Neutrino phenomenology Lecture 3: Aspects of neutrino astrophysics

Transcription

1 Neutrino phenomenology Lecture 3: Aspects of neutrino astrophysics Winter school Schladming 2010 Masses and constants Walter Winter Universität Würzburg ν

2 Contents (overall) Lecture 1: Testing neutrino mass and flavor mixing Lecture 2: Precision physics with neutrinos Lecture 3: Aspects of neutrino astrophysics 2

3 Contents (lecture 3) Introduction/repetition Solar oscillations (varying matter density) Neutrinos from cosmic accelerators and the determination of other neutrino properties: The sources The fluxes Flavor composition and propagation Detection Flavor ratios Compementarity to Long baseline searches? Test of other new physics properties Example: Neutrino lifetime Summary 3

4 Nobel prize 2002 "for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos Raymond Davis Jr detected over 30 years neutrinos from the Sun Evidence for nuclear fusion in the Sun s interior! Masatoshi Koshiba detected on twelve of the (10 16 ) neutrinos, which passed his detector, from an extragalactic supernova explosion. Birth of neutrino astronomy 4

5 Repetition

6 Standard Solar ν Model Neutrinos are produced as electron neutrinos at the source, in the deep interior of the Sun Neutrinos propagate to the surface of the Sun and leave it The neutrinos loose coherence on the way to the Earth, i.e., propagate as mass eigenstates pp-fusion chain Neutrino spectra 6

7 Ordinary matter: electrons, but no µ, τ Coherent forward scattering in matter: Net effect on electron flavor Matter effects proportional to electron density n e and baseline Hamiltonian in matter (matrix form, two flavors): Matter effects (MSW) (Wolfenstein, 1978; Mikheyev, Smirnov, 1985) Y: electron fraction ~ 0.5 (electrons per nucleon) 7

8 Parameter mapping In vacuum: In matter: 8

9 Neutrino oscillations in the Sun

10 Constant vs. varying matter density For constant matter density: H is the Hamiltonian in constant density For varying matter density: time-dep. Schrödinger equation (H explicitely time-dependent!) Transition amplitudes; ψ x : mixture ψ µ and ψ τ 10

11 Adiabatic limit Use transformation: Amplitudes of mass eigenstates in matter and insert into time-dep. SE [ ] Adiabatic limit: Matter density varies slowly enough such that differential equation system decouples! 11

12 Propagation in the Sun Neutrino production as ν e (fusion) at high n e Neutrino propagates as mass eigenstate in matter (DE decoupled); ξ: phase factor from propagation In the Sun: n e (r) ~ n e (0) exp(-r/r 0 ) (r 0 ~ R sun /10); therefore density drops to zero! Detection as electron flavor: Disappearance of solar neutrinos! 12

13 Solar oscillations In practice: A >> 1 only for E >> 1 MeV For E << 1 MeV: vacuum oscillations Averaged vacuum oscillations: P ee =1-0.5 sin 2 2θ Standard prediction Adiabatic MSW limit: P ee =sin 2 θ ~ 0.3 Galbiati, Neutrino

14 Some additional comments on stellar environments How do we know that the solar neutrino flux is correct? SNO neutral current measurement Why are supernova neutrinos so different? Neutrino densities so high that neutrino-self interactions Leads to funny collective effects, as gyroscope B. Dasgupta 14

15 Neutrinos from cosmic accelerators

16 Neutrino fluxes Cosmic rays of high energies: Extragalactic origin!? If protons accelerated, the same sources should produce neutrinos galactic extragalactic (Source: F. Halzen, Venice 2009) 16

17 Different messengers Shock accelerated protons lead to p, γ, ν fluxes p: Cosmic rays: affected by magnetic fields γ: Photons: easily absorbed/scattered ν: Neutrinos: direct path (Teresa Montaruli, NOW 2008) 17

18 Different source types Model-independent constraint: E max < Z e B R (Lamor-Radius < size of source) Particles confined to within accelerator! Interesting source candiates: GRBs AGNs (?) (Hillas, 1984; version from M. Boratav) 18

19 The sources Generic cosmic accelerator

20 From Fermi shock acceleration to ν production Example: Active galaxy (Halzen, Venice 2009) 20

21 Synchroton radiation Where do the photons come from? Typically two possibilities: Thermal photon field (temperature!) Synchroton radiation from electrons/positrons (also accelerated)? Determined by particle s minimum energy E min =m c 2 (~ (E min ) 2 B ) B ~ (1-s)/2+1 determined by spectral index s of injection (example from Reynoso, Romero, arxiv: ) 21

22 Pion photoproduction Multi-pion production Power law injection spectrum from Fermi shock acc. Resonant production, direct production (Photon energy in nucleon rest frame) Different characteristics (energy loss of protons) (Mücke, Rachen, Engel, Protheroe, Stanev, 2008; SOPHIA) 22

23 Pion photoproduction (2) Often used: Δ(1232)-resonance approximation In practice: this resonance hardly ever dominates for charged pions. Example: GRB (Hümmer, Rüger, Spanier, Winter, 2010) The neutrino fluxes from the Δ-approximation are underestimated by a factor > 2.4 (if norm. to photons from π 0 ) 23

24 Neutrino production Described by kinematics of weak decays (see e.g. Lipari, Lusignoli, Meloni, 2007) Complication: Pions and muons loose energy through synchroton radiation for higher E before they decay aka muon damping Dashed: no losses Solid: with losses (example from Reynoso, Romero, arxiv: ) 24

25 The fluxes Single source versus diffuse flux versus stacking

26 Neutrinos from a point source Example: GRBs observed by BATSE (Guetta et al, astro-ph/ ) Applies to other sources in atmospheric BG-free regime as well Conclusion: Most likely (?) no significant statistics with only one source! 26

27 Diffuse flux (e.g. AGNs) (Becker, arxiv: ) Comoving volume Advantage: optimal statistics (signal) Disadvantage: Backgrounds (e.g. atmospheric, cosmogenic) Single source spectrum Source distribution in redshift, luminosity Decrease with luminosity distance 27

28 Stacking analysis Idea: Use multi-messenger approach (Source: IceCube) (Source: NASA) GRB gamma ray observations (e.g. BATSE, Fermi-GLAST, ) Coincidence! Neutrino observations (e.g. AMANDA, IceCube, ) Good signal over background ratio, moderate statistics Limitations: Redshift only measured for a small sample (BATSE) Use empirical relationships A few bursts dominate the rates Selection effects? Extrapolate neutrino spectrum event by event (Becker et al, astro-ph/ ; from BATSE satellite data) 28

29 Flavor composition and propagation Neutrino flavor mixing

30 Astrophysical neutrino sources produce certain flavor ratios of neutrinos (ν e :ν µ :ν τ ): Pion beam source (1:2:0) Standard in generic models Muon damped source (0:1:0) Muons loose energy before they decay Neutron beam source (1:0:0) Neutrino production by photo-dissociation of heavy nulcei Flavor composition at the source (Idealized) NB: Do not distinguish between neutrinos and antineutrinos 30

31 Pion beam source (more realistic) Neutron decays Nominal line 1:2 Kinematics of weak decays: muon helicity! (Hümmer, Rüger, Spanier, Winter, 2010; see also Lipari, Lusignoli, Meloni, 2007) 31

32 Flavor composition at the source (More realistic) Flavor composition changes as a function of energy Pion beam and muon damped sources are the same sources in different energy ranges! Use energy cuts? (from Kashti, Waxman, astro-ph/ ; see also: Kachelriess, Tomas, 2006, 2007; Lipari et al, 2007 for more refined calcs) 32

33 Neutrino propagation Key assumption: Incoherent propagation of neutrinos Flavor mixing: Example: For θ 13 =0, θ 12 =π/6, θ 23 =π/4: (see Pakvasa review, arxiv: , and references therein) NB: No CPV in flavor mixing only! But: In principle, sensitive to Re exp(-i δ) ~ cosδ Take into account Earth attenuation! 33

34 The detection Neutrino telescopes

35 IceCube High-E cosmic neutrinos detected with neutrino telescopes Example: IceCube at south pole Detector material: ~ 1 km 3 antarctic ice (1 million m 3 ) Short before completion 35

36 Neutrino astronomy in the Mediterranean: Example ANTARES 36

37 Different event types Muon tracks from ν µ Effective area dominated! (interactions do not have do be within detector) Relatively low threshold Electromagnetic showers (cascades) from ν e Effective volume dominated! ν τ : Effective volume dominated Low energies (< few PeV) typically hadronic shower (ν τ track not separable) Higher Energies: ν τ track separable Double-bang events Lollipop events Glashow resonace for electron antineutrinos at 6.3 PeV (Learned, Pakvasa, 1995; Beacom et al, hep-ph/ ; many others) e µ τ ν e ν µ ν τ ν τ 37

38 Flavor ratios and their limitations

39 Definition The idea: define observables which take into account the unknown flux normalization take into account the detector properties Three observables with different technical issues: Muon tracks to showers (neutrinos and antineutrinos added) Do not need to differentiate between electromagnetic and hadronic showers! Electromagnetic to hadronic showers (neutrinos and antineutrinos added) Need to distinguish types of showers by muon content or identify double bang/lollipop events! Glashow resonance to muon tracks (neutrinos and antineutrinos added in denominator only). Only at particular energy! 39

40 Applications of flavor ratios Can be sensitive to flavor mixing, neutrino properies Example: Neutron beam Many recent works in literature (Kachelriess, Serpico, 2005) (e.g. for neutrino mixing and decay: Beacom et al ; Farzan and Smirnov, 2002; Kachelriess, Serpico, 2005; Bhattacharjee, Gupta, 2005; Serpico, 2006; Winter, 2006; Majumar and Ghosal, 2006; Rodejohann, 2006; Xing, 2006; Meloni, Ohlsson, 2006; Blum, Nir, Waxman, 2007; Majumar, 2007; Awasthi, Choubey, 2007; Hwang, Siyeon,2007; Lipari, Lusignoli, Meloni, 2007; Pakvasa, Rodejohann, Weiler, 2007; Quigg, 2008; Maltoni, Winter, 2008; Donini, Yasuda, 2008; Choubey, Niro, Rodejohann, 2008; Xing, Zhou, 2008; Choubey, Rodejohann, 2009; Bustamante, Gago, Pena- Garay, 2010, ) 40

41 Complementarity to longbaseline experiments

42 Appearance channels Oscillation probability of interest to measure θ 13, δ CP, mass hierachy (in A) Almost zero for narrow band superbeams (Cervera et al. 2000; Akhmedov et al., 2004) 42

43 Flavor ratios: Approximations Astro sources for current best-fit values: Superbeams: (Source: hep-ph/ ) 43

44 SB-Reactor-Astrophysical Complementary information for specific best-fit point: Curves intersect in only one point! (Winter, 2006) 44

45 Particle properties from flavor ratios (examples) see Pakvasa, arxiv: for a review of other examples: mass varying neutrinos, quantum decoherence, Lorentz/CPT violation,

46 Constraining δ CP No δ CP in Reactor exps Astro sources (alone) Combination: May tell something on δ CP Problem: Pion beam has little δ CP sensitivity! (Winter, 2006) 46

47 Neutrino lifetime Neutrino flux (oscillations averaged): τ i (E)=τ 0 E/m: lab frame lifetime of mass eigenstate ν i Strongest bound from SN1987A: τ/m > 10 5 s/ev on ν e Lifetime refers to mass eigenstates, but flavor eigenstates are observed Unclear if bound on ν 1 or ν 2 Astrophysical neutrinos probably best direct test of neutrino lifetime Distinguish: Complete decays: L >> τ i (E) Incomplete decays: L <~ τ i (E) 47

48 Complete decays 99% CL allowed regions (present data) R R Using the observables R and S, some complete decay scenarios can be excluded! (Maltoni, Winter, 2008) 1 1 Unstable Stable 48

49 Incomplete decays Decay into ν 1 with τ/m ~ 0.1: Bhattacharya, Choubey, Gandhi, Watanabe,

50 Summary and conclusions Matter effects in the Sun tests Neutrino oscillations in vacuum MSW effect Standard solar model The observation of astrophysical neutrinos is important for Identification of cosmic ray accelerators Test of source properties Test of neutrino properties Literature: e.g. Giunti, Kim: Fundamentals of neutrino physics and astrophysics, Oxford,

51 Limitations of flavor ratios Flavor ratios depend on energy if energy losses of muons important Distributions of sources or uncertainties within one source Unbalanced statistics: More useful muon tracks than showers (Lipari, Lusignoli, Meloni, 2007; see also: Kachelriess, Tomas, 2006, 2007) 51

52 Complementarity LBL-Astro Superbeams have signal ~ sin δ CP (CP-odd) Astro-FLR have signal ~ cos δ CP (CP-even) Complementarity for NBB However: WBB, neutrino factory have cosδ-term! Smallest sensitivity (Winter, 2006) 52

53 Neutrino decays on cosmological distances? 2 3 possibilities for complete decays Intermediate states integrated out LMH: Lightest, Middle, Heaviest I: Invisible state (sterile, unparticle, ) 123: Mass eigenstate number (LMH depends on hierarchy) a 1-a H M L? (Maltoni, Winter, 2008; see also Beacom et al ; Lipari et al 2007; ) b 1-b #7 53