1. Olivier Martineau, LPNHE Paris – IN2P3 – CNRS VLV T 2015 workshop Rome, September 14, 2015 Proposal for a Giant Radio Array for Neutrino Detection Kumiko Kotera

2. GRAND neutrino detection principle   Earth + mountains as target for neutrino interaction Fargion et al, arxiv:0002.453, Bertou et al., arxiv:0104.452 Radio detection of subsequent EAS (good at large zenith angles) on a HUGE array [ o(100’000km²) ] Extensive air shower Radio detection E th ~10 17 eV

3. A giant radio array on ground for UHE neutrino detection? GRAND workshop, LPNHE, Paris, Feb 2015 https://indico.in2p3.fr/event/10976/ 35 participants from the field (UHE CRs,  and, air shower radio detection, …) & conex topics. Main output: be ambitious! GRAND worth if we aim at guaranteed detection of cosmogenic neutrinos.

4. Pure Iron No source evolution Mixed composition Source evolution Kotera et al., arxiv:1009.1382 Iron rich, low E max No source evolution Ahlers et al., arxiv:1208.4181 Cosmogenic neutrinos fluxes Cosmogenic neutrinos fluxes @ EeV energies primarly depend on UHECRs chemical composition & source evolution. Combinaison with PeV measurments explains Gal/Extragal transition. Cosmogenic neutrinos are a great tool to study UHECRs! Sensitivity = 3 10 -11 GeV/cm²/s/sr would allow to test all models & provide ~100 /year for most reasonable models. … what would it take to achieve this sensitivity?

5. GRAND proposal: people involved Tianshan Radio Experiment for Neutrino Detection (TREND): French IN2P3 & Chinese CAS collaboration for air shower autonomous radio-detection; ~15 researchers + engineers. Kumiko Kotera @ IAP Paris (phenomenology) Krijn de Vries @ VUB Brussels (radio simulations) Jaime Alvarez-Muniz + Washington Carvalho @ Santiago di Compostella (radio simulations) Charles Timmermans @ NIKHEF (AUGER-AERA) Others in Sweden (Chad Finley), USA, France Anybody interested is welcome! ICRC proceedings, arXiv:1508.01919

6. GRAND neutrino sensitivity study End-to-end MC simulation being setup: Neutrino simulation : from the  trajectory to the  decay products. Custom 1D simulation scheme. Written in C++. External dependencies : Pythia6.4 and TAUOLA /FORTRAN. Scattering is neglected. Radio E-field computation : from the  decay products to the radio E field. Codes: ZhAires (arxiv:1107.1189) & EVA. Work in progress... Issues: -Simulations of very inclined showers -Ground reflexion effects -Huge CPU requests! Antenna response computation: from the radio E-field to the antenna current/voltage response. NEC code.

7. GRAND sensitivity preliminary study - Layout Toy setup: 60’000 antennas deployed over 220x270km² in Tianshan mountains (Western China), site of the TREND & 21CMA experiments. +150 +100 +50 0 -50 -100-150 -150 -100 -50 0 +50 +100 +150 Easting [km] Northing [km] Tianshan mountains 60’000km² Urumqi Ulastai Beijing

8. GRAND sensitivity preliminary study - Principle E>3 10 16 eV 5km 120km  =1-10° MC down to  decay (E in 10 17 - 10 21 eV,  in [85-95°]) Simplified criteria for subsequent shower detection: – Antenna fired if: in direct view of shower in a light cone of few degs (  =f(E), [1-10°]) Tau decay point distant by [5,120] kms. – Detection if : one cluster of 8+ antennas fired. Shower energy > 3 10 16 eV / 10 17 eV

9. GRAND sensitivity preliminary study - Results 3.10 17 eV 3.10 18 eV 3.10 19 eV 3.10 20 eV Downward Going (mountains) Upward Going (Earth) ~ Horizontal trajectories. Mountains are sizable tragets. Earth becomes opaque at higher energies 60000km² simulation setup: factor 3 to 10 better sensitivity compared to ARA in 10 17 -10 19 eV E range. GRAND E th =3.10 16 eV E th =10 17 eV

10. Nb of triggers/antenna GRAND 200’000km² layout « Hotspots » with event rates well above average (large slopes facing distant mountain range). Possible strategy: deploy sub-arrays on hotspots only [size = o(10’000km²)?]. Total detection area x3 (~200’000km²) may result in x10 in sensitivity. Sub-arrays could be separated by large distances… and very well be on different continents! Strategy to be validated/refined through complete MC study. +150 +100 +50 0 -50 -100-150 -150 -100 -50 0 +50 +100 +150 Easting [km] Northing [km] 60’000km²

11. GRAND sensitivity preliminary study - Results 3.10 17 eV 3.10 18 eV 3.10 19 eV 3.10 20 eV Downward Going (mountains) Upward Going (Earth) ~ Horizontal trajectories. Mountains are sizable tragets. Earth becomes opaque at higher energies GRAND 200’000km² full array at 3 10 -11 Gev/cm²/s/sr (?) To be confirmed! GRAND E th =3.10 16 eV E th =10 17 eV

12. GRAND challenge: technical aspects How realistic/affordable is it to deploy, run & maintain a 200’000 antennas array? Possible answer: keep it as basic as possible! – Basic (analog) trigger (T0) on transient signal. – Record 4 words/trigger [Max amplitude x 3 channels + trig time by GPS] – Rely on commercial solutions for electronics & data transfer. – <1W & <200$ / antenna probably achievable. – … Possibly not as crazy as it first sounds! 1.5m 5kg Antennas are ridiculously basic detectors. Science case definition will interfer! [see later]

13. GRAND challenge: background rejection Atmospheric neutrinos – Negligeable above 10 16 eV. HE muons from UHECRs showers – Back of the enveloppe calculation based on Chirkin (hep-ph/0407078): 3 10 -6 decays/year over full array above 10 16 eV. (Misreconstructed) standard cosmic ray showers – Cut 1° below horizon (mountains ) 1°  5  for 0.2° angular resolution 5 10 -7 suppression factor Affects marginaly detection efficiency: <10% – Discrimination on young (neutrinos) vs old (CRs) showers (?) 0.2° angular resolution at worst for  t = 3ns 8 antennas triggering ICECUBE arxiv:1405.5303

14. GRAND challenge: background rejection Terrestrial background 3 10 8 events/year (?) TREND project (2009-2014): ~10Hz coinc rate for 1.5km² arXiv:1007.4359 Neutrino signal: 0-100 events/year Rejection factor: R~10 9 Discriminating parameters: Trigger pattern at ground? Polarisation? AUGER, arXiv:1402.3677v2

15. GRANDproto Hybrid setup with 35 3-polar antennas + 24 scintillators. Target: (standard) air showers coming from North with 40°<  <70° & 10 17 eV<E<10 18 eV. Principle: select radio candidates from polar info, use scintillator array as a cross-check => qualitative determination of rejection factor. Deployment on-going, to be completed before june 2016. Proposal to perform similar tests @ AUGER-AERA.

16. Other science with GRAND sensitivity + angular resolution <0.1° would open the door for neutrino astronomy @ VHE. Huge effective area + performances for EAS reconstruction: great tool for UHECR physics above 10 19 eV. Epoch of reionization (?) Fast Radio Bursts (?) Choices will necessarily impact detector design. Science case to be defined in more details! Work in progress. 60000km² setup GRAND 200’000km² setup

17. Conclusion GRAND could be a great tool for VHE astronomy. GRAND proposal being set-up (science case + neutrino sensitivity) Possible (?) timeline: – mid-2016: proposal completed – 2019: engeneering array (o(1000km²)) – 2022: GRAND Join us!