Detecting Ultra High Energy Neutrinos with LOFAR M.Mevius for the LOFAR NuMoon and CR collaboration

Outline Measurement principle Results from “pilot” experiment WSRT Why LOFAR? Challenges Status and outlook Summary Detecting UHE Neutrinos with LOFAR

Neutrino/Cosmic Ray 100MHz Radio waves Detection: Radio Antennas Principle of the measurement 10 7 km 2 3Detecting UHE Neutrinos with LOFAR

Askaryan Effect: Coherent Cherenkov Emission Leading cloud of electrons, v  c Typical size of order 10cm -> Coherent Cherenkov 3GHz (line source) Length of shower, L  few m 150 MHz : point source Important for angular spreading ~10 cm ~2 m Cosmic ray shower Wave front Detecting UHE Neutrinos with LOFAR

Cosmic rays, Position on Moon Calculations for E cr = eV With decreasing ν increasing probability: ∫ over surface Moon D  ν -3 Trade off: higher energies 3 GHz 100 MHz 3 GHz 100 MHz Detecting UHE Neutrinos with LOFAR

Detecting UHE Neutrinos with LOFAR6 Use Westerbork radio observatory NuMoon WSRT 2 bands over Moon 11 dishes of 25 m diameter, MHz band

Results No pulse seen in 40 h data  90% confidence limit on neutrino flux O. Scholten, S. Buitink, J. Bacelar, R. Braun, A. G. de Bruyn, H. Falcke, K. Singh, B. Stappers, R. G. Strom, and R. al Yahyaoui PRL 103(2009) Astronomy and Astrophysics – accepted for publication Detecting UHE Neutrinos with LOFAR

Low Frequency Radio Array HBA –tiles: 4x4 dual dipoles MHz 1 station : 48 tiles Core (baselines up to 2 km), Remote (100 km), international (e-lofar, 1000 km) – Use core for online trigger, all stations offline LOFAR Detecting UHE Neutrinos with LOFAR Beam forming: coherently add data of antennas Different delay schemes: Simultaneous multiple beams

Why LOFAR? Low frequency ( MHz): Best detection probabilities especially at very high energies Large Collecting Area (Core only: ~3 x WSRT) Many narrow beams: – Beam size central core:~ 0.05 degree – Excellent for noise reduction Buffer Boards: store raw data for short time – Sophisticated trigger algorithm – Raw/ full bandwidth data available for offline analysis Noise elimination offline Detecting UHE Neutrinos with LOFAR

Challenges Data rate: – Raw time series : ~1 TB/s ->Trigger – Online trigger: ~1GB/event => dead time Ideally: trigger once every few minutes Detecting UHE Neutrinos with LOFAR

Trigger Buffer boards store the data for 1(4)s : TRIGGER: Reconstruct pulse – Dedispersion – Extra peaks due to holes in frequency selection (248 out of 512 channels) Select pulse over background (Anti-) coincidence – Real pulse from specific location on the Moon Use pointing accuracy of LOFAR – Pulse should be seen in all (sub) stations Other... - : Simulated pulse -: Reconstructed pulse Detecting UHE Neutrinos with LOFAR

Challenges Data rate: – Raw time series : ~1 TB/s – Online trigger: ~1GB/event Ideally: trigger once every few minutes Ionosphere: Detecting UHE Neutrinos with LOFAR

Ionosphere Time varying ionized layer in the atmosphere ( km) Effect: frequency dependent delay Δt = ∙TEC /v 2 Total Electron Content (10 16 electrons/m 2 ) typical TECU Detecting UHE Neutrinos with LOFAR 1.Different stations “see” different part of the ionosphere (long baselines) -> blurry images relative TEC 2.Dispersion Absolute TEC Online: ~ 1TEC Can be improved in off-line analysis

Ionospheric Calibration Calibrator sources in several directions: fix phase screen – Relative phases only Absolute TEC: – GPS measurements Direction? Online? – Faraday rotation of polarized light Rotation angle = RM ∙λ 2 RM depends on TEC and magnetic field Use polarized light of rim of the Moon?? – See poster by Rebecca McFadden Known frequency dependence could also serve for confirmation of the signal: – Earth based: no dispersion – Reflections of the Moon: double dispersion – Signal itself is also polarized (freq dependence of Faraday rotation) Detecting UHE Neutrinos with LOFAR

Challenges Data rate: – Raw time series : ~1 TB/s – Online trigger: ~1GB/event => dead time! Ideally: trigger once every few minutes Ionosphere: – Dispersion: spread of the signal over several time bins – Beam forming: stations looking through different parts of the ionosphere (long baselines -> off-line) Pulsed Noise: – Data Rate – Confusion with signal (off-line) Detecting UHE Neutrinos with LOFAR

Noise Analysis TBB data (time series per HBA tile) of 1 station Offline beamforming: combine raw data of all antennas with appropriate phase corrections to reconstruct beams in all sky directions Noise pulse in beamformed data Sum of power in 5 consecutive bins of beamformed data in an arbitrary direction. ~0.2s These events mimic our signal!! Detecting UHE Neutrinos with LOFAR

Noise Analysis (2) Very preliminary analysis shows some hotspots for the transient noise Use pointing capabilities to reduce this noise Using e-lofar(i.e. well separated stations + better pointing accuracy) probably powerful for man made noise reduction For illustration only: need to collect more test data Combine data of different stations Point to Moon – Are we able to see reflections? How can we eliminate the pulse noise in the offline analysis? Detecting UHE Neutrinos with LOFAR Number of outliers in power histograms for all directions in the sky. ~0.4s Azimuth/Elevation: center is pointing at zenith circle indicates horizon

Status Station roll-out in progress LOFAR officially opened on 12 th of June 2010 Trigger and noise studies ongoing – Test runs with raw TBB data dumps First trigger implementation in 2010 First data Detecting UHE Neutrinos with LOFAR

19 Neutrinos Theoretical predictions: Waxman-Bahcall limit GZK induced flux Topological defects LOFAR core E-LOFAR Detecting UHE Neutrinos with LOFAR

Summary Radio detection of the Askaryan effect of neutrinos hitting the Moon promising at low frequencies – Especially for very high energies WSRT results improved limit by almost order of magnitude LOFAR is an excellent instrument for this study Expected results from LOFAR within predictions of top down models Detecting UHE Neutrinos with LOFAR

extra Detecting UHE Neutrinos with LOFAR

TBB buffer 1 (4) seconds CEP (groningen) Tied array beam forming (core) Several (~50) beams to cover Moon Dedispersion PPF -1 to time domain Reconstruct Pulse Trigger Data Path Detecting UHE Neutrinos with LOFAR HBA-tiles Analogue beam forming Digitization (200 MHz) PPF to freq domain Station beam forming Channel selection (248/512) Removal of sharp RFI lines Dump Offline analysis Freq. channel

Data Path Detecting UHE Neutrinos with LOFAR

Spreading around Cherenkov-cone Sine profile L=1.7 m, E=10 20 GHz n=1.8 O.S. etal., Astropart.Phys Old parametrization Based on physics principles Detecting UHE Neutrinos with LOFAR

NuMoonExperiment NuMoon Experiment Use MHz window Moon: radius=1700 km; area = km 2 Low Attenuation: λ r = 9[m] / [GHz] Use MHz window Moon: radius=1700 km; area = km 2 Low Attenuation: λ r = 9[m] / [GHz] Detecting UHE Neutrinos with LOFAR

Cosmic Rays Sensitive to flux beyond GKZ limit Detection threshold taken at F det = 25 F noise Δ ν =20 MHz, 4 bands ν =140 MHz WSRT: F det = 15,000 Jy Paper in preparation LOFAR: F det = 500 Jy Detecting UHE Neutrinos with LOFAR