Particle theory

Abstract:

We report on a search for extremely-high energy neutrinos with energies greater than 106GeV using the data taken with the IceCube detector at the South Pole. The data was collected between April 2008 and May 2009 with the half-completed IceCube array. The absence of signal candidate events in the sample of 333.5 days of live time significantly improves model-independent limits from previous searches and allows to place a limit on the diffuse flux of cosmic neutrinos with an E-2 spectrum in the energy range 2.0×106-6.3×109GeV to a level of E2φ≤3.6×10 -8GeVcm-2sec-1sr-1. © 2011 American Physical Society.

Abstract:

DAMA observes an annual modulation in their event rate, as might be expected from dark matter scatterings, while CoGeNT has reported evidence for a similar modulation. The simplest interpretation of these findings in terms of dark matter-nucleus scatterings is excluded by other direct detection experiments. We consider the robustness of these exclusions with respect to assumptions regarding the scattering and find that isospin-violating inelastic dark matter helps alleviate this tension and allows marginal compatibility between experiments. Isospin-violation can significantly weaken the XENON constraints, while inelasticity enhances the annual modulation fraction of the signal, bringing the CoGeNT and CDMS results into better agreement.

Abstract:

Between May 2009 and May 2010, the IceCube neutrino detector at the South Pole recorded 32 billion muons generated in air showers produced by cosmic rays with a median energy of 20 TeV. With a data set of this size, it is possible to probe the southern sky for per-mille anisotropy on all angular scales in the arrival direction distribution of cosmic rays. Applying a power spectrum analysis to the relative intensity map of the cosmic ray flux in the southern hemisphere, we show that the arrival direction distribution is not isotropic, but shows significant structure on several angular scales. In addition to previously reported large-scale structure in the form of a strong dipole and quadrupole, the data show small-scale structure on scales between 15 degrees and 30 degrees. The skymap exhibits several localized regions of significant excess and deficit in cosmic ray intensity. The relative intensity of the smaller-scale structures is about a factor of 5 weaker than that of the dipole and quadrupole structure. The most significant structure, an excess localized at right ascension 122.4 degrees and declination -47.4 degrees, extends over at least 20 degrees in right ascension and has a post-trials significance of 5.3 sigma. The origin of this anisotropy is still unknown.

Abstract:

We present the results of time-integrated searches for astrophysical neutrino sources in both the northern and southern skies. Data were collected using the partially completed IceCube detector in the 40-string configuration recorded between 2008 April 5 and 2009 May 20, totaling 375.5 days livetime. An unbinned maximum likelihood ratio method is used to search for astrophysical signals. The data sample contains 36,900 events: 14,121 from the northern sky, mostly muons induced by atmospheric neutrinos, and 22,779 from the southern sky, mostly high-energy atmospheric muons. The analysis includes searches for individual point sources and stacked searches for sources in a common class, sometimes including a spatial extent. While this analysis is sensitive to TeV-PeV energy neutrinos in the northern sky, it is primarily sensitive to neutrinos with energy greater than about 1 PeV in the southern sky. No evidence for a signal is found in any of the searches. Limits are set for neutrino fluxes from astrophysical sources over the entire sky and compared to predictions. The sensitivity is at least a factor of two better than previous searches (depending on declination), with 90% confidence level muon neutrino flux upper limits being between E 2 dΦ/dE ∼ 2-200 × 10 -12 TeV cm-2 s-1 in the northern sky and between 3-700 × 10-12 TeV cm-2 s-1 in the southern sky. The stacked source searches provide the best limits to specific source classes. The full IceCube detector is expected to improve the sensitivity to dΦ/dEE ∝ -2 sources by another factor of two in the first year of operation. © 2011. The American Astronomical Society. All rights reserved.