342 research outputs found
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
All-sky search for time-integrated neutrino emission from astrophysical sources with 7 years of IceCube data
Since the recent detection of an astrophysical flux of high energy neutrinos,
the question of its origin has not yet fully been answered. Much of what is
known about this flux comes from a small event sample of high neutrino purity,
good energy resolution, but large angular uncertainties. In searches for
point-like sources, on the other hand, the best performance is given by using
large statistics and good angular reconstructions. Track-like muon events
produced in neutrino interactions satisfy these requirements. We present here
the results of searches for point-like sources with neutrinos using data
acquired by the IceCube detector over seven years from 2008--2015. The
discovery potential of the analysis in the northern sky is now significantly
below , on average
lower than the sensitivity of the previously published analysis of four
years exposure. No significant clustering of neutrinos above background
expectation was observed, and implications for prominent neutrino source
candidates are discussed.Comment: 19 pages, 17 figures, 3 tables; ; submitted to The Astrophysical
Journa
Neutrinos and Cosmic Rays Observed by IceCube
The core mission of the IceCube Neutrino observatory is to study the origin
and propagation of cosmic rays. IceCube, with its surface component IceTop,
observes multiple signatures to accomplish this mission. Most important are the
astrophysical neutrinos that are produced in interactions of cosmic rays, close
to their sources and in interstellar space. IceCube is the first instrument
that measures the properties of this astrophysical neutrino flux, and
constrains its origin. In addition, the spectrum, composition and anisotropy of
the local cosmic-ray flux are obtained from measurements of atmospheric muons
and showers. Here we provide an overview of recent findings from the analysis
of IceCube data, and their implications on our understanding of cosmic rays.Comment: Review article, to appear in Advances in Space Research, special
issue "Origins of Cosmic Rays
Lowering IceCubeâs energy threshold for point source searches in the southern sky
Observation of a point source of astrophysical neutrinos would be a "smoking gun" signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current nu(mu) interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (similar to 100 TeV) starting event in the sample found that this event alone represents a 2.8 sigma deviation from the hypothesis that the data consists only of atmospheric background
Search for astrophysical sources of neutrinos using cascade events in IceCube
The IceCube neutrino observatory has established the existence of a flux of
high-energy astrophysical neutrinos inconsistent with the expectation from
atmospheric backgrounds at a significance greater than . This flux has
been observed in analyses of both track events from muon neutrino interactions
and cascade events from interactions of all neutrino flavors. Searches for
astrophysical neutrino sources have focused on track events due to the
significantly better angular resolution of track reconstructions. To date, no
such sources have been confirmed. Here we present the first search for
astrophysical neutrino sources using cascades interacting in IceCube with
deposited energies as small as 1 TeV. No significant clustering was observed in
a selection of 263 cascades collected from May 2010 to May 2012. We show that
compared to the classic approach using tracks, this statistically-independent
search offers improved sensitivity to sources in the southern sky, especially
if the emission is spatially extended or follows a soft energy spectrum. This
enhancement is due to the low background from atmospheric neutrinos forming
cascade events and the additional veto of atmospheric neutrinos at declinations
.Comment: 14 pages, 9 figures, 1 tabl
The contribution of Fermi-2LAC blazars to the diffuse TeV-PeV neutrino flux
The recent discovery of a diffuse cosmic neutrino flux extending up to PeV
energies raises the question of which astrophysical sources generate this
signal. One class of extragalactic sources which may produce such high-energy
neutrinos are blazars. We present a likelihood analysis searching for
cumulative neutrino emission from blazars in the 2nd Fermi-LAT AGN catalogue
(2LAC) using an IceCube neutrino dataset 2009-12 which was optimised for the
detection of individual sources. In contrast to previous searches with IceCube,
the populations investigated contain up to hundreds of sources, the largest one
being the entire blazar sample in the 2LAC catalogue. No significant excess is
observed and upper limits for the cumulative flux from these populations are
obtained. These constrain the maximum contribution of the 2LAC blazars to the
observed astrophysical neutrino flux to be or less between around 10
TeV and 2 PeV, assuming equipartition of flavours at Earth and a single
power-law spectrum with a spectral index of . We can still exclude that
the 2LAC blazars (and sub-populations) emit more than of the observed
neutrinos up to a spectral index as hard as in the same energy range.
Our result takes into account that the neutrino source count distribution is
unknown, and it does not assume strict proportionality of the neutrino flux to
the measured 2LAC -ray signal for each source. Additionally, we
constrain recent models for neutrino emission by blazars.Comment: 18 pages, 22 figure
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