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Emilio Migneco

Emilio Migneco Erice ISCRA School 2004 Introduction to High energy neutrino astronomy Topics 1) Introduction to high energy neutrino astronomy Motivations for HE neutrino astronomy HE neutrino sources Neutrino telescopes operation principles Backgrounds

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Emilio Migneco

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  1. Emilio Migneco Erice ISCRA School 2004 Introduction to High energy neutrino astronomy

  2. Topics 1) Introduction to high energy neutrino astronomy Motivations for HE neutrino astronomy HE neutrino sources Neutrino telescopes operation principles Backgrounds 2) Future cubic kilometer arrays Review of existing detectors and projects Future detectors: impact of site parameters architecture experimental challenges simulations and expected performances

  3. Neutrino astronomy Neutrinos are elementary particles with “special” properties: • light • neutral • interact by weak force Good astrophysical probes: not deflected  point back to the source not absorbed  travel Gpc distances (overcome GZK effect) But they are difficult to detect I have done a terrible thing I invented a particle that cannot be detected W.Pauli

  4. The known cosmic neutrino spectrum The measurements of (low energy) solar, SN and atmospheric neutrino fluxes is permitting to solve open questions in astrophysics, nuclear and particle physics... Davis and Koshiba Nobel laureates 2002 SuperKamiokande neutrino image of the Sun HST image of SN 1987A ?

  5. High energy astrophysics • The detection of high energy gammas and CR are milestones in modern astrophysics but there are still open questions • Particle acceleration mechanism in astrophysical sources • Identification of high energy CR sources • Solution of UHECR puzzle • Heavy dark matter content in the Universe

  6. protons E-2.7 Ankle Galactic protons E-2.7 The high energy cosmic ray standard paradigm Knee Galactic nuclei E-3 Gaisser Sources of high energy protons exists and dominate the CR spectrum at E> 1018.5 eV

  7. “Top – Down” and “Bottom – Up” processes MX~102124 eV CR  1021 eV E-2 spectrum gammas and neutrinos decay or annihilation Top Down Bottom Up acceleration CR  1021 eV flat spectrum p,e at rest gammas and neutrinos

  8. Astrophysical sources of UHE particles These values are typical for very bright sources Bright AGN L1047 erg/sec GRB L1052 erg/sec Fermi acceleration to high energies requires Hillas • Large cosmic objects • Intense magnetic field • High shockwave velocity Emax =1020 eV GRB

  9. Possible extra Galactic sources of CR: AGN The term AGNs (Active Galactic Nuclei) gathers a number of astrophysical objects • Massive Black Hole • Accretion disk (UV + lines) • Collimated jets QSO GB1508+5714 Chandra QSO 3C273 QSO 3C279 EGRET The brightest observed steady sources: L=10421047 erg/s When the jet is directed towards the Earth  luminosity increases  ”Blazars”

  10. Possible extra Galactic sources of CR: GRB GRB (Gamma Ray Bursts) are the most powerful emissions of gamma rays ever observed. Happens at cosmological distances The observation rate is few/day GRB 030329 ESO L=1051 1053 erg/s t  1100 s (1/3 <2 sec) GRB have recentely been shown to be associated with SN, as indicated by the GRB030329 – SN 2003dh correlation (GRB 030329 z=0.17)

  11. Limits of HE gamma and proton astronomy The UHE CR and gamma horizon is limited by interactions with low energy background radiation

  12. IR,CMBR  e+e- ECMBR ~ 6.6·10-4 eV  E ~ 1013.5 eV Lower energy photons interact also with IR backgrond NCMBR N (GZK) Absorption of high energy photons and protons ECMBR ~ 6.6·10-4 eV  Ep ~ 1019.5 eV nCMBR ~ 400 cm-3 p~ 100 barn See also T. Stanev,2004 for p-IR interactions Guaranteed sources of neutrinos

  13. The GZK effect 5 Gpc Closest AGNs Galactic radius (15 kpc)

  14. High Energy neutrinos production Are the astrophysical sources of High Energy CR also candidate sources of HE neutrinos ? The interaction of protons with ambient gas or photon field may produce neutrino fluxes

  15. Neutrino production • Proton interactions • p  p (SNR,X-Ray Binaries) • p   (AGN, GRB, microQSO) • decay of pions and muons Halzen • Proton acceleration • Fermi mechanism • proton spectrum dNp/dE ~E-2 Astrophysical jet Neutrino production in cosmic accelerators Particle accelerator electrons are responsible for gamma fluxes (synchrotron, IC)

  16. HE proton interaction on ambient p or   0 HE proton Muons and muon-neutrinos   Target protons + -  Shock wave SN shells, clouds,.. CANGAROO observationsof RXJ1713.7-3946 fit with TeV gamma ray production by 0 decay (?) Beam dump in astrophysical jet environment (GRB,AGN,microQSO) HE proton muons and neutrinos Matter shells pions Target photons Shock waves Beam dump in SNR environment

  17. Neutrino fluxes chemical composition Tau neutrinos are unlikely produced in the sources (M= 1.7 GeV) They can be detected at the Earth as “oscillated” muon neutrinos: If the muon interaction time (IC) is larger than the muon decay time electron neutrinos and antineutrinos are also produced

  18. Limits of HE gamma and proton astronomy High energy protons 50 Mpc Astrophysical source neutrinos High energy gammas 10 Mpc Low energy protons deflected

  19. Motivations of high energy neutrino astronomy Extend the high energy CR and  Horizon (<50 Mpc) Identify the sources of UHE particles Explore deep inside the source (where »1 for CR and ) Probe hadronic models in astrophysical sources

  20. High energy neutrino fluxes Astrophysical sources are expected to produce a diffuse high energy neutrino flux with spectral index 2 The most powerful and/or the closest sources could give a clear point-like neutrino signal Time correlations between  events and photons will be clear signatures for transient source detection

  21. The WB bound An upper limit to the diffuse neutrino flux was set by Waxman and Bahcall assuming that the detected UHECR sources are the only neutrino sources • The WB bound is valid for: • Sources optically thin to UHECR (responsible for the observed spectrum) • Sources in which CR acceleration takes place (top-down excluded) “thick sources” MPR bound “thin sources” atmospheric WB bound Waxman Mannheim GeV

  22. Possible extragalactic sources and fluxes Ruled out by new AMANDA data (preliminary) pAGN cores ppAGN cores p blazar GRB AGN GZK Diffuse neutrino fluxes Learned Mannheim Nellen Stecker WB Limit Mannheim Waxman Bierman Bright and nearby GRB could produce intense directional fluxes (e.g. GRB 030329) as well as brightest AGNs (3C273, 3C279)

  23. Galactic Sources of HE neutrinos SNR, extensively discussed: (see T. Stanev) CRAB, Protheroe Most powerful GX339-4 SS433 microquasar Distefano Another important source of TeV neutrinos could be the Galactic centre (SGR-A*) which is a very active gamma source Galactic sources do not contribute to UHECR fluxes, therefore are not limited by WB bound. Even if much less intense, their proximity to the Earth may yield detectable neutrino fluxes

  24. High energy neutrino detection Detection of HE astrophysical neutrinos is achieved through CC neutrino interaction with matter with charged lepton production Neutrino astronomy requires reconstruction of direction and energy of the reaction products (charged leptons)

  25. Neutrino cross section At >TeV energies the muon and the neutrino are co-linear m nm N q X Reconstruction of the  trajectory allows the identification of the  direction Neutrinos are detected indirectly, following a DIS on a target nucleus N: 10-33 cm2 10-35cm2 1 TeV 1 PeV Gandhi

  26. Muon Range 2·104 In water 2·103 Range (m) 1 TeV 1 PeV Gaisser E(GeV) Muons have long tracks in water Due to its larger mass (m/ me~200) radiative losses of muons are strongly suppressed with respect to electrons

  27. Muon vs electron range 10 GeV 100 GeV Geant 3.21 1 TeV Electron Muon 100 TeV Spiering Wiebush

  28. Neutrino detection probabilty Due to the long muon range the target volume is much bigger than the detector instrumented volume       Instrumented detector D<R Probabilty to produce a detectable (E>Emin) muon

  29. Neutrino-induced muon fluxes • Neutrino flux spectrum • Probabilty to produce a detectable (E>Emin) muon • Earth transparency to HE neutrinos  >PeV neutrinos search for “horizontal” tracks PEarth 1 TeV E,min=1GeV P·10-3 10 TeV 100 TeV LogE(GeV) deg The number of muon events in units of detection area A and observation time T is:

  30. Detection area for astrophysical UHE neutrino fluxes The expected number of events for WB sources is roughly: The observation of TeV neutrino fluxes requires km2 scale detectors

  31. Diffuse Guaranteed (GZK): few / year ? Diffuse GRB: 20 / year Diffuse AGN (thin): few / year (thick): >100 / year Expected astrophysical neutrino induced muons in 1 km2 Waxman Mannheim Point-like GRB (030329): 110 / burst AGN (3C279): few / year Galactic SNR (Crab): few / year ? Galactic microquasars: 1  100 / year Waxman Dermer Protheroe Distefano

  32. km3 scale neutrino detectors • The requirement of large neutrino interaction target • induced Markov and Zheleznykh to propose the use of natural targets. • Deep seawater and polar ice offers: • huge (and inexpensive) target for neutrino interaction; • good optical characteristics as Cherenkov radiators; • shielding from cosmic background.

  33. atmospheric muon ~5000 PMT Underwater Cherenkov detectors: detection principles Cherenkov light neutrino muon Connection to the shore depth >3000m neutrino

  34. 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

  35. Cherenkov light emission and propagation The Cherenkov light is efficiently emitted by relativistic particles in water at UV-blue wavelengths under the condition: n() > 1 n(300700nm) ~ 1.35 C~ 42° Superkamiokande muon event

  36. 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). pseudo vertex De Jong

  37. Detector granularity Spacing of optical sensors inside the instrumented volume must be of the order of the light absorption lenght in water (70 m for blue light) Visible light About 5000 optical sensors are needed to fill up one km3

  38. Backgrounds Neutrino detectors must identify few astrophysical events on top of diffuse atmospheric backgrounds

  39. Backgrounds: atmospheric muons and neutrinos • Atmospheric neutrinos: • upward tracks are good neutrino candidates; • event direction and energy criteria can be used to discriminate background from astrophysical signals. • Atmospheric muons: • downgoing events background is due to mis-reconstructed (fake) tracks; • improve analysis filters for atmospheric muon background rejection. ANTARES

  40. 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

  41. First detection of HE neutrino events Proof of the underwater (and underice) Cherenkov detection technique has been achieved by AMANDA (South Pole) and BAIKAL-NT (Lake Baikal) detectors

  42. The AMANDA neutrino sky AMANDA PRELIMINARY (neutrino 2004 conference) The atmospheric neutrino spectrum has been measured by AMANDA and BAIKAL See Silvestri’s talk AMANDA and BAIKAL have demontrated the viability of neutrino detection with underwater and underice Cherenkov detectors at TeV energy scale

  43. The future neutrino telescopes >3000 m The quest to reach the km2 effective area is open ! IceTop Wait for the next lecture... 1400 m 2400 m Southern Hemisphere ICECUBE Northern Hemisphere Mediterranean km3

  44. Summary • High energy astrophysical neutrino fluxes are expected on the base of CR and  observations • Neutrino detection will provide unique informations on astrophysical sources: • overcomes the limitations of  and CR astronomy due to absorption on CMBR at cosmological distances; • evidence on the role of hadronic processeses in astrophysics • Neutrino events correlated in space and time with point-like (transient) sources will be probably the first evidence of detection of astrophysical neutrinos • The expected fluxes from sources implies >1km2 effective area to detect TeV-PeV neutrinos

  45. Other scientific goals Galactic SN: search for intense fluxes of electron anti-neutrinos need low optical background  task for AMANDA-ICECUBE Dark Matter: search for neutrinos ( 10 GeV) originated by the annihilation of neutralinos in the Sun, Earth, Galactic Centre low energy threshold, good event direction reconstruction

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