La rivelazione di neutrini astrofisici

Transcription

1 La rivelazione di neutrini astrofisici T. Montaruli Università di Bari & INFN Neutrino Astrophysics Motivations Physics Issues Current Neutrino Telescopes and Experimental Results Future Outlook XV IFAE, Lecce,, Aprile

2 Probes of of the Universe Photons: straight-line propagation but reprocessed in sources and extragalactic backgrounds absorb E γ > TeV (pair production on IR, CMBR, radio) Protons: directions scrambled by magnetic fields (deflection<1 E>50 EeV) Neutrons: γcτ 10kpc for E ~EeV Absorption length of photons and protons UHE particles (γ, p, n, ) have small path-lengths respect to Hubble scale (GZK cut-off) γ+ir pγ e + e - p photopion Mrk 501 Survey of remote regions and engines inside sources through neutrinos: small interaction cross section and undeflected [also gravitational waves!] discovery potential γ+radio γ+cmwb Gal Cen <100 Mpc E~ TeV 2

3 ~E % of SN power is enough to feed CRs: erg per SN + ~3 SN per century in disk ~ erg/cm 3 s knee ~3000 TeV The cosmic ray connection Cosmic ray spectrum: 10 6 ev to ~10 20 ev New component with hard spectrum? Kinetic energy per nucleus (ev) Power spectrum for diffusive shock acceleration with differential index α ~ -2; but α ankle~10 EeV observed ~ -2.7 due to 1 par km -2 yr -1 propagation effects and escape time from Galaxy ~E -3 Cosmic ν s can provide an answer to the debated question: Which are the sources of the HE cosmic rays (E> ev)? Ankle: extragalactic sources (Galaxy cannot contain EHECR, no such powerful galactic source candidates, no evident anisotropy correlated with galactic plane 3

4 The ankle and the GZK cut-off GZK cut-off due to interactions of CRs (E> ev) on CMBR [Greisen 66; Zatsepin & Kuzmin66] EHECR data: light composition favored 1 event/km 2 /century Bahcall & Waxman, Phys. Lett B 556 (2003): Fly s Eye, HiRes, Yakutsk consistent with UHE protons + GZK at 7σ. AGASA (30% of total exposure) favors more exotic models. Change energy scale No need or exotic models to explain EHECR! 4

5 ν production and sources Top-down: decays of unstable or meta-stable particles produced by radiation, interaction or collapse of topological defects or decay of relic particles Z decays due to UHE ν interaction on relic ν s (Weiler, 1982) Cosmogenic ν s: UHE ν interactions on CMB (Engel Seckel, Stanev, 2001) Bottom-up (beam-dump model): cosmic accelerator + interaction on matter or γ s: π 0 γ-astronomy π ± ν-astronomy Jets of AGN, GRB fireballs Accretion shocks in galaxy clusters, Galaxy mergers Young supernova remnants (p or heavy ion accelaration) Pulsars, Magnetars (large magnetic fields) Micro-quasars (binaries with jets seen in radio) Proton acceleration: E max ~ ΓBR and if collapsed objects E max ~ ΓBM 5

6 The link with γ astronomy Neglecting γ absorption (large uncertainty) Φ ν Φ γ 1 st order Fermi acceleration mechanism: harder spectra than atmospheric ν s Observations consistent with em mechanisms BUT first evidence in a SNR of hadronic mechanism? RXJ CANGAROO, Nature Syncrotron π 0 IC Reimer et al, A&A 390, L43 (2002): any GeV emission should be compatible with EGRET measured flux 3EG J (even if not coincident with CANGAROO source) 6

7 Detected Sources emitting γs γs s with E>TeV AMANDA location ANTARES location 11 visible 100% of day 3 visible 100% of day 8 never visible 8 visible >50% of day 3 visible 20-50% of day 8 visible <20% of day RXJ not visible BL Lacs, Pulsars and SNRs Cygnus OB2: association of stars AMANDA location: sources always at same elevation, constant sensitivity with time possible advantage for transient sources BUT INSENSITIVE TO HALF OF THE SKY Earth shadowing not considered, only visibility 7

8 ν interaction cross-section very low huge detectors (km 3 ) not feasible Detection principle underground! Markov/ Greisen idea (1960) ν + N µ + X Target is surrounding matter M = ρ R µ S (E µ = 1 TeV : R µ = 2.5 km) 3d PMT array reconstructs µ tracks and cascades. Also ν e and ν τ can be detected (better energy resolution but worse ν µ angular resolution) ν 8

9 Cosmic νs s Oscillations ν interaction length ~Earth TeV ν τ undergoes regeneration through CC + τ decay cosmic ν s at surce: ν e :ν µ :ν τ = 1:2:0 (if µ s decay) oscillations with atm ν s parameters and L ~ Mpc ν e :ν µ :ν τ = 1:1:1 E -1 diff. spectrum ν τ /ν µ : 2.85, 1.29 (reduced to 1.11, 1.07 for E -2 ) ν e /ν µ secondaries/ν τ : 37%,6% (reduced to 2.2%,0.2% for E -2 ) 9

10 Environment ( 40 K, bioluminescence) and electronics Atmospheric ν s Atmospheric µ s (sea/ice shielding) Rejection: direction and energy, time for bursters E -2 ANTARES Atmospheric νs The backgrounds Angle averaged E 2.5 dφ/de (GeV 1.5 cm -2 s -1 sr -1 ) Problem: 2 orders of magnitude uncertainty on current predictions of prompt νs Prompt ν s: Costa, Astrop. Phys. 16 (2001) log 10 E ν (GeV) 10

11 Neutrino telescope parameters Background free region: direction and/or time constraint, energy cut upper limits scale with 1/exposure Background limited region: upper limits scale with 1/sqrt(exposure) Sensitivity: N are events from ν source and B events from atm ν background number of sigmas=n/sqrt(b) (AT) / θ θ = angular resolution AT = exposure Discovery potential at 100 TeV: source luminosity to have 10 events/km 2 /yr with P ν --> µ ~ 10-4 and N = f ν /E ν P ν µ AT L ν ~4πd 2 f ν 4πd /[AT (km 2 yr)] in erg/s Pulsars/SNRs/magnetars/µquasars erg/s (5 kpc) AGN/BL Lacs/GRBs > erg/s (>100 Mpc) ~200 ev/yr/km 2 W&B limit ( E -2 GeV cm -2 s -1 sr -1 ) 11

12 Effective areas Event rates Effective area (volume): includes reconstruction efficiencies, affected by absorption length and coincidence requests to suppress backgrounds, strongly dependent on spectrum Selected event rate A eff = Incident muon flux ANTARES: for hard spectra bulk of the events at TeV 12

13 ν Angular and energy resolutions Resolution dominated by kinematic angle θ νµ Resolution dominated by reconstructon Limiting value ~0.15 Energy resolution log(e rec /E MC ) µ Factor 3 Factor 2 Reconstruction resolution limited by phototube TTS and light diffusion in water 13

14 µ cm -2 s southern sky 4 years Super-Kamiokande 5.6 years MACRO Point-like sources northern sky 170 days AMANDA-B ANTARES 1 yr Expected sensitivity AMANDA data declination (degrees) 14

15 ν µ limits for E -2 Diffuse fluxes All flavors [2] AMANDA II (νe)[3](prelim) AMANDA Cascades (ν e +ν µ +ν τ ) 130 d (PRD67, 2003): GeV cm -2 s -1 sr -1 AMANDAII 197d: GeV cm -2 s -1 sr -1 AMANDA (ν µ ) 130 d (astro-ph/030328): GeV cm -2 s -1 sr -1 AMANDA UHE >10 16 ev: 2 (no sys)/4.8 (sys) 10-6 GeV cm -2 s -1 sr -1 Baikal (ν e +2ν µ ) 234 d NT200+70d NT96 (Neutrino02): GeVcm -2 s -1 sr -1 15

16 Search for Dark Matter Neutralinos from the Sun Relativistic Monopoles 16

17 AMANDA B-10:302 OM s/10 strings Results recently published on atm ν s (30% sys), diffuse muon fluxes & cascades ( TeV), UHE ν s (> PeV), WIMPs, SNs Ang. resolution 3.9 (EAS check) E resolution ~30-60% Effective area E µ > 10 TeV > 10 4 m 2 AMANDA II: about factor of m 120 m Absorption length (480 nm): 110 m Effective scatter length ~ 25 m 17

18 Baikal Neutrino Telescope 1100 m depth in Siberian Lake 3.6 km off-shore 51 N 104 E deployment+eas on ice platform Ang. res OMs on 8 strings Absorption length (480 nm): 28 m Effective scatter length > 200 m Planned upgrade Future 1300 OMs/91 strings 70m 37 cm QUASAR PMTs 70m

19 ANTARES antares.in2p3..in2p3.fr Shore station Absorption length (460 nm): m Effective scatter length > 100 m 12 equipped strings 90 OMs/line ~60m float Optical module Compass, tilt meter 2475m Electro-optical submarine cable ~40km 350m active ~100m anchor Electronics containers Readout cables 19 Junction box Teresa Montaruli, Acoustic IFAE, Lecce, beacon 24 Aprile 2003

20 Detector Deployment: achievemets and planning Collaboration formed Nov 99- Jun 00: demonstrator line deployment + operation atmospheric µs R&D D and Site evaluation programme to select a suitable site Jun 00: implosion test Oct 01: Electro Optical Cable Technical design report completed Mar 01: sea bed survey Deployment of 12 lines 16-17/03/03 17/03/03 Connections by submarine 12/02/03 Instrumentation line deployed 24/12/02: Prototype line deployed 7-9/12/02: Junction box deployed Apr 02: 900 OM production at Saclay 20

21 NEMO Actual proposal of general layout for Km 3 detector NEMO.RD Issues: selection of the optimal site for km 3 site in Mediterranean (Capo Passero) R&D on materials and mechanical structures suited for long-term measurements in sea water and on low power consumption electronics 1400 m feasibility study and physics simulations Test site off-shore Catania: first multi-purpose underwater Lab connected to shore in real time 200 m 200 m main JB Shore station 25 km Electro-Optical Cable (installed Sep01) to JB splits for 2 sites GEOSTAR (seismologic monitoring),... main electro optical cable n. 64 towers, 16 storeys/tower, 600 m implemented 4096 PMTs 21

22 Conclusions Cosmic neutrinos are reasonably expected but fluxes are low AMANDA and Baikal are already producing results at the level of SK and MACRO, AMANDA II 1 order of magnitude better, BUT all flavors Towards a km3 detector: ICE/sea water have complementary optical properties ICE: larger scattering but longer absorption lengths (better calorimeter but worse angular resolution) deployment from ice platform but no recovery EAS to check pointing capabilities, no 40 K and bioluminescence 2 detectors in upper and lower emisphere are needed to ensure full sky coverage ICECUBE: 4800 OM s/80 strings construction in austral summer Funding request: $295 M ANTARES 2 lines taking data at 2500 m ANTARES/NEMO joined their efforts to study feasibilty of Med detector NESTOR: Mar floor with 12 OM s at 4000 m connected to shore by 28 km EOC taking data 22