ARIANNA: Searching for Extremely Energetic Neutrinos

Lisa GerhardtLawrence Berkeley National Laboratory &

University of California, Berkeley

NSD Monday Morning Meeting

November 23, 2009

Energetic nuclei create massive showers when the slam into our atmosphere

Spectrum falls as E-2.7

From galactic and extra-galactic sources

LHCRHIC

DirectMeasurements

IndirectMeasurements

Cosmic Rays

KneeAnkle

R. Engel

~1 particle/(km2*yr): Need a massive detector to see highest energy cosmic rays

Auger: 3000 km2, seen O(100) cosmic rays with E > 4 x 1019 eV since 2004

The Most Energetic in the World…

Highest Energy CRs Are Protons?

• Auger sees a correlation between the direction of CR events with E > 6 x 1019 eV and AGNs within 75 Megaparsecs away (244 million light years)

• Suggests these CRs must be protons

Centaurus-AClosest AGN

(2 events)

AugerHiRes

Dep

th o

f sh

ow

er m

axim

um

Or Not… But other observables are consistent with a mixed composition, in disagreement with AGN coincidence results.

Turn towards heavier composition

Neutrinos from CRs• Only ~100 CRs seen ever with energy above 4 x 1019 eV• Flux falls ~E-3

• At these energies cosmic microwave

background photons look pretty tasty

• Further reduces flux, but produces neutrinos via decay

• Called “GZK” or cosmogenic neutrinos, E > 1017 eV

€

p+ γCMB → Δ+ → + +n

Ene

rgy

(eV

)

Propagation Distance (Mpc)

1022 eV

1021 eV

1020 eV

“Guaranteed” Neutrinos

• CMB flux and pγ interaction cross section are well known

• Flux of GZK neutrinos depends on the composition of the CRs

• And evolution of the universe• A lot of interesting potential,

but a really low flux

Flu

x w

eigh

ted

by r

edsh

ift

1+z

Need a Big Detector

GZK Flux ~10/km2/yr

interaction length 500 km

Event rate (per km3yr) ~0.02

Only see half the sky ~0.01

Need O(100 km3) detector and >5 years to see ~10 events

Expected

Flux Band

Current Limits

Towards a GZK Neutrino Detector

• Instrumenting ~100 km3 for optical neutrino detection is prohibitively expensive– IceCube: 1km3 cost $300 million

• Seeing GZK neutrinos requires– Clear signal emission (large S/N)– Large natural medium with a long attenuation length

• Ice, sand

• Radio detection of neutrinos satisfies both

1018 eV neutrino

radio waves

Radio Signals From Cascades: Askaryan’s Idea

• GZK neutrino interaction will produce an electron-gamma shower– Shower in matter will be 20% more

electrons than positrons

γ + e-(atom) γ + e- e+ + e- γ + γ

• Excess charge moving faster than c in medium emits Cherenkov radiation

• At optical wavelengths (400 nm): << Lshower

Power Nelec

• At radio wavelengths (>m): >> Lshower

Power (Nelec)2

Askaryan’s Idea Con’t

• Cherenkov radiation will add coherently if

>> Lshower

• In dense material Lshower ~ 10 cm

Zas, Halzen, and Stanev PRD 45:362 (1992)

Observations of Askaryan Effect• Used beamline at SLAC• ~109 electrons at 28.5 GeV• Total shower energy ~3 x 1019 eV

Ten tons of high quality carving ice

Hand chipped!

e-

PRL 99:171101 (2007)

ANITA Radio telescope

Coherent Emission Measured

PRL 99:171101 (2007)

Coherent

radiation

Power E2

Good agreement with predictions for ice, salt, and sand

GZK Neutrino Detection Requirements

• Clear signal emission (large S/N)– Power E2

– Excellent for GZK E>1018 eV

• Large natural medium with a long attenuation length– Ice is a strong candidate

1018 eV neutrino

radio waves

Ross Ice Shelf

• 650 m thick ice sheet over Ross Sea• 800 km across, roughly the size of Texas• Near McMurdo Station, so “easy” to get to• Used ANITA antennas to measure attenuation

length and reflection from ice/sea water interface

On the ShelfCold Scientist

(David Saltzberg)

Horn Antennas

Tent! Ingenious Use of Natural Building Materials

Ice/Sea Mirror

• Nice reflection of radio waves seen at ice/water interface– <3 dB loss measured

• Attenuation length ~350 m– Conservative, assumes no loss

at reflection

• Anthropogenic background is very low– A few flights over in the

summer

Arbitrary Amplitude

Scaling

GZK Neutrino Detection Requirements

• Clear signal emission (large S/N)– Power E2

– Excellent for GZK E>1018 eV

• Large natural medium with a long attenuation length– Ice, sand

1018 eV neutrino

radio waves

Radio Neutrino Experiments • GLUE, LOFAR,… look for neutrinos skimming the

surface of the Moon– High energy threshold (>1020 eV)

• FORTE: satellite that looks for neutrino interactions in Greenland

• ANITA: balloon circled the South Pole for ~45 days

• RICE: Radio antenna buried in the South Pole amongst AMANDA (optical detector)

Existing LimitsMoon

ANITA(balloon)

RICE(in situ)

Expected GZK signal range

AMANDA/IceCube(optical)

Moon and balloon far from active

volume. Requires a

high neutrino

energy to see signal.

ARIANNA• Designed to fill in “gap” between optical and balloon neutrino detectors• Surface deployment on Ross Ice Shelf

– Antennas buried ~1 m in the ice, listen for neutrinos below– Placement in active volume gains 2-3 decades in lower energy range– Takes advantage of ice/water reflection

• Allows surface detectors to see the downgoing GZK neutrinos– Greatly increases visible solid angle– Surface deployment is much cheaper than in-ice (drilling, etc.)

Ice

Water

ARIANNA Array

• Each station will have 8 antennas– Allow resolution of GZK

neutrino direction

• Ultimate plan is to have 10,000 stations on 300 m a grid: 1000 km3 viewing volume

• Total cost comparable to IceCube (1 km3) array

ARIANNA Sensitivity

Estimated sensitivity of full ARIANNA array

ARIANNA energy range an excellent match for GZK signal. Expect O(100) events/year.

Prototype Station

• Field camp this Austral summer to test prototype station

• Hybrid hardware: Previous ANITA hardware and LBNL developed upgrades

• S. Klein and T. Stezelberger depart on 11/28/09 with prototype– Verify attenuation lengths and

reflection

– Test antenna behavior in snow

Solar Panels

Electronics Box

Cold Scientist

Picture from a previous deployment

Conclusion• GZK neutrinos offer insight into the composition of the

highest energy CRs and the evolution of the universe• GZK neutrino interactions emit radio signals which

scale with neutrino energy and can be heard over long distances

• ARIANNA proposed to use excellent ice/water radio reflection of the Ross ice shelf to look for GZK neutrinos

• Prototype station testing begins next week• Spencer and Thorsten: Good luck and stay warm

Why Neutrinos?• Protons are bent by the

magnetic field of the galaxy

• Photons and protons can be absorbed by intervening objects and will annihilate with CMB

• Neutrinos are the only particles that can reach us from distant energetic objects

p

γ

Anatomy of a CR Shower

• Detect CRs through secondaries in their enormous cascades– Use intricate simulation models to determine CR

composition and energy from these measurements

• Very energetic nuclei that create showers of charged leptons, hadrons and photons in the atmosphere– Most energetic particles ever:

3 x 1020 eV - 3 orders of magnitude higher than LHC