1 / 36

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

regina
Download Presentation

Photohadronic processes and neutrinos

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related