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

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 = eV  =  0 E -2 spectrum Tens of GZK /year? th = eV

Terrestrial background GRAND bckgd event rate estimation: TREND50: ~30kEvents/day/km² (~ valid coincs in 317 DAQ days) GRAND: <15 events/day/km² (safe estimate) evts/year over full array Target rejection factor: 10 9 Expected event rate: events/year Factor 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).

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

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: v2

 = 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 & trig’d antennas location: GRAND-proto  = 65°,  = 8° x (EW) y (NS) z P   TREND antenna Reconstructed source position GRAND proto site PRELIMINARY LAYOUT

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 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

1000m  = 1.1°  = 89.0° E = eV  = 0.8°  = 88.1° E = eV  = 1.2°  = 88.2° E = 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 = eV → eV (same geometry) No significant change in  and .

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 eV, [65°,8°] Expected  for voltage + noise + noise

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= = for 5 antennas ( for 8 antennas) x (EW) y (NS) z P

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

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

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= proton shower, antenna 300m from core

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.