Limits on a muon flux from neutralino annihilations in the Sunwith the IceCube 22-string detector

Limits on a muon flux from neutralino annihilations in the Sun
with the IceCube 22-string detector

R. Abbasi Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    Y. Abdou Dept. of Subatomic and Radiation Physics, University of Gent, B-9000 Gent, Belgium    M. Ackermann DESY, D-15735 Zeuthen, Germany    J. Adams Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand    M. Ahlers Dept. of Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK    K. Andeen Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    J. Auffenberg Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    X. Bai Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    M. Baker Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    S. W. Barwick Dept. of Physics and Astronomy, University of California, Irvine, CA 92697, USA    R. Bay Dept. of Physics, University of California, Berkeley, CA 94720, USA    J. L. Bazo Alba DESY, D-15735 Zeuthen, Germany    K. Beattie Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    J. J. Beatty Dept. of Physics and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210, USA Dept. of Astronomy, Ohio State University, Columbus, OH 43210, USA    S. Bechet Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium    J. K. Becker Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany    K.-H. Becker Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    M. L. Benabderrahmane DESY, D-15735 Zeuthen, Germany    J. Berdermann DESY, D-15735 Zeuthen, Germany    P. Berghaus Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    D. Berley Dept. of Physics, University of Maryland, College Park, MD 20742, USA    E. Bernardini DESY, D-15735 Zeuthen, Germany    D. Bertrand Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium    D. Z. Besson Dept. of Physics and Astronomy, University of Kansas, Lawrence, KS 66045, USA    M. Bissok III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    E. Blaufuss Dept. of Physics, University of Maryland, College Park, MD 20742, USA    D. J. Boersma Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    C. Bohm Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    J. Bolmont DESY, D-15735 Zeuthen, Germany    S. Böser DESY, D-15735 Zeuthen, Germany    O. Botner Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden    L. Bradley Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    J. Braun Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    D. Breder Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    T. Burgess Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    T. Castermans University of Mons-Hainaut, 7000 Mons, Belgium    D. Chirkin Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    B. Christy Dept. of Physics, University of Maryland, College Park, MD 20742, USA    J. Clem Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    S. Cohen Laboratory for High Energy Physics, École Polytechnique Fédérale, CH-1015 Lausanne, Switzerland    D. F. Cowen Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA Dept. of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA    M. V. D’Agostino Dept. of Physics, University of California, Berkeley, CA 94720, USA    M. Danninger Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    C. T. Day Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    C. De Clercq Vrije Universiteit Brussel, Dienst ELEM, B-1050 Brussels, Belgium    L. Demirörs Laboratory for High Energy Physics, École Polytechnique Fédérale, CH-1015 Lausanne, Switzerland    O. Depaepe Vrije Universiteit Brussel, Dienst ELEM, B-1050 Brussels, Belgium    F. Descamps Dept. of Subatomic and Radiation Physics, University of Gent, B-9000 Gent, Belgium    P. Desiati Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    G. de Vries-Uiterweerd Dept. of Subatomic and Radiation Physics, University of Gent, B-9000 Gent, Belgium    T. DeYoung Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    J. C. Diaz-Velez Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    J. Dreyer Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany    J. P. Dumm Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    M. R. Duvoort Dept. of Physics and Astronomy, Utrecht University/SRON, NL-3584 CC Utrecht, The Netherlands    W. R. Edwards Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    R. Ehrlich Dept. of Physics, University of Maryland, College Park, MD 20742, USA    J. Eisch Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    R. W. Ellsworth Dept. of Physics, University of Maryland, College Park, MD 20742, USA    O. Engdegård Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden    S. Euler III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    P. A. Evenson Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    O. Fadiran CTSPS, Clark-Atlanta University, Atlanta, GA 30314, USA    A. R. Fazely Dept. of Physics, Southern University, Baton Rouge, LA 70813, USA    T. Feusels Dept. of Subatomic and Radiation Physics, University of Gent, B-9000 Gent, Belgium    K. Filimonov Dept. of Physics, University of California, Berkeley, CA 94720, USA    C. Finley Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    M. M. Foerster Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    B. D. Fox Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    A. Franckowiak Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany    R. Franke DESY, D-15735 Zeuthen, Germany    T. K. Gaisser Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    J. Gallagher Dept. of Astronomy, University of Wisconsin, Madison, WI 53706, USA    R. Ganugapati Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    L. Gerhardt Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Dept. of Physics, University of California, Berkeley, CA 94720, USA    L. Gladstone Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    A. Goldschmidt Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    J. A. Goodman Dept. of Physics, University of Maryland, College Park, MD 20742, USA    R. Gozzini Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    D. Grant Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    T. Griesel Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    A. Groß Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand Max-Planck-Institut für Kernphysik, D-69177 Heidelberg, Germany    S. Grullon Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    R. M. Gunasingha Dept. of Physics, Southern University, Baton Rouge, LA 70813, USA    M. Gurtner Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    C. Ha Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    A. Hallgren Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden    F. Halzen Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    K. Han Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand    K. Hanson Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    Y. Hasegawa Dept. of Physics, Chiba University, Chiba 263-8522, Japan    J. Heise Dept. of Physics and Astronomy, Utrecht University/SRON, NL-3584 CC Utrecht, The Netherlands    K. Helbing Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    P. Herquet University of Mons-Hainaut, 7000 Mons, Belgium    S. Hickford Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand    G. C. Hill Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    K. D. Hoffman Dept. of Physics, University of Maryland, College Park, MD 20742, USA    K. Hoshina Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    D. Hubert Vrije Universiteit Brussel, Dienst ELEM, B-1050 Brussels, Belgium    W. Huelsnitz Dept. of Physics, University of Maryland, College Park, MD 20742, USA    J.-P. Hülß III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    P. O. Hulth Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    K. Hultqvist Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    S. Hussain Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    R. L. Imlay Dept. of Physics, Southern University, Baton Rouge, LA 70813, USA    M. Inaba Dept. of Physics, Chiba University, Chiba 263-8522, Japan    A. Ishihara Dept. of Physics, Chiba University, Chiba 263-8522, Japan    J. Jacobsen Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    G. S. Japaridze CTSPS, Clark-Atlanta University, Atlanta, GA 30314, USA    H. Johansson Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    J. M. Joseph Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    K.-H. Kampert Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    A. Kappes Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    T. Karg Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    A. Karle Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    J. L. Kelley Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    P. Kenny Dept. of Physics and Astronomy, University of Kansas, Lawrence, KS 66045, USA    J. Kiryluk Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Dept. of Physics, University of California, Berkeley, CA 94720, USA    F. Kislat DESY, D-15735 Zeuthen, Germany    S. R. Klein Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Dept. of Physics, University of California, Berkeley, CA 94720, USA    S. Klepser DESY, D-15735 Zeuthen, Germany    S. Knops III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    G. Kohnen University of Mons-Hainaut, 7000 Mons, Belgium    H. Kolanoski Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany    L. Köpke Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    M. Kowalski Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany    T. Kowarik Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    M. Krasberg Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    K. Kuehn Dept. of Physics and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210, USA    T. Kuwabara Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    M. Labare Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium    S. Lafebre Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    K. Laihem III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    H. Landsman Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    R. Lauer DESY, D-15735 Zeuthen, Germany    H. Leich DESY, D-15735 Zeuthen, Germany    D. Lennarz III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    A. Lucke Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany    J. Lundberg Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden    J. Lünemann Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    J. Madsen Dept. of Physics, University of Wisconsin, River Falls, WI 54022, USA    P. Majumdar DESY, D-15735 Zeuthen, Germany    R. Maruyama Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    K. Mase Dept. of Physics, Chiba University, Chiba 263-8522, Japan    H. S. Matis Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    C. P. McParland Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    K. Meagher Dept. of Physics, University of Maryland, College Park, MD 20742, USA    M. Merck Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    P. Mészáros Dept. of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    E. Middell DESY, D-15735 Zeuthen, Germany    N. Milke Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany    H. Miyamoto Dept. of Physics, Chiba University, Chiba 263-8522, Japan    A. Mohr Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany    T. Montaruli Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    R. Morse Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    S. M. Movit Dept. of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA    K. Münich Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany    R. Nahnhauer DESY, D-15735 Zeuthen, Germany    J. W. Nam Dept. of Physics and Astronomy, University of California, Irvine, CA 92697, USA    P. Nießen Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    D. R. Nygren Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    S. Odrowski Max-Planck-Institut für Kernphysik, D-69177 Heidelberg, Germany    A. Olivas Dept. of Physics, University of Maryland, College Park, MD 20742, USA    M. Olivo Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden    M. Ono Dept. of Physics, Chiba University, Chiba 263-8522, Japan    S. Panknin Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany    S. Patton Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    C. Pérez de los Heros Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden    J. Petrovic Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium    A. Piegsa Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    D. Pieloth DESY, D-15735 Zeuthen, Germany    A. C. Pohl Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden    R. Porrata Dept. of Physics, University of California, Berkeley, CA 94720, USA    N. Potthoff Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    P. B. Price Dept. of Physics, University of California, Berkeley, CA 94720, USA    M. Prikockis Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    G. T. Przybylski Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA    K. Rawlins Dept. of Physics and Astronomy, University of Alaska Anchorage, 3211 Providence Dr., Anchorage, AK 99508, USA    P. Redl Dept. of Physics, University of Maryland, College Park, MD 20742, USA    E. Resconi Max-Planck-Institut für Kernphysik, D-69177 Heidelberg, Germany    W. Rhode Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany    M. Ribordy Laboratory for High Energy Physics, École Polytechnique Fédérale, CH-1015 Lausanne, Switzerland    A. Rizzo Vrije Universiteit Brussel, Dienst ELEM, B-1050 Brussels, Belgium    J. P. Rodrigues Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    P. Roth Dept. of Physics, University of Maryland, College Park, MD 20742, USA    F. Rothmaier Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    C. Rott Dept. of Physics and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210, USA    C. Roucelle Max-Planck-Institut für Kernphysik, D-69177 Heidelberg, Germany    D. Rutledge Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    D. Ryckbosch Dept. of Subatomic and Radiation Physics, University of Gent, B-9000 Gent, Belgium    H.-G. Sander Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany    S. Sarkar Dept. of Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK    K. Satalecka DESY, D-15735 Zeuthen, Germany    S. Schlenstedt DESY, D-15735 Zeuthen, Germany    T. Schmidt Dept. of Physics, University of Maryland, College Park, MD 20742, USA    D. Schneider Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    A. Schukraft III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    O. Schulz Max-Planck-Institut für Kernphysik, D-69177 Heidelberg, Germany    M. Schunck III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    D. Seckel Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    B. Semburg Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    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USA    O. Tarasova DESY, D-15735 Zeuthen, Germany    A. Tepe Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany    S. Ter-Antonyan Dept. of Physics, Southern University, Baton Rouge, LA 70813, USA    C. Terranova Laboratory for High Energy Physics, École Polytechnique Fédérale, CH-1015 Lausanne, Switzerland    S. Tilav Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA    M. Tluczykont DESY, D-15735 Zeuthen, Germany    P. A. Toale Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA    D. Tosi DESY, D-15735 Zeuthen, Germany    D. Turčan Dept. of Physics, University of Maryland, College Park, MD 20742, USA    N. van Eijndhoven Dept. of Physics and Astronomy, Utrecht University/SRON, NL-3584 CC Utrecht, The Netherlands    J. Vandenbroucke Dept. of Physics, University of California, Berkeley, CA 94720, USA    A. Van Overloop Dept. of Subatomic and Radiation Physics, University of Gent, B-9000 Gent, Belgium    B. Voigt DESY, D-15735 Zeuthen, Germany    C. Walck Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    T. Waldenmaier Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany    M. Walter DESY, D-15735 Zeuthen, Germany    C. Wendt Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    S. Westerhoff Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    N. Whitehorn Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA    C. H. Wiebusch III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany    A. Wiedemann Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany    G. Wikström Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden    D. R. Williams Dept. of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA    R. Wischnewski DESY, D-15735 Zeuthen, Germany    H. Wissing III Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany Dept. of Physics, University of Maryland, College Park, MD 20742, USA    K. Woschnagg Dept. of Physics, University of California, Berkeley, CA 94720, USA    X. W. Xu Dept. of Physics, Southern University, Baton Rouge, LA 70813, USA    G. Yodh Dept. of Physics and Astronomy, University of California, Irvine, CA 92697, USA    S. Yoshida Dept. of Physics, Chiba University, Chiba 263-8522, Japan
July 25, 2019
Abstract

A search for muon neutrinos from neutralino annihilations in the Sun has been performed with the IceCube 22-string neutrino detector using data collected in 104.3 days of live-time in 2007. No excess over the expected atmospheric background has been observed. Upper limits have been obtained on the annihilation rate of captured neutralinos in the Sun and converted to limits on the WIMP-proton cross-sections for WIMP masses in the range 250 - 5000 GeV. These results are the most stringent limits to date on neutralino annihilation in the Sun.

pacs:
95.35.+d, 98.70.Sa, 96.50.S-, 96.50.Vg
preprint: APS/123-QEDthanks: Affiliated with Universität Erlangen-Nürnberg, Physikalisches Institut, D-91058, Erlangen, Germanythanks: On leave of absence from Università di Bari and Sezione INFN, Dipartimento di Fisica, I-70126, Bari, Italythanks: Affiliated with School of Pure and Applied Natural Sciences, Kalmar University, S-39182 Kalmar, Swedenthanks: Corresponding author.
E-mail address: wikstrom@physto.se (G. Wikström).

IceCube Collaboration

Non-baryonic cold dark matter in the form of weakly interacting massive particles (WIMPs) is one of the most promising solutions to the dark matter problem dark (). The minimal supersymmetric extension of the Standard Model (MSSM) provides a natural WIMP candidate in the lightest neutralino  mssm (). This particle is weakly interacting only and, assuming R-parity conservation, is stable and can therefore survive today as a relic from the Big Bang. A wide range of neutralino masses, , from 46 GeV pdg () to a few tens of TeV high_limit_new () is compatible with observations and accelerator-based measurements. Within these bounds it is possible to construct models where the neutralino provides the needed relic dark matter density.

Relic neutralinos in the galactic halo may become gravitationally trapped in the Sun and accumulate in its center, where they can annihilate each other, producing standard model particles. These may decay, creating neutrinos which can escape and reach the Earth. The search presented here aims at detecting neutralino annihilations indirectly by observing an excess of such high energy neutrinos from the Sun. Limits on the neutrino flux from the Sun have previously been reported by BAKSAN baksan (), MACRO macro (), Super-Kamiokande superk (), and AMANDA sunWimp ().

The IceCube detector icecube () records Cherenkov light in the ice from relativistic charged particles created in neutrino interactions. In 2007 the detector consisted of an array of 22 vertical strings with 60 Digital Optical Modules (DOMs) each, deployed in the clear Antarctic ice at the South Pole at depths between 1450 m and 2450 m below the ice surface. The vertical spacing between DOMs is 17 m and the horizontal distance between strings is 125 m. Each DOM consists of a pressurized glass sphere containing a 25 cm photomultiplier tube (PMT) and a digitizer board. The PMT waveforms are stored when nearest or next-to-nearest DOMs fire within 1 s. The trigger selects time windows when eight DOMs produce waveforms within 5 s. The reconstructed first photon arrival times are used to determine the muon direction.

The background in the search for neutrinos from the Sun comes from air showers created by cosmic ray interactions in the atmosphere. The showers cause downwards going atmospheric muon events, triggering at several hundred Hz, and atmospheric muon neutrino events, triggering at a few mHz. When the Sun is below the horizon, the neutrino signal can be distinguished from the atmospheric muon background by selecting events with upward-going reconstructed muon tracks.

Figure 1: The product of the output values of the two SVMs for the experimental data, a simulated signal ( = 1000 GeV, hard spectrum) and the background. The background has been scaled to match the data rate and it is shown divided into three components: atmospheric neutrinos and single and coincident atmospheric muons.

The dataset used in this analysis consists of   triggering events taken while the Sun was below the horizon, corresponding to 104.3 days of livetime between June 1st and September 23rd, 2007. The events were processed through several filters to reduce the content of atmospheric muon events and to enrich the dataset in muon-neutrino events. The analysis was performed in a blind manner such that the azimuth of the Sun was not looked at until the selection cuts were finalized.

Events were first required to have at least ten hit DOMs, and the zenith angle of the line-fit reco () first-guess reconstructed track was required to be larger than . Selected events were subjected to Log-Likelihood (LLH) fitting of muon tracks reco (), which uses the probability distribution of the photon arrival times. Cuts were then placed on the zenith angle of this reconstruction () and the width of the likelihood optimum (), to select upwards going events of good quality. Very loose cuts were placed on several kinematic quantities to remove a small number of outlying events. The final background reduction was then done using Support Vector Machines (SVMs) svm (), multi-variate learning machines used to classify events as signal-like or background-like. Twelve event observables, that correlated modestly with one another (correlation coefficient ), were used to train two SVMs with six input observables each. The use of two SVMs allowed minimal correlation () between the six observables for each SVM. Training was done with simulated signal events, and a set of real data, not used in the analysis, was taken as background. The observables describe the quality of the track reconstructions and the geometry and the time evolution of the hit pattern, most notably through the opening angle between the line-fit and the LLH tracks, , the mean minimal distance between the LLH track and the hit DOMs, and the number of hit strings. The SVM input distributions for data and simulated backgrounds were generally in good agreement.

Figure 2: Cosine of the angle between the reconstructed track and the direction of the Sun, , for data (squares) with one standard deviation error bars, and the atmospheric background expectation from atmospheric muons and neutrinos (dashed line). Also shown is a simulated signal ( = 1000 GeV, hard spectrum) scaled to events (see Table I).

Three types of background were simulated: atmospheric muon events from single and coincident air showers were simulated using CORSIKA cors (), and atmospheric events were simulated following the Bartol spectrum bartol (). Solar-WIMP signals were simulated with WimpSim blen (). Two neutralino annihilation channels, (hard channel) which produces a harder neutrino energy spectrum, and (soft channel) which gives rise to a softer neutrino energy spectrum, were simulated for five masses = 250, 500, 1000, 3000, and 5000 GeV. The neutrinos were propagated through the Sun and to the Earth with full flavour oscillation. Absorption in the Sun is important for neutrinos with energies above a few hundred GeV. A muon and a hadronic shower were generated in the ice near the detector. At the vertices the mean energy of simulated signal muons ranges from about 30 GeV to about 150 GeV depending on signal model, see Table 1. For the hard channel decreases for TeV owing to neutrino absorption in the Sun and secondary neutrino generation. The muon contribution from tau decay was evaluated to be insignificant and tau vertices were therefore neglected. Propagation of muons through the ice was simulated mmc (), and the Cherenkov light propagation from the muon to the DOMs was performed with pho (), taking into account measured ice properties iceprop ().

Fig. 1 shows the distributions of the product of the two SVM output values, . As can be seen in the figure the distribution of simulated background is in good agreement with data. The final event sample was selected by requiring . This cut increased the ratio by a factor of 8.

Simulations predict that the final data sample of 6946 events has an atmospheric event content of 56%, and that the remainder consists of mis-reconstructed atmospheric muon events. The loose cuts maintain a large effective volume, defined as the detector volume with selection efficiency, since the final signal determination was done on the basis of direction.

After calculating the Sun’s position, the observed number of events as a function of the angle to the Sun, , is compared to the atmospheric background expectation in Fig. 2. The angular distribution is consistent with the expected background and no excess of events from the Sun is observed.

Figure 3: Upper limits at the 90% confidence level on the muon flux from neutralino annihilations in the Sun for the soft () and hard () annihilation channels, adjusted for systematic effects, as a function of neutralino mass. The shaded area represents MSSM models not disfavoured by direct searches cdms (); xenon10 (). A muon energy threshold of 1 GeV was used when calculating the flux. Also shown are the limits from MACRO macro (), Super-K superk (), and AMANDA sunWimp ().

Using likelihood-ratio hypothesis tests the observed distribution is fitted with a sum of distributions of the simulated signal and the expected background. Here, the expected background is detemined by using real data with randomized azimuth direction of the Sun. We then follow the unified Feldman-Cousins approach fc () to construct the confidence intervals on the number of signal events . The upper 90% confidence limit ranges between and events depending on signal case, see Table 1.

Simulation studies were used to estimate the systematic uncertainty on the signal effective volume . Uncertainties in the photon propagation in ice and absolute DOM efficiency dominate, contributing to depending on the signal model. The total systematic uncertainty on ranges from for the highest to for the lowest . Deviations in the event rate between data and background simulations are within the systematic uncertainty. These uncertainties are included in the results presented below.

From the upper limits on we calculate the limit on the neutrino to muon conversion rate , for the livetime . Using the signal simulation blen (), we can convert this rate to a limit on the neutralino annihilation rate in the Sun, , see Table 1. Results from different experiments are commonly compared by calculating the limit on the muon flux above 1 GeV, , which is also shown in Table 1 together with the sensitivity, , the median limit obtained from simulations with no signal. A downward fluctuation in the data close to the position of the Sun results in limits lower than the sensitivity. Within , corresponding to the rightmost bin in Fig. 2, the fluctuation has a probability of 8.8%. In this bin we expect less than 0.4 background events from solar atmospheric neutrinos sanu ().

Figure 4: Upper limits at the 90% confidence level on the spin-dependent neutralino-proton cross-section for the soft () and hard () annihilation channels, adjusted for systematic effects, as a function of neutralino mass. The shaded area represents MSSM models not disfavoured by direct searches cdms (); xenon10 () based on . Also shown are the limits from CDMS cdms (), COUPP coupp (), KIMS kims () and Super-K superk ().
Channel
(GeV) () () () () () () (GeV) () ()
250 Hard 7.5 68.7
500 Soft 8.5 28.8
Hard 6.8 111
1000 Soft 7.5 40.8
Hard 6.8 146
3000 Soft 7.8 55.8
Hard 6.4 149
5000 Soft 7.5 59.9
Hard 6.8 142
Table 1: Upper limits on the number of signal events , the conversion rate , the neutralino annihilation rate in the Sun , the muon flux , and the neutralino-proton scattering cross-sections (spin-independent, , and spin-dependent, ), at the 90% confidence level including systematic errors. The sensitivity (see text) is shown for comparison. Also shown is the median angular error , the mean muon energy , the effective volume , and the effective area .

The 90% confidence upper limit on as a function of is shown in Fig. 3, compared to other limits macro (); superk (); sunWimp (), and MSSM model predictions dsusy (). In the plot, the shaded area represents neutralino models not disfavoured by the direct detection experiments CDMS cdms () and XENON-10 xenon10 (), based on their limit on the spin-independent neutralino-proton cross-section.

The limits on the annihilation rate can be converted into limits on the spin-dependent, , and spin-independent, , neutralino-proton cross-sections, allowing a more direct comparison with the results of direct search experiments. Since capture in the Sun is dominated by , indirect searches are expected to be competitive in setting limits on this quantity. Assuming equilibrium between the capture and annihilation rates in the Sun, the annihilation rate is directly proportional to the cross-section. A limit on is found by setting to zero, and vice versa. We have used DarkSUSY dsusy () and the method described in conv () to perform the conversion. The results are shown in Table 1. We assumed a local WIMP density of , and a Maxwellian WIMP velocity distribution with a dispersion of 270 km/s. Planetary effects on the capture were neglected. Fig. 4 shows the IceCube-22 limits on compared with other bounds cdms (); coupp (); kims (); superk (), and the MSSM model space defined as for Fig. 3. Indirect searches for dark matter in the Sun complement direct searches on Earth in several respects. WIMPs in the Sun would accumulate over a long period and therefore sample over different dark matter densities in the galactic halo. This gravitational accumulation is sensitive to low WIMP velocities while direct detection recoil experiments are more sensitive at higher velocities.

In conclusion, we have presented the most stringent limits to date on neutralino annihilations in the Sun, improving on the 2001 AMANDA sunWimp () limits by at least a factor of six for hard channels. We also present the most stringent limits on the spin-dependent WIMP-proton cross-section for neutralino masses above 250 GeV. The full IceCube detector with the DeepCore extension dc () is expected to test viable MSSM models down to 50 GeV.

We acknowledge support from the following agencies: U.S. National Science Foundation-Office of Polar Programs, U.S. National Science Foundation-Physics Division, U. of Wisconsin Alumni Research Foundation, U.S. Department of Energy, NERSC, the LONI grid; Swedish Research Council, K. & A. Wallenberg Foundation, Sweden; German Ministry for Education and Research, Deutsche Forschungsgemeinschaft; Fund for Scientific Research, IWT-Flanders, BELSPO, Belgium; the Netherlands Organisation for Scientific Research; M. Ribordy is supported by SNF (Switzerland); A. Kappes and A. Groß are supported by the EU Marie Curie OIF Program. We thank J. Edsjö for DarkSUSY support.

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