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Emilio Migneco Erice ISCRA School 2004 Introduction to High energy neutrino astronomy Topics 1) Introduction to high energy neutrino astronomy Motivations for HE neutrino astronomy HE neutrino sources Neutrino telescopes operation principles Backgrounds

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emilio migneco
Emilio Migneco

Erice ISCRA School 2004

Introduction to High energy neutrino astronomy


1) Introduction to high energy neutrino astronomy

Motivations for HE neutrino astronomy

HE neutrino sources

Neutrino telescopes operation principles


2) Future cubic kilometer arrays

Review of existing detectors and projects

Future detectors:

impact of site parameters


experimental challenges

simulations and expected performances

neutrino astronomy
Neutrino astronomy

Neutrinos are elementary particles with “special” properties:

  • light
  • neutral
  • interact by weak force

Good astrophysical probes:

not deflected  point back to the source

not absorbed  travel Gpc distances (overcome GZK effect)

But they are difficult to detect

I have done a terrible thing I invented a particle that cannot be detected


the known cosmic neutrino spectrum
The known cosmic neutrino spectrum

The measurements of (low energy) solar, SN and atmospheric neutrino fluxes is permitting to solve open questions in astrophysics, nuclear and particle physics...

Davis and Koshiba Nobel laureates 2002

SuperKamiokande neutrino image of the Sun

HST image of SN 1987A


high energy astrophysics
High energy astrophysics
  • The detection of high energy gammas and CR are milestones in modern astrophysics but there are still open questions
  • Particle acceleration mechanism in astrophysical sources
  • Identification of high energy CR sources
  • Solution of UHECR puzzle
  • Heavy dark matter content in the Universe
the high energy cosmic ray standard paradigm




Galactic protons


The high energy cosmic ray standard paradigm


Galactic nuclei



Sources of high energy protons exists and dominate the CR spectrum at E> 1018.5 eV

top down and bottom up processes
“Top – Down” and “Bottom – Up” processes

MX~102124 eV

CR  1021 eV

E-2 spectrum

gammas and neutrinos

decay or


Top Down

Bottom Up


CR  1021 eV

flat spectrum

p,e at rest

gammas and neutrinos

astrophysical sources of uhe particles
Astrophysical sources of UHE particles

These values are typical for very bright sources

Bright AGN

L1047 erg/sec


L1052 erg/sec

Fermi acceleration to high energies requires


  • Large cosmic objects
  • Intense magnetic field
  • High shockwave velocity

Emax =1020 eV


possible extra galactic sources of cr agn
Possible extra Galactic sources of CR: AGN

The term AGNs (Active Galactic Nuclei) gathers a number of astrophysical objects

  • Massive Black Hole
  • Accretion disk (UV + lines)
  • Collimated jets

QSO GB1508+5714 Chandra

QSO 3C273

QSO 3C279


The brightest observed steady sources:

L=10421047 erg/s

When the jet is directed towards the Earth  luminosity increases  ”Blazars”

possible extra galactic sources of cr grb
Possible extra Galactic sources of CR: GRB

GRB (Gamma Ray Bursts) are the most powerful emissions of gamma rays ever observed.

Happens at cosmological distances The observation rate is few/day

GRB 030329


L=1051 1053 erg/s

t  1100 s (1/3 <2 sec)

GRB have recentely been shown to be associated with SN, as indicated by the GRB030329 – SN 2003dh correlation

(GRB 030329 z=0.17)

limits of he gamma and proton astronomy
Limits of HE gamma and proton astronomy

The UHE CR and gamma horizon is limited by interactions with low energy background radiation

absorption of high energy photons and protons

IR,CMBR  e+e-

ECMBR ~ 6.6·10-4 eV  E ~ 1013.5 eV

Lower energy photons interact also with IR backgrond


Absorption of high energy photons and protons

ECMBR ~ 6.6·10-4 eV  Ep ~ 1019.5 eV

nCMBR ~ 400 cm-3

p~ 100 barn

See also T. Stanev,2004 for p-IR interactions

Guaranteed sources of neutrinos

the gzk effect
The GZK effect

5 Gpc

Closest AGNs

Galactic radius (15 kpc)

high energy neutrinos production
High Energy neutrinos production

Are the astrophysical sources of High Energy CR also candidate sources of HE neutrinos ?

The interaction of protons with ambient gas or photon field may produce neutrino fluxes

neutrino production in cosmic accelerators

Neutrino production

  • Proton interactions
  • p  p (SNR,X-Ray Binaries)
  • p   (AGN, GRB, microQSO)
  • decay of pions and muons


  • Proton acceleration
  • Fermi mechanism
  • proton spectrum dNp/dE ~E-2

Astrophysical jet

Neutrino production in cosmic accelerators

Particle accelerator

electrons are responsible for gamma fluxes (synchrotron, IC)

he proton interaction on ambient p or
HE proton interaction on ambient p or 


HE proton

Muons and muon-neutrinos

Target protons



Shock wave

SN shells,


CANGAROO observationsof RXJ1713.7-3946 fit

with TeV gamma ray production by 0 decay (?)

Beam dump in astrophysical jet environment (GRB,AGN,microQSO)

HE proton

muons and neutrinos

Matter shells


Target photons

Shock waves

Beam dump in SNR environment

neutrino fluxes chemical composition
Neutrino fluxes chemical composition

Tau neutrinos are unlikely produced in the sources (M= 1.7 GeV)

They can be detected at the Earth as “oscillated” muon neutrinos:

If the muon interaction time (IC) is larger than the muon decay time electron neutrinos and antineutrinos are also produced

limits of he gamma and proton astronomy18
Limits of HE gamma and proton astronomy

High energy protons 50 Mpc




High energy gammas

10 Mpc

Low energy protons deflected

motivations of high energy neutrino astronomy
Motivations of high energy neutrino astronomy

Extend the high energy CR and  Horizon (<50 Mpc)

Identify the sources of UHE particles

Explore deep inside the source (where »1 for CR and )

Probe hadronic models in astrophysical sources

high energy neutrino fluxes
High energy neutrino fluxes

Astrophysical sources are expected to produce a diffuse high energy neutrino flux with spectral index 2

The most powerful and/or the closest sources could give a clear point-like neutrino signal

Time correlations between  events and photons will be clear signatures for transient source detection

the wb bound
The WB bound

An upper limit to the diffuse neutrino flux was set by Waxman and Bahcall assuming that the detected UHECR sources are the only neutrino sources

  • The WB bound is valid for:
  • Sources optically thin to UHECR (responsible for the observed spectrum)
  • Sources in which CR acceleration takes place (top-down excluded)

“thick sources”

MPR bound

“thin sources”


WB bound

Waxman Mannheim


possible extragalactic sources and fluxes
Possible extragalactic sources and fluxes

Ruled out by

new AMANDA data (preliminary)

pAGN cores

ppAGN cores

p blazar




Diffuse neutrino fluxes

Learned Mannheim



WB Limit




Bright and nearby GRB could produce intense directional fluxes (e.g. GRB 030329) as well as brightest AGNs (3C273, 3C279)

galactic sources of he neutrinos
Galactic Sources of HE neutrinos

SNR, extensively discussed:

(see T. Stanev)

CRAB, Protheroe

Most powerful





Another important source of TeV neutrinos could be the Galactic centre (SGR-A*) which is a very active gamma source

Galactic sources do not contribute to UHECR fluxes, therefore are not limited by WB bound. Even if much less intense, their proximity to the Earth may yield detectable neutrino fluxes

high energy neutrino detection
High energy neutrino detection

Detection of HE astrophysical neutrinos is achieved through CC neutrino interaction with matter with charged lepton production

Neutrino astronomy requires reconstruction of direction and energy of the reaction products (charged leptons)

neutrino cross section
Neutrino cross section

At >TeV energies the muon and the neutrino are co-linear






Reconstruction of the  trajectory allows the identification of the  direction

Neutrinos are detected indirectly, following a DIS on a target nucleus N:

10-33 cm2


1 TeV

1 PeV


muon range
Muon Range


In water


Range (m)

1 TeV

1 PeV



Muons have long tracks in water

Due to its larger mass (m/ me~200) radiative losses of muons are strongly suppressed with respect to electrons

muon vs electron range
Muon vs electron range

10 GeV

100 GeV

Geant 3.21

1 TeV


Muon 100 TeV

Spiering Wiebush

neutrino detection probabilty
Neutrino detection probabilty

Due to the long muon range the target volume is much bigger than the detector instrumented volume

Instrumented detector D<R

Probabilty to produce a detectable (E>Emin) muon

neutrino induced muon fluxes
Neutrino-induced muon fluxes
  • Neutrino flux spectrum
  • Probabilty to produce a detectable (E>Emin) muon
  • Earth transparency to HE neutrinos  >PeV neutrinos search for “horizontal” tracks


1 TeV



10 TeV

100 TeV



The number of muon events in units of detection area A and observation time T is:

detection area for astrophysical uhe neutrino fluxes
Detection area for astrophysical UHE neutrino fluxes

The expected number of events for WB sources is roughly:

The observation of TeV neutrino fluxes requires km2 scale detectors

expected astrophysical neutrino induced muons in 1 km 2


Guaranteed (GZK): few / year ?

Diffuse GRB: 20 / year

Diffuse AGN (thin): few / year

(thick): >100 / year

Expected astrophysical neutrino induced muons in 1 km2




GRB (030329): 110 / burst

AGN (3C279): few / year

Galactic SNR (Crab): few / year ?

Galactic microquasars: 1  100 / year





km 3 scale neutrino detectors
km3 scale neutrino detectors
    • The requirement of large neutrino interaction target
    • induced Markov and Zheleznykh to propose the use of natural targets.
    • Deep seawater and polar ice offers:
  • huge (and inexpensive) target for neutrino interaction;
  • good optical characteristics as Cherenkov radiators;
  • shielding from cosmic background.
underwater cherenkov detectors detection principles

atmospheric muon

~5000 PMT

Underwater Cherenkov detectors: detection principles

Cherenkov light



Connection to the shore




the km3 telescope a downward looking detector
The km3 telescope: a downward looking detector

Upgoing and horizontal muon tracks are neutrino signatures

Neutrino telescopes search for muon tracks induced by neutrino interactions

The downgoing atmospheric  flux overcomes by several orders of magnitude the expected  fluxes induced by  interactions.

On the other hand, muons cannot travel in rock or water more than  50 km at any energy

cherenkov light emission and propagation
Cherenkov light emission and propagation

The Cherenkov light is efficiently emitted by relativistic particles in water at UV-blue wavelengths under the condition: n() > 1

n(300700nm) ~ 1.35

C~ 42°


muon event

cherenkov track reconstruction
Cherenkov track reconstruction

Cherenkov photons emitted by the muon track are correlated by the causality relation:

The track can be reconstructed during offline analysis of space-time correlated PMT signals (hits).

pseudo vertex

De Jong

detector granularity
Detector granularity

Spacing of optical sensors inside the instrumented volume must be of the order of the light absorption lenght in water (70 m for blue light)

Visible light

About 5000 optical sensors are needed to fill up one km3


Neutrino detectors must identify few astrophysical events on top of diffuse atmospheric backgrounds

backgrounds atmospheric muons and neutrinos
Backgrounds: atmospheric muons and neutrinos
  • Atmospheric neutrinos:
  • upward tracks are good neutrino candidates;
  • event direction and energy criteria can be used to discriminate background from astrophysical signals.
  • Atmospheric muons:
  • downgoing events background is due to mis-reconstructed (fake) tracks;
  • improve analysis filters for atmospheric muon background rejection.


atmospheric muon background vs depth
Atmospheric muon background vs depth







Downgoing muon background is strongly reduced as a function of detector installation depth.

Depth >3000 m (1 km rock) is suggested for detector installation

first detection of he neutrino events
First detection of HE neutrino events

Proof of the underwater (and underice) Cherenkov detection technique has been achieved by AMANDA (South Pole) and BAIKAL-NT (Lake Baikal) detectors

the amanda neutrino sky
The AMANDA neutrino sky


(neutrino 2004 conference)

The atmospheric neutrino spectrum has been measured by AMANDA and BAIKAL

See Silvestri’s talk

AMANDA and BAIKAL have demontrated the viability of neutrino detection with underwater and underice Cherenkov detectors at TeV energy scale

the future neutrino telescopes
The future neutrino telescopes

>3000 m

The quest to reach the km2 effective area is open !


Wait for the next lecture...

1400 m

2400 m

Southern Hemisphere


Northern Hemisphere

Mediterranean km3

  • High energy astrophysical neutrino fluxes are expected on the base of CR and  observations
  • Neutrino detection will provide unique informations on astrophysical sources:
  • overcomes the limitations of  and CR astronomy due to absorption on CMBR at cosmological distances;
  • evidence on the role of hadronic processeses in astrophysics
  • Neutrino events correlated in space and time with point-like (transient) sources will be probably the first evidence of detection of astrophysical neutrinos
  • The expected fluxes from sources implies >1km2 effective area to detect TeV-PeV neutrinos
other scientific goals
Other scientific goals

Galactic SN:

search for intense fluxes of electron anti-neutrinos

need low optical background  task for AMANDA-ICECUBE

Dark Matter:

search for neutrinos ( 10 GeV) originated by the annihilation of neutralinos in the Sun, Earth, Galactic Centre

low energy threshold, good event direction reconstruction