Phys. 23, 477, 2005): dn/dn~ 3 ·10-8n-2.2 cm-2 s-1 GeV-1 n = 50 GeV1 PeV Aharonian et al. Nature 432, 75, 2004 Expected neutrino events in 3 years of data taking: Sensitivity: (d/d)90 is expressed in GeV-1/cm2 s Selected events: Ns: source events; Nb: bkg events.

  20. Outlook • 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° • ICECUBE2.4·10-9 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.

  21. Simulation of atmospheric neutrino background Weighted Events 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 Nrec  3.7·105 reconstructed events Bartol+RQPM 1 year The atmospheric neutrino events are weighted to the Bartol + RQPM (highest prediction) flux Events at the detector NBartol+RQPM  4·104 expected events/year

  22. Simulation of atmospheric muon background Weighted Events Weighted Events 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): Okada 1 year 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 Events at the detector 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): Okada 1 year NOkada  4·108 expected events/year tgen  4 days Events at the detector

  23. Simulation 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): 1 year 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 Events at the detector 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): 1 year NOkada  5·108 expected events/year tgen  4 days Events at the detector

  24. Atmospheric muon background for a point-like source Weighted Counts Weighted Counts Distribution of equatorial coordinates of the reconstructed atmospheric muons. • 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.

  25. Event detection for a point-like ( = -60˚) neutrino source Energy spectra of reconstructed and selected neutrino events (3 years) neutrino energy range 102-108 GeV =1 =1.5 reconstruction selection =2 =2.5

  26. Estimate of the detector angular resolution Event Selection: Nhitmin= 20 cut= -7.6 S1year=5.5 estimated angular resolution: = 0.19 ± 0.02 deg median angle of selected events: Reconstructed Selected = 0.22 deg

  27. Study of the telescope absolute pointing Moon rest frame Moon rest frame Moon rest frame 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.

  28. The km3 telescope: a downward looking detector Upgoing and horizontal muon tracks are neutrino signatures 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

  29. Atmospheric muon background vs depth Bugaev BAIKAL ANTARES AMANDA NEMO NESTOR Downgoing muon background is strongly reduced as a function of detector installation depth. Depth >3000 m (1 km rock) is suggested for detector installation

  30. Cherenkov track reconstruction 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 pseudo vertex ANTARES

  31. Event 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<rminr  angular distance from source position The optimal values of cut,Nfitmin,maxandrminare chosen optimizing the detector sensitivity.

  32. Sensitivity for a point-like ( = -60˚) neutrino source (3 years) Neutrino energy range: 102 - 108 GeV (d/d)90 is expressed in GeV-1/cm2 s Search bin: NEMO 0.5˚ IceCube 1˚ =2 IceCube sensitivity values from Ahrens et al. Astrop. Phys. 20 (2004) 507

  33. Sensitivity for a point-like neutrino source (3 years) Detector sensitivity as a function of the source declination The detector sensitivity gets worse with increasing declination due to the decrease of the diurnal visibility. =2 <cut> = -7.3 no selection in Nfit max = 90°-101° <rbin> = 0.5° Diurnal visibility: Time per day spent by the source below the Astronomical Horizon with respect to the latitude of the Capo Passero site. Equatorial coordinates

  34. Microquasar: LS 5039 HESS observed TeV -rays from LS 5039 Aharonian et al. Science 309, 746, 2005 (0.25 TeV) = 5.1  0.8·10-12 ph/cm2 s  = 2.12  0.15 f(0.1 TeV) ~10-10 erg/cm2 s Aharonian et al. astro-ph/0508658 Expected neutrino events in 3 years of data taking: Ns: source events; Nb: bkg events. f,90 is expressed in erg/cm2 s

  35. SNR: RX J1713.7-3946 Expected neutrino flux: Alvarez-Muñiz & Halzen (ApJ 576, L33, 2002): dn/dn~ 4 ·10-8n-2 cm-2 s-1 GeV-1 nmax = 10 TeV Costantini & Vissani (Astrop. Phys. 23, 477, 2005): dn/dn~ 3 ·10-8n-2.2 cm-2 s-1 GeV-1 n = 50 GeV1 PeV Aharonian et al. Nature 432, 75, 2004 Expected neutrino events in 3 years of data taking: Ns: source events; Nb: bkg events. (d/d)90 is expressed in GeV-1/cm2 s

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