1. Flux Limits for Ultra-High Energy Neutrinos
Physics Radio pulse, Ev>1022 eV
results
status
Olaf Scholten
KVI, Groningen
August 2011
ICRC, Beijing

2. Principle of the measurement
Small flux ≈ 1 / km2 / sr / century above 1020 eV!
Lunar area ≈ 107 km2
Cosmic ray or neutrino
Detection:
Westerbork/LOFAR antennas
107 km2
100MHz Radio waves
Proefje door Tjalling Nijboer en Martin Stokroos:
Statische electriciteit van wrijfstok is hoorbaar via radio ontvanger op de middengolf.
Principle of the measurement
August 2011
ICRC, Beijing

3. Askaryan effect: Coherent Cherenkov emission
~10 cm
~2 m
Cosmic ray
shower
Wave front
Recent evidence: Askaryan effect in CR airshowers
K.D. de Vries, AstroParticle Physics & arXiv:
H. Schoorlemmer for PAO, ARENA 2010
Important magnitudes:
Leading cloud of electrons, v  c
Typical size of order 10cm
Coherent Čerenkov for ν  2-5 GHz
cos θc =1/n , θc=56o for ∞ shower length
Length of shower, L  2-3 m
strong angular spreading for ν  100 MHz

4. Cosmic rays, Position on Moon
Calculations for
Ecr= eV
3 GHz
100 MHz
100 MHz
3 GHz
With decreasing ν
increasing probability:
∫ over surface Moon
Detection probability  ν-3
rim
inside
O.S. et al, Astropart.Phys. 26 (2006) 219

5. Results WSRT observations
No pulse of 240kJy seen in 46.7 h data 
90% confidence limit on neutrino flux
O.S. et al, PRL 103(2009)191301
Buitink, et al., A&A 521, A47 (2010).

6. NuMoon Experiment @ LOFAR
New generation of
radio-telescopes,
many (3000)
simple wire antennas
Total collecting area  0.25 km2
Cover whole moon,
Sensitivity 25 times better than WSRT.
Band: MHz
Multiple tied-array beams
August 2011
ICRC, Beijing

7. Nano-second pulse finding
Determine power over threshold in
sliding window of length N
Aim: Determine optimum window length N
Threshold: set to 1 accidental count per minute
Correcting for atmospheric dispersion,
with accuracy ΔSTEC TECU
Strength of pulse added to background in units of noise power
August 2011
ICRC, Beijing
Optimum: N=10-15

8. Beam shape depends on station layout
Station layout: 4 km x 4 km
Beam profile
φ=210o
φ=120o Δφ
Side-lobes suppressed
Max: Δφ= φ=120o
Min: Δφ= φ=210o
Conclusion:
need fewer than 50 beams to cover visible Lunar surface
August 2011
ICRC, Beijing

9. Background noise
Radio stations: narrow-band RFI  can easily be filtered out
Human activity: Broad-band RFI  potential problem !
Data:
8 half stations for 10 seconds
direction Virgo A
Amplitude spectrum
Gaussian
 No problems expected
Pulsed (broad-band )RFI suppressed further by
anti-coincidence filter between the different radio beams
August 2011
ICRC, Beijing

10. Neutrinos Conclusion: With LOFAR able to
LOFAR, 1 week
Conclusion:
With LOFAR able to
reach sensitivity level W-B estimate

11. Conclusions NuMoon Future: NuMoon @ WSRT: New limit for E > 1023 eV
LOFAR: Sensitive to W-B flux
Future:
SKA
Extend limit to lower E
Improve Flux limit
NuMoon
NuMoon collaboration:
O.S., Stijn Buitink, Heino Falcke , Clancy James, Maaijke Mevius, Ben Stappers, Kalpana Singh, Richard Strom , Sander ter Veen
August 2011
ICRC, Beijing

12. Cosmic rays Pierre Auger model-independent limit
Pierre Auger extrapolation
S. ter Veen, et al. , Phys. Rev. D 82, (2010).
August 2011
ICRC, Beijing