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Arguelles C.A.,University of Wisconsin - Madison | Arguelles C.A.,Wisconsin IceCube Particle Astrophysics Center | Halzen F.,University of Wisconsin - Madison | Halzen F.,Wisconsin IceCube Particle Astrophysics Center | And 4 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

By combining the color dipole model of the nucleon with the assumption that cross sections behave asymptotically as ln2(s), we are able to describe the data for photon, neutrino and hadron interactions with protons at all energies; s is the center-of-mass energy of the interacting particles. Specifically, we extrapolate the perturbative QCD calculations into the regime of small fractional parton momenta x using a color dipole description of the proton target that guarantees an asymptotic ln2(s) behavior of all cross sections. The ambiguity of introducing a parametrization associated with the dipole approximation is mitigated by the requirement that the saturation of the small-x structure functions produce ln2(s)-behaved asymptotic cross sections, in agreement with the data. The same formalism allows us to calculate the cross section for the hadronic pair production of charm particles. The results, in particular those for the high-energy neutrino and charm cross sections, are relevant for evaluating the sensitivity as well as the background in neutrino telescopes. © 2015 American Physical Society. © 2015 American Physical Society.

Taylor A.M.,Dublin Institute for Advanced Studies | Ahlers M.,Wisconsin IceCube Particle Astrophysics Center | Ahlers M.,University of Wisconsin - Madison | Hooper D.,Fermi National Accelerator Laboratory | Hooper D.,University of Chicago
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Using recent measurements of the spectrum and chemical composition of the highest energy cosmic rays, we consider the sources of these particles. We find that these data strongly prefer models in which the sources of the ultra-high-energy cosmic rays inject predominantly intermediate mass nuclei, with comparatively few protons or heavy nuclei, such as iron or silicon. If the number density of sources per comoving volume does not evolve with redshift, the injected spectrum must be very hard (α≃1) in order to fit the spectrum observed from Earth. Such a hard spectral index would be surprising and difficult to accommodate theoretically. In contrast, much softer spectral indices, consistent with the predictions of Fermi acceleration (α≃2), are favored in models with negative source evolution. With this theoretical bias, these observations thus favor models in which the sources of the highest energy cosmic rays are preferentially located within the low-redshift universe. © 2015 us. © 2015 American Physical Society. American Physical Society.

In 2013, IceCube researchers made an important contribution to astrophysics when they reported the first detection of high energy cosmic neutrinos, opening a new astronomical window to the universe and some of its most violent phenomena. The five-year, $35 million cooperative agreement calls for the continued operation and management of the observatory, which is located at NSF's Amundsen-Scott South Pole Station. The agreement begins April 1, and may be renewed for another five-year period if the detector and collaboration continue to operate successfully. Funding for IceCube comes through an award from the Division of Polar Programs in NSF's Geosciences Directorate and from the Directorate for Mathematical and Physical Sciences (MPS) Division of Physics. Through the Division of Polar Programs, NSF manages the U.S. Antarctic Program that supports researchers at universities throughout the country. The program also provides infrastructure to support researchers in the field. "NSF is excited to support the science made possible by the IceCube Observatory because it's at the cutting edge of discovery," said Scott Borg, head of Polar Programs' Antarctic sciences section. "But to make ambitious research of this kind a reality requires cooperation within the agency, which is why we're delighted that our support for IceCube is in partnership with MPS. It's also science on a global scale, relying on strong international cooperation to be successful." The collaboration that operates the IceCube observatory includes individuals representing 47 institutions from 12 different countries. It includes sub-awards to the Lawrence Berkeley National Laboratory, Pennsylvania State University, the University of Delaware, the University of Maryland, the University of Alabama at Tuscaloosa, Michigan State University and the University of Wisconsin-River Falls. Since IceCube's inception 15 years ago and the completion of its construction five years ago—centered around a detector array consisting of 5,000 optical sensors frozen in the ice a mile beneath the South Pole—has been administered through UW-Madison, in recent years under the auspices of the Wisconsin IceCube Particle Astrophysics Center (WIPAC). "This is extremely good news," says Francis Halzen, a UW-Madison professor of physics and the principal investigator for the project. "Over the years, we have come to know what it takes to successfully operate the detector." IceCube was the first scientific instrument to detect ultra high-energy neutrinos from beyond our solar system. The neutrinos packed a billion times more energy than those detected in conjunction with the 1987 supernova observed in the Large Magellanic Cloud. Recent reports from the IceCube collaboration have confirmed the observatory's detection of high-energy neutrinos from beyond our galaxy—so-called cosmic neutrinos. Neutrinos are nearly massless particles created in nuclear reactions and. In nature, they are created by some of the most energetic events in the universe. Scientists believe colliding black holes, the violent cores of galaxies, supernovas and pulsars accelerate neutrinos, many billions of which pass through the Earth every second. Because they have almost no mass and rarely interact with matter, they are extremely difficult to detect and require instruments the size of IceCube—which occupies a cubic kilometer of Antarctic ice—to capture the fleeting bursts of light created when the occasional neutrino crashes into another particle. But the elusive qualities that make neutrinos so hard to detect also make them interesting to scientists. Since the particles glide through space unhindered by stars, planets and the powerful magnetic fields that pock the universe, they remain virtually pristine and harbor valuable clues about their yet-to-be-confirmed sources. IceCube has proven a workhorse of a telescope, according to Halzen. It remains operational 99 percent of the time, and has so far detected more than a million neutrinos—"A few hundred of which are astronomically interesting," Halzen said. "Five years ago, it was about discovering cosmic neutrinos. Now it's about doing astronomy and particle physics with them," notes Halzen of the quest to follow the particles' tracks back to their sources, a feat yet to be accomplished. Olga Botner, the IceCube collaboration spokesperson and a professor of physics and astronomy at Sweden's Uppsala University, said that "All over the world, IceCube is considered the flagship of neutrino astronomy." "IceCube's discovery of extraterrestrial neutrinos is a major breakthrough and a crucial first step into as yet unexplored parts of our violent universe," she said. "It also represents a step towards the realization of a 50 years old dream—to figure out what cosmic upheavals create the ultra-high energy cosmic rays, detected on Earth with energies millions of times larger than those achievable by even the most powerful man-made accelerators." Headquartered at UW-Madison, IceCube includes a staff of nearly 60 scientists, engineers and technicians in Madison. "There are many technical challenges underlying the operation of a large neutrino observatory at the South Pole, that would be hard to anticipate," says Kael Hanson, IceCube's director of operations and a UW-Madison professor of physics. IceCube's complexity, ability to gather large data sets, and standing among the world's frontline astrophysical detectors makes it a contributor to emerging computational technologies for managing and analyzing novel scientific information. Halzen says the performance of the IceCube detector has steadily improved and a key goal will be to speed up the analysis of neutrinos of interest in order to quickly alert other observatories. "We're going to detect interesting neutrinos in real time and we can send word to other observatories," Halzen said. "If we can do it in real time, we can be much more effective and we can alert, for example, optical observatories and other detectors" for combined observing. If neutrino detectors, and possibly also gravitational wave detectors, can provide early warnings to other telescopes, "We might have the astronomical event of the 21st century," Halzen said. Explore further: IceCube Neutrino Observatory reports first evidence for extraterrestrial high-energy neutrinos

Arguelles Delgado C.A.,Wisconsin IceCube Particle Astrophysics Center | Salvado J.,University of Wisconsin - Madison | Weaver C.N.,Wisconsin IceCube Particle Astrophysics Center
Computer Physics Communications | Year: 2015

Simple Quantum Integro-Differential Solver (SQuIDS) is a C++ code designed to solve semi-analytically the evolution of a set of density matrices and scalar functions. This is done efficiently by expressing all operators in an SU(N) basis. SQuIDS provides a base class from which users can derive new classes to include new non-trivial terms from the right hand sides of density matrix equations. The code was designed in the context of solving neutrino oscillation problems, but can be applied to any problem that involves solving the quantum evolution of a collection of particles with Hilbert space of dimension up to six. Program summary Program title: SQuIDS Catalogue identifier: AEXG-v1-0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEXG-v1-0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU Lesser General Public License, version 3 No. of lines in distributed program, including test data, etc.: 18198 No. of bytes in distributed program, including test data, etc.: 137607 Distribution format: tar.gz Programming language: C++11. Computer: 32- and 64-bit x86. Operating system: Linux, Mac OS X, FreeBSD. RAM: Proportional to the number of nodes, the dimension of the Hilbert space, the number of scalar functions, and the number of density matrices used in the problem. Classification: 11.1. External routines: GNU Scientific Library (http://www.gnu.org/software/gsl/). Nature of problem: Solve the evolution of open quantum systems of Hilbert space dimension N with self interactions and interaction with classical fields. Solution method: The SU(N) algebra is implemented as a C++ object and is embedded into the GSL ordinary differential equation solver. Restrictions: The code is only implemented up to Hilbert spaces of dimension six, but a Mathematica notebook is provided in order to generate higher dimensional solutions. Furthermore, only ordinary differential equation solution methods that require only the first derivative can be used. Running time: Proportional to the number of nodes, the dimension of the Hilbert space, the number of scalar functions, the number of density matrices, and the numerical precision used in the problem. © 2015 Elsevier B.V.

Kelley J.L.,Wisconsin IceCube Particle Astrophysics Center
AIP Conference Proceedings | Year: 2014

In order to detect cosmic ray air showers and neutrinos, the software data acquisition (DAQ) system of the IceCube Neutrino Observatory forms triggers on patterns of Cherenkov light deposition in the detector based on temporal and/or spatial coincidences. Here we describe the algorithms used for triggering, as well as the fast merging algorithm used to combine the time-ordered hit streams from the optical modules. We also present recently implemented and planned modifications of the DAQ that take advantage of our newly upgraded multi-core computer systems at the South Pole. © 2014 AIP Publishing LLC.

Sandstrom P.,Wisconsin IceCube Particle Astrophysics Center
AIP Conference Proceedings | Year: 2014

The Precision IceCube Next Generation Upgrade (PINGU) will require optical sensors with similar performance as the digital optical modules (DOMs) of IceCube, but implemented in a higher-density array. A new design for the PINGU DOM (PDOM) is being pursued that retains the proven mechanical elements of the IceCube DOM, yet takes advantage of recently commercialized high-speed digitizer technology. The main features of the proposed PDOM electronics are discussed, along with status and plans for development. Proposed modifications to the IceCube string architecture that will accommodate the smaller vertical PDOM spacing are presented. © 2014 AIP Publishing LLC.

Ahlers M.,University of Wisconsin - Madison | Ahlers M.,Wisconsin IceCube Particle Astrophysics Center | Bai Y.,University of Wisconsin - Madison | Barger V.,University of Wisconsin - Madison | Lu R.,University of Wisconsin - Madison
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2016

We study the contribution of Galactic sources to the flux of astrophysical neutrinos recently observed by the IceCube Collaboration. We show that in the simplest model of homogeneous and isotropic cosmic ray diffusion in the Milky Way the Galactic diffuse neutrino emission consistent with γ-ray (Fermi-LAT) and cosmic ray data (KASCADE, KASCADE-Grande and CREAM) is expected to account for only 4%-8% of the IceCube flux above 60 TeV. Direct neutrino emission from cosmic-ray-gas (pp) interactions in the sources will require an unusually large average opacity above 0.01. On the other hand, we find that the IceCube events already probe Galactic neutrino scenarios via the distribution of event arrival directions. Based on the latter, we show that most Galactic scenarios can only have a limited contribution to the astrophysical signal: diffuse Galactic emission (50%), quasidiffuse emission of neutrino sources (65%), extended diffuse emission from the Fermi bubbles (25%) or unidentified TeV γ-ray sources (25%). The arguments discussed here leave, at present, dark matter decay unconstrained. © 2016 American Physical Society.

Bai Y.,University of Wisconsin - Madison | Salvado J.,University of Wisconsin - Madison | Salvado J.,Wisconsin IceCube Particle Astrophysics Center | Stefanek B.A.,University of Wisconsin - Madison
Journal of Cosmology and Astroparticle Physics | Year: 2015

Although there is overwhelming evidence of dark matter from its gravitational interaction, we still do not know its precise gravitational interaction strength or whether it obeys the equivalence principle. Using the latest available cosmological data and working within the framework of ΛCDM, we first update the measurement of the multiplicative factor of cosmology-relevant Newton's constant over the standard laboratory-based value and find that it is consistent with one. In general relativity, dark matter equivalence principle breaking can be mimicked by a long-range dark matter force mediated by an ultra light scalar field. Using the Planck three year data, we find that the dark matter ''fifth-force'' strength is constrained to be weaker than 10-4 of the gravitational force. We also introduce a phenomenological, post-Newtonian two-fluid description to explicitly break the equivalence principle by introducing a difference between dark matter inertial and gravitational masses. Depending on the decoupling time of the dark matter and ordinary matter fluids, the ratio of the dark matter gravitational mass to inertial mass is constrained to be unity at the 10-6 level.

Ahlers M.,Wisconsin IceCube Particle Astrophysics Center | Ahlers M.,University of Wisconsin - Madison | Halzen F.,Wisconsin IceCube Particle Astrophysics Center | Halzen F.,University of Wisconsin - Madison
Reports on Progress in Physics | Year: 2015

We appraise the status of high-energy neutrino astronomy and summarize the observations that define the 'IceCube puzzle.' The observations are closing in on the source candidates that may contribute to the observation. We highlight the potential of multi-messenger analysis to assist in the identification of the sources. We also give a brief overview of future search strategies that include the realistic possibility of constructing a next-generation detector larger by one order of magnitude in volume. © 2015 IOP Publishing Ltd.

Bai Y.,University of Wisconsin - Madison | Barger A.J.,University of Wisconsin - Madison | Barger A.J.,University of Hawaii at Manoa | Barger V.,University of Wisconsin - Madison | And 4 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We investigate whether a subset of high-energy events observed by IceCube may be due to neutrinos from Sagittarius A∗. We check both spatial and temporal coincidences of IceCube events with other transient activities of Sagittarius A∗. Among the seven IceCube shower events nearest to the Galactic center, we have found that event 25 has a time very close to (around three hours after) the brightest x-ray flare of Sagittarius A∗ observed by the Chandra X-ray Observatory with a p-value of 0.9%. Furthermore, two of the seven events occurred within one day of each other (there is a 1.6% probability that this would occur for a random distribution in time). Thus, the determination that some IceCube events occur at similar times as x-ray flares and others occur in a burst could be the smoking gun that Sagittarius A∗ is a point source of very-high-energy neutrinos. We point out that if IceCube Galactic center neutrino events originate from charged pion decays, then TeV gamma rays should come from neutral pion decays at a similar rate. We show that the CTA, HAWC, H.E.S.S. and VERITAS experiments should be sensitive enough to test this. © 2014 American Physical Society.

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