1. ARIANNA: Searching for Extremely Energetic Neutrinos Lisa Gerhardt Lawrence Berkeley National Laboratory & University of California, Berkeley NSD Monday Morning Meeting November 23, 2009

2. Energetic nuclei create massive showers when the slam into our atmosphere Spectrum falls as E -2.7 From galactic and extra-galactic sources LHC RHIC Direct Measurements Indirect Measurements Cosmic Rays

3. Knee Ankle R. Engel ~1 particle/(km 2 *yr): Need a massive detector to see highest energy cosmic rays Auger: 3000 km 2, seen O(100) cosmic rays with E > 4 x 10 19 eV since 2004 The Most Energetic in the World…

4. Highest Energy CRs Are Protons? Auger sees a correlation between the direction of CR events with E > 6 x 10 19 eV and AGNs within 75 Megaparsecs away (244 million light years) Suggests these CRs must be protons Centaurus-A Closest AGN (2 events)

5. Auger HiRes Depth of shower maximum Or Not… But other observables are consistent with a mixed composition, in disagreement with AGN coincidence results. Turn towards heavier composition

6. Neutrinos from CRs Only ~100 CRs seen ever with energy above 4 x 10 19 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 > 10 17 eV Energy (eV) Propagation Distance (Mpc) 10 22 eV 10 21 eV 10 20 eV

7. “Guaranteed” Neutrinos CMB flux and p  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 Flux weighted by redshift 1+z

8. Need a Big Detector GZK Flux~10/km 2 /yr interaction length500 km Event rate (per km 3 yr)~0.02 Only see half the sky~0.01 Need O(100 km 3 ) detector and >5 years to see ~10 events Expected Flux Band Current Limits

9. Towards a GZK Neutrino Detector Instrumenting ~100 km 3 for optical neutrino detection is prohibitively expensive –IceCube: 1km 3 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 10 18 eV neutrino radio waves

10. 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  + e - (atom)   + e - e + + e -   +  Excess charge moving faster than c in medium emits Cherenkov radiation

11. At optical wavelengths (400 nm): << L shower Power  N elec At radio wavelengths (>m): >> L shower Power  (N elec ) 2 Askaryan’s Idea Con’t Cherenkov radiation will add coherently if >> L shower In dense material L shower ~ 10 cm Zas, Halzen, and Stanev PRD 45:362 (1992)

12. Observations of Askaryan Effect Used beamline at SLAC ~10 9 electrons at 28.5 GeV Total shower energy ~3 x 10 19 eV Ten tons of high quality carving ice Hand chipped! e-e- PRL 99:171101 (2007) ANITA Radio telescope

13. Coherent Emission Measured PRL 99:171101 (2007) Coherent radiation Power  E 2 Good agreement with predictions for ice, salt, and sand

14. GZK Neutrino Detection Requirements Clear signal emission (large S/N) –Power  E 2 –Excellent for GZK E>10 18 eV Large natural medium with a long attenuation length –Ice is a strong candidate 10 18 eV neutrino radio waves

15. 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

16. On the Shelf Cold Scientist (David Saltzberg) Horn Antennas Tent! Ingenious Use of Natural Building Materials

17. 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

18. GZK Neutrino Detection Requirements Clear signal emission (large S/N) –Power  E 2 –Excellent for GZK E>10 18 eV Large natural medium with a long attenuation length –Ice, sand 10 18 eV neutrino radio waves

19. Radio Neutrino Experiments GLUE, LOFAR,… look for neutrinos skimming the surface of the Moon –High energy threshold (>10 20 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)

20. Existing Limits Moon 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.

21. 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

22. 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 km 3 viewing volume Total cost comparable to IceCube (1 km 3 ) array

23. ARIANNA Sensitivity Estimated sensitivity of full ARIANNA array ARIANNA energy range an excellent match for GZK signal. Expect O(100) events/year.

24. 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

25. 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

27. 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 

28. 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 10 20 eV - 3 orders of magnitude higher than LHC