1. The GRAND proto A prototype array to evaluate the potential of the radio polarization measurement for EAS identification

2. GRAND neutrino sensitivity GRAND would reach ~5x better sensitivity than Antartica projects. To be checked/optimized with full MC. PRELIMINARY GRAND : 90% CL limit assuming 0 candidates in 3 years threshold = 3 10 16 eV  =  0 E -2 spectrum Tens of GZK /year? th = 3 10 16 eV

3. Terrestrial background GRAND bckgd event rate estimation: TREND50: ~30kEvents/day/km² (~1.5 10 7 valid coincs in 317 DAQ days) GRAND: <15 events/day/km² (safe estimate) 3 10 8 evts/year over full array Target rejection factor: 10 9 Expected event rate: 0-100 events/year Factor 5 10 -4 L=30 TREND-50 event multiplicity L=5 TREND50 → GRAND: Area x40000 Antenna density /25 (Trig density /2000): Large step size helps kill background! In principle only signals triggering the full TREND50 array would have a chance to trigger 5+ antennas in GRAND (antenna density).

4. GRAND background rejection Trigger pattern E sh =10 18 eV  =90° 472 antennas triggered … probably not enough (shortest tracks) E sh =10 18 eV  =87° 27 antennas triggered

5. EAS polarization EAS radio emission associated to 2 major sources: – Geosynchrotron effect F L = q v.B geo E field linearly polarized:  B geo  direction of propagation – Charge excess: radial polarization Polarization info can be predicted, provided other shower parameters (E, , x core ) are known. Very unlikely that bckgrd event would exhibit similar polarization signature. Polarization as a reliable signature for EAS (?) AERA, arXiv:1402.3677v2

6.  = atan(max|V y |/max|V x |)  =atan(max|V plane |/max|V z |) Test setup: «GRAND-proto»: a hybrid setup to evaluate quantitativly bckgrd rejection potential of polarization information 32 3-polar antennas + 21 scintilator array Deployed at the noisiest location of TREND array, aiming at showers coming from North. Principle: – Wave triggers 5+ antennas – Reconstruct direction of origin & polarization @ trig’d antennas location: GRAND-proto  = 65°,  = 8° x (EW) y (NS) z P   TREND antenna Reconstructed source position GRAND proto site PRELIMINARY LAYOUT

7. Principle of EAS polarization measurment in GRAND-proto – For all trig’d antennas, simulate expected polarization assuming signal due to air shower. Sim Vx Sim Vy Sim Vz Expected  for E field Expected  for voltage Simulated shower 10 17 eV, [65°,8°] If experimental polar matches one from simulated shower: EAS tag Off-line validation of EAS candidates with scintillator array (requires 100% efficiency for scintillator array) Quantitative evaluation of EAS identification based on wave polarization. Gu Junhua

8. 1000m  = 1.1°  = 89.0° E = 10 17 eV  = 0.8°  = 88.1° E = 5 10 17 eV  = 1.2°  = 88.2° E = 10 17 eV Polarization computation precision Direction reconstruction: <2° in GRANDproto (much better in GRAND) GRAND: very inclined showers Core position (& energy?) probably poorly reconstructed. Charge excess contribution hard to evaluate. PRELIMINARY test with simulated data: – Shift  x core = 1000m – E = 10 17 eV →5 10 17 eV (same geometry) No significant change in  and .

9. Polarization computation precision Noise at antenna output → V≠0 in any case … → Error for extreme values (  = 0° or 90°) But remains below 15° according to simulation. (Signal treatment / other variable to improve result?) Sim VxSim Vy Sim Vz Expected  for E field Expected  for voltage Simulated shower 10 17 eV, [65°,8°] Expected  for voltage + noise + noise

10. How GRANDproto can be instrumental for GRAND (ie can we test rejection power R=10 9 ?) - Valid dataset  event for which EAS nature can be cross checked Events from direction (  ) for which  scint = 100% [simulation] Events from below horizon / known bckgrd sources - Expected event rate? 100Hz → 4 months live to reach total stat of 10 9 events. 10Hz → ~3years live to reach total stat of 10 9 events. Principle of EAS polarization measurment in GRAND How good do we have to be? A very rough estimate. If we achieve 15° precision on reconstructed  : – Random polar may be tagged as valid for one antenna with p=0.028 – p=0.028 5 = 1.6 10 -8 for 5 antennas (3.5 10 -13 for 8 antennas) x (EW) y (NS) z P

11. GRANDproto status Top view Bottom view 2D butterfly antennas @ Nançay (CODALEMA) Didier Charrier, SUBATECH Butterfly antennas: active dipoles

12. GRAND-proto status Radio antenna status – Radio array: 3D active antennas – All LNAs delivered, 6 prototype antennas in test in January-March 2014. 1 event triggering all 3 channels

13. GRANDproto status Radio DAQ : → Jacques David (analog stage) & Patrick Nayman (digital stage) Driving concept [a la EASIER]: -Voltage HF oscillation due to antenna response -Physics info mainly contained in the signal enveloppe -Enveloppe detection allows slower digitization. Scintillator array : → Feng Zhaoyang (simulation status) → Gou QuanBu (harware status) Detector fully funded, deployment May 2015-early 2016 Efield Voltage Enveloppe TREND50 simulation E=10 17.5 proton shower, antenna 300m from core

14. Conclusion Terrestrial bckgrd probably the main challenge for neutrino signal identification in GRAND. Polarization measurement (or whatever easily reconstructable variable related to it) as a way to tag showers? GRANDproto to test this hypothesis. Development phase on its way, deployment in the coming year.