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Overview of the ANITA Experiment

Eric W. Grashorn Center for Cosmology & AstroParticle Physics The Ohio State University. Overview of the ANITA Experiment. Cosmogenic Neutrinos. > 10 18 eV neutrinos predicted by many acceleration and interaction processes at source locations

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Overview of the ANITA Experiment

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  1. Eric W. Grashorn Center for Cosmology & AstroParticle Physics The Ohio State University Overview of the ANITA Experiment

  2. Cosmogenic Neutrinos • > 1018 eV neutrinos predicted by many acceleration and interaction processes at source locations • Observations, interaction physics suggest ultra-high energy cosmic rays will interact with the CMB to produce neutrinos • Berezinsky & Zatsepin, 1970, require > 1018 eV neutrinos • Lack of neutrinos could mean • UHECRs are not hadrons (?!) • Lorentz invariance wrong (!!) • New physics… • Expected fluxes are small • 1 neutrino per km2 per week! Courtesy Peter Gorham

  3. ANITA • ANtarctic Impulsive Transient Antenna • International collaboration: 42 collaborators, 13 institutions, 3 counties

  4. ANITA • Ballon-borne payload, designed to detect broadband radio neutrino signals • Askaryan effect • coherent radio emission • Eth ~1018.5 eV • Advantages: • Ice is transparent to radio • Low cost (~$10M) • Target volume ~1.6x106 km3! • reduces to ~ 103 km3 sr • Disadvantages • Short duty cycle Gorham et al., Astropart Phys. 2009

  5. Askaryan Effect • Coherent radio emission from excess negative charge in EM shower • Positrons annihilated, electrons scattered into shower • Longer than 10-20 cm at radio wavelengths • Appears as a single charge Z~108 e- • Coherent, P~E2 • Fast, impulsive signal Saltzberg & Gorham, PRL 2001

  6. ANITA 1 Payload • 32 Quad ridge, dual polarization feedhorns • 16 in lower ring, 16 in mid/upper rings • Each effectively observes 22.5º in azimuth, pointed 10ºdown from horizontal • Antennas in lower and either mid or upper ring make up one “phi sector” • Design constraints: • Fast digitization, low power consumption • Custom electronics, • 72 channels of 2.6 GSa/s • Power system provides ~500W Courtesy Jeff Kowalski

  7. Event Detection • Better than 60 ps timing • Pulse-phase interferometer resolution of radio impulse • < 0.3º elev. • ~1º azimuth • Neutrino direction • 2º elevation • Earth absorption • 5º azimuth • Polarization angle of detected impulse Gorham et al., Astropart Phys. 2009

  8. Radio Neutrino Event • Simulated 3 x 1018 eV neutrino • false color image of E-field strength of emerging Cherenkov cone • Color scale is normalized to the peak (blue) in each pane Gorham et al., Astropart Phys. 2009

  9. Backgrounds • “Carrier Wave” (CW); near sinusoidal • High narrow-band power, can saturate the system • Impulsive • Electronic switching phenomena • Sources: • “Anthropogenic” • “Unintentional” impulsive satellite signals- solid state relays, actuators • Terrestrial signals- easy to identify because encampments are sparse • Cosmic Ray Air Showers: could produce H-pol signal Note: no physics background in V-pol!

  10. Event Display • Event most likely West Antarctica camp noise • Triggers: • Yellow, L1: impulse exceeds SNR in 3 of 8 channels on individual antenna; ~150 kHz • Green, L2: coincidence between adjacent L1 in the same ring; ~40kHz • Blue, L3: coincidence between L2 triggers in same phi sector; ~5Hz Gorham et al., Astropart Phys. 2009

  11. ANITA 1 Flight Path • 35 days aloft, 3.5 orbits • Average ice depth, integrated over the entire horizon Gorham et al., Astropart Phys. 2009

  12. ANITA 1 Sensitivity • Effective livetime: 17.3 days • False color map in celestial coordinates (RA, Dec) • For 1020 eV neutrinos Gorham et al., Astropart Phys. 2009

  13. ANITA 1 Data • 8.2 M hardware triggers • Cuts optimized on 10% data set (blind analysis) • Require upcoming plane wave, impulsive broadband, isolated from camps and other events. Gorham et al., Astropart Phys. 2009

  14. ANITA 1 Results • Phys. Rev. Lett. 103, 051103 (2009) • 6 H-pol, 0 V-pol survive cuts • H-pol originate above ice sheet (not n candidates) • Fresnel transmission • Askaryan impulse generation • In absence of observed n, a limit is set • First result to constrain GZK n production models Gorham et al., Phys. Rev. Lett., 2009

  15. ANITA 2 Improvements • “Dynamic Phi-Masking” • Active suppression of phi-sector readout during transit over noisy areas • McMurdo, South Pole, etc • Automatically activated • 8 “nadir” antennas • One antenna shared w/ 2 phi sectors • Modified trigger: • 2 of 3 channels, plus full-band (no H-pol) • Improve Tsys by 40K • New front end • Overall energy threshold improvement: • Factor of ~1.7 • ANITA gains as Eth-2, so ~ factor of 3 event rate increase Courtesy Ryan Nichol

  16. ANITA 2 Flight Path • 2+ Orbits • Time aloft: 30d 14h 45m • Compared to ANITA1… • More time near E. Antarctica • Less time near SP • Dynamic phi masking seemed to work as advertised Courtesy Kim Palladino

  17. ANITA 2 Status • About 30 M events • Nearly four-fold increase over ANITA 1 • Recovery completed • Minimal problems • Only one feedhorn damaged! • Analysis underway Courtesy Brian Hill

  18. Further Work • Cosmic Rays • Naïve MC shows ANITA 1 expects 4.5 CR events • Consistent with 6 detected H-pol • More sophisticated MC • Radio Extensive Air-shower Simulation (REAS) code (T. Huege) • Geosynchrotron mechanism • Neutrinos from GRB • Initial ANITA 1 calculations from K. Paladino thesis

  19. Summary • ANITA 1 results Published • Instrument paper: Astropart. Phys. 32, 10 (2009) • Physics result: Phys. Rev. Lett. 103, 051103 (2009) • New ANITA 1 limits exclude GZK n productionmodel parameter space for the first time • ANITA 2, with improved sensitivity, completed a 30 day mission January 20 • More time spent over deeper ice than ANITA 1 • New result is coming soon…

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