Astrophysical Neutrinos: A Thorny Problem

Jodi Lamoureux, LBNL/NERSC June 2002


Astrophysical Neutrinos: Astrophysical Neutrinos: A Thorny ProblemA Thorny Problem

• Astrophysical Hadron Accelerators

• The Neutrino Connection

• Ideal km3 Detection

• Summary of Experimental Limits

• Conclusions


Neutrino Astronomy: The Neutrino Astronomy: The ConceptConcept

• Stable particles: p, • Accelerator: magnetic

shocks and relativistic blast waves.

• Targets are traditional HEP • Astrophysical Sources:

– GRB, AGN, Galaxy/Sag-A, SN– GZK ( p + CMB )– Topological defects

• Cosmic Rays:– Atmospheric Muons– Atmospheric Neutrinos


CR and Photon SpectraCR and Photon Spectra

1 particle per m2-second

Knee1 particle per m2-year

Ankle1 particle per km2-year

GeV TeV PeV EeV

Cos

mic

Ray

Flu

x (

m2 s

r s

GeV

) -1• CR spectrum is nearly E-2 dN/dE

– Fermi acceleration is the best theory for high energy CR spectrum.

– Below knee – galactic protons– Above knee – galactic ions– Above ankle – extragalactic

protons?– Above GZK - ???

Waxmann & Bachall hep-ph/0206217

• Photon spectrum– Not Generally a power-law:

Blackbody, Synchrotron, Compton – CR contribution:

p + 0 + X

– Universe Opaque to TeV 1st Confirmation from SN remnants.

Rad

io

CM

B

Vis

ible

GeV

-r

ays

TeV TeV absorbedabsorbed

KpcKpc


Hadronic Photons in the Hadronic Photons in the NewsNews

• Cangaroo reported in May: • TeV power-law spectrum of

photons from overlap region of two SN~6 kpc distance~3-10 G~ 100 p/cm3 ambient density

• Fermi accelerated protons:p + p 0 + X

• Ruled out

– Synchrotron emission (solid)– inverse compton emission (dot)– Bremsstrahlung (dash)

• June 25 preprint: ”No evidence yet for hadronic TeV emision…”Reimer & Pohl Astro-ph/0205256 v3.

Enomoto, et al. Nature 416, April 2002


CR Acceleration CandidatesCR Acceleration Candidates

• Most candidates assume elastic “collisionless” acceleration.

Lamar Radius ~ E/ZB

– Pulsars – Active Galaxies – Radio Galaxy Lobes– GRB – relativistic expanding fireball


Proton Acceleration SitesProton Acceleration SitesJets from AGNJets from AGNM87 in VirgoM87 in Virgo


Accretion DisksAccretion Disks

Pulsar in CrabPulsar in Crab Pulsar VelaPulsar Vela

Active GalaxyActive GalaxyNGC 4261NGC 4261


Crab Movie Courtesy ofCrab Movie Courtesy of

J.Hester, K.Mori, D.Burrows, P.Scowen, M.Haverson, C. Michel, J.Gallagher, J.Graham

2001 HST and Chandra Monitoring of the Crab Synchrotron Nebula, Bull. AAS, 199 126.14


Conclusions about Conclusions about AcceleratorsAccelerators

• Jury is still out on hadronic emission of TeV gamma rays.

• CR are consistent with Fermi-acceleration but identifying localized sources is hard.

• Photons reveal a number of possible sites… pulsars, AGN, GRB, SN remnants

• So, what do we expect in the way of neutrinos?


0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6

Anatomy of High Energy Anatomy of High Energy Neutrino SourcesNeutrino Sources

• Assume accelerated protons are impinging on a target of photons or protons.

• Proton must interact min path*column density• Decay: n, + and 0 max or path < decay length• Escape: and p max path*

p + + + X

+ e+ + e

p + 0 + X

p + n + X p + e- + e

-0.1

0.1

0.3

0.5

0.7

0.9

1.1

1.3

1.5

1.7

0.00001 0.001 0.1 10 1000 100000

Survival Probability ~ exp[-(p + X)*path*]


Anatomy of High Energy Anatomy of High Energy Neutrino SourcesNeutrino Sources

• GRB ?GRB ?

• WB Bound

• AGN Jet ?

& MPR Bound

Regions:Regions:1.1. CR don’t interactCR don’t interact2.2. CR CR p, p, , ,3.3. CR CR , ,4.4. CR CR

HiddenSources

• GZK


Anantomy of High Energy Anantomy of High Energy Neutrino SourcesNeutrino Sources

• RX J1713.7-3946

Not included in this view:Not included in this view:• Hydrodynamics, magnetic shocks, local density Hydrodynamics, magnetic shocks, local density variations, heavy ions and serendipitous source variations, heavy ions and serendipitous source configurations.configurations.• Energy budgetsEnergy budgets


Astrophysical Muon Neutrino Astrophysical Muon Neutrino FluxFlux

• Diffuse flux:WB, MPR, GZK, galaxyAtmospheric

• Point sources: AGN, Sgr-A, galactic center,RX-J1713.7-3946Background * 1 deg/20,000

deg

• Variable sources: GRBBackground * 1 deg/20,000

deg * time coincidence factor.

E

d/

dE

(km

-2 y

r-1 s

r-1)

Albuquerque, Lamoureux, Smoot, hep-ph/0109177

TeV PeV EeVTeV PeV EeV


Oscillations & Muon Neutrino Oscillations & Muon Neutrino Flux Flux

• Astrophysical Sources are far enough away that that flavors mix…

: e:

2 : 1 : 0 w/o osc 1 : 1 : 1 with osc

• Atmospheric are produced locally and oscillations reduce the flux by less than 10%.

E

d/

dE

(km

-2 y

r-1 s

r-1)


TeV PeV EeVTeV PeV EeV


Detecting Neutrinos 101Detecting Neutrinos 101

• Deep Inelastic Scattering– Charge currentpX

epeX

– Neutral current pX

• Neutrino flux is attenuated as it passes through the earth.

COS(z)

COS(z) = 0

COS(z) = 1



Detecting Muons 101Detecting Muons 101

• Muon energy is ~80% of neutrino energy• Degrades in transit.• Measured through radiation deposited in

the detector

Through-going Contained


Muon Radiation 101Muon Radiation 101

• Muons radiate energy as they travel through ice.– Cerenkov light is a small

fraction of the ionization component described by Bethe-Bloch equation.

– Above 1 TeV other processes dominate: Bremstraahlung PhotonsElectron PairsPhoto-nuclear

• Linear energy relation• Resolution has long tail



Up-going Muon Flux in an Up-going Muon Flux in an Ideal kmIdeal km22 Detector (w/o Detector (w/o

oscillations)oscillations)Diffuse flux as a function of

energy deposited in the detector.– Km2 detector is sensitive to 1/3rd of WB limit after 1 yr. 1/5th of WB limit after 2-3 yrs– If diffuse flux is comes from

<10 sources, Km2 detector will identify them.

GRB:Atm flux/(20000*T) = back-free 15 events/year

Sagittarius A East– 0 to 40 events/year at

Mediterranean latitudes. RX J1713.7-3946

– 12 events/yearSouthern hemisphere



UHE Muon Flux in an Ideal UHE Muon Flux in an Ideal KmKm22 Detector Detector

Engel, Stanev, astro-ph/0101216

EeV

• GZK have Ultra High Energy – Above the horizon at EeV.– Radiated energy is enormous. – Without reconstructing tracks:

number of photons in the detector gives lower limit to muon energy.

– Effective area grows with energy 1 km2 @ E=1015 GeV 8 km2 @ E=1020 GeV

• Fewer than 0.5 events/(km2 yr) expected from GZK.


Recent Experimental Recent Experimental SearchesSearches

• AMANDA– Preliminary Muon Neutrino E-2 flux Veff ~ 0.01 km2 @

TeV Hill & Leuthold, ICRC 2001– All-flavor E-2 limits from cascades Veff ~ 0.002 km3 @

TeVCowen, Neutrino 2002 Conf… paper submitted this week

• RICE– Radio-Cerenkov E-2 flux Veff ~ 1+-0.5 km2 @

EeVKravchenko et al. astro-ph/0206371

• Super-K– Neutrinos from GRB

Fukuda et al. astro-ph/0205304


Summary of Experimental Summary of Experimental ResultsResults


ConclusionsConclusions

• Astrophysical sources:– WB bound for CR inspired neutrino sources is conservative.– The CR spectrum does not necessarily imply a significant neutrino flux.– GRB, AGN, pulsars & SN remnants are possible hadron acceleration

sites.– Hadronic photons (0 ) compete with sychrotron & inverse

compton to explain HE photons– Hidden sources aren’t inspired by experimental observations, but there

is phase-space for E up to ~EeV.• Ideal Km3 detector will be able to discover:

– Astrophysical ~E-2 fluxes down to 1/3 WB bound after 1 year.(with 100% duty cycle and reasonable energy resolution)

– Models of GRB, Sgr-A, RX J1713.7-3946 (in “up-going” hemisphere)– UHE neutrinos (0.5 event/km2 yr), but may be detected from half a

kilometer outside a detector in ice.– Neutrino detection would settle HAD/EM acceleration debate and

possibly localize sources CR.• The search is on in a variety experimental venues.


Photon Transport 101Photon Transport 101

• Cerenkov Light– PMTs are sensitive to 300 nm

to 600 nm wavelengths– Muons and secondaries

radiate Cerenkov light.– Cascades – tracks radiate

Cerenkov light. Hadronic component is 0.8*<EM>.

• Absorption length ~100 m• Effective scattering length

~25 m• Light is isotropized well

before it is absorbed. • To first order, sampling is

insensitive to geometric position or PMT orientation.

• Current arrays sample a very small fraction of the total Cerenkov light…

Total PMT area/detector surface area ~ 10-5

J. Ahrends, et. al, submitted PRD


Atmospheric Neutrinos in Atmospheric Neutrinos in AMADNAAMADNA

J. Ahrends, et. al, astro-ph/0205109


Atmospheric Neutrinos in Atmospheric Neutrinos in AMANDAAMANDA

• Primary quality cuts:– Likelihood of track fit high– High fraction of unscattered

hits– Long track length– Hits spread smoothly along

track– Hits aren’t spherically

distributed– Low prob of being down-

going



Atmospheric Neutrinos in Atmospheric Neutrinos in AMANDAAMANDA

• At cut level 7:• 204 candidates with 10% background• Rate is 0.65 (+0.65 –0.3) times the predicted atmospheric neutrino rate.

• Angular distributions of events are consistent with Atmospheric Neutrinos

Vertical Up-going

Horizon




Atmospheric Neutrino Atmospheric Neutrino Spectrum Spectrum in AMANDAin AMANDA

E = 50 GeV

E (center) = 20 GeV

Simulated Energy Threshold:

AMANDA measures flux in the energy range:

66 GeV < E < 3.4 TeV



Astrophysical Neutrino LimitAstrophysical Neutrino Limit

event multiplicity

Data

Atmos. MC

10 E

01020304050607080

01 02 03 04 05 06 07 08 09 0 1000 10 20 30 40 50 60 70 80 90 100


Atmospheric Neutrino Atmospheric Neutrino SpectrumSpectrum

in AMANDAin AMANDA

• Preliminary AMANDA limit:

dN/dE < 10-6 E-2

(cm-2 s-1 sr -1 GeV -1 )

• Rules out the most optimistic MPR power-spectrum limit.

G. Hill , ICRC 2001


The Future… IceCube The Future… IceCube

• IceCube:80 strings60 PMTs/string Depth: 1.4-2.4

Km


IceCube ConceptIceCube Concept

1400 m

2400 m

AMANDA

South Pole

IceTop

Skiway

• IceTop: 2 PMTs in a “pool” at the

top of each

string.

3D air-shower detector


10 TeV Muon

PeV Tau6 PeV Muon

375 TeV Electron

Simulated IceCube Simulated IceCube EventsEvents

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Astrophysical Neutrinos: A Thorny Problem