Presentation on theme: "Photohadronic processes and neutrinos Summer school High energy astrophysics August 22-26, 2011 Weesenstein, Germany Walter Winter Universität Würzburg."— Presentation transcript:
Photohadronic processes and neutrinos Summer school High energy astrophysics August 22-26, 2011 Weesenstein, Germany Walter Winter Universität Würzburg TexPoint fonts used in EMF: AAAAA A A A
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
Lecture 1 Introduction
4 Neutrino production in astrophysical sources Example: Active galaxy (Halzen, Venice 2009) max. center-of-mass energy ~ 10 3 TeV (for GeV protons)
5 Different messengers Shock accelerated protons lead to p,, fluxes p: Cosmic rays: affected by magnetic fields (Teresa Montaruli, NOW 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 > GeV) on CMB GZK cutoff + cosmogenic neutrino flux (Source: F. Halzen, Venice 2009 ) In the source: E p,max up to GeV? GZK cutoff? 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 Pole Detector material: ~ 1 km 3 antarctic ice Completed 2010/11 (86 strings) Recent data releases, based on parts of the detector: Point sources IC-40 [IC-22] arXiv: , arXiv: GRB stacking analysis IC-40 arXiv: Cascade detection IC-22 arXiv: 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
9 Neutrino astronomy in the Mediterranean: Examples: ANTARES, KM3NeT
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: E max ~ Z e B R (Larmor-Radius < size of source) Particles confined to within accelerator! Sometimes: define acceleration rate t -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 eV Test points
Simulation of sources (qualitatively)
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 in ratio ( 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-pion production Different characteristics (energy loss of 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 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 / - 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 effects Pions and muons loose energy through synchroton radiation for higher E before they decay – aka muon damping (example from Reynoso, Romero, 2008) Dashed: no losses Solid: with losses Affect spectral shape and flavor composition of neutrinos significantly peculiarity for neutrinos ( 0 are electrically neutral!) … more tomorrow …
18 Astrophysical neutrino sources produce certain 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-dissociation of heavy nuclei) At the source: Use ratio e / (nus+antinus added) Flavor composition at the source (Idealized – energy independent)
Neutrino propagation and detection
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: , 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 e Effective 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/ ; many others) e e
23 Neutrino detection: Muon tracks Number of events depends on neutrino effective area and observ. time t exp : Neutrino effective area ~ detector area x muon range (E); but: cuts, uncontained events, … Time-integrated point source search, IC-40 (arXiv: ) 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/(A eff t exp ) 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: ) IC-40 Differential limit Fluxes typically below that Integral limit Applies to E -2 flux only Energy range somewhat arbitrary (e.g. 90% of all events) NB: Spectral shape important because of instrument response!
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 Atmospheric neutrino dominated Cosmic muon dominated
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: ) 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 showers Do 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 ; 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 dependence flavor 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
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, 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 energy Muon neutrinos take 0.05 E p 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) 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) Advantage: optimal statistics (signal) Disadvantage: Backgrounds (e.g. atmospheric) (Becker, arXiv: ) Single source spectrum Source distribution in redshift, luminosity Comoving volume Decrease with luminosity distance
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: Its 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