Tuning in to UHE Neutrinos in Antarctica – The ANITA Experiment

1. Tuning in to UHE Neutrinos in Antarctica – The ANITA Experiment QSOs Nearest Blazars Virgo cluster 3o Cen A M31 galaxy 10o ANITA Experiment at altitude of ~120,000 ft The pulse propagates through the ice, is refracted at the ice surface of the ice and travels to the ANITA instrument antennas where the waveform is digitized and recorded. AIR n ICE The neutrino interacts in the ice creating a shower of particles and a Cherenkov radio pulse. Ultra-high energy neutrino travels through the Antarctic ice. Flight system block diagram Experimental Verification of Askaryan Radio Pulses in 2000 at SLAC D. Saltzberg et al. PRL 86 (2001), 2802. ANITA-LITE Impulse Analysis ANITA-LITE: Precursor to ANITA • ANITA-LITE was dominated by local payload noise • Circularly polarized impulses are closest to true impulses • Glitches most likely from balloon support instrument package (SIP) • ANITA-LITE Flew December 2003 as a piggy-back on the TIGER experiment. • 2-horn Instrument with 2GS/sec 8-bit digitization • The flight lasted 19.2 days at an average altitude of 125,000 feet. • Injected 5 sigma impulsive signal to test neutrino selection cuts. UHF tone bursts were sent as a calibration signal to ANITA-LITE from the ground at the start of the flight. • ANITA goal: 300 ps at ~3 sigma trigger threshold. • ANITA-LITE already 50% better! • Critical to pulse interferometry. J. T. Link P. Miočinović Univ. of Hawaii – Manoa Neutrino 2004, Paris, France Neutrinos – Window to the Ultra High Energy Universe How ANITA Detects High Energy Neutrinos ANtarctic Impulsive Transient Antenna • 40 quad-ridge horn antennas with frequency sensitivity from 200-1200 MHz. • 3 GS/sec low power 12-bit digitization • Flown at 120,000 feet on a NASA Long Duration Balloon • Universe optically thick to high energy photons above 10 TeV as they interact with IR and CMB background photons: • Above ~10 EeV protons interact with CMB: • Neutrinos have a low interaction cross-section and can propagate unhindered and unaffected by magnetic fields through the universe at the highest energies. gg  e+e- pg  D  p  n Resolution of the ANITA Instrument Radio Detection – The best way to detect UHE Neutrinos! • Quad-ridge horns give fast and non-dispursive response to impulsive radio events in two linear polarizations, with 60-70 degree beamwidth, 200-1200 MHz bandwidth and gain of ~10 dBi at 300 MHz. • The antennas are arranged so that a neutrino pulse should be picked up by at least 6 antennas which allows ANITA to act as a pulse-phase interferometer. • Intrinsic beamsize is calculated to be ~3o in elevation by ~10o in azimuth for arrival direction of the radio pulse. • The neutrino arrival direction can then be constrained to ~1-2o in elevation due to Earth absorption, and by 3-5o in azimuth by polarization angle • Askaryan Effect  coherent radio Cherenkov emission • A cascade of particles produces an imbalance of charge and hence Cherenkov radiation. • Some of this radiation is in the form of radio photons. Because the interaction region is small compared to the wavelength of radio photons they propagate coherently, thus radio power is proportional to the square of cascade energy • If the cascade occurs in a radio-transparent medium (such as ice where the mean attenuation length is measured to be 1200 meters) the impulsive radio signal can be detected! • Quadratic rise of signal power with cascade energy and the transparency of medium make the RF detection of high energy neutrinos one of the most cost effective detection methods. D = Distance from cascade Radio regime Optical regime ANITA Neutrino Detection Limits • Radio detection based limits: • RICE limits for 3500 hours livetime • GLUE limits~120 hours livetime • FORTE (N. Lehtinen, UH) limits on ~3 days of satellite observations of Greenland ice sheet June 2004 (90 days) • Expected ANITA sensitivity: • Left: limits derived for nm & ne with full-mixing parametrization • Right: effective volumes based on new Monte Carlo simulation CONCLUSIONS ANITA-LITE: Instrument Performance • No events detected by ANITA-LITE pass impulsive selection cuts, while 70% of simulated neutrino signal events do. The total livetime of the experiment was 6 days, and the effective volume is under study. • The full ANITA experiment will fly in December 2006 from Antarctica. • ANITA is currently under study for an upgrade to a NASA SMEX Mission of Opportunity which would allow for two instruments to be built and yearly flights to occur for at least 3 years starting in December 2006. The ANITA-LITE antennas were able to discern the excess radio power in the direction of the Sun and the Galactic Center.