1. Simulation of a hybrid optical, radio, and acoustic neutrino detector Justin Vandenbroucke with D. Besson, S. Boeser, R. Nahnhauer, P. B. Price IceCube Collaboration meeting, Berkeley March 23, 2005

2. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 The goal ~EeV neutrinos, particularly GZK neutrinos, could be a valuable source for astro- and particle physics IceCube or Auger could detect ~1 GZK neutrino per year, but ~10 GZK events/yr would give a quantitative measurement including energy, angular, and temporal distributions allowing tests of cosmic ray production models and new physics Other projects (e.g. ANITA, SalSA) are actively seeking this goal. Should IceCube also seek it?

3. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Why a hybrid extension to IceCube? Like Auger and detectors at accelerators, use >1 technique monitoring the same interaction region Difficult to reach 10 GZK events/yr with optical alone At ~EeV, radio and acoustic methods could outdo optical Detecting events in coincidence between 2-3 methods more convincing than detections with one method alone Coincident events allow calibration of the radio and acoustic methods with the optical method Hybrid reconstruction gives superior energy and direction resolution than with one method, or allows reconstruction of coincident events that cannot be reconstructed with one method alone Extended IceCube could be pre-eminent neutrino telescope at all cosmic energies?

4. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 EeV fluxes Z-burst and topological defect models predict large EeV fluxes but are observationally disfavored The GZK flux is a fairly conservative EeV source Optimize the hybrid detector for a high rate of events from the Engel, Seckel, Stanev (ESS) GZK flux model, but Do not only seek GZK events. Measure whatever is there at ~EeV and design to detect events over a wide energy range Then the IceCube observatory measures the neutrino spectrum over ~10 orders of magnitude!

5. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 The ESS GZK flux model z max = 8, n = 3 Unclear which   to use (unclear effect on star formation rate) For now use the lower rate

6. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 First-pass simulation: keep it simple Assume exactly the 2  downgoing neutrinos make it to the detector, independent of energy, within our 10 16 - 10 20 eV range For radio and acoustic: assume the LPM effect completely washes out signal from EM component of e CC events, so For all flavors and both CC and NC we detect only the hadronic shower, with E sh = 0.2E for all events, independent of energy Generate incident directions uniformly in downward 2 , and vertices uniformly in a fiducial cylinder At each of a set of discrete energies, expose each of the 3 detector components to the same set of Monte Carlo events

7. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 An example hybrid array Optical: 80 IceCube + 13 IceCube-Plus holes at a 1 km radius Radio/Acoustic: 91 holes, 1 km spacing; ~5 radio + ~200 acoustic receivers per hole

8. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Optical simulation Check Halzen & Hooper’s rate estimate with standard simulation tools; run a common event set through optical radio and acoustic simulations For now, only simulate the muon channel (later add showers) Propagate muons with mmc Use amasim with MAM ice (no layering) Local coincidence trigger: 10 coincidences with 2 out of 5 in 1000 ns For optical-only events, apply N ch > 182 to reject atmospheric background Do not apply N ch requirement when radio or acoustic also triggers

9. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Optical Effective volume

10. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Muon track length Length (km) Count

11. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Radio simulation Dipole antennas in pairs to resolve up-down ambiguity 30% bandwidth, center frequency = 300 MHz in air Effective height = length/  Radio absorption model: based on measurements by Besson, Barwick, & Gorham (accepted by J. Glac.) Trigger: require 3 pairs in coincidence Use full radio MC

12. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Predicted depth (temperature)-dependent acoustic absorption at ~10 kHz In simulation, integrate over absorption from source to receiver

13. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Acoustic pancake contours

14. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Acoustic event rate depends on S/N and hole spacing RMS Noise (mPa) Hole spacing, km (91 string hexagonal array) 0.250.512 51.72.64.54.0 23.65.59.69.1 15.68.615 Trigger: ≥ 3 strings hit ESS events per year: Need low-noise sensors (DESY) and low-noise ice (South Pole?) Frequency filtering may lower effective noise level For hybrid MC, set threshold at 9 mPa

15. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Acoustic neutrino direction and vertex reconstruction - With 3 strings hit, it’s easy: - Fit a plane to hit receivers. - Upward normal points to neutrino source. - Within that plane, only 2D vertex reconstruction is necessary, done by intersecting 2 hyperbola determined by 3 arrival times.

16. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Acoustic angular resolution Resolution due to pancake thickness: expose array (0.5 km hole spacing) to isotropic 10 19 eV flux, determine hit receiver, fit plane to hit receivers, compare plane normal with true neutrino direction Result (not including noise hits):

17. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Hybrid reconstruction Typical UHE vertices are outside the optical detector - optical might measure muon energy at detector but needs muon energy at vertex and doesn’t know the vertex Get the vertex from radio/acoustic shower detection. Combining them gives good energy and pointing resolution Very little radio or acoustic scattering - hits are always prompt and timing information straightforward So hybrid sets of 4 receivers hit (e.g. 3+1, 2+2, 2+1+1) may be sufficient for vertex reconstruction using time differences of arrival Different radiation patterns between the methods leads to non-degenerate hit geometry for good reconstruction Not a problem that timing resolutions are different: Put them on the same footing by multiplying by respective signal velocities (position resolutions are comparable)

18. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 O, R, A independent effective volumes

19. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Coincident effective volumes - RA, AO, ORA curves in preparation -Preliminary results: RA overlap ~10-30 % AO overlap ~10%

20. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 Event rates Log(E/eV)ESS Events per year with E > E Optical (muons only)RadioAcousticR-O hybrid 16.50.68.17.60.4 17.50.48.07.60.4 18.50.14.77.60.2 19.50.00.71.30 cf. Halzen & Hooper IceCube-Plus muon rate: 1.2 These results depend on a wide parameter space: - Acoustic ice properties and noise level - Optimizing the array (eg hierarchical spacing such as adding R/A receivers to the optical holes) could increase rates (factor of ~2?) - Adding the optical shower channel will increase rates. First results are encouraging.

21. IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005 ~91 radio/acoustic strings for < 20% of the IceCube cost? Holes: ~3 times smaller in diameter and ~1.5 km deep Don LeBar (ICDS) drilling estimate: $33k per km hole length after $400k drill upgrade (cf. SalSA ~$600k/hole) Sensors: simpler than PMT’s Cables and DAQ: Only ~5 radio channels per string (optical fiber). ~200 acoustic modules per string, but: Send acoustic signals to local in-ice DAQ module (16 sensor modules per DAQ module) which builds triggers and sends to surface Acoustic bandwidth and timing requirements are easy (c sound ~10 -5 c light !) Acoustic bandwidth per string = 0.1-1 Gbit, can fit on a single ethernet cable per string