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Magnetic field and flavor effects on the neutrino fluxes from cosmic accelerators. WIN 2011 January 31-February 5, 2011 Cape Town , South Africa Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Introduction

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Magnetic field and flavor effects on the neutrino fluxes from cosmic accelerators

Magnetic field and flavor effects on the neutrino fluxes from cosmic accelerators

WIN 2011

January 31-February 5, 2011Cape Town, South Africa

Walter Winter

Universität Würzburg

TexPoint fonts used in EMF: AAAAAAAA

Contents from cosmic accelerators

  • Introduction

  • Simulation of sources, a self-consistent approach

  • Neutrino propagation and detection;flavor ratios

  • On gamma-ray burst (GRB) neutrino fluxes

  • Summary

Neutrino production in astrophysical sources
Neutrino production in astrophysical sources from cosmic accelerators

max. center-of-mass energy ~ 103 TeV(for 1021 eV protons)

Example: Active galaxy(Halzen, Venice 2009)

Neutrino detection icecube
Neutrino detection: IceCube from cosmic accelerators

  • Example: IceCube at South PoleDetector material: ~ 1 km3antarctic ice

  • Completed 2010/11 (86 strings)

  • Recent data releases, based on parts of the detector:

    • Point sources IC-40arXiv:1012.2137

    • GRB stacking analysis IC-40arXiv:1101.1448

    • Cascade detection IC-22arXiv:1101.1692

Example grb stacking
Example: GRB stacking from cosmic accelerators

(Source: IceCube)

  • Idea: Use multi-messenger approach

  • Predict neutrino flux fromobserved photon fluxesevent by event

  • Good signal over background ratio (atmospheric background), moderate statistics

(Source: NASA)


Neutrino observations(e.g. IceCube, …)

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

(Example: IceCube, arXiv:1101.1448)

Ic 40 data meet generic bounds
IC-40 data meet generic bounds from cosmic accelerators


  • Generic flux based on the following assumptions:- GRBs are the sources of (highest energetic) cosmic rays- Fraction of energy the protons loose in pion production ~ 20%(Waxman, Bahcall, 1999; Waxman, 2003)

What do such bounds actually mean more generically? Limit

IC-40 stacking limit

Fraction of p energy lost into pion production(related to optical thicknessof pg/ng interactions)

Baryonic loading(ratio between protons andelectrons/positrons in the jet)


When do we expect a n signal some personal comments
When do we expect a from cosmic acceleratorsn signal?[some personal comments]

  • Unclear if specific sources lead to neutrino production; spectral energy distribution can be often described by leptonic processes as well (e.g. inverse Compton scattering, …)

  • However: whereever cosmic rays are produced, neutrinos should be produced as well (pg, pp!)

  • There are a number of additional candidates, e.g.

    • „Hidden“ sources (e.g. „slow jet supernovae“ without gamma-ray counterpart)(Razzaque, Meszaros, Waxman, 2004; Ando, Beacom, 2005; Razzaque, Meszaros, 2005; Razzaque, Smirnov, 2009)

    • Large fraction of Fermi-LAT unidentified sources?

  • From the neutrino point of view: „Fishing in the dark blue sea“? Looking at the wrong places?

  • Need for tailor-made neutrino-specific approaches?

Simulation of sources

Simulation of sources from cosmic accelerators

Meson photoproduction
Meson photoproduction from cosmic accelerators

  • 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: Often slow, difficult to handle; 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

Neucosma key ingredients neu trinos from cosm ic a ccelerators
NeuCosmA key ingredients from cosmic accelerators(„Neutrinos from Cosmic Accelerators“)

  • What it can do so far:

    • Photohadronics based on SOPHIA(Hümmer, Rüger, Spanier, Winter, 2010)

    • Weak decays incl. helicity dependence of muons(Lipari, Lusignoli, Meloni, 2007)

    • Cooling and escape

  • Potential applications:

    • Parameter space studies

    • Flavor ratio predictions

    • Time-dependent AGN simulations etc. (photohadronics)

    • Monte Carlo sampling of diffuse fluxes

    • Stacking analysis with measured target photon fields

    • Fits (need accurate description!)

Kinematics ofweak decays: muon helicity!

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

A self consistent approach
A self-consistent approach from cosmic accelerators

  • 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)

  • Requires few model parameters, mainly

  • Purpose: describe wide parameter ranges with a simple model; minimal set of assumptions for n!?


Model summary
Model summary from cosmic accelerators

Dashed arrows: include cooling and escape

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

Opticallythinto neutrons


Energy losses


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

An example 1
An example (1) from cosmic accelerators

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

  • Meson production described by(summed over a number of interaction types)

    • Only product normalization enters in pion spectra as long as synchrotron or adiabatic cooling dominate

  • Maximal energy of primaries (e, p) by balancing energy loss and acceleration rate

Maximum energy: e, p

Hümmer, Maltoni, Winter, Yaguna, 2010

An example 2
An example (2) from cosmic accelerators

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

  • Secondary spectra (m, p, K) become loss-steepend above a 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 will not affect the flavor composition

    • Flavor ratios most robust predicition for sources?

Cooling: charged m, p, K




Hümmer, Maltoni, Winter, Yaguna, 2010

An example 3
An example (3) from cosmic accelerators

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

m cooling break



p cooling break

Pile-up effect Flavor ratio!



Hümmer, Maltoni, Winter, Yaguna, 2010

The hillas plot
The Hillas plot from cosmic accelerators

  • Hillas (necessary) condition for highest energetic cosmic rays (h: acc. eff.)

  • Protons, 1020 eV, h=1:

  • We interpret R and B as parameters in bulk frame

    • High bulk Lorentz factors G relax this condition!

Hillas 1984; version adopted from M. Boratav

Magnetic field and flavor effects on the neutrino fluxes from cosmic accelerators

Flavor composition at the source from cosmic accelerators(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! from cosmic accelerators

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, Maltoni, Winter, Yaguna, 2010; see also: Kashti, Waxman, 2005; Kachelriess, Tomas, 2006, 2007; Lipari et al, 2007)

Parameter space scan
Parameter space scan from cosmic accelerators

  • 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, Maltoni, Winter, Yaguna, 2010

Neutrino propagation and detection

Neutrino propagation and detection from cosmic accelerators

Neutrino propagation
Neutrino propagation from cosmic accelerators

  • 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)

Which sources can specific data constrain best
Which sources can specific data constrain best? from cosmic accelerators

  • Constrain individual fluxes after flavor mixing with existing data

Point sources IC-40arXiv:1012.2137

Energy flux density


(work in preparation)

Measuring flavor
Measuring flavor? from cosmic accelerators

  • 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 from cosmic accelerators

  • 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 from cosmic accelerators

  • Basic dependencerecovered afterflavor mixing

  • However: mixing parameter knowledge ~ 2015 (Daya Bay, T2K, etc) required

Hümmer, Maltoni, Winter, Yaguna, 2010

New physics in r
New physics in R? from cosmic accelerators

Energy dependenceflavor comp. source

Energy physics

(Example: [invisible] neutrino decay)


Stable state


Unstable state

Mehta, Winter, arXiv:1101.2673

Which sources are most useful
Which sources are most useful? from cosmic accelerators

  • Most useful:Sources for which different flavor compositions are present; requires substantial B

  • Some dependence on new physics effect

aL=108 GeV

No of decayscenarios which canbe identified

Mehta, Winter, arXiv:1101.2673

On grb neutrino fluxes

On GRB neutrino fluxes from cosmic accelerators

Waxman bahcall reproduced
Waxman-Bahcall, reproduced from cosmic accelerators

  • Difference to above: target photon field ~ observed photon field used

  • Reproduced original WB flux with similar assumptions

  • Additional charged pion production channels included,also p-!

broken power law(Band function)

p decays only

~ factor 6

Baerwald, Hümmer, Winter, arXiv:1009.4010

Fluxes before flavor mixing
Fluxes before flavor mixing from cosmic accelerators



Baerwald, Hümmer, Winter, arXiv:1009.4010

After flavor mixing
After flavor mixing from cosmic accelerators


  • Different flux shape

    • Can double peak structure be used?

    • How reliable is stacking analysis from IC-40?

  • Different normalization

    • Expect actually more neutrinos than in original estimates

    • Baryonic loading x fpstronger constrained?

    • GRBs not the sourcesof highest energetic CR?

(full scale)

(full scale)

Baerwald, Hümmer, Winter, arXiv:1009.4010; see also: Murase, Nagataki, 2005; Kashti, Waxman, 2005; Lipari, Lusignoli, Meloni, 2007

Summary from cosmic accelerators

  • Particle production, flavor, and magnetic field effects change the shape of astrophysical neutrino fluxes

    • Description of the „known“ (particle physics) components should be as accurate as possible for data analysis

  • 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)

  • However: flavor ratios should be interpreted as energy-dependent quantities

  • The flux shape and flavor ratio of a point source can be predicted in a self-consistent way if the astrophysical parameters can be estimated, such as from a multi-messenger observation (R: from time variability, B: from energy equipartition, a: from spectral shape)