PEV NEUTRINOS FROM THE PROPAGATION OF ULTRA-HIGH ENERGY COSMIC RAYS Esteban Roulet CONICET, Bariloche, Argentina
THE ENERGETIC UNIVERSE multi-messenger astronomy γ ν p γ rays neutrinos Fermi Amanda UHE Cosmic rays Auger
DIFFUSE PHOTON BACKGROUND
THE NEUTRINO SKY
COSMIC RAY SPECTRUM Power law flux stochastic (Fermi) acceleration in shocks Small fractional energy gain after each shock crossing flux dn ~E with 2 2.4 de Energy
TYPES OF COSMIC RAY DETECTORS E<100 GeV satellites ~ TeV Cherenkov telescopes E > PeV Arrays of particle detectors
Examples of powerful astrophysical Objects/potential CR accelerators AGN 0.1 100 GeV Pulsar SNR GRB Radio Galaxy Colliding galaxies Diffuse emission
TeV Astrophysical Sources
Discriminating leptonic vs. hadronic scenarios (a way to know if protons are indeed accelerated in SNR) Brems: e+ gas γ+... Synch: e+ Bfield e+ Xray Hadronic: CR+ γ ( p) π+ X 0 IC: e+ Xray γ+ e π γ γ, π e+ ν e + ν μ+ ν μ e.g. CasA spectrum brems IC π0 Leptonic? Hadronic? Often inconclusive, observation of neutrinos would be unambiguous!
FERMI found 2 SN remnants with clear signals of gammas from pion decays (low E supp.) Proton acceleration in SuperNovae to beyond 10 TeV proved, associated flux expected 2013, Science, 339, 807
Distant sources are strongly attenuated by background photons (starlight, CMB, radio,...): e e Photon attenuation length z=0.165 BLLac (H2356 309 ) e Mpc TeV γ γ PeV EeV e e IC γ B Synchrotron Can even measure IR background from observed attenuation beyond few TeV, high redshift Universe is unobservable with photons
CR AIR SHOWER DETECTORS AUGER, 3000 km2 Longitudinal distribution in air Lateral distribution at ground ρ[g /cm2] (FD duty cycle ~15%) Measure Xmax Energy calibration angular resolution < 1o (SD duty cycle ~100%)
n tot Photons produce deep showers nuclei of mass A behave as p with with E/A shallower showers
COMPOSITION FROM Xmax
E3 x FLUX (before Auger) knee 2nd knee ankle GZK?
the Greisen-Zatsepin-Kuzmin effect (1966) AT THE HIGHEST ENERGIES, PROTONS LOOSE ENERGY BY INTERACTIONS WITH THE CMB BACKGROUND pγ π o p pγ π n PROTONS CAN NOT ARRIVE WITH E > 6x1019 ev FROM D > 200 Mpc Aharonian, Cronin γ= p p e e (Berezinsky & Zatsepin 69) A A ' nucleons Fe For Fe nuclei: after ~ 200 Mpc the leading fragment has E < 6x1019 ev ligther nuclei get disintegrated on shorter distances Epele, ER 1 Mpc ( ⁰ produce GZK photons) ( ± produce cosmogenic neutrinos) 100 Mpc (fewer neutrinos produced)
AUGER spectrum Ankle: 1- Galactic extragalactic transition? (ankle model) 2 - or e+e- dip in Xgal protons? (dip model) GZK: proton or Fe suppression? (and/or exhaustion of sources?) pairs γπ p attenuation length p attenuation
Attenuation lengths vs E Gpc Mpc TeV γ γ bckg e + e PeV EeV Protheroe
diffuse background ASSOCIATED PHOTON FLUXES 0 0 + p γ π p π γγ p γ pe e γ γ bckg e + e e γ bckg e γ Cascades down to GeV-TeV dip scenario (E 2.45) Egret Fermi GeV ankle scenario (E 2) cascade photons GZK photons Kalashev et al.0704.2463 - dip models lead to significant cascade fluxes from pair production - ankle models (harder fluxes) lead to larger GZK photon fluxes TeV
AUGER SD photon bound photon showers are quite penetrating (small curvature radius) and lack muons (electromagnetic signal in detectors have long rise times) essentially no UHE photon candidates observed Astroparticle Physics 29 (2008) 243 256 photon fraction: < 2% at E > 10 EeV < 31% at E > 40 EeV GZK excludes most top-down models, but still above optimistic GZK photons
COSMOGENIC NEUTRINO FLUXES: Berezinsky et al., arxiv:1003.1496 Ahlers et al., arxiv:1005.2620 γ ν - ankle models (harder fluxes) lead to larger cosmogenic neutrino fluxes than dip models - fluxes at EeV could be comparable to CR fluxes, but cross section tiny (~ 10 nb) probability of interacting in atmosphere small (~10-5 for vertical)
Neutrino detection in AUGER Only neutrinos can produce young horizontal showers For downgoing showers: (assuming 1:1:1 flavor ratios) 38% from ν e, 18% from ν µ, 29% from ν τ air, 15% from ν τ mountain but Earth skimming ν τ searches are more sensitive
Fargion 2000, Bertou et al '01 Feng et al. '02 Up going Earth skimming ν τ showers σ CC 10 32 cm2 E0.36 (E [ EeV ]) 1 700 km L< 0.36 nσcc E Ldec< γc τ E 50 km τ decay ντ τ h< 1 km νμ ν τ θ 90 o < 5o Ω< 1 sr Lloss 10 km (bremss, pair, photonuclear) Probability of interacting in the last 10 km ~ 0.01 Effective exposure ~ 0.1 km2 sr (c.f. ~ 104 km2 sr for UHECR)
AUGER BOUNDS ON DIFFUSE NEUTRINO FLUX unlike hadronic CRs, neutrinos can produce young horizontal showers above the detector (in particular from upcoming near horizontal tau lepton induced showers) young (em) shower old (muonic) shower Horizontal young showers? ZERO CANDIDATES
( E 2 ) ApJL 2012 0 events observed bounds scale linearly with exposure
NEUTRINO TELESCOPES (10 GeV to PeV and beyond) km3 detector at South Pole, completed by 2011, looking at northern ν sky (and to southern sky above PeV) Amanda ANTARES NEMO NESTOR km3 detector at Mediterranean looking at southern neutrino sky (proposed km3net & GVD in Baikal)
Deep inelastic Neutrino nucleon interactions 10 nb NC 0.4 CC E Earth opaque for E>40 TeV Need to look above horizon
One may even distinguish neutrino flavors muon neutrino (track) electron neutrino (cascade, also from NC) tau neutrino (double bang) E γc τ 50 m PeV
No point sources observed by Icecube nor Antares
Targeted searches (galactic and extra-galactic candidates): SNR, AGN,...
ICECUBE stacked search for neutrinos coincident with observed GRB 2008/2010 (~ 200 northern GRB) Nature 2012 Bound factor 4 below standard predictions GRB are not main source of UHECRs or production models need revision Revised model: (Hummer et al.): E losses, flavor mix, spectral shapes...
BOUNDS ON DIFFUSE NEUTRINO FLUXES
High energy atmospheric neutrinos decay length L= c L 6 km E /100 GeV L K 7.5 km E K /TeV L D 2 km E D /10 PeV Atmospheric s mainly from pion decays at low energies, K c but above 100 GeV pions are stopped before decay kaons become the main source, but above ~100 TeV prompt charm decays dominate
Prompt charm production Enberg et al. /0808.0418 from, K decays For E > 200 TeV mostly from c decays from c-decays 2 cc M sample gluon density distribution at x 2 2x F s x < 10-5 for E >1015 ev 2 need to extrapolate from measured values also requires to include NLO processes
The two highest energy neutrino events observed by ICECUBE E= 1.04 and 1.14 PeV (+ 0.17) 1E-8 (PRD 2012)
Recently 26 additional events found above ~ 20 TeV 21 showers and 7 tracks (consistent with 1:1:1 flavor ratios) +5 Only ~ 10.6-3.6 expected from atmospheric background (Science 2013)
Distribution in E and declination compatible with isotropic E-2 flux with cutoff E 2 Φ ( E ) 3E-8GeV /cm2 s sr, E < few PeV Recent Big Bird event of 2 PeV
Cosmogenic neutrinos from proton sources: Threshold: + p γ π n s=( p p+ p γ ) 2> (m p+ mπ ) 2 E p > mπ (2m p + mπ ) 70 EeV 3 4 Eγ E γ /10 ev 1020 ev for CMB photons, 1017 ev for optical photons energies: + π + μ + νμ e + ν μ νμ νe E ν E ν E ν E π / 4 E p / 20 μ p γ π n n pe νe E ν e Redshift (production at 0<z<4) : π dec Redshifted energy E ν π dec Eν 5 EeV (1+ z )(E γ /10 3 ev ) μ e mn m p m e 4 E n 4 10 E n 2 mn TCMB=(1+z) 2.7 K redshifted threshold Ep 20(1+ z ) EeV from interactions with CMB photons PeV from interactions with UV/O/IR photons or PeV from n-decays from interactions with CMB?
ER, Sigl, vvliet & Mollerach ArXiv 1209.4033, JCAP 2013 Mostly decays from UV/IR int X 500 CMB alone n-decays Height of PeV peak from n-decay related to height of EeV peak from -decay [ d Φ ν d Φν ν n decay π decay 2 d Φ (E ν ) ( Eν ) Eν d loge d loge de e μ n dec e ] 15 E ν=6 10 ev E n d ν e d E π ν [ d Φν E de 2 ν π dec μ ] 18 E ν =10 ev μ
and for different source evolutions & cascade bound ν e n decay Allowed height of EeV flux implies bound on PeV peak from n-decay [ 2 d Φ all ν Eν de ] E ν=10 18 [ ν 8 GeV 2 d Φ < 5 10 E ν de cm2 s sr ev νe flux from n-decay tiny at PeV e ] n dec 10 < 10 15 E ν =6 10 ev GeV cm2 s sr
Cosmogenic neutrinos from nuclei: A ' Ae νe A γ A'+ nucleons photo-disintegration: n pe ν e Giant dipole resonance for E' ~ 10-30 MeV p γ π+ n + + π e ν μ νμ ν e Threshold: 20 A 2 10 ev s=( p A+ p γ ) > (m A+ 10 MeV ) E A> 56 E γ /10 3 ev 2 Photo-pion: 2 A γ A' + π For Fe, similar cutoff as p lighter nuclei smaller cutoffs (need to account for nuclear suppression) For E/A > 1017 ev, nuclei disintegrate 'a lot' (from IR & CMB) low energy neutrinos from n-decays (& beta decay) E ν 4 10 4 E / A Secondary nucleons with E/A interact producing pions for E/A < 1017 ev interaction probabilities small few nuclei disintegrate, fewer nuclei emit pions, but those may still dominate PeV neutrino flux production
Mostly decays from UV/IR int of nuclei Mostly decays from CMB int of emitted nucleons n-decays PeV from n-decays bounded by EeV neutrons, which are bounded by overall CR fluxes [ d Φ ν d log E e ] n dec 15 E ν =10 ev [ d Φ' n ' d log E ] < 18 E =2 10 ev [ 1 d Φ CR 2 d log E ] 18 E =2 10 ev [ ν 2 d Φ Eν de n dec e ] < 10 15 E ν=10 ev 11 GeV cm2 s sr
Mixed extragalactic p / Fe composition with low cutoff (E p < 4 EeV) p component below ankle leads to significant PeV fluxes from -decay no EeV due to low cutoff
Flavor oscillations Incoherent flavor conversions (Pakvasa et al 2008) P α β = i U α i 2 U β i 2 -decays: (ν e : νμ : ν τ )=(1 :1 :0) (0.78: 0.61: 0.61) ( νe : νμ : ν τ )=(0 :1: 0) (0.22 :0.39 : 0.39) n-decays: (ν e : νμ : ν τ )=(0 :0 :0) (0 :0 : 0) ( νe : νμ : ν τ )=(1 :0 : 0) (0.56 : 0.22: 0.22) (adopting TBM) sin 2 Θ23 1/2 sin 2 Θ12 1/3 sin 2 Θ13 0
THE GLASHOW RESONANCE ν e e W f f ' resonant for: M 2W E= =6.3 PeV 2 me at the peak, CC σ ( ν e e all ) 350 σ (ν i N l i X ) but peak narrow (0.17 PeV), electron antineutrino flavor not dominant, ne/nn = 5/9 overall contribution to the IceCube rates of from decays is similar to the CC+NC ones within 2.5 PeV of the resonance does not allow to achieve strong enhancements
PeV neutrinos of Galactic origin? Correlated with Fermi diffuse gammas? produced by interaction with gas in galactic arms? Neronov et al 1307.2158 Correlated with Fermi Bubbles? Razzaque 1309.2756 But: Composition becoming heavy above the knee, individual sources too faint, Bounds from CASA-MIA on 100 TeV gammas,...
PeV neutrinos of extra-galactic origin? Sources could be AGN, GRBs,. Need about 10% of energy in few x1016 CRs to go to pions Optical photons at or around the source could be the target Sources need not be too far away (unlike for cosmogenic nus) Is there a gap between 300 TeV and 1 PeV? PeV neutrinos from dark matter decay? Need more data to test spectrum, cutoff, tracks/showers, arrival directions,. IceCube will soon provide that
CONCLUSIONS Detection of 2 PeV produced a revolution in the field of astronomy - are they atmospheric? (enhanced by charm production) - are they cosmogenic? (produced during propagation of CRs) Significant PeV fluxes can arise from 1016 1017 ev protons producing in interactions with UV/IR (but probably not enough) Cosmogenic neutrinos from n-decays tiny at PeV energies Glashow resonance has moderate impact (narrow width, only anti- e) - are they Galactic? Produced by CR interaction with ISM - are they produced at the sources? (GRB, AGN, ) We are at the dawn of the era of high energy neutrino astronomy