1. 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: AAAAAAAA

2. Contents Introduction
Simulation of sources, a self-consistent approach
Neutrino propagation and detection; flavor ratios
On gamma-ray burst (GRB) neutrino fluxes
Summary

3. Neutrino production in astrophysical sources
max. center-of-mass energy ~ 103 TeV (for 1021 eV protons)
Example: Active galaxy (Halzen, Venice 2009)

4. Neutrino detection: IceCube
Example: IceCube at South Pole Detector material: ~ 1 km3 antarctic ice
Completed 2010/11 (86 strings)
Recent data releases, based on parts of the detector:
Point sources IC-40 arXiv:
GRB stacking analysis IC-40 arXiv:
Cascade detection IC-22 arXiv:

5. Example: GRB stacking Idea: Use multi-messenger approach
Predict neutrino flux from observed photon fluxes event by event
Good signal over background ratio (atmospheric background), moderate statistics
(Source: IceCube)
(Source: NASA)
Coincidence!
Neutrino observations (e.g. IceCube, …)
GRB gamma-ray observations (e.g. Fermi GBM, Swift, etc)
(Example: IceCube, arXiv: )

6. IC-40 data meet generic bounds
(arXiv: )
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)
IC-40 stacking limit
What do such bounds actually mean more generically? Limit
Fraction of p energy lost into pion production (related to optical thickness of pg/ng interactions)
Baryonic loading (ratio between protons and electrons/positrons in the jet) X

7. When do we expect a n 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?

8. Simulation of sources

9. 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 physics Mücke, Rachen, Engel, Protheroe, Stanev, 2000 Limitations: Often slow, difficult to handle; helicity dep. muon decays!
Parameterizations based on SOPHIA
Kelner, Aharonian, 2008 Fast, but no intermediate muons, pions (cooling cannot be included)
Hümmer, Rüger, Spanier, Winter, 2010 Fast (~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

10. NeuCosmA key ingredients („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 of weak decays: muon helicity!
from: Hümmer, Rüger, Spanier, Winter, ApJ 721 (2010) 630

11. 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)
Requires few model parameters, mainly
Purpose: describe wide parameter ranges with a simple model; minimal set of assumptions for n!? ?

12. Hümmer, Maltoni, Winter, Yaguna, Astropart. Phys. 34 (2010) 205
Model summary
Dashed arrows: include cooling and escape
Dashed arrow: Steady state Balances injection with energy losses and escape Q(E) [GeV-1 cm-3 s-1] per time frame N(E) [GeV-1 cm-3] steady spectrum
Optically thin to neutrons
Injection
Energy losses
Escape
Hümmer, Maltoni, Winter, Yaguna, Astropart. Phys. 34 (2010) 205

13. Hümmer, Maltoni, Winter, Yaguna, 2010
An example (1)
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

14. Hümmer, Maltoni, Winter, Yaguna, 2010
An example (2)
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 Ec Ec Ec
Hümmer, Maltoni, Winter, Yaguna, 2010

15. An example (3) a=2, B=103 G, R=109.6 km m cooling break
Synchrotron cooling
Spectral split
p cooling break
Pile-up effect  Flavor ratio!
Pile-up effect
Slope: a/2
Hümmer, Maltoni, Winter, Yaguna, 2010

16. Hillas 1984; version adopted from M. Boratav
The Hillas plot
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

17. Flavor composition at the source (Idealized – energy independent)
Astrophysical neutrino sources produce certain 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-dissociation of heavy nuclei)
At the source: Use ratio ne/nm (nus+antinus added)

18. However: flavor composition is energy dependent!
Muon beam  muon damped
Pion beam
Energy window with large flux for classification
Typically n beam for low E (from pg)
Undefined (mixed source)
Pion beam  muon damped
Behavior for small fluxes undefined
(from Hümmer, Maltoni, Winter, Yaguna, 2010; see also: Kashti, Waxman, 2005; Kachelriess, Tomas, 2006, 2007; Lipari et al, 2007)

19. Hümmer, Maltoni, Winter, Yaguna, 2010
Parameter space scan
All relevant regions recovered
GRBs: in our model a=4 to reproduce pion spectra; pion beam  muon damped (confirms Kashti, Waxman, 2005)
Some dependence on injection index
a=2
Hümmer, Maltoni, Winter, Yaguna, 2010

20. Neutrino propagation and detection

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

22. Which sources can specific data constrain best?
Point sources IC-40 arXiv:
Energy flux density
Constrain individual fluxes after flavor mixing with existing data
PRELIMINARY
(work in preparation)

23. 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: ) 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 t nt

24. 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 showers Do 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 ; 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…)

25. Parameter uncertainties
Basic dependence recovered after flavor mixing
However: mixing parameter knowledge ~ 2015 (Daya Bay, T2K, etc) required
Hümmer, Maltoni, Winter, Yaguna, 2010

26. Energy dependence flavor comp. source
New physics in R?
Energy dependence flavor comp. source
Energy dep. new physics
(Example: [invisible] neutrino decay) 1
Stable state 1
Unstable state
Mehta, Winter, arXiv:

27. Which sources are most useful?
Most useful: Sources for which different flavor compositions are present; requires substantial B
Some dependence on new physics effect
aL=108 GeV
No of decay scenarios which can be identified
Mehta, Winter, arXiv:

28. On GRB neutrino fluxes

29. Waxman-Bahcall, reproduced
broken power law (Band function)
p decays only
~ factor 6
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-!
Baerwald, Hümmer, Winter, arXiv:

30. Fluxes before flavor mixingne nm
Baerwald, Hümmer, Winter, arXiv:

31. After flavor mixing Consequences: 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 fp stronger constrained?
GRBs not the sources of highest energetic CR?
(full scale)
(full scale)
Baerwald, Hümmer, Winter, arXiv: ; see also: Murase, Nagataki, 2005; Kashti, Waxman, 2005; Lipari, Lusignoli, Meloni, 2007

32. Summary
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)