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Photohadronic processes and neutrinos. Summer school “High energy astrophysics” August 22-26, 2011 Weesenstein , Germany Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Lecture 1 (non-technical) Introduction, motivation - PowerPoint PPT Presentation
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Photohadronic processes and neutrinos
Summer school “High energy astrophysics”August 22-26, 2011
Weesenstein, Germany
Walter Winter
Universität Würzburg
2
Contents
Lecture 1 (non-technical)
Introduction, motivation Particle production (qualitatively) Neutrino propagation and detection Comments on expected event rates
Lecture 2 Tools (more specific) Photohadronic interactions, decays of secondaries,
pp interactions A toy model:
Magnetic field and flavor effects in fluxes Glashow resonance? (pp versus p) Neutrinos and the multi-messenger connection
4
Neutrino production in astrophysical sources
Example: Active galaxy(Halzen, Venice 2009)
max. center-of-mass energy ~ 103 TeV
(for 1012 GeV protons)
5
Different messengers
Shock accelerated protons lead to p, , fluxes p: Cosmic rays:
affected by magnetic fields
(Te
resa
Mo
nta
ruli, N
OW
2008)
: Photons: easily absorbed/scattered : Neutrinos: direct path
6
galactic extragalactic
Evidence for proton acceleration,
hints for neutrino production Observation of
cosmic rays: need to accelerate protons/hadrons somewhere
The same sources should produce neutrinos: in the source (pp,
p interactions) Proton (E > 6 1010
GeV) on CMB GZK cutoff + cosmogenic neutrino flux
(Source: F. Halzen, Venice 2009)
In the source:
Ep,max up to 1012 GeV?
GZKcutoff?
UHECR
7
Example: Gamma-ray bursts
(Ahlers, Gonzales-Garcia, Halzen, 2011)
Direct+cosmogenic fluxes come typically together:
Neutrino flux produced within
source
Neutrons from same
interactions escape the
sources cosmogenic
neutrino flux
8
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-40
arXiv:1101.1448 Cascade detection IC-22
arXiv:1101.1692 Have not seen anything (yet)
What does that mean? Are the models wrong? Which parts of the parameter space
does IceCube actually test?
Neutrino detection: IceCube
http://icecube.wisc.edu/
10
When do we expect a signal?[some personal comments]
Unclear if specific sources lead to neutrino production and at what level; spectral energy distribution can be often described by other radiation processes processes as well (e.g. inverse Compton scattering, proton synchrotron, …)
However: whereever cosmic rays are produced, neutrinos should be produced to some degree
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)
What about Fermi-LAT unidentified/unassociated 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?
[unbiased by gamma-ray and cosmic ray observations] Also: huge astrophysical uncertainties; try to describe at
least the particle physics as accurate as possible!
11
The parameter space? Model-independent
(necessary) condition:
Emax ~ Z e B R
(Larmor-Radius < size of source)Particles confined to
within accelerator! Sometimes: define
acceleration ratet-1
acc = Z e B/E(: acceleration efficiency)
Caveat: condition relaxed if source heavily Lorentz-boosted (e.g. GRBs)
(Hillas, 1984; version adopted from M. Boratav)
(?)
Protons to 1020 eV
„Test points“
13
Photohadronics (primitive picture)
Delta resonance approximation:
+/0 determines ratio between neutrinos and gamma-rays
High energetic gamma-rays;might cascade down to lower E
If neutrons can escape:Source of cosmic rays
Neutrinos produced inratio (e::)=(1:2:0)
Cosmic messengers
Cosmogenic neutrinos
14
Photohadronics (more realistic)
(Photon energy in nucleon rest frame)
(Mücke, Rachen, Engel, Protheroe, Stanev, 2008; SOPHIA)
Resonant production,
direct production
Multi-pionproduction
Differentcharacteristics(energy lossof protons;
energy dep.cross sec.)
res.
15
Starting point: (1232)-resonance approximation
Limitations:- No - production; cannot predict / - ratio (affects neutrino/antineutrino)- High energy processes affect spectral shape (X-sec. dependence!)- Low energy processes (t-channel) enhance charged pion production Charged pion production underestimated compared to 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, 2008
Fast, but no intermediate muons, pions (cooling cannot be included) Hümmer, Rüger, Spanier, Winter, 2010
Fast (~3000 x SOPHIA), including secondaries and accurate / - ratios; also individual contributions of different processes (allows for comparison with -resonance!)
Engine of the NeuCosmA („Neutrinos from Cosmic Accelerators“) software
Meson photoproduction
T=10 eV
from:Hümmer, Rüger, Spanier, Winter,
ApJ 721 (2010) 630
More tomorrow
16
Typical source models
Protons typically injected with power law (Fermi shock acceleration!)
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 a more complicated combination of
radiation processes (see other lectures)
Minimal set of assumptions for production? tomorrow!
?
17
Secondary decays and magnetic field effects
Described by kinematics of weak decays(see e.g. Lipari, Lusignoli, Meloni, 2007)
Complication: Magnetic field effectsPions and muons loose energy through synchroton radiation for higher E before they decay – aka „muon damping“
(example from Reynoso,
Romero, 2008)
Dashed:no lossesSolid:with losses
Affect spectral shape and flavor composition ofneutrinos significantly
peculiarity for neutrinos (0 are electrically neutral!)… more tomorrow …
18
Astrophysical neutrino sources producecertain flavor ratios of neutrinos (e::):
Pion beam source (1:2:0)Standard in generic models
Muon damped source (0:1:0)at high E: Muons lose 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 p (also possible: photo-dissociationof heavy nuclei)
At the source: Use ratio e/ (nus+antinus added)
Flavor composition at the source(Idealized – energy independent)
20
Neutrino propagation (vacuum)
Key assumption: Incoherent propagation of neutrinos
Flavor mixing: Example: For 13 =0, 23=/4:
NB: No CPV in flavor mixing only!But: In principle, sensitive to Re exp(-i ) ~ cos
(see Pakvasa review, arXiv:0803.1701,
and references therein)
21
Earth attenuation
High energy neutrinos interact in the Earth:
However: Tau neutrino regeneration through (17%) + +
(C. Quigg)
Earth
Detector
22
Neutrino detection (theory)
Muon tracks from Effective area dominated!(interactions do not have do be within detector)
Electromagnetic showers(cascades) from eEffective volume dominated!
Effective volume dominated Low energies (< few PeV) typically
hadronic shower ( track not separable)
Higher Energies: track separable
Double-bang events Lollipop events
Glashow resonace for electron antineutrinos at 6.3 PeV
NC showers
(Learned, Pakvasa, 1995; Beacom et al, hep-ph/0307025; many others)
e
e
23
Neutrino detection: Muon tracks
Number of events depends on neutrino effective area and observ. time texp:
Neutrino effective area ~ detector area x muon range (E); but: cuts, uncontained events, …
Time-integrated point source search, IC-40 (arXiv:1012.2137)
Earth opaque to
: via
[cm-2 s-1 GeV-1]
24
Computation of limits (1) Number of events N can be translated into
limit by Feldman-Cousins approach
(Feldman, Cousins, 1998)
This integral limit is a single number given for particular flux, e.g. E-2, integrated over a certain energy range
25
Computation of limits (2)
Alternative: Quantify contribution of integrand in
when integrating over log E:
Differential limit: 2.3 E/(Aeff texp)
Is a function of energy, applies to arbitrary fluxes if limit and fluxes sufficiently smooth over ~ one decade in E
26
Comparison of limits (example)
(arXiv:1103.4266)
IC-40
Differential limitFluxes typically
below that
Integral limit
Applies to E-2 flux only
Energy range somewhat arbitrary (e.g. 90% of all events)
NB: Spectralshape important
because ofinstrumentresponse!
27
Neutrino detection: backgrounds
Backgrounds domination:
Background suppression techniques: Angular resolution (point sources) Timing information from gamma-ray counterpart
(transients, variable sources) Cuts of low energy part of spectrum (high energy
diffuse fluxes)
Earth
Detector
Atmosphericneutrinodominated
Cosmicmuondominated
28
Measuring flavor? (experimental)
In principle, flavor information can be obtained from different event topologies: Muon tracks - Cascades (showers) – CC: e, , NC: all flavors Glashow resonance (6.3 PeV): e
Double bang/lollipop: (sep. tau track)(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
29
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
Flavor ratios at detector
(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…)
30
New physics in R? Energy dependenceflavor comp. source
Energy dep.new physics
(Example: [invisible] neutrino decay)
1
1
Stable state
Unstable state
Mehta, Winter, JCAP 03 (2011) 041; see also Bhattacharya, Choubey, Gandhi, Watanabe, 2009/2010
32
Upper bound from cosmic rays Injection of CR protons inferred from observations:
(caveats: energy losses, distribution of sources, …) Can be used to derive upper bound for neutrinos (Waxman,
Bahcall, 1998 + later; Mannheim, Protheroe, Rachen, 1998)
Typical assumptions: Protons lose fraction f<1 into pion
production within source About 50% charged and 50%
neutral pions produced Pions take 20% of proton energy Leptons take about ¼ of pion energyMuon neutrinos take 0.05 Ep
Warning: bound depends on flavors considered, and whether flavor mixing is taken into account!
f = 1
f ~ 0.2
33
Comments on statistics
At the Waxman-Bahcall bound: O(10) events in full-scale IceCube per year
Since (realistically) f << 1, probably Nature closer to O(1) eventDo not expect significant statistics from single
(cosmic ray) source!Need dedicated aggregation methods:
Diffuse flux measurement Stacking analysis, uses gamma-ray counterpart
(tomorrow)
However: WB bound applies only to accelerators of UHECR! Only protons!
34
Diffuse flux (e.g. AGNs)
Advantage: optimal statistics (signal)
Disadvantage: Backgrounds(e.g. atmospheric)
(Becker, arXiv:0710.1557)
Single sourcespectrum
Sourcedistributionin redshift,luminosity
Comovingvolume
Decreasewith
luminositydistance
35
Consequences of low statistics[biased]
Neutrinos may tell the nature (class) of the cosmic ray sources, but not where exactly they come from
Consequence: It‘s a pity, since UHECR experiments will probably also not tell us from which sources they come from …
Comparison to -rays: Neutrino results will likely be based on accumulated statistics. Therefore: use input from -ray observations (tomorrow …)Clues for hadronic versus leptonic models?Again: probably on a statistical basis …
Consequences for source simulation? Time-dependent effects will not be observable in
neutrinos Spectral effects are, however, important because of
detector response
36
Summary (lecture 1)
Neutrino observations important for Nature of cosmic ray sources Hadronic versus leptonic models
Neutrino observations are qualitatively different from CR and -ray observations: Low statistics, conclusions often based on
aggregated fluxes Charged secondaries lead to neutrino
production: flavor and magnetic field effects