RESULTS FROM THE ANITA EXPERIMENT - SLAC National ...

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Dec 15, 2006 - ANITA instrument is a long duration balloon (LDB) payload designed to detect radio. Cherenkov signals from neutrino induced showers in ...
RESULTS FROM THE ANITA EXPERIMENT (Analysis A) Jiwoo Nam12,13,for ANITA Collaboration: P.W. Gorham1, S.W. Barwick5, J.J. Beatty3,D.Z. Besson9, W.R. Binns11, C. Chen12, P. Chen4,12,13,J.M. Clem8, A. Connolly6,7, P.F. Dowkontt11, M.A. DuVernois1, R.C. Field4, D.J. Goldstein5, A. Goodhue6, C. Hast4, C.L. Hebert 1, S. Hoover6, M.H. Israel11, A. Javaid8, J. Kowalski1, J.G. Learned1, K.M. Liewer2, J.T. Link 1,12, E. Lusczek10,S. Matsuno1, B.C. Mercurio3, C. Miki1, P. Miocinovic1, J. Nam12,13, C.J. Naudet2, J. Ng4, R.J. Nichol7, K.J. Palladino3, K. Reil4, A. RomeroRomero-Wolf1, M. Rosen1, D. Saltzberg6, D. Seckel8, G.S. Varner1, D. Walz4, F. Wu5 1

Dept. of Physics and Astronomy, University of Hawaii - Manoa, 2Jet Propulsion Laboratory, 3Dept. of Physics, The Ohio State University Columbus, 4Stanford Linear Accelerator Center, 5Dept. of Physics and Astronomy, University of California - Irvine, 6Dept. of Physics and Astronomy, University of California - Los Angeles, 7 Dept. of Physics and Astronomy, University College London, 8Dept. of Physics and Astronomy, University of Delaware, 9Dept. of Physics and Astronomy, University of Kansas, 10Dept. of Physics, University of Minnesota, 11Dept. of

Physics, Washington University, 12Inst. of Astrophysics, National Taiwan University, 13Leung Center For Cosmology and Particle Astrophysics, National Taiwan University,

ABSTRACT

14Currently

at NASA Goddard

ANITA CONCEPT

The ANITA (ANtarctic Impulsive Transient Antenna) experiment is a balloon-borne neutrino telescope which consists of an array of 32 broadband horn antennas. It successfully completed a 35 day flight over Antarctica during the 2006-2007 austral summer. The primary goal of ANITA is to search for astrophysical neutrinos with energies E > 1019 eV by detecting radio Cherenkov signals from neutrino-induced showers in the Antarctic ice. We present results from analyses of ANITA data.

ANITA instrument is a long duration balloon (LDB) payload designed to detect radio Cherenkov signals from neutrino induced showers in Antarctic ice. ANITA has excellent sensitivity in the energy interval between 1019 and 5x1020 eV. With large volumes in view and excellent transparency of the Antarctic ice, ANITA provides a good opportunity for discovery.

ASKARYAN EFFECT

Cutaway view of Antarctic ice sheet and typical flight path of LDB. Blue circle indicates an instantaneous balloon field of view which is about one million km2.

A neutrino induced cascade produces a coherent radio Cherenkov pulse.

In 1962 G. Askaryan predicted that coherent radio Cherenkov radiation would result from charge asymmetry developed in an electromagnetic shower in a dielectric medium. He also noted that it could be exploited for the detection of ultra-high energy particles (E>1018 eV) interacting in large target volumes, such as the Antarctic ice sheets.

~ 680km to horizon

~ 37km

Antarctic ice sheet

The Askaryan effect has been verified experimentally for different media including sand, rock salt and ice.

1~4km

Refracted RF

ν Incident neutrinos With energies above ~0.5 EeV

ν

Particle Cascade

Air Ice Cherenkov Cone o at 56 in ice ANITA Instantaneous sky coverage band. ANITA sees a band of sky just below the visible horizon.

FLIGHT (2006~2007) Shower RF field strength profile with typical Askaryan pulse (inset) in SLAC (2002) rock salt target experiment.

Cherenkov pulse power vs shower energy. Data are consistent with coherent radiation.

Polarization measurement confirmed 100% linearly polarized signal.

Radio Cherenkov propagation in air and field strength map for several frequencies. Neutrino direction constrained to ~3 σ for antennas in the maximum voltage phi sector.

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Establish angular reconstruction and select good events.

18 days of data, net 40% livetime ~50% analysis efficiency for detection Z-burst UHECR model (νν annihilation Æhadrons) excluded Highest Toplogical defect models also excluded

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A precise direction is reconstructed using arrival timing information. We obtained time resolution 40-60 ps for arrival time differences between two antennas. We performed a χ2 fit using 5-6 channels of timing information. Achieved angular resolutions are 0.2o (zenith) and 0.8o (azimuth). The resolution in azimuth is worse than in zenith due to the shorter distances between antennas in the horizontal direction and additional timing jitter in clock synchronizations between digitization boards. Reconstruction efficiency is ~98% for S/N greater than 4.5 σ while mis-reconstruction rate is less than 0.02%.

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An example of impulsive event

ANITA-I (06-07 flight, this work, preliminary)

Select impulse events

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Check events against existing camps, anything that repeats.

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Test events with a likelihood function. The likelihood consists of 3 PDFs; χ2 of angular reconstruction fit, number of cycles of time domain waveform and voltage ratio of V-pol to H-pol. The PDFs are obtained with ANITA MC simulation with the GZK (ESS model) flux distribution.

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same board

40 ps

inter board

60 ps

RESULTS

Time resolution: 40~60 ps

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19695 events (9600 V-pol, 10095 H-pol) are left after good reconstruction and impulsive event selections.

σ=0.8o

Most events are associated with camps, travellers, and automatic weather stations.

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Angular resolution

Event map with borehole pulses

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6 H-pol events are found to be isolated.

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No events passed likelihood threshold.

GZK Signal All Recon. Data 6 Isolated Events

Norlization

σ=0.2o

Event map with full data set.

Arb.

zenith

OUTLOOK

V-Pol. Event H-Pol. Event Base/Camp/AWS Traveler Route

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azimuth

35 days of data, net 51% livetime. ~80% analysis efficiency νe νμ ντ included full-mixing assumed +/- factor of 3 systematic uncertainty, because of a disagreement between two independent ANITA MC simulators (Further investigations would improve it).

Cut

Log Likelihood

Many analyses are ongoing for other important topics such as neutrino flavor identification, neutrino cross section measurement, air shower produced radio Cherenkov detection, and a monopole search. ANITA II is scheduled to fly in 2008. We expect a factor 4 sensitivity improvement with upgrades to the trigger, additional antennas under the lower tier, front-end electronics and DAQ.

This research is made possible with support from NASA grant NAG5-5387 Basic and Department of Energy Office of Science High Energy Physics Division, the National Science Council of Taiwan under contract number 96-2811-M-002-001 and the LeCosPa Center of National Taiwan University. Special thanks to the SLAC Experiment Facilities Department, the National Science Foundation, the McMurdo Support Staff and the Columbia Scientific Balloon Facility. The presenter of this poster is a LeCosPa Distinguished Assistant Fellow.

The XXIII International Conference on Neutrino Physics and Astrophysics, May 25-31, 2008 Christchurch, New Zealand