Flavor ratios in neutrino telescopes for decay and oscillation measurements
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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

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

galactic extragalactic

Neutrino fluxes

  • Cosmic rays of high energies:Extragalactic origin!?

  • If protons accelerated, the same sources should produce neutrinos

(Source: F. Halzen, Venice 2009)

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

  • 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)

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

The sources

Generic cosmic accelerator

From Fermi shock acceleration to n production

Example: Active galaxy(Halzen, Venice 2009)

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

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

  • 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

Single source versus diffuse flux versusstacking

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)

(Becker, arXiv:0710.1557)

  • Advantage: optimal statistics (signal)

  • Disadvantage: Backgrounds(e.g. atmospheric,cosmogenic)


Single sourcespectrum

Sourcedistributionin redshift,luminosity

Decreasewith luminositydistance

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 and propagation

Neutrino flavor mixing

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 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

  • 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

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


Neutrino astronomy in the Mediterranean: Example ANTARES


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

… 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

  • 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

  • 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)

Complementarity to long-baseline experiments

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

~ Identical Detectors, L ~ 1.1 km

Start: 2009?

(Source: S. Peeters, NOW 2008)

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

  • Off-axis technology to suppress backgrounds

  • Beam spectrum more narrow

  • Examples:T2KNOnA

T2K beamOA 1 degreeOA 2 degreesOA 3 degrees


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

  • Astro sources for current best-fit values:

  • Superbeams:

(Source: hep-ph/0604191)

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)



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

(Winter, 2006)

Octant complementarity

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

(Winter, 2006)

Particle physics applications

… of flavor ratios

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?



(Winter, 2006)

R: 10%


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

(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

  • 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

  • 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

  • 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

  • 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.)

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