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Neutrino fluxes and flavor ratios from cosmic accelerators, and the Hillas plot. Matter to the deepest 2011 September 13-18, 2011 Ustron, Poland Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Introduction Simulation of sources

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neutrino fluxes and flavor ratios from cosmic accelerators and the hillas plot

Neutrino fluxes and flavor ratios from cosmic accelerators, and the Hillas plot

Matter to the deepest 2011

September 13-18, 2011Ustron, Poland

Walter Winter

Universität Würzburg

TexPoint fonts used in EMF: AAAAAAAA

  • Introduction
  • Simulation of sources
  • Neutrino propagation, new physics tests?
  • Neutrino detection
  • Multi-messenger constraints on GRBs
  • Summary
neutrino detection icecube
Neutrino detection: IceCube
  • Example: IceCube at South PoleDetector material: ~ 1 km3 antarctic ice
  • Completed 2010/11 (86 strings)
  • Recent data releases, based on parts of the detector:
    • Point sources IC-40 [IC-22]arXiv:1012.2137, arXiv:1104.0075
    • GRB stacking analysis IC-40arXiv:1101.1448
    • Cascade detection IC-22arXiv:1101.1692
  • Have not seen anything (yet)
    • What does that mean?
    • Are the models too optimistic?
    • Which parts of the parameter space does IceCube actually test?

parameter space hillas plot
Parameter space: Hillas plot?
  • Model-independent (necessary) conditionfor acceleration ofcosmic rays:Emax ~ h Z e B R(Larmor-Radius < size of source; h: acceleration efficiency)
    • Particles confined to within accelerator!

[Caveat: condition relaxed if source heavily Lorentz-boosted (e.g. GRBs)]

„Test points“


Protons to 1020 eV

Hillas 1984; version adopted from M. Boratav

simulation of sources a self consistent approach
Simulation of sources:A self-consistent approach
  • Target photon field typically:
    • Put in by hand (e.g. obs. spectrum: GRBs)
    • Thermal target photon field
    • From synchrotron radiation of co-accelerated electrons/positrons (AGN-like)
    • From more complicated comb. of radiation processes
  • Requires few model parameters, mainly
  • Purpose: describe wide parameter ranges with a simple model unbiased by CR and g observations minimal set of assumptions for n production?


model summary

High-energyprocesses etc.included

[Method: Hümmer, Rüger, Spanier, Winter, ApJ 721 (2010) 630]

Model summary

Dashed arrows: include cooling and escape

Opticallythinto neutrons

Dashed arrow: Steady state equationBalances injection with energy losses and escapeQ(E) [GeV-1 cm-3 s-1] per time frameN(E) [GeV-1 cm-3] steady spectrum


Energy losses


Hümmer, Maltoni, Winter, Yaguna, Astropart. Phys. 34 (2010) 205

an example secondaries
An example: Secondaries

a=2, B=103 G, R=109.6 km

  • Secondary spectra (m, p, K) become loss-steepend abovea critical energy
    • Ec depends on particle physics only (m, t0), and B
    • Leads to characteristic flavor composition
    • Any additional cooling processes mainly affecting the primaries willnot affect the flavor composition
    • Flavor ratios most robustprediction for sources?
    • The only way to directly measure B?

Cooling: charged m, p, K


Pile-up effect Flavor ratio!




Hümmer et al, Astropart. Phys. 34 (2010) 205


Flavor composition at the source(Idealized – energy independent)

  • 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)at high E: Muons loose energy before they decay
  • Muon beam source (1:1:0)Cooled muons pile up at lower energies (also: heavy flavor decays)
  • Neutron beam source (1:0:0)Neutron decays from pg(also possible: photo-dissociationof heavy nuclei)
  • At the source: Use ratio ne/nm (nus+antinus added)
however flavor composition is energy dependent
However: flavor composition is energy dependent!

Pion beam

Muon beam muon damped

Energywindowwith largeflux for classification

Typicallyn beamfor low E(from pg)

Pion beam muon damped

Undefined(mixed source)

Behaviorfor smallfluxes undefined

(from Hümmer et al, Astropart. Phys. 34 (2010) 205; see also: Kashti, Waxman, 2005; Kachelriess, Tomas, 2006, 2007; Lipari et al, 2007)

parameter space scan
Parameter space scan
  • All relevant regions recovered
  • GRBs: in our model a=4 to reproduce pion spectra; pion beam  muon damped (confirmsKashti, Waxman, 2005)
  • Some dependence on injection index


Hümmer et al, Astropart. Phys. 34 (2010) 205

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

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

neutrino detection muon tracks

Max Ep

Neutrino detection:Muon tracks
  • Differential limit 2.3 E/(Aeff texp)illustrates what spectra thedata limit best

Auger 2004-2008 Earth skimming nt

IC-40 nm

Spectral shape is important because instrument response is very sensitive to it!

(Winter, arXiv:1103.4266; diff. limits from IceCube, arXiv:1012.2137; Auger, arXiv:0903.3385)

which point sources can specific data constrain best
Which point sources can specific data constrain best?

Constraints to energy flux density

Inaccessible (atm. BG)

Inaccessible (atm. BG)

Deep Core

IC cascades?


Auger North?




(Winter, arXiv:1103.4266)

measuring flavor
Measuring flavor?
  • In principle, flavor information can be obtained from different event topologies:
    • Muon tracks - nm
    • Cascades (showers) – CC: ne, nt, NC: all flavors
    • Glashow resonance: ne
    • Double bang/lollipop: nt

(Learned, Pakvasa, 1995; Beacom et al, 2003)

  • In practice, the first (?) IceCube “flavor“ analysis appeared recently – IC-22 cascades (arXiv:1101.1692)Flavor contributions to cascades for E-2 extragalatic test flux (after cuts):
      • Electron neutrinos 40%
      • Tau neutrinos 45%
      • Muon neutrinos 15%
    • Electron and tau neutrinos detected with comparable efficiencies
    • Neutral current showers are a moderate background



flavor ratios at detector
Flavor ratios at detector
  • At the detector: define observables which
    • take into account the unknown flux normalization
    • take into account the detector properties
  • Example: Muon tracks to showersDo not need to differentiate between electromagnetic and hadronic showers!
  • Flavor ratios have recently been discussed for many particle physics applications

(for flavor 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; Choubey, Rodejohann, 2009; Esmaili, Farzan, 2009; Bustamante, Gago, Pena-Garay, 2010; Mehta, Winter, 2011…)

parameter uncertainties
Parameter uncertainties
  • Basic dependencerecovered afterflavor mixing
  • However: mixing parameter knowledge ~ 2015 (Daya Bay, T2K, etc) required

Hümmer et al, Astropart. Phys. 34 (2010) 205

new physics in r
New physics in R?

Energy dependenceflavor comp. source

Energy physics

(Example: [invisible] neutrino decay)


Stable state


Unstable state

Mehta, Winter, JCAP 03 (2011) 041; see also Bhattacharya, Choubey, Gandhi, Watanabe, 2009/2010

gamma ray burst fireball model ic 40 59 data meet generic bounds
Gamma-ray burst fireball model:IC-40/59 data meet generic bounds

(arXiv:1101.1448, PRL 106 (2011) 141101)

  • Generic flux based on the assumption that GRBs are the sources of (highest energetic) cosmic rays (Waxman, Bahcall, 1999; Waxman, 2003; spec. bursts:Guetta et al, 2003)

IC-40 stacking limit

  • Does IceCube really rule out the paradigm that GRBs are the sources of the ultra-high energy cosmic rays?
  • Flavor and magnetic field effects in GRB neutrino fluxes - see before [+ Baerwald, Hümmer, Winter, Phys. Rev. D83 (2011) 067303]
  • Re-computation of fireball phenomenology, comparison with numerics … [work in progress]
  • Systematics in stacked (summed) neutrino fluxes? [next slides]
example grb stacking
Example: GRB stacking

(Source: IceCube)

  • Idea: Use multi-messenger approach
  • Predict neutrino flux fromobserved photon fluxesburst by burst
  • quasi-diffuse fluxextrapolated

(Source: NASA)


Neutrino observations(e.g. IceCube, …)

GRB gamma-ray observations(e.g. Fermi GBM, Swift, etc)

Observed:broken power law(Band function)

(Example: IceCube, arXiv:1101.1448)

systematics in aggregated fluxes
Systematics in aggregated fluxes
  • The problem: statement on source class based on many sources (statistics!)
  • IceCube: Signal from 117 bursts “stacked“ (summed) for current limit(arXiv:1101.1448)
    • Is that sufficient?
  • Peak contribution in a region of low statistics
    • Systematical error on quasi-diffuse flux (90% CL) at least
      • 50% for 100 bursts
      • 35% for 300 bursts
      • 25% for 1000 bursts

Weight function:contr. to total flux

Distribution of GRBsfollowing star form. rate


10000 bursts

(Baerwald, Hümmer, Winter, arXiv:1107.5583)

  • Peculiarity of neutrinos: Flavor and magnetic field effects change the shape and flavor composition of astrophysical neutrino fluxes
  • Another peculiarity: number of events from single source probably small; need dedicated methods for statistics aggregation with their own systematics
  • Flavor ratios, though difficult to measure, are interesting because
    • they may be the only way to directly measure B (astrophysics)
    • they are useful for new physics searches (particle physics)
    • they are relatively robust with respect to the cooling and escape processes of the primaries (e, p, g)
meson photoproduction
Meson photoproduction
  • Often used: D(1232)-resonance approximation
  • Limitations:
    • No p- production; cannot predict p+/ p- ratio (affects neutrino/antineutrino)
    • High energy processes affect spectral shape
    • Low energy processes (t-channel) enhance charged pion production
    • Charged pion production underestimated compared to p0 production by factor of 2.4 (independent of input spectra!)
  • Solutions:
    • SOPHIA: most accurate description of physicsMücke, Rachen, Engel, Protheroe, Stanev, 2000Limitations: Monte Carlo simulation; helicity dep. muon decays!
    • Parameterizations based on SOPHIA
      • Kelner, Aharonian, 2008Fast, but no intermediate muons, pions (cooling cannot be included)
      • Hümmer, Rüger, Spanier, Winter, 2010Fast (~3000 x SOPHIA), including secondaries and accurate p+/ p- ratios; also individual contributions of different processes (allows for comparison with D-resonance!)
      • Engine of the NeuCosmA („Neutrinos from Cosmic Accelerators“) software

from:Hümmer, Rüger, Spanier, Winter, ApJ 721 (2010) 630

T=10 eV

effect of photohadronics
Effect of photohadronics
  • Reproduced original WB flux with similar assumptions
  • Additional charged pion production channels included, also p-!

p decays only

~ factor 6

Baerwald, Hümmer, Winter, Phys. Rev. D83 (2011) 067303

fluxes before after flavor mixing
Fluxes before/after flavor mixing





Baerwald, Hümmer, Winter, Phys. Rev. D83 (2011) 067303; see also: Murase, Nagataki, 2005; Kashti, Waxman, 2005; Lipari, Lusignoli, Meloni, 2007

re analysis of fireball model
Re-analysis of fireball model

(one example)

  • Correction factors from:
    • Cosmological expansion (z)
    • Some crude estimates, e.g. for fp (frac. of E going pion production)
    • Spectral corrections (compared to choosing the break energy)
    • Neutrinos from pions/muons
  • Photohadronics and magnetic field effects change spectral shape Baerwald, Hümmer, Winter, PRD83 (2011) 067303
  • Conclusion (this parameter set): Fireball flux ~ factor of five lower than expected, with different shape


(Hümmer, Baerwald, Winter, in prep.)