IceRay: an IceCube-Centered Radio GZK Array John Kelley University of Wisconsin, Madison for the IceRay working group ARENA08, Rome

Goals Extend IceCube into the EeV range via a radio array (detecting Askaryan emission) –50 km 2 (initial phase) to km 2 (final target) –substantial rates of GZK / year O(1º) angular resolution Subset of events which trigger both radio and optical arrays –Allows calorimetry of both shower and outgoing lepton –Invaluable for cross-calibration / unambiguous GZK identification

The IceRay Working Group Hawai’i: P. Allison, M. DuVernois, P. Gorham, J. Learned, C. Miki, B. Morse, L. Ruckman, and G. Varner Wisconsin: A. Karle, F. Halzen, and H. Landsman Ohio State: J. Beatty Maryland: K. Hoffman Delaware: D. Seckel Penn State: D. Cowen and D. Williams MIT: I. Kravchenko Taiwan: P. Chen UCL: R. Nichol and A. Connolly

Design: Frequency Range Attenuation length of ice is better at low frequency (< 500 MHz) Solid angle also better at low freq. SNR goes as sqrt(bandwidth) Go low freq., high bandwidth: MHz

Design: Depth Firn shadowing: shallow rays can’t get to surface! I. Kravchenko et al., Astropart.Phys (2003)

Ray Tracing 50m200m

Ray Tracing, cont. 400m1km

Drilling Deeper is better for V eff  (up to ~400m) IceCube EHWD: too cumbersome (and expensive) Independent firn drill: easily drill to 50-80m, possibly deeper with modifications Realistic goal: 200m

50 km 2 Baseline Studies Higher density, shallow (50m) vs. sparse, deep (200m)

Simulation Results UH IceRay MC; crosschecked with Bartol, RICE MC, and ARIANNA MC IceRay-36 / 50m depth IceRay-18 / 200m depth

Acceptance and Event Rates Initial phase achieves 3-9 ev/year for “standard” fluxes Final phase: ~100 ev/year

“Golden” Hybrid Events Triggering both IceRay and IceCube: rates are low, but extremely valuable for calibration High-energy extension (IceCube+ above) with 1.5km ring helps a lot Sub-threshold cross- triggering can also help IceRay-36 / shallow

ANITA Experience South Pole isn’t so radio-quiet –strong impulsive sources ( -like) – MHz range noisy (where you want to be for ice) –understanding / eliminating background is key for large-scale radio array MCM SP…SP MCM SP..SP..SP MCM SP ….SP…..SP courtesy of P. Gorham

Surface Testbed Station 12+2 antennas –6 V pol 6 H pol –Discones for V pol –Batwings for H pol –5m circle –2.5m depth below screen –Stacked in pairs for vertical resolution 15m Cu mesh ground screen DAQ & receivers in shielded boxes ~1.5m depth just above screen Also: –1 monitor antenna above screen, but ~1m deep –Pulser bicone ~15m away, in 24” augered hole, 2.5-3m deep courtesy of C. Miki, Univ. of Hawai’i

Antenna Assembly discone batwing C. Miki with antenna pair

Receivers & DAQ system RF receivers: –ANITA design, ~76 dB gain, 140K noise temperature –Bandpass MHz IceCube radio readout (ICRR): –Based on LABRADOR digitizer + Virtex-4 FPGA combination –Similar to ANITA design, 16 chan, –Interfaces to std. IceCube DOM readout + leverage AURA DAQ courtesy of G. Varner

Terminated Amplifier Module

IceRay Brains

DOM MB, TRACR, and ICRR

Test Setup — UH Manoa 10/24/07 Nearly end-to-end test DAQ and waveform analysis Cold test with dry ice also successful Hardware is ready for deployment

Summary / Outlook AURA (see talk by H. Landsman): leverage deep IceCube holes Surface testbed: detailed background characterization, hardware prototypes IceRay: greatly extend IceCube+AURA; GZK neutrino measurement with optical cross- calibration

Extra Slides

Discones Checked with nec2dx_firn –Code modified for n=1.35 Reasonable mode structure, MHz 100 MHz 200 MHz 300 MHz400 MHz 600 MHz

Batwing (Horizontal Pol.) 100 MHz175 MHz 375 MHz 150 MHz 225 MHz Primary mode2ndary mode

Simulation Details –Throw events over 6 km radius disk, 300m to 2500m depth – MHz bandwidth for each antenna, low gain (dipole- like response) –12 antennas (6 H pol, 6 V pol ) per station –> 4  on 5 antennas required to trigger (to ensure near 100% reconstruction efficiency), use T sys ~ 360K (230K ice +130K receiver) –Exclude shallow zenith angles due to firn refraction shadowing

Cu mesh Ground screen Ground screen goals: –suppress surface noise from Pole –block aircraft RFI –block galactic & solar RF emission (strong at 100MHz) Size: ~ 3 times antenna array diam,  ~15m High-quality EMI mesh is really needed for best performance n=1.35  =48 o Incident RFI from pole Refracts into surface  better angle ~1/4 wave radius  Suppress Fresnel diffraction

Surface Cable 1700m Ericsson shielded 3-quad connects to spare quads at SJB Adaptor for direct DOM hookup (comms testing / debugging) also complete