Radiowave Detection at South Pole Radiowave detection of neutrinos And other exotica (monopoles, e.g.) Quick summary of existing experiments: RICE+AURA= NARC And prototypes: IceRay The future: Askaryan Radio Array 100 km2+ areal coverage Possible acoustic component +surface antenna array for RF air shower. $6M pricetag, 5-year plan N.B. ALSO R&D programs at MinnaBluff (ARIANNA) and Vostok (RADICAL)
Detector Volume: The Challenge for UHE Neutrinos What detection volume is needed? Flux of GZK neutrinos < 1 neutrino / km2 / year / steradian Peak energies ~2 decades below GZK cutoff (photoproduction off CMB, etc...) Neutrino interaction length is ~500 km in ice (Eν 1019 ev), so an incident neutrino at Eν 1019 ev has ~0.002 chance of interacting in 1 km of ice. - Detector can see at most half the sky Earth blocks upcoming neutrino. Therefore, 2pi sr rates in detector are ~0.02 neutrinos / km3 / year Need to thoroughly monitor at least 50 km3 to see 1 event in a year! A detector > 1000 km3-str is required To obtain a detection volume this large, one must use: emission with large S/N natural materials in situ with long attenuation length
Gurgen Askaryan (1928-1997) How to go beyond 10 km3 neutrino detector? Optical attenuation/scattering lengths of order 100 m BUT VHF/UHF radio attenuation lengths of order 1000 m Acoustic (10 s khz) attenuation lengths may be as long ν-induced showers will produce short (< 1nsec for RF) intense burst of radiation for good SNR above ~100 PeV.
Beyond 10 km3? Two Good Ideas by Askaryan #1. UHE event will induce an e/γ shower: In electron-gamma shower in matter, there will be 20% more electrons than positrons. Compton scattering: γ + e-(at rest) γ + epositron annihilation: e+ + e-(at rest) γ + γ
Two Good Ideas by Askaryan Halzen, Zas, Stanev, Alvarez #2. Excess charge moving faster than c/n in matter emit Cherenkov Radiation dpcr dν νdν Each charge emits field E eik r and Power Etot 2 In dense material RMoliere~ 10cm λ<<rmoliere (optical case), random phases P N λ>>rmoliere (microwaves), coherent P N2 Modern simulations + Maxwell s equations
Experimental Realizations RICE: 1996-present 16 in-ice antennas at South Pole, co-deployed in AMANDA holes to depths of 100-300 m. + above-surface Rx Coaxial cable signal transmission to surface digitization ANITA: 2003-present NARC: 2006-present 32 dual-polarization horns mounted on balloon, synoptic viewing of Antarctica during ~30-day circumpolar flight. 2nd flight completed Jan 2009. Adaptation of IceCube DOM for radiowave frequencies ( DRM ). LABRADOR digitizer in-ice; 250-1500 m depths. Possible 100 km3 volume prototype IceRay: 2007-present Also large scale prototype shallow deployment (50 m)
Why South Pole? Cold ice is radio-transparent! (bottom reflection data from 1/09) And NOT birefringent! (all polarizations arrive in synch) Signal propagation transverse to local ice flow direction Signal propag ation parallel to local ice flow
Not birefringent? Conflicts with measurements at Taylor Dome (not so surprising) And measurements at Dome Fuji (somewhat surprising) And initial measurements of ice flow (v vs. depth) by AMANDA Signal propagation transverse to local ice flow direction Signal propag ation parallel to local ice flow
Radio neutrino detection rate as a function of position across continent Model ingredients: a) surface temperature measurements across Antarctica b) Barwick, Besson, Gorham 2004 measurements of RF attenuation length at Pole c) Lab Measurements of Latten(Temp) d) AMANDA measured temperature profile at South Pole e) Universal temperature gradient curve based on measurements at 5 locations across Antarctica
RICE/NARC (nee' AURA) RICE currently going through full data re-analysis. Enhanced Monte Carlo simulations Enhanced neutrino reconstruction efficiency Re-analyze data in search for air shower cores impacting surface=>down-coming shower. NARC: Two sets of deployments: 2006-2007: two receiver clusters + 3 transmitters 2008-2009: three receiver clusters + 3 transmitters
Front-end antennas and digitizing/trigger hardware
ESS GZK
Plan for the future: Measure GZK flux in 10-1000 PeV energy interval ARA
ARA
Summary Radiowave detection promising, but needs a) good sensitivity in 10 PeV-1000 PeV energy interval, b) high-quality target ice (present @SP) + Large areal coverage (simulations underway) Current experiments can't quite get there Hope to initiate next-generation experiment within the next 1-2 years. Co-deploy hardware during last 2 IceCube drilling seasons Supplemented by acoustic + radiowave air shower detection
Laboratory Observations of RF Askaryan Effect Silica sand (SLAC 2000, photon initiated, PRL 86, 2802 (2001)) Salt bricks (SLAC 2002, photon initiated, PRD 72, 023002 (2005)) Ice (SLAC 2006, electron initiated, analysis in progress) NEW ANITA views showers in Ice Target, July 2006 @ SLAC
Signal Coherence Prf / Nexcess (1 + f(λ) Nexcess), where Nexcess / Eshower coherence regime: E-field proportional to Esh Prf proportional to Esh2 SLAC T444 (2000) in sand SLAC T460 (2002) Askaryan in salt
Intensity matches Shower Profile Sand Salt
Cherenkov Radiation is 100% Polarized E S U
Sampling, buffer depth, timing, etc. 2 GSa/sec->1 Gsa/s Try to circumvent RCO correction 256 ns->10 microseconds RAPCAL, but only if it works Full suite of trigger diagnostic information available Test at temperature & pressure ahead of time and verify coincident reconstruction of a transmitter in the lab prior to deployment.
Frequency + Phase Reconstruct time domain pulse Reconstructed signal is a brief, unresolved, bipolar pulse of radiation Details of analysis in PRD 74, 043002 (2006)
Frequency Content log (intensity) (Analysis cutoff at 7.5 GHz) Users of Askaryan radiation do not go above ~1.2 GHz
GRID Reconstruction of RICE Tx X vs. Y for surface RICE Tx (true~(350,120))
Features of a real prototype... 500 MHz bandwidth vs ~200 MHz bandwidth http://wiki.icecube.wisc.edu/index.php/aura07-08_tests (3 db points)