1. 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

2. 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 (~1.10-7to 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

3. 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

4. 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

5. The 21CM Array layout (Xinjiang/China)
LNA
ARRAY
FILTER
FILTERS
Optical transmitter
Fiber
[ Mhz]
60dB
200 MS/s
81quad-core PC (On- line filtering process)
data room
Optical receiver
ADC
81 pods of 127 antennas.
10287 ( MHz) Log periodic antennas
2 arms (4km NS +3km EW)
Solar cells powered
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6. First unique advantage of the 21CMA site
Google Earth
21CMA
Target & shield volume : km3 year - exposure : ~ cm2. s
(for a point-like source)

7. Second unique advantage of the 21CMA site
Absence of RF or anthropic signals above 15 Mhz => [ Mhz] quiet band
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8. 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 [ Mhz ] band-filter
D.ARDOUIN ARENA 2008
Time 10 ms

9. 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 .
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10. Perspectives Atmosphere length available: 5.7-10.5 km
average detection efficiency of 1.2 to between and eV
Preliminary estimation ~0.3 event. yr-1 (based on energy flux E2.F= [GeV.s-1.cm-2.sr-1]
Data acquisition presently running
D.ARDOUIN ARENA 2008

11. 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