High Energy Neutrino Astronomy

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High Energy Neutrino Astronomy

• By Marieke Navin

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CONTENTS

• Why Neutrinos?
• Scientific Objectives
• Neutrino Astronomy
• Indirect Dark Matter Searches
• Detection Principles
• The Detectors
• Results so far

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WHY LOOK FOR HIGH ENERGY NEUTRINOS?

• Neutrinos carry no charge
• Charged cosmic rays deflected by magnetic fields
• Neutrinos can be traced back to point of origin
• Neutrinos are stable particles
• Neutrinos only interact via weak nuclear force
• Photons attenuated by interactions with Infrared
  Radiation and CMBR, Universe opaque to high
  energy gamma rays
• High energy protons also interact with CMBR mean
  free path 50-100Mpc
• Incredibly small cross-section 1.2x10-43cm2 can
  escape from even optically thick sources
• Neutrinos may be the only high energy particle to
  escape hot dense sources
• Allows highest redshifts to be probed in a way
  not possible with any other particle type
• NEUTRINOS OFFER UNIQUE NEW WINDOW ON THE
  UNIVERSE!

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HOW ARE NEUTRINOS PRODUCED?

• Interactions and decays of hadrons
• (Hadrons)?p ? µ ?? ? e ?? anti-?? ?e
• (Hadrons) ??- ??- ?µ ? e- ?? anti-?? ?e

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HOW ARE NEUTRINOS PRODUCED?

• Particle Annihilation
• cc ? W W- ? ? ?- ?? anti-??
• Charged Current Absorption/Emission
• p e- ? n ?e
• n e ? p anti-?e
• Pair Production - all neutrino types
• e e- ? ? anti-?

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NEUTRINO ASTRONOMY GOALS

• Origin of Cosmic rays
• Protons (90), He nuclei (10), some heavier
  nuclei
• Energies 108 to 1020 eV
• Hadron acceleration
• Proton dominated cosmic ray flux above ankle
  suggests extra galactic sources which accelerate
  protons - possible sources high energy neutrinos

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ASTROPHYSICAL SOURCES
Search for neutrinos from cosmic acceleration
processes in Galactic and extragalactic sources

• GALACTIC
• MICROQUASARS

• EXTRAGALACTIC
• ACTIVE GALACTIC NUCLEI (AGN)
• GAMMA RAY BURSTS (GRB)
• p?????
• DIFFUSE FLUXES

cannonballs
fireball

• SUPERNOVA REMNANTS

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NEUTRINO ASTRONOMY GOALS

• Confirm source as site of hadron acceleration
• Confirm source direction and identify optical
  counterpart
• Information about conditions in core of source
• Search for ultra-high energy neutrinos
• Search for neutrinos from annihilation of Weakly
  Interacting Massive Particles (WIMPS)

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EVIDENCE FOR DARK MATTER

• Galactic
• Rotation
• curves

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EVIDENCE FOR DARK MATTER

• Gravitational lensing, predicted by Einstein
• Here multiple images of a background object can
  be seen in the galaxy cluster CL00241654
• Light from this object is bent and focused by the
  matter in the cluster
• Analysis of these distortions enable the matter
  profile of the cluster to to be mapped

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EVIDENCE FOR DARK MATTER

• Baryons could contribute to the dark matter
  problem in the form of non-luminous objects.
• The amount of baryonic matter in the Universe is
  related to abundances of elements such as 2H,
  3He, 4He and 7Li produced at the start of the
  Universe.
• ?Bh2 0.025 ? 0.001
• Significant amount of density of the Universe
  non-baryonic

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CANDIDATES FOR DARK MATTER

• Hot Dark Matter
• Cold Dark Matter
• WIMPS
• 85 total matter content of Universe consists of
  non-baryonic cold dark matter
• Supersymmetry theory offers candidate the
  Lightest Supersymmetric Particle
• The lightest neutralino - a natural WIMP
  candidate

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INDIRECT DARK MATTER DETECTION

• WIMPS (neutralinos) become massive astrophysical
  objects - Sun, Earth, Galactic Centre
• Neutralinos self annihilate into fermions or
  combinations of gauge and Higgs bosons
• Subsequent decays of c, b, t quarks, Z, W, Higgs
  bosons can produce significant flux of high
  energy neutrinos
• Complements direct detection

c
?
Sun over time neutralino population builds up
at the core to an equilibrium value
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DETECTION PRINCIPLES

• Neutrino telescopes use Cherenkov radiation to
  detect the charged lepton produced when a high
  energy neutrino undergoes charged current
  interaction in or near the detector volume.
• Use water or ice as Cherenkov medium
• Light detected by lattice of Photomultiplier
  Tubes (PMTs) housed in transparent spheres spread
  over a large volume

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Detecting High Energy Neutrinos
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DETECTION PRINCIPLES

• Creation of upward going muons which pass through
  detector emitting Cherenkov light
• Searching for upward going muons uses Earth as a
  filter against cosmic ray muons
• Observation upward going muon provides
  unambiguous signal of neutrino interaction near
  the detector
• Measure direction of muon passing through
  detector by detecting arrival times of Cherenkov
  photons on detectors with known positions
• Infer neutrino direction - associate high energy
  neutrinos with astrophysical source or site for
  dark matter annihilation.

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Current Projects
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THE ANTARES DETECTOR

• Astronomy with a Neutrino Telescope and Abyss
  environmental RESearch
• 40 km of south coast France, depth 2.4km
• Consists of 12 strings spaced 60m apart
• Each string composed 25 storeys intervals 14.5m
• Each storey supports 3 optical modules (OMs)
  containing PMT and LED beacon for calibration (on
  4 storeys per string)

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ANTARES Detector Design
EO cable to shore
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ANTARES
Glass sphere (Nautilus)
LED pulser
Large area photocathode
Location Mediterranean Sea, off the southern
French coast Collaboration France, Spain, UK,
Russia, Holland, Italy, Germany Detector 900
PMTs Status Under construction, full deployment
by 2005
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AMANDA

• Antarctic Muon And Neutrino Detector Array
• Array of 19 lines supporting 677 PMTs in
  Antarctic ice at depth up to 2km
• Detector area few 104 m2 for 1TeV muons
• Complements ANTARES

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AMANDA

• Location South Pole
• Collaboration US, Sweden, Germany, Belgium
• Detector (Amanda II) 19 Strings, 677 OMs, 200m
  diameter 400m height
• Depth 1150m to 2350m Status Data taking

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RESULTS FROM AMANDA

• Absorption properties of ice
• - Max absorption length 100m at Amanda 11 depths
• Scattering properties of ice
• - Scattering length 20m for wavelength
  corresponding to longest absorption lengths
• Atmospheric Neutrinos
• - Reconstruct upward-going muons produced by
  atmospheric neutrinos

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RESULTS FROM AMANDA

• Point Source Search
• Good angular resolution and absolute pointing
• Good effective size for as much as the sky as
  possible
• Neutrino flux sensitivity 0.22 x 10-7cm-2s-1
• No evidence extraterrestrial neutrino sources

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RESULTS FROM AMANDA

• Gamma Ray Bursts (GRBs)
• - no observed correlated emission of high
  energy neutrinos from any burst sample
• Diffuse limits

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TO THE FUTURE - IceCube

• Instrumented detector volume 1km3
• 4800 PMTs, 80 km length strings
• Depths 1.4 to 2.4km
• Construction commences 2004
• Higher efficiency, superior angular resolution
• Low background - detect excess anti-?e events
  from galactic supernova

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CONCLUSIONS

• MeV neutrino astronomy established
• GeV to PeV energy neutrinos which must accompany
  production of high energy cosmic rays await
  detection
• First generation experiments data-taking or in
  advanced stages construction
• History shows that probing the Universe in new
  window yields unexpected phenomena