ARA The Askaryan Radio Array A new instrument for the detection of highest energy neutrinos.

1. ARAThe Askaryan Radio Array A new instrument for the detection of highest energy neutrinos. Hagar Landsman

2. Outline Neutrino astronomy – The “Whys?” and “Hows?”. The “Askaryan Radio Array” (ARA). Status and results from the first year. Down the road. Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

3. Highest energy neutrinos….Why ? • There is a high energy universe out there we know very little about! • HE Neutrinos are expected to be produced together with photons and protons through pions decay. • Neutrinos add complimentary information to gamma astronomy • With neutrinos we can look further away • Cosmic rays with energies of more than 1020eV were observed. • Their source, or acceleration mechanism are unknown. • Sufficiently energetic Cosmic rays interact on photon background and loose energy • Less Protons - No energetic CR from large distances (>50MPc) • More Neutrinos - Flux of neutrino : “Guaranteed source” p + g D * n + p venmne ve p+ g  D *  n + p “GZK Neutrinos” venm ne ve p Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

4. Cosmic ray connection I CR accelerated in jets: AGN or GRB CR accelerated in shocks

5. Possible media: Lunar regolith (20m attenuation length) Parker telescope, GLUE, WSRT Ice (1000-1500m attenuation length) FORTE (Satellite), ANITA (Ballon), ARA Salt (100-500m) SalSA Air To thin Water RF Lossy Desert sand ( as opposed to silica) RF Lossy

6. Cosmic Ray connection IIPropgation • Neutrino produxtion during propgation • Intensity depends on: • Spectrum at sources • Evolution of sources • Composition of UHECR (heavy nuclei give less neutrinos)

7. UHECR messenger • Photons • Interactions in source/transit • Hadronic or EM • Neutrinos • No interactions in source • Fewer in detector • hadronix

8. Is the cut off the GZK limit • Current neutrino limits disfavors UHECR inside reletivastic jets • More data is coming with full IceCube • Is the cutoff the GZK effect • Cosmogenic neutrinos

9. Neutrino Astronomy Detection principle m+ n Astrophysical Neutrino interact in (near) detector volume, creating energetic charged particles . The charged particles create Cherenkov radiation An array of detectors is looking for the photons. m n Threshold for muons=159 MeV Threshold for electron=0.77 MeV Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

10. Neutrino Astronomy Detection principle m+ n • Technique: • Optical, Radio, Acoustics • Transparent Media: • Water, Ice, Salt • Location: • In, above or around medium m n Spacing between detectors determines threshold energy. Size of detector effects sensitivity Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

11. Neutrino Astronomy SN 1987A – Birth of Neutrino astronomy • First detection of astrophysical neutrinos. • 24 neutrinos measured Several hours before optical signal from SN1987A • (core collapse --> shock wave) • Neutrinos energy ~10s MeV • 40m diameter (16m for KamiokandeII) • 50 kilo-ton (3,000ton) of water • Numbers in brackets corresponds to “Kamiokande II” Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

12. Neutrino Astronomy IceCube • Construction ended December 2010 • 2.5 km deep in antarctic ice • Optimized for GeV-TeV range • Cubic kilometer instrumented with • ~5000PMTs • more than 1 giga-ton of ice Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

13. Neutrino fluxes Measured and expected ~ 100 m2 area ~ 1 km2 area ~ 100 km2 area Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

14. Why not Build a Larger IceCube?IceCube can detect cosmogenic neutrinos, but not enough of them … • Current IceCube configuration: • Yields less than 1 cosmogenic event/year • Making IceCube bigger is an option: • Some geometry optimization is possible, though: • Still need dense array scattering • Still need deep holes for better ice • Any additional string will cost ~1M $* Simulated 9EeV event IceCube (80 strings) More than 60% of DOMs triggered A larger detector requires a more efficient and less costly technology. *Rough estimation, Real cost will likely be higher Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

15. Solution: Use Cherenkov photons in RF • Longer attenuation length in ice larger spacing  less hardware • Less scattering for RF In ice. • Cherenkov radiation pattern is preserved • Don’t need many hits to resolve direction • No need to drill wide holes • Better ice at the top. No need to drill deep. • Antennas are more robust than PMTs. • The isolated South Pole is RF quite and • any EMI activity is regulated • Deep ice (2.5km) contributes to effective volume • It is easy to detect RF Gurgen Askaryan (1928-1997) Remember: Less photons are emitted in longer wave length. Smaller signal in the radio frequencies…. But for high energy cascades this RF radiation becomes coherence and enhanced “Askaryan effect” PavelAlekseyevich Cherenkov (1904-1990) Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

16. Askaryan Effect

17. Antarctic skaryanEffect Heritage RICE Radio Ice Cerenkov Experiment Array of single dipole antennas deployed between 100 and 300m near the South Pole, covered an area of 200m x 200m. (mostly in AMANDA holes) Used digital oscilloscope on surface for data acquisition IceCube Radio Co deployed with IceCube at 30m, 350m and 1400 m. Full in ice digitization. The Askaryan effect Was measured in a special SLAC experiment . Extensive simulation of the radiation cone exist, and predictions are in agreement with the measurement. ANITA ANtarctic Impulsive Transient Antenna : surveys the ice cap from high altitude for RF refracted out of the ice (~40 km height of fly, ~1.1M km2 field of view) Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

18. ARA Concept • 80 km2 area • 37 stations equally spaced on a triangular grid • Large separation between stations (1.3km) • 3 stations forms a “super cluster” • Sharing power, comms, and calibration source • Station: • 4 closely spaced strings • 200m deep • Digitization and Triggering on surface DAQ Housing Vpol Antenna Hpol Antenna • String: • 4 antennas, V-pol and H-pol • Designed to fit in 15cm holes • 150-800 MHz sensitivity • Cable pass through antenna ~30m 18 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

19. ARA Concept The goal is to count events, not reconstruct the angles as would be needed for observatory class instrument • Optimized for neutrino counting: • A single station can provide and form a trigger • Decreases trig time window, lower background • and therefore thresholds. • Lowers the energy threshold. allowing single string hits. • Detecting down-going events: (4.4sr) • Between +45 above, -5 below horizon • Deep ice contributes in higher energies 200m ~30m 1300m γ 2.5 km Interaction vertex RF radiation Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

21. ARA expected performance detector sensitivities How strong should a source be, for it to be detected by a detector IceCube (3 years) Auger Tau (3 years) GZK RICE 2006 ARA (3 years) Pure Iron UHECR ANITA (3 flights) 21 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

22. ARA - A New collaboration was born NSF Grant “Collaborative Research: MRI-R2 Instrument Development of the Askaryan Radio Array, a Large-scale Radio Cherenkov Detector at the South Pole“ phase 1 funded More than 10 institutions from US, Europe, Taiwan, Japan Including IceCube & ANITA & RICE leading institutes. Growing collaboration. Strong interests from others Regular collaboration meetings http://ara.physics.wisc.edu 22 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

23. Phase 1: 3 years plan • Large array challenges: • Power source • Power and communication distribution • Drilling (size, depth, drilling time) • EMI • 2010-2011 • Install testbed • EMI survey away from the station • Test ice properties • Begin testing station prototypes • Calibration activities • Install 3 deep RF Pulsers • Conduct Drilling tests • Install 3 Wind turbines for testing • 2011-2012 • Install ARA in ice station • Install Power/comm hub • 2012-2013 • Install ARA in ice station • Install autonomous Power/comm hub 23 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

24. ARA ‘TestBed’Installed in the 2010-2011 season • Successfully installed ~3.2 km away from the Pole. • 16 antennas at different depths, down to ~20m. • Different freq ranges (between 50-1000MHz) • Signal digitization and triggering happens on a central • box on the surface. • Power and comms through cables. • Current status: • Detector is up and running. • Very high efficiency and live time. • No unexpected EMI source. • Up to now, no evidence for wind generated EMI 24 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

25. ARA ‘TestBed’ station Trigger rates Off season 9:00 pm weather balloon launch 9:00 am weather balloon launch • Test Bed is taking data continuously • Trigger rates are low and stable – below 4 Hz • Clear winter/summer rate change • Weather balloon launches CW clearly seen 25 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

26. ARA ‘TestBed’ stationEMI noise – seeing Galactic center Noise measured on the surface antennas Ch 2 Ch 1 Total Thermal Expected galactic • Data used from January 18 to April 14 • Using two surface antennas • Galactic noise clearly seen over thermal (~ -130 dbW) 26 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

27. ARA ‘TestBed’ StationDeep pulsers on IceCube strings • Deep (2450m) pulser seen by all antennas in the ARA testbed! • Testbed is a horizontal distance of ~1.6 km away- total distance 3.2 km. • Time delays between different antennas used to estimate T resolution. mV mV ns ns σtime=97 ps mV ns 27 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

28. ARA ‘TestBed’ stationField Attenuation Length measurement • Point-to-point measurement • Baseline of 3.2 km Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

29. ARA ‘TestBed’ stationSpecial Bonus: Solar Flare Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

30. Ice Properties

31. Ice Properties: Attenuation length • Depends on ice temperature. Colder ice at the top. • Reflection Studies (2004) (Down to bedrock, 200-700MHz): “normalize” average attenuation according to temperature profile. Besson et al. J.Glaciology, 51,173,231,2005 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

32. Ray tracing from pulser to SATRA Top antenna -5m surface Reflected rays Bottom antenna -35m Direct rays Depth [m] Source at -250m Measured time differences: Time differences between direct rays And between direct and reflected rays can be calculated XY separation [m] Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

33. Average WF recorded in hole 16Time difference between direct and secondary rays Top antenna ~44 bins = ~139 ns Bottom antenna Simulated results: Top antenna ~14ns Bottom Antenna ~137ns ARENA 2010, Nantes IceCube RF extension Hagar Landsman

34. Index of refraction

35. Challenges in design and construction • Horizontal polarization antennas to fit in holes • Cable shadowing • Calibration sources • Power and communication distribution • Drilling • Shelter during constructions • Low power everything ARA hot water drill sleds Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

36. The Game Plan Establish cosmogenic neutrino fluxes Resolve Energy Spectrum Neutrino direction Reconstruction Flavor analysis Particle physics • Small set of well established events. • Coarse energy reco • Energy reconstruction by denser sampling of each event • Angular resolution of less than 0.1 rad ~10 Events/year ~1000 36 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

37. Summary • A collaboration has been formed to build an englacial array large enough to detect cosmogenic neutrinos • An array concept has been proposed. The first phase funded. • Successful first South-Pole season. Second season on going NOW! • First results are promising • Facing several challenges in building and operating a large scale detector such as power distributions and fast drilling. • Eventual large scale array will determine cosmogenic neutrino flux and tackle associated long standing questions of cosmic rays. 37 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

38. Backup 38

39. Antarctic ice propertiesIndex of refraction n(z) Receiver Ray traces 200m 0 Transmitter 1 Depth [km] 2 3 0 1 2 3 4 Distance [km] Horizon for 3 different receiver depths Ray traces 1500m 0 0 1000m 1 200m 0.6 Depth [km] Depth [km] 20 m 2 1.2 3 1.8 0 1 2 3 4 0 0.5 1 1.5 2 2.5 Distance [km] Horizon [km] 39 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

40. Antennas design: • 150-850 MHz • Designed to fit in 15cm holes • Azimuthal symmetric • Cables pass through antenna. No shadowing. 40 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

41. Askaryan effect Hadronic EM Neutrino interact in ice  showers  Many e-,e+, g Vast majority of shower particles are in the low E regime dominates by EM interaction with matter  Interact with matter  Excess of electrons  Cherenkov radiation Less Positrons: Positron in shower annihilate with electrons in matter e+ +e- gg Positron in shower Bhabha scattered on electrons in matter e+e-  e+e- More electrons: Gammas in shower Compton scattered on electron in matter e- + g  e- +g Coherent for wavelength larger than shower dimensions Moliere Radius in Ice ~ 10 cm: This is a characteristic transverse dimension of EM showers. <<RMoliere (optical), random phases P N >>RMoliere (RF), coherent  P N2 Charge asymmetry: 20%-30% more electrons than positrons. Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

42. Salt Ice Typical pulse profile Strong <1ns pulse 200 V/m Simulated curve normalized to experimental results Measurements of the Askaryan effect • Were preformed at SLAC (Saltzberg, Gorham et al. 2000-2006) on variety of mediums (sand, salt, ice) • 3 Gev electrons are dumped into target and produce EM showers. • Array of antennas surrounding the target Measures the RF output • Results: • RF pulses were correlated with presence of shower • Expected shower profiled verified D.Salzberg, P. Gorham et al. • Expected polarization verified (100% linear) • Coherence verified. • New Results, for ANITA calibration – in Ice

43. Deep pulser installation Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

44. Ice Properties: Index Of Refraction 1.77 • RICE Measurements (2004, Down to 150 m, 200MHz-1GHz) • Ice Core Measurements (…-1983, down to 237 meters) Kravchenko et al. J.Glaciology, 50,171,2004 Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

45. Ray tracing from pulser to SATRA Top antenna -5m surface Reflected rays Bottom antenna -35m Direct rays Depth [m] Source at -250m Measured time differences: Time differences between direct rays And between direct and reflected rays can be calculated XY separation [m] Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

46. SATRA Average envelope WFs For In Ice Pulser events Hole 8, Bottom Hole 8, Top Hole 9, Bottom Hole 9, Top Hole 16, Bottom Hole 16, Top ~44 bins = ~139 ns Simulated results=137 ns Simulated results=14 ns Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

47. Askaryan effect is for real Extensive theoretical and computational modeling work exists. Verified in SLAC measurement Agreement between both Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

48. Two drills tested Rapid Air Movement drill (RAM): 4” holes. Never used at pole before Cutter head drill holes, shaving extracted using compressed air Extra compressor required at SP altitude. Limited by air pressure leakage through firn 60m at 15 minutes

49. South Pole Heritage Obviously the people involved know what they are doing ! Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa

50. ARA expected performance Effective volume 1000 Ongoing simulation studies to optimize detector geometry, and make the best use of the 2.5km ice target. 100 Effective volume [km3sr] 10 17 18 19 20 Neutrino Energy [eV] Hagar Landsman ARA Israel Physical Society Meeting, 2011, Haifa