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Flavor ratios in neutrino telescopes for decay and oscillation measurements. NuPAC meeting Chennai (Mahabalipuram), India April 6, 2009 Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Motivation The sources The fluxes

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flavor ratios in neutrino telescopes for decay and oscillation measurements

Flavor ratios in neutrino telescopes for decay and oscillation measurements

NuPAC meeting

Chennai (Mahabalipuram), India

April 6, 2009Walter Winter

Universität Würzburg

TexPoint fonts used in EMF: AAAAAAAA

  • Motivation
  • The sources
  • The fluxes
  • Flavor composition and propagation
  • The detectors
  • Flavor ratios, and their limitations
  • The LBL complementarity
  • Particle physics applications
  • Summary and conclusions
neutrino fluxes
galactic extragalacticNeutrino fluxes
  • Cosmic rays of high energies:Extragalactic origin!?
  • If protons accelerated, the same sources should produce neutrinos

(Source: F. Halzen, Venice 2009)

different messengers
Different messengers
  • Shock accelerated protons lead to p, g, n fluxes
    • p: Cosmic rays:affected by magnetic fields
  • g: Photons: easily absorbed/scattered
  • n: Neutrinos: direct path

(Teresa Montaruli, NOW 2008)

different source types
Different source types
  • Model-independent constraint:Emax < Z e B R(Lamor-Radius < size of source)
    • Particles confined to within accelerator!
  • Interesting source candiates:
    • GRBs
    • AGNs

(Hillas, 1984; Boratav et al. 2000)

motivation this talk

Motivation (this talk)

What can we learn from neutrinos coming from astrophysical sources about neutrino properties?Especially: Neutrino flavor mixing and decays

the sources

The sources

Generic cosmic accelerator

from fermi shock acceleration to n production
From Fermi shock acceleration to n production

Example: Active galaxy(Halzen, Venice 2009)

synchroton radiation
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 Emin=m c2(~ (Emin)2 B )

~ (1-s)/2+1determined by spectral index s of injection

(example from Reynoso, Romero, arXiv:0811.1383)

pion photoproduction
Pion photoproduction

Powerlaw injection spectrumfrom Fermishock acc.


Differentcharacteristics(energy lossof protons)

(Photon energy in nucleon rest frame)

Resonant production

(Mücke, Rachen, Engel, Protheroe, Stanev, 2008; SOPHIA)

neutrino production
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 lossesSolid:with losses

(example from Reynoso, Romero, arXiv:0811.1383)

the fluxes

The fluxes

Single source versus diffuse flux versusstacking

neutrinos from a single source
Neutrinos from a single source
  • Example: GRBs observed by BATSE
  • Applies to other sources in atmosphericBG-free regime as well …
  • Conclusion: Most likely no significant statistics with only one source!

(Guetta et al, astro-ph/0302524)

diffuse flux e g agns
Diffuse flux (e.g. AGNs)

(Becker, arXiv:0710.1557)

  • Advantage: optimal statistics (signal)
  • Disadvantage: Backgrounds(e.g. atmospheric,cosmogenic)


Single sourcespectrum

Sourcedistributionin redshift,luminosity

Decreasewith luminositydistance

stacking analysis
Stacking analysis

(Source: IceCube)

  • Idea: Use multi-messenger approach
  • 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?

(Source: NASA)


Neutrino observations(e.g. AMANDA,IceCube, …)

GRB gamma ray observations(e.g. BATSE, Fermi-GLAST, …)

Extrapolateneutrino spectrumevent by event

(Becker et al, astro-ph/0511785;from BATSE satellite data)

Flavor composition at the source(Idealized)
  • Astrophysical neutrino sources producecertain flavor ratios of neutrinos (ne:nm:nt):
  • 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-dissociationof heavy nulcei
  • NB: Do not distinguish between neutrinos and antineutrinos
flavor composition at the source more realistic
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/0507599;see also: Kachelriess, Tomas, 2006, 2007; Lipari et al, 2007 for more refined calcs)

neutrino propagation
Neutrino propagation
  • Key assumption: Incoherent propagation of neutrinos
  • Flavor mixing:
  • Example: For q13 =0, q12=p/6, q23=p/4:
  • NB: No CPV in flavor mixing only!But: In principle, sensitive to Re exp(-i d) ~ cosd
  • Take into account Earth attenuation!

(see Pakvasa review, arXiv:0803.1701, and references therein)

the detection

The detection

Neutrino telescopes

  • High-E cosmic neutrinos detected with neutrino telescopes
  • Example: IceCube at south poleDetector material: ~ 1 km3antarctic ice (1 million m3)
  • Status 2008: 40 of 80 Strings


different event types
Different event types
  • Muon tracks from nmEffective area dominated!(interactions do not have do be within detector)Relatively low threshold
  • Electromagnetic showers(cascades) from neEffective volume dominated!
  • nt: Effective volume dominated
    • Low energies (< few PeV) typically hadronic shower (nt track not separable)
    • Higher Energies:nt track separable
      • Double-bang events
      • Lollipop events
  • Glashow resonace for electron antineutrinos at 6.3 PeV








(Learned, Pakvasa, 1995; Beacom et al, hep-ph/0307025; many others)

flavor ratios

Flavor ratios

… and their limitations

  • 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!
applications of flavor ratios
Applications of flavor ratios
  • Can be sensitiveto flavor mixing,neutrino properies
  • Example: Neutron beam
  • Many recent works inliterature(e.g. for neutrino mixing and decay: Beacom et al 2002+2003; 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)

(Kachelriess, Serpico, 2005)

the limitations
The limitations
  • Flavor ratios dependon energy if energylosses of muonsimportant
  • Distributionsof sources oruncertainties withinone source
  • Unbalanced statistics:More useful muontracks than showers

(Lipari, Lusignoli, Meloni, 2007; see also:Kachelriess, Tomas, 2006, 2007)

terrestrial neutrino sources
Terrestrial neutrino sources

There are three possible ways to create neutrinos artificially:

  • Beta decays:
    • Example: Nuclear fission reactors
  • Pion decays:
    • From accelerators:
  • Muon decays:
    • Muons created through pion decays!












reactor experiment double chooz
Reactor experiment: Double Chooz

~ Identical Detectors, L ~ 1.1 km

Start: 2009?

(Source: S. Peeters, NOW 2008)

beam experiment minos
Beam experiment: MINOS
  • Running experiment in the USfor the determination of the atmospheric osc. parameters
  • Uses pion decays

Beam line (Protons)

Near detector: 980 t

Ferndetektor: 5400 t

735 km

Source: MINOS

narrow band superbeams
Narrow band superbeams
  • Off-axis technology to suppress backgrounds
  • Beam spectrum more narrow
  • Examples:T2KNOnA

T2K beamOA 1 degreeOA 2 degreesOA 3 degrees


appearance channels
Appearance channels
  • Oscillation probability of interest to measure q13, dCP, mass hierachy (in A)

Almost zerofor narrow band superbeams

(Cervera et al. 2000; Akhmedov et al., 2004)

flavor ratios approximations
Flavor ratios: Approximations
  • Astro sources for current best-fit values:
  • Superbeams:

(Source: hep-ph/0604191)

complementarity lbl astro
Complementarity LBL-Astro
  • Superbeams have signal ~ sin dCP(CP-odd)
  • Astro-FLR have signal ~ cos dCP(CP-even)
  • Complementarity for NBB
  • However: WBB, neutrino factory have cosd-term!

(Winter, 2006)


sb reactor astrophysical
  • Complementary information for specific best-fit point:Curves intersect in only one point!

(Winter, 2006)

octant complementarity
Octant complementarity
  • In principle, one can resolve the q23 octant with astrophysical sources

(Winter, 2006)

particle physics applications

Particle physics applications

… of flavor ratios

constraining d cp
Constraining dCP
  • No dCP in
    • Reactor exps
    • Astro sources(alone)
  • Combination:May tell something on dCP
  • Problem: Pion beam has little dCP sensitivity!

(Winter, 2006)

earlier mh measurement
Earlier MH measurement?



(Winter, 2006)

R: 10%


decay scenarios
Decay scenarios
  • 23 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)










(Maltoni, Winter, 2008; see also Beacom et al 2002+2003; Lipari et al 2007; …)

scenario identification
Scenario identification

(Maltoni, Winter, 2008)

99% CLallowed regions(present data)


Some informationeven if only ~ 10 useful events!(Pion beam source;L: no of eventsobserved in #1)

generalized source
Generalized source
  • Define (fe:fm:ft)=(X:1-X:0) at source (no nt in flux)

X=0: Muon damped source

X=1/3: Pion beam sourceX=1: Neutron beam source

(Maltoni, Winter, 2008)http://theorie.physik.uni-wuerzburg.de/~winter/Resources/AstroMovies.html

unknown source diff flux
Unknown source/diff. flux
  • Cumulative flux (X marginalized X<=Xmax)

X<=1/3: Cosmic accelerator with arbitrary pion/muon coolingX<=1: Any source without nt production

(Maltoni, Winter, 2008)http://theorie.physik.uni-wuerzburg.de/~winter/Resources/AstroMovies.html

synergies with terrestrial exps
Synergies with terrestrial exps
  • Pion beam, 100 muon tracks, only m1 stableDouble Chooz + Astrophysical, only R measured!
  • Independent of flavor composition at source!

(Maltoni, Winter, 2008)

summary and conclusions
Summary and conclusions
  • In this talk: argumentation from sources via propagation to detection with the purpose of physics applications
  • Flavor ratio measurements might be complementary to LBL physics if
    • Neutrinos decay (or have other exotic properties) or
    • Discovery of High-E neutrino flux within 5-10 years (T2K/NOvA-timescales) and
    • At least some statistics (esp. in showers)
  • Individual sources: In which cases can we predict the flavor ratio at the source?
  • Fluxes: If we accumulate statistics, which additional uncertainties enter?
  • Detector:
    • Ability to detect showers?
    • What about double bang and lollipop events?
  • Timescales: Can we expect some information at the timescale of the upcoming terrestrial experiments?



(Huber, Lindner, Schwetz, Winter, in prep.)