Development of the 21CMA radio-detection array (Xinjiang/China) for the observation of UHE neutrinos showers Didier Charrier1, Pascal Lautridou1, Olivier Martineau-Huynh2 , Olivier Ravel1 , Xiang-Ping Wu3, Meng Zhao3, D.A.1 1 ) Subatech-Nantes (France) ; 2) LPNHE-Paris (France) ;3) NAOC - Bejing (China) D.ARDOUIN ARENA 2008

Objectives Neutrinos: possible direct messengers for sources above 10^15 eV beyond several Mpc Very low event rates imply km3 sensitive volumes (IceCube, ANTARES,NEMO,AUGER,…) only upper limits set (~1.10-7to10-6 GeV.cm-2.s-1.sr-1 ) Use of high density target medium (Earth, rocks) to generate n-N interactions (=> leptons). D.ARDOUIN ARENA 2008

2 constraints above PeV energies : limited medium thickness and large detection area to follow-up lepton-decay => Earth skimming or through-mountains neutrino trajectories ( cf D Fargion- F Vannucci) XD X0 XS Xint n n converter target detection volume t decay + shielding Conditions met at 21CMA combined with radio-technique characterisation of air -showers D.ARDOUIN ARENA 2008

A few advantages of radio-detection Radio technique allows large effective detection volumes coherence effect in the RF domain , very good electric signal sensitivity (up to several kms ) => large detection acceptance => sampling of a longer development phase of the EAS ~100% duty cycle. Signal recognition firmly demonstrated self- triggering mode with an array of antennas under control (see presentations by P.Lautridou/CODALEMA and B.Revenu/RAuger) D.ARDOUIN ARENA 2008

The 21CM Array layout (Xinjiang/China) LNA ARRAY FILTER FILTERS Optical transmitter Fiber [50-100 Mhz] 60dB 200 MS/s 81quad-core PC (On- line filtering process) data room Optical receiver ADC 81 pods of 127 antennas. 10287 (50-200 MHz) Log periodic antennas 2 arms (4km NS +3km EW) Solar cells powered D.ARDOUIN ARENA 2008

First unique advantage of the 21CMA site Google Earth 21CMA Target & shield volume : 20 000 km3 year - exposure : ~2.10 20 cm2. s (for a point-like source)

Second unique advantage of the 21CMA site Absence of RF or anthropic signals above 15 Mhz => [20-200 Mhz] quiet band D.ARDOUIN ARENA 2008

Operating procedure and first tests of UHCR radio-detection at the 21CMA Stand-alone antenna mode 81 Quad-processor PCs & on-line software trigger (duty cycle 100%) Search on each stored buffer for a sample of events satisfying : v > vav+ n. s waveform -Event-by-event transient radio signal analysis -Arrival direction and wave form reconstruction (FFT) Example of coinc. transient events on 3 antennas with [50-100 Mhz ] band-filter D.ARDOUIN ARENA 2008 Time 10 ms

some criteria for discrimination of n-t showers Event-by-event air-shower profiles and trajectories obtained in a customary way (see P.Lautridou/CODALEMA) Low elevation and 80° azimutal antenna acceptance diagram Large antenna multiplicity along (or close to ) the arm directions ( shielding effect for other CR trajectories) Correlation between the spatial profile of decay-shower and the spreading of the electric signal Trajectory elevation filter (accuracy Dq < 0.1° ) against downwards usual CR showers using the time sequence ( Dt~ 5 ns ) over successive fired antennas and known environment relief profile . D.ARDOUIN ARENA 2008

Perspectives Atmosphere length available: 5.7-10.5 km average detection efficiency of 1.2 to 6.10-3 between 10 18 and 10 20 eV Preliminary estimation ~0.3 event. yr-1 (based on energy flux E2.F= 4.10-8 [GeV.s-1.cm-2.sr-1] Data acquisition presently running D.ARDOUIN ARENA 2008

Conclusion Demonstration of the whole 21CMA set-up ability for CR transient signal characterisation This neutrino conversion method associated with a radio-detection of resulting t - decay showers is capable of achieving a sensitivity similar that of existing big detectors. The multiplicity, longitudinal spread and elevation dependence of the radio signals are expected to pin-down the n-t origin (and energy dependence) of the inclined t-showers. Possible study of isotropy distribution of UHECR arrival directions with an azimuthal exploration of events D.ARDOUIN ARENA 2008