Understanding High Energy Neutrinos Paolo Lipari: INFN Roma Sapienza NOW-2014 Conca Specchiulla 12th september 2014
An old dream is becoming a reality : Observing the Universe with Neutrinos ( A new way to look at the Sky ) The Sun SuperNova 1987A The Earth (geo-neutrinos) Neutrinos from the High Energy Universe (recent result from IceCube) [!?]
A glimpse of the promised land Christian Spiering:
A glimpse of the promised land 1. Could the glimpse be a Mirage? (playing the devil's advocate ) 2. What can we say about the high energy neutrino land from the shape of the very first outline? 3. When can we expect the first landing? [the first detection of an astrophysical source]
Neutrinos from the High Energy Universe Neutrino associated to the production and propagation of very high energy relativistic particles (hadrons). 1. Astrophysical object (or event) that accelerates protons and nuclei to relativistic energies. 2. Target material (gas, or radiation field) 3. Interactions of the relativistic particles with the production of unstable [weakly decaying] particles. 4. The decays produce neutrinos.
Jakob van Santen
Foreground to the astrophysical neutrino signal Atmospheric Neutrinos
Neutrino Flux: decomposition of the flux into an astrophysical signal of extraterrestrial neutrinos and a foreground of atmospheric neutrinos
Each component of the neutrino flux has characteristics: Flavor composition Angular distribution Energy distribution
The atmospheric neutrino flux depends only on the zenith angle. The astrophysical neutrino fluxes depend on celestial coordinates. The establishment of a celestial coordinate dependence of the neutrino fluxes would be unambiguous evidence for an astrophysical signal. But: largest predicted astrophysical neutrino flux is expected as a featureless isotropic extragalactic flux.
125 m string separation 17 m between PMT's IceCube
Analysis of contained events in ICECUBE SCIENCE (16 december 2013) Evidence for High Energy Extraterrestrial Neutrinos in the IceCube Detector New publication Phys.Rev.Lett astro-ph/1405.5303 2 years 3 years of data
Contained events
TRACK
Shower
IceCube contained events 3-years Total Number of Events : Background from Down-going Muons Atmospheric Neutrinos Excess = 5.7 sigmas 36(+1)
IceCube contained events 3-years Total Number of Events : 37 Background from Down-going Muons Atmospheric Neutrinos conventional Excess = 5.7 sigmas charm
Estimate of the neutrino flux by IceCube in the energy range: 40 TeV - 2 PeV (isotropic, equal flux for all flavors)
Playing the Devil's Advocate Could the extraterrestrial neutrino excess be attributed to atmospheric neutrinos? Atmospheric Neutrinos conventional charm Are these theoretical predictions (and their estimated uncertainties) correct?
Significance of the excess of events: naive (incorrect!) way. Poisson statistics [37 events, background of 15=8.4 + 6.6] Significance =
Each component of the neutrino flux has characteristics: Flavor composition Angular distribution Energy distribution Analysis of Energy Spectrum. angular distribution flavor composition of the data
A caveat from the old experts
Predictions of Magister Eligius : Neutrino induced muons
Confirming Evidence from neutrino-induced muons!
IceCube 3 years data [Contained events (from PRL)]
Excess at HIGH ENERGY
Excess at down-going vertical direction
Estimating the Fluxes of Atmospheric Neutrinos 1. Cosmic Ray fluxes 2. Modeling of Hadronic Interactions. 3. Geometry of the Earth atmosphere (density profile)
Primary Cosmic Ray Flux [only some data points are shows] p He Direct Measurements Air Shower Measurements all particles
Primary Cosmic Ray Flux [Spectral features] p He Knee Ankle
Primary Cosmic Ray Flux p He Knee Is this the flux (and energy density) of extragalactic Cosmic Rays? Ankle
1. Readjust the results of different experiments
2. Composition model [3 source components] [3 Peters cycles
Nuclei very ineffective for neutrino production All nucleons (bound + free) p
Gaisser, Stanev, Tilav (fit + composition p He model) Proton Flux All nucleon Flux
Angle integrated Neutrino fluxes
Angle integrated Neutrino fluxes Charm decay component
IceCube fit of the extraterrestrial component (per each flavor) GZK neutrinos
Flavor Content [flux ratios]
Flavor Content 1. More than Decay forbidden (tau mass) 2. Absence of 3. More 2-body decay of pion/kaon than Kinematics of pion decay
Charged Pions decay into muon-neutrinos Electron neutrinos generated by 3-body decays of kaons. [2-body decay V-A structure of the interaction]
Flavor Content 1. Equal and Universality 2. Small (10%) 3. slightly less 2 body decay of Ds than Kinematics of charm decay
Flavor Content 1. Equal and,
Oscillation Probability Average to zero (for size of source region)
Relative fluxes at the observers starting from 2 nu_mu and 1 nu_e (standard mixture for a pion chain-decay origin) = best fit
More in general: For an arbitrary flavor composition emission Significant presence of tau-neutrinos
Flavor Content In principle key role for
Tau neutrinos can be directly detected [ Double Bang events ] But also the ratio Shower / Tracks is sensitive to the presence of tau neutrinos.
Is there an excess of showers versus tracks in the IceCube data? Result is compatible with Equal fluxes for all neutrino flavors. A more quantitative statement would be desirable
Angular Distribution : Atmospheric standard: Atmospheric charm: characteristic enhancement for horizontal directions quasi-isotropic Decay probability: [Competition between decay and interaction]
Geometry of Particle Decay Zenith angle dependence
Characteristic zenith angle distribution of Standard atmospheric neutrinos
Absorption of neutrinos in the Earth
Up/Down Ratio
Tom Gaisser
From Jacob Van Santen
Effect of VETO on rejecting atmnospheric neutrinos
Effect allows to separate Atmosphericcharm from isotropic astrophysical
[2 years data] Down-going Up-going Very large asymmetry [why?] 24 4
[2 years data] Down-going Up-going Time dependence?! (at 3 sigma level). very unlikely. [3 rd 24 4 4 5 year]
Energy distribution of Atmospheric Neutrinos. (and absolute normalization of the fluxes) Reflects: 1. The shape (and normalization) of the primary all nucleon flux [Problem of CR at Knee ] 2. The properties of particle production in Hadronic interactions. [Large uncertainties for charmed particle production]
Devil's advocate ad hoc additional proton component All particle spectrum All nucleon spectrum proton spectrum
Dynamics of charm production in hadronic interactions Perturbative QCD calculation (gluon flusion dominant)
Recent measurements of charm cross section at LHC (small phase space coverage).
Possibility of Intrinsic charm Qualitative idea: Large component of charm in the Proton Parton Distribution Function.
(Very) speculative possibility to increase significantly the charm neutrino production, without direct conflict with the data. [example P.L. astro-ph/1308.2086].
The study of neutrinos around 1 PeV sees the intersection of 3 problems: 1. Astrophysical Neutrino Sources 2. The determination of the ALL NUCLEON flux [proton component and mass composition above the knee] 3. The dynamics of non-perturbative charm production in hadronic interactions The available information is sufficiently redundant to solve the three problems simultaneously.
Super-Kamiokande Analogy with the discovery of Neutrino oscillations from the study of atmospheric neutrinos, Determination of Oscillation Parameters: and the determination of the oscillation parameters. Set of parameters that describe the MC prediction
Simultaneous Fit of Astrophysical Component (with a number of parameters) Atmospheric Component (set of parameters) [5.7 sigma evidence of Astrophysical neutrinos. (what are the chi2 of the fits?) Estimating the All-nucleon flux (from the VHE atmospheric flux) is very interesting for an understanding of VHE cosmic rays
Interpreting an Astrophysical Neutrino Signal Compare the (high energy) Neutrino Sky with the Gamma Ray sky
Prediction on the Neutrino Sky based on observations of Gamma Rays [in the 0.1-100 GeV energy range] FERMI telescope
Superposition of a diffuse flux (disk of the Galaxy) and an ensemble of point-like or quasi point-like sources
1. Ensemble of (quasi)-point sources 2. Diffuse Galactic Flux (generated by cosmic rays magnetically confined in the Milky Way) 3. Isotropic flux. (attributed to an ensemble of unresolved extragalactic sources)
2FGL 2nd FERMI Catalog 24 months of observations 1873 sources E > 100 MeV
Diffuse Emission Galactic coordinates
Inverse Compton Description reasonably successful. [but several ambiguities and open problems remain.] Bremsstrahlung
Angle integrated (4pi) Gamma Ray fluxes
Remarkable matching between the isotropic gamma-ry flux and the neutrino-flux. Same origin?
Extragalactic Flux of Neutrinos Isotropic flux of particles (reflecting the isotropy of the Universe) Neutrino injection [Particles injected per unit volume, unit time and unit energy. ] Time (redshift) dependence Cosmological evolution.
Relation between the injection and the neutrino flux
Injection is a power law Flux is a power law:
Power Density of the neutrino sources
Cosmological evolution Constant injection
Gamma Rays sources in the FERMI-LAT 2nd catalog. (galactic declination distribution)
FLUX of all sources
Flux (E = [1-100 GeV]) distribution of the 1015 sources in the Galactic Pole region
Flux (E = [1-100 GeV]) distribution of the 1015 sources in the Galactic Poles region 2 brightest sources PSR J1836+5295 (galactic) Blazar 3C 454.3
Brightest extragalactic source In the FERMI-LAT catalog blazar 3C454.3 z=0.859
Cumulative Flux (1015 sources)
Gamma Rays in [1-100 GeV] energy interval. Resolved flux Unresolved flux
Gamma Rays in [1-100 GeV] energy interval. Resolved flux Unresolved flux Brightest extragalactic source 2% of total flux? Indication for IceCube
EXTRA-GALACTIC or include GALACTIC contribution?
Galactic versus extra-galactic
Distribution in Galactic Latitude (concentration on the galactic plane?) Distribution in Longitude (concentration near galactic center??)
Fluxes from resolved sources in the FERMI-LAT 2nd catalog
Extrapolation of flux pf the FERMI-LAT Galactic sources of IceCube energies
Diffuse isotropic flux Extragalactic Resolved sources Milky Way resolved sources IceCube Astrophysical Neutrinos
The evidence for an astrophysical component in the IceCube data is becoming compelling. The disentangling of the different components is delicate Astrophysical/galactic, Astrophysical/extragalactic Atmospheric/conventional Atmospheric/charm need to take into account carefully all systematic uncertainties. The astrophysical neutrino land is in sight. more data is needed. Perhaps source identification soon. [Obviously]