We report initial results of the first flight of the Antarctic Impulsive
Transient Antenna (ANITA-1) 2006-2007 Long Duration Balloon flight, which
searched for evidence of a diffuse flux of cosmic neutrinos above energies of 3
EeV. ANITA-1 flew for 35 days looking for radio impulses due to the Askaryan
effect in neutrino-induced electromagnetic showers within the Antarctic ice
sheets. We report here on our initial analysis, which was performed as a blind
search of the data. No neutrino candidates are seen, with no detected physics
background. We set model-independent limits based on this result. Upper limits
derived from our analysis rule out the highest cosmogenic neutrino models. In a
background horizontal-polarization channel, we also detect six events
consistent with radio impulses from ultra-high energy extensive air showers.Comment: 4 pages, 2 table

Allison, P

ANITA Collaboration

Barwick, SW

Beatty, JJ

Besson, DZ

Binns, WR

Chen, C

Chen, P

Clem, JM

Connolly, A

Dowkontt, PF

DuVernois, MA

Field, RC

Goldstein, D

Goodhue, A

Gorham, PW

Hast, C

Hebert, CL

Hoover, S

Israel, MH

Kowalski, J

Learned, JG

Liewer, KM

Link, JT

Lusczek, E

Matsuno, S

Mercurio, BC

Miki, C

Miocinovic, P

Nam, J

Naudet, CJ

Ng, J

Nichol, RJ

Palladino, K

Reil, K

Romero-Wolf, A

Rosen, M

Ruckman, L

Saltzberg, D

Seckel, D

Varner, GS

Walz, D

Wang, Y

Wu, F

English

arXiv

Gorham, P. W.

National Taiwan University Repository

New Limits on the Ultrahigh Energy Cosmic Neutrino Flux from the ANITA Experiment

We report initial results of the first flight of the Antarctic Impulsive Transient Antenna (ANITA-1) 2006-2007 Long Duration Balloon flight, which searched for evidence of a diffuse flux of cosmic neutrinos above energies of E-nu similar or equal to 3 x 10(18) eV. ANITA-1 flew for 35 days looking for radio impulses due to the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. We report here on our initial analysis, which was performed as a blind search of the data. No neutrino candidates are seen, with no detected physics background. We set model-independent limits based on this result. Upper limits derived from our analysis rule out the highest cosmogenic neutrino models. In a background horizontal-polarization channel, we also detect six events consistent with radio impulses from ultrahigh energy extensive air showers

UCL Discovery

New Limits on the Ultrahigh Energy Cosmic Neutrino Flux from the ANITA ExperimentP.W. Gorham,1 P. Allison,1 S.W. Barwick,2 J. J. Beatty,3 D. Z. Besson,4 W.R. Binns,5 C. Chen,12 P. Chen,6 J.M. Clem,7A. Connolly,11 P. F. Dowkontt,5 M.A. DuVernois,9 R. C. Field,6 D. Goldstein,2 A. Goodhue,8 C. Hast,6 C. L. Hebert,1S. Hoover,8 M.H. Israel,5 J. Kowalski,1 J. G. Learned,1 K.M. Liewer,10 J. T. Link,1,* E. Lusczek,9 S. Matsuno,1B. C. Mercurio,3 C. Miki,1 P. Miocˇinovic´,1 J. Nam,2,12 C. J. Naudet,10 J. Ng,6 R. J. Nichol,11 K. Palladino,3 K. Reil,6A. Romero-Wolf,1 M. Rosen,1 L. Ruckman,1 D. Saltzberg,8 D. Seckel,7 G. S. Varner,1 D. Walz,6 Y. Wang,12 and F. Wu12(ANITA Collaboration)1Department of Physics and Astronomy, University of Hawaii, Manoa, Hawaii 96822, USA2Department of Physics, University of California, Irvine California 92697, USA3Department of Physics, Ohio State University, Columbus, Ohio 43210, USA4Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA5Department of Physics, Washington University in St. Louis, Missouri 63130, USA6Stanford Linear Accelerator Center, Menlo Park, California, 94025, USA7Department of Physics, University of Delaware, Newark, Delaware 19716, USA8Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA9School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA10Jet Propulsion Laboratory, Pasadena, California 91109, USA11Department of Physics, University College London, London, United Kingdom12Department of Physics, Graduate Institute of Astrophysics, & Leung Center for Cosmology and Particle Astrophysics,National Taiwan University, Taipei, Taiwan(Received 16 December 2008; revised manuscript received 15 April 2009; published 30 July 2009)We report initial results of the first flight of the Antarctic Impulsive Transient Antenna (ANITA-1)2006–2007 Long Duration Balloon flight, which searched for evidence of a diffuse flux of cosmicneutrinos above energies of E ’ 3 1018 eV. ANITA-1 flew for 35 days looking for radio impulses dueto the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. Wereport here on our initial analysis, which was performed as a blind search of the data. No neutrinocandidates are seen, with no detected physics background. We set model-independent limits based on thisresult. Upper limits derived from our analysis rule out the highest cosmogenic neutrino models. In abackground horizontal-polarization channel, we also detect six events consistent with radio impulses fromultrahigh energy extensive air showers.DOI: 10.1103/PhysRevLett.103.051103 PACS numbers: 98.70.Sa, 95.55.Vj, 96.50.sdIn all standard models for ultrahigh energy cosmic-ray(UHECR) propagation, their range is ultimately limited bythe opacity of the cosmic microwave background radiation.The UHECR energy above which this becomes significantis about 6 1019 eV in the current epoch. This cuts offtheir travel beyond distances of order 50 Mpc as first notedby Greisen [1], and Zatseptin and Kuzmin [2] (GZK). As aresult of this absorption, the UHECR energy above thisGZK cutoff is ultimately converted to photons, neutrinos,and lower energy hadrons. The resulting neutrinos werefirst described by Berezinsky and Zatsepin (BZ) [3]. Instandard UHECR source models the BZ neutrino fluxespeak at energies about 2 orders of magnitude below theGZK energy. Thus a ‘‘guaranteed’’ flux of neutrinos atenergies of E ¼ 1017–20 eV exists. Its detection is oneof the clearest ways to reveal the nature and cosmic distri-bution of the UHECR sources [4], which is one of thelongest-standing problems in high-energy astrophysics.The ANITA-1 Long Duration Balloon experiment wasdesigned specifically to search for this cosmogenic BZneutrino flux. ANITA-1 exploits the Askaryan effect, inwhich strong coherent radio emission arises from electro-magnetic showers in any dielectric medium [5]. The effectwas first observed in 2000 [6], and has now been clearlyconfirmed and characterized for ice as the medium, as partof the preflight calibration of the ANITA-1 payload [7]. Aprior flight of a prototype payload called ANITA-lite in2003–2004 led to validation of the technique and initialneutrino flux limits that ruled out several UHE neutrinomodels [8].In a previous paper [9], we describe in detail theANITA-1 instrument, payload, and flight system.Reference [9] also includes details of the instrument per-formance during the flight, estimates of the overall sensi-tivity of the instrument to neutrino fluxes, and discussionsof possible backgrounds. Because of the complexity of thePRL 103, 051103 (2009) P HY S I CA L R EV I EW LE T T E R Sweek ending31 JULY 20090031-9007=09=103(5)=051103(5) 051103-1  2009 The American Physical Societyflight system and methodology, we refer the reader toRef. [9] for more detail when necessary.The ANITA-1 payload (Fig. 1) launched from WilliamsField, Antarctica near McMurdo station, on December 15,2006, and executed more than three circuits of the con-tinent, landing on the Antarctic plateau about 480 km fromAmundsen-Scott (South Pole) Station after 35 days aloft.Anomalous stratospheric conditions led to a misalign-ment of the polar vortex for the 2006–2007 season. TheANITA-1 payload’s trajectory thus spent a large fraction ofthe time overWest Antarctica where the ice sheet is smallerand shallower. In addition, the payload field of view to thehorizon (at a distance of about 650 km at typical altitudesof 35–37 km above mean sea level, or 33–35 km above theice surface), often included the two largest occupied sta-tions in Antarctica, McMurdo and Amundsen-Scott, result-ing in high levels of anthropogenic electromagneticinterference (EMI). Despite these effects, the payload ac-cumulated a net exposure livetime of 17.3 days with amean ice depth in the field of view of 1.2 km, comparableto the attenuation length of the ice at sub-GHz radiofrequencies [10]. ANITA-1 was thus able to synopticallyview a volume of ice of 1:6 Mkm3. Our volumetricacceptance to a diffuse neutrino flux, accounting for thesmall solid angle of acceptance for any given volumeelement, is several hundred km3 water-equivalent stera-dians at E ’ 1019 eV [9].ANITA-1’s antennas are 32 dual-linear-polarization,quad-ridged horns, each with a field of view which aver-ages about 50 angular diameter over their 200–1200 MHzworking bandwidth. The antennas are arranged in upperand lower rings, each with 16 antennas at azimuthal inter-vals of 22.5. All antennas point at 10 below the horizon-tal, to maximize sensitivity to the largest portion of thevolume near the horizon at 6 below the horizontal. Thecombined view of all antennas covers the entire lowerhemisphere down to angles of about 55, comprising99.4% of the area within the horizon. Radio impulses thatexceed the ambient thermal noise by about 5 in at leastfour antennas in coincident upper- and lower-ring pairsproduce a trigger [9], and the entire antenna set of wave-forms are then digitized and stored for later analysis.Thermal noise fluctuations produce random triggers at arate of about 4–5 Hz, yielding a continuous monitor ofinstrument health. These events are incoherent in phaseand produce a completely negligible background to actualcoherent radio impulses.The event analysis is conceptually simple, but requiresdetailed calibration of the instrument to achieve goodprecision. In the results reported here, the initial softwarecut requires that 6 adjacent antennas have signals consis-tent with an incoming plane wave in both amplitude andtime. Using a method of pulse-phase interferometry, wedetermine the best arrival direction of the radio impulseplane wave, and this direction and its associated uncer-tainty is then mapped onto the Antarctic ice surface byreference to onboard payload navigation instruments, withan angular precision of 0:2  0:8 in elevation and azi-muth [9].To minimize bias, the analysis cuts were optimized on a10% randomized sample of the entire data set, and theremaining 90% was blinded from the analysts until the cutswere fixed. The cuts proceed as follows: (i) Events that donot reconstruct to a coherent plane wave in arrival directionare rejected as random thermal noise; events that recon-struct from directions above the horizon are also rejected.(ii) Events that reconstruct but have nonimpulsive wave-forms from relatively narrow-band sources (100 MHz)are rejected. (iii) Events that cluster with one another insource location to within reconstruction errors projectedonto the ice, or 50 km radius, whichever is greater, arerejected. True source candidates must be single, isolatedevents. (iv) Events that coincide in source location withany known active or inactive station, camp, aircraft flightpath, or expedition traverse path, to within reconstructionangular errors projected onto the ice, or 50 km radius,whichever is greater, are rejected as being associatedwith anthropogenic activity. Even inactive camps or thoselong-abandoned are considered a risk, since leftover equip-ment might serve as a site for charge accumulation andassociated electromagnetic discharges which could be mis-taken for signals. (v) Events whose radio waveforms arenot predominantly vertically polarized (Vpol) are rejectedbecause, from considerations of the Askaryan impulsegeneration process, and the Fresnel transmission throughthe ice surface, they cannot originate from a particleshower within the ice sheet. Conversely, strongly horizon-tally polarized (Hpol) events are likely to originate fromabove the ice from similar considerations.FIG. 1 (color). View of the ANITA-1 payload in launch con-figuration, with photovoltaics at the top and bottom, and antennaclusters between. The side of each square antenna mouth is about0.9 m, and the payload stands about 8 m tall.PRL 103, 051103 (2009) P HY S I CA L R EV I EW LE T T E R Sweek ending31 JULY 2009051103-2Table I shows the results of the total event sample beforeand after unblinding, including the signal efficiency foreach cut separately. The 10% initial sample is included inthe 100% totals. Note that the isolation cut (iii) is the singlemost stringent criterion in rejecting impulsive events, andthis shows that the vast majority of triggers are not single,isolated events. Signal efficiency in each case was testedwith a simulated event sample injected randomly into thedata stream, and the final energy-averaged efficiency of allcuts is estimated to be 81%.In Fig. 2 we show the before-and-after maps of recon-structed ANITA-1 events superposed on the Antarctic con-tinent. The strong correlation to a small number of stationsis evident. The 6 surviving Hpol events (none of whichappeared in the 10% sample) are by contrast widely dis-tributed across the continent, with no known camps orbases, either current or former, anywhere in their locale.We have investigated the possibility of impulsive signalsfrom earth-orbiting satellites seen in reflection off the icesurface as a source for these events. This hypothesis isruled out because the waveforms for these events do notshow any evidence of differential group delay from iono-spheric dispersion which is several ns per MHz in the 200–400 MHz frequency range where these events have most oftheir spectral power. In fact the signals are all of durationsless than 10 ns. We know of no other anthropogenicsources for these events.Our first-order simulations of the high-frequency tailof geo-synchrotron radio emission [12–14] from ultra-high energy cosmic ray extensive air showers (EAS)suggest that these signals may be EAS events seen inreflection off the ice surface [9]. Such events are expectedto be predominantly Hpol because of the strong Fresnelreflectivity in the region near Brewster’s angle, and theoverall initial preference for Hpol because of the morevertical polar magnetic fields. We expect a handful ofsuch events for the flight, all of which arise fromUHECR EAS with energies above 1019 eV; however, theuncertainties are large [9]. While these events do not con-stitute a background for our neutrino search because oftheir incorrect polarization, they are a potentially interest-ing signal in their own right. Further analysis, including asearch for similar events from above the horizon, is inprogress.FIG. 2 (color). Left: Plot of all reconstructed events, in both horizontal and vertical polarization; major Antarctic stations areindicated on the map. Right: events remaining after cuts to remove anthropogenic interference. Six events remain in the horizontallypolarized group, but these are noncandidates for neutrino events, as discussed in the text.TABLE I. Event totals vs analysis cuts and estimated signal efficiencies for the ANITA-1 data set, both for the 10% (blind) and 100%(unblinded) sample.Cut requirement passed: Hpol 10% Vpol 10% Hpol 100% Vpol 100% Efficiency(0) Hardware-Trigger 8:2 M . . . . . . . . .(i) Upcoming wavefront 1546 1878 15 997 16 311 [11] 0.93(ii) Impulsive 956 1085 10 095 9600 0.98(iii) Event-isolated 0 0 8 1 0.94(iv) Camp-isolated 0 0 6 0 0.96(v) Vpol dominant 0 0 0 0 0.99PRL 103, 051103 (2009) P HY S I CA L R EV I EW LE T T E R Sweek ending31 JULY 2009051103-3Based on the approach described in Refs. [15,16], theresulting model-independent 90% CL limit on neutrinofluxes with standard model cross sections [17] is shownin Fig. 3. Here we have included the net livetime and 81%analysis efficiency. Exclusion of the volume of ice near allcamps and events reduces the net effective volume by a fewpercent. We have estimated residual systematic uncertain-ties in the neutrino acceptance by variational modeling ofvarious parameters that affect it. The most significanteffects and their percentage impact in the uncertainty are:neutrino cross section, þ60%, 40% per factor of 2variation; ice surface roughness, 45% per factor of 2in assumed rms value; photonuclear cross section, þ15%,10% per2. The root-sum-square effect of all system-atics leads to a þ80%, 60% overall systematic uncer-tainty in the acceptance. These model-independent limitsare calibrated such that a model spectrum that matched thelimit over one decade of energy would yield approximately2.3 events; this choice is appropriate to smoothly varyingmodels. The limits are for the sum over all three neutrinoflavors, as ANITA-1 had roughly equal sensitivity to e,, , and the flavors should be equally mixed to firstorder via oscillations for all BZ neutrino models. We plotonly an approximate set of bands for the BZ neutrinomodels, which are too numerous to individually plot here.Table II gives the total number of events expected fromselected representative UHE neutrino models, includingthe case of a model which saturates the canonicalWaxman-Bahcall flux bounds for both evolved and stan-dard UHECR sources [24]. ANITA-1 strongly limits thehighest BZ neutrino models, which require extremely high-energy cutoffs in the parent cosmic-ray sources’ spectralenergy distributions. Our limits thus suggest that UHECRsource spectra extending to 1023 eV are disfavored.ANITA-1 sensitivity approaches a class of models heredenoted as ‘‘strong-source evolution’’ models, which as-sume that the UHECR source evolution follows the cosmicevolution of more energetic sources, for example, gamma-ray burst host galaxies [23]; these midrange models areconstrained at about the 60% CL but none are ruled out yet.The ANITA-1 90% CL integral flux limit on a pure E2spectrum for 1018:5 eV  E  1023:5 eV is E2F2ðþ1:6;1:2½systematicÞ 107 GeVcm2 s1 sr1, thestrongest bounds to date on the UHE neutrino flux atenergies above 3 1018 eV.We thank the National Aeronautics and SpaceAdministration, the National Science Foundation Officeof Polar Programs, the Department of Energy Office ofScience High Energy Physics Division, the UK Scienceand Technology Facilities Council, and especially the staffof the Columbia Scientific Balloon Facility.*Present address: NASA Goddard Space Flight Center,Greenbelt, Maryland, 20771, USA.[1] K. Greisen, Phys. Rev. Lett. 16, 748 (1966).[2] G. T. Zatsepin and V.A. Kuzmin, Pis’ma Zh. Eksp. Teor.Fiz. 4, 114 (1966) [JETP Lett. 4, 78 (1966)].[3] V. S. Beresinsky and G. T. Zatsepin, Phys. Lett. B 28, 423(1969).TABLE II. Expected numbers of events N from several UHEneutrino models, and confidence level CL ¼ 100½1expðNÞ for exclusion by ANITA-1 observations.Model & references Predicted N CL, %Baseline BZ modelsProtheroe & Johnson 1996 [18] 0.22 19.7Engel, Seckel, Stanev 2001 [19] 0.12 11.3Barger, Huber, & Marfatia 2006 [20] 0.38 31.6Strong-source evolution BZ modelsEngel, Seckel, Stanev 2001 [19] 0.39 32.3Kalashev et al. 2002 [21] 1.03 64.3Aramo et al. 2005 [22] 1.04 64.6Barger, Huber, & Marfatia 2006 [20] 0.89 58.9Yuksel & Kistler 2007 [23] 0.56 42.9BZ models that saturate all bounds:Kalashev et al. 2002 [21] 10.1 >99:99Aramo et al. 2005 [22] 8.50 >99:98Waxman-Bahcall fluxes:Waxman, Bahcall 1999,evolved sources [24]0.76 53.2Waxman, Bahcall 1999,standard [24]0.27 23.7FIG. 3 (color). ANITA-1 limits based on no surviving candi-dates for 17.3 days of live time. Other limits are from AMANDA[25], RICE [26], ANITA-lite [8], Auger [27], HiRes [28], andFORTE [15]. The BZ (GZK) neutrino model range is determinedby a variety of models [18–22,29,30].PRL 103, 051103 (2009) P HY S I CA L R EV I EW LE T T E R Sweek ending31 JULY 2009051103-4[4] D. Seckel and T. Stanev, Phys. Rev. Lett. 95, 141101(2005).[5] G. A. Askaryan, JETP 14, 441 (1962); JETP 21, 658(1965).[6] D. Saltzberg et al., Phys. Rev. Lett. 86, 2802 (2001).[7] P.W. Gorham et al. (ANITA Collaboration), Phys. Rev.Lett. 99, 171101 (2007).[8] S.W. Barwick et al. (ANITA Collaboration) Phys. Rev.Lett. 96, 171101 (2006).[9] P.W. Gorham et al. (ANITA Collaboration),arXiv:0812.1920 [Astropart. Phys. (to be published)].[10] S. Barwick, D. Besson, P. Gorham, and D. Saltzberg, J.Glaciol. 51, 231 (2005).[11] The factor of 8.7 rather than the expected factor of 10increase in Vpol events from the 10% to 100% datasample is due to the highly nonrandom nature of theanthropogenic backgrounds that dominate these samples.[12] T. Huege and H. Falcke, Astropart. Phys. 24, 116 (2005);arXiv:astro-ph/0501580.[13] H. Falcke and P. Gorham, Astropart. Phys. 19, 477 (2003).[14] D. A. Suprun, P.W. Gorham, and J. L. Rosner, Astropart.Phys. 20, 157 (2003).[15] N. Lehtinen, P. Gorham, A. Jacobson, and R. Roussel-Dupre´, Phys. Rev. D 69, 013008 (2004).[16] L. A. Anchordoqui, J. L. Feng, H. Goldberg, and A.D.Shapere, Phys. Rev. D 66, 103002 (2002).[17] R. Gandhi, Nucl. Phys. B, Proc. Suppl. 91, 453(2001).[18] R. J. Protheroe and P.A. Johnson, Astropart. Phys. 4, 253(1996).[19] R. Engel, D. Seckel, and T. Stanev, Phys. Rev. D 64,093010 (2001).[20] V. Barger, P. Huber, and D. Marfatia, Phys. Lett. B 642,333 (2006).[21] O. E. Kalashev, V. A. Kuzmin, D. V. Semikoz, and G. Sigl,Phys. Rev. D 66, 063004 (2002).[22] C. Aramo et al., Astropart. Phys. 23, 65 (2005).[23] H. Yuksel and M.D. Kistler, Phys. Rev. D 75, 083004(2007).[24] E. Waxman and J. Bahcall, Phys. Rev. D 59, 023002(1998).[25] M. Ackermann et al. (IceCube Collaboration) Astrophys.J. 675, 1014 (2008).[26] I. Kravchenko et al., Phys. Rev. D 73, 082002 (2006).[27] J. Abraham et al. (Pierre Auger Collaboration), Phys. Rev.Lett. 100, 211101 (2008).[28] R. U. Abbassi et al. (HiRes Collaboration), Astrophys. J.684, 790 (2008).[29] O. E. Kalashev, V. A. Kuzmin, D. V. Semikoz, and G. Sigl,Phys. Rev. D 65, 103003 (2002).[30] M. Ave, N. Busca, A. V. Olinto, A.A. Watson, andT. Yamamoto, Astropart. Phys. 23, 19 (2005).PRL 103, 051103 (2009) P HY S I CA L R EV I EW LE T T E R Sweek ending31 JULY 2009051103-5

New Limits on the Ultra-high Energy Cosmic Neutrino Flux from the ANITA
  Experiment

New Limits on the Ultra-high Energy Cosmic Neutrino Flux from the ANITA Experiment

Abstract

Similar works

Full text

Available Versions

National Taiwan University Repository

UCL Discovery