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Photohadronic processes and neutrinos

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

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Photohadronic processes and neutrinos

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  1. Photohadronic processes and neutrinos Summer school “High energy astrophysics” August 22-26, 2011 Weesenstein, Germany Walter Winter Universität Würzburg TexPoint fonts used in EMF: AAAAAAAA

  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 n fluxes • Glashow resonance? (pp versus pg) • Neutrinos and the multi-messenger connection

  3. Lecture 1 Introduction

  4. Neutrino production in astrophysical sources max. center-of-mass energy ~ 103 TeV(for 1012 GeV protons) Example: Active galaxy(Halzen, Venice 2009)

  5. 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)

  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, pg interactions) • Proton (E > 6 1010 GeV) on CMB  GZK cutoff + cosmogenic neutrino flux UHECR In the source:Ep,max up to 1012 GeV? GZKcutoff? (Source: F. Halzen, Venice 2009)

  7. Example: Gamma-ray bursts • Direct+cosmogenic fluxes come typically together: Neutrons from same interactions escape the sources  cosmogenic neutrino flux Neutrino flux produced within source (Ahlers, Gonzales-Garcia, Halzen, 2011)

  8. 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 wrong? • Which parts of the parameter space does IceCube actually test? http://icecube.wisc.edu/

  9. Neutrino astronomy in the Mediterranean: Examples: ANTARES, KM3NeT http://antares.in2p3.fr/

  10. When do we expect a n 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-1acc = h Z e B/E(h: acceleration efficiency) • Caveat: condition relaxed if source heavily Lorentz-boosted (e.g. GRBs) „Test points“ (?) Protons to 1020 eV (Hillas, 1984; version adopted from M. Boratav)

  12. Simulation of sources (qualitatively)

  13. Photohadronics (primitive picture) If neutrons can escape:Source of cosmic rays Neutrinos produced inratio (ne:nm:nt)=(1:2:0) Delta resonance approximation: Cosmogenic neutrinos p+/p0 determines ratio between neutrinos and gamma-rays High energetic gamma-rays;might cascade down to lower E Cosmic messengers

  14. Photohadronics (more realistic) Dres. Multi-pionproduction Differentcharacteristics(energy lossof protons;energy dep.cross sec.) (Photon energy in nucleon rest frame) Resonant production,direct production (Mücke, Rachen, Engel, Protheroe, Stanev, 2008; SOPHIA)

  15. Meson photoproduction • Starting point: D(1232)-resonance approximation • Limitations: • No p- production; cannot predict p+/ p- 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 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 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 n 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“ Dashed:no lossesSolid:with losses Affect spectral shape and flavor composition ofneutrinos significantly peculiarity for neutrinos (p0 are electrically neutral!)… more tomorrow … (example from Reynoso, Romero, 2008)

  18. 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 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 pg(also possible: photo-dissociationof heavy nuclei) • At the source: Use ratio ne/nm (nus+antinus added)

  19. Neutrino propagation and detection

  20. Neutrino propagation (vacuum) • 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)

  21. Earth attenuation • High energy neutrinos interact in the Earth: • However: Tau neutrino regeneration through nt t  (17%) m + nm + nt (C. Quigg) Earth Detector

  22. Neutrino detection (theory) • Muon tracks from nmEffective area dominated!(interactions do not have do be within detector) • 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 • NC showers t nt nt e ne m nm (Learned, Pakvasa, 1995; Beacom et al, hep-ph/0307025; many others)

  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 [cm-2 s-1 GeV-1] nt: viat m Earth opaque to nm (arXiv:1012.2137)

  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 inwhen 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) Differential limitFluxes typically below that IC-40 nm NB: Spectralshape importantbecause ofinstrumentresponse! Integral limitApplies to E-2 flux only Energy range somewhat arbitrary (e.g. 90% of all events)

  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 Atmosphericneutrinodominated Cosmicmuondominated Detector

  28. Measuring flavor? (experimental) • In principle, flavor information can be obtained from different event topologies: • Muon tracks - nm • Cascades (showers) – CC: ne, nt, NC: all flavors • Glashow resonance (6.3 PeV): ne • Double bang/lollipop: nt (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 t nt

  29. 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…)

  30. New physics in R? Energy dependenceflavor comp. source Energy dep.new physics (Example: [invisible] neutrino decay) 1 Stable state 1 Unstable state Mehta, Winter, JCAP 03 (2011) 041; see also Bhattacharya, Choubey, Gandhi, Watanabe, 2009/2010

  31. How many neutrinos do we expect to see?

  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 fp<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 energy • Muon neutrinos take 0.05 Ep • Warning: bound depends on flavors considered, and whether flavor mixing is taken into account! fp = 1 fp ~ 0.2

  33. Comments on statistics • At the Waxman-Bahcall bound: O(10) events in full-scale IceCube per year • Since (realistically) fp << 1, probably Nature closer to O(1) event • Do 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) (Becker, arXiv:0710.1557) • Advantage: optimal statistics (signal) • Disadvantage: Backgrounds(e.g. atmospheric) Comovingvolume Single sourcespectrum Sourcedistributionin redshift,luminosity 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 g-rays: Neutrino results will likely be based on accumulated statistics. Therefore: use input from g-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 g-ray observations: • Low statistics, conclusions often based on aggregated fluxes • Charged secondaries lead to neutrino production: flavor and magnetic field effects

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