55280135
Discovery of TeV gamma-ray emission from PKS 0447-439 and derivation of an upper limit on its redshift
Very high-energy gamma-ray emission from PKS 0447-439 was detected with the H. E. S. S. Cherenkov telescope array in December 2009. This blazar is one of the brightest extragalactic objects in the ...
118516643
Anisotropies in the diffuse gamma-ray background from dark matter with Fermi LAT: a closer look
This thesis addresses the isotropic diffuse gamma-ray background, as measured by the Fermi gamma ray space telescope, and its implications for indirect detection of dark matter. We describe the measurement of the isotropic background, including also an alternative analysis method besides the one published by the Fermi-LAT collaboration. The measured isotropic diffuse background is compatible with a power law differential energy spectrum with a spectral index of -2.41 ± 0.05 and -2.39 ± 0.08, for the two analysis methods respectively. This is a softer spectrum than previously reported by the EGRET experiment. This rules out any dominant contribution with a significantly different shape, e.g. from dark matter, in the energy range 20 MeV to 102.4 GeV. Instead we present upper limits on a signal originating from annihilating dark matter of extragalactic origin. The uncertainty in the dark matter signal is primarily dependent on the cosmological evolution of the dark matter distribution. We use recent N-body simulations of structure formation, as well as a semi-analytical calculation, to assess this uncertainty. We investigate three main annihilation channels and find that in some, but not in all, of our scenarios we can start to probe, and sometimes rule out, interesting parameter spaces of particle physics models beyond the standard model.We also investigate the possibility to use the angular anisotropies of the annihilation signal to separate it from a background originating from conventional sources, e.g. from active galactic nuclei. By carefully modelling the performance of the Fermi gamma-ray space telescope and galactic foregrounds we find that this method could be as sensitive as using information from the energy spectrum only.
118846253
Future dark matter searches with the GLAST-LAT
The Large Area Telescope, one of two instruments on the Gamma-ray Large Area Space Telescope mission, scheduled for launch by NASA in early 2008, is a high-energy gamma-ray telescope, sensitive to an energy range from approximately 20 MeV to more than 300 GeV and exceeding the sensitivity of its predecessor EGRET by nearly two orders of magnitude. Annihilation of Weakly Interacting Massive Particles (WIMP), predicted in many extensions of the Standard Model of Particle Physics, may give rise to a signal in gamma-ray spectra from many cosmic sources. In this contribution we give an overview of the searches for WIMP Dark Matter performed by the GLAST-LAT collaboration, in particular we discuss the sensitivity of GLAST to thermal WIMP dark matter in the galactic center and to high energy (50 -150 GeV) gamma-ray lines resulting from WIMP pair annihilation into two gamma-rays.
117090989
Statistical analysis of detection of, and upper limits on, dark matter lines
In this note we present calculations of coverage and power for three different methods which could be used to calculate upper limits and/or claim discovery in a GLAST‐LAT search for a dark matter line. The methods considered are Profile Likelihood, Bayesian factors and likelihood ratio confidence intervals and the calculations are done considering a simple benchmark model of two uncorrelated Poissonian measurements. Profile likelihood has the best coverage properties, the standard χ2 test the worst. For the power, the situation is vice‐versa. In choosing a method one has to consider the false detection rate (1 ‐ coverage) and counterweigh it to the possible achievable power.
18437847
Fluctuation studies and energy reconstruction in a segmented calorimeter
In order to better understand energy estimation of electromagnetic showers in segmented calorimeters, detailed Geant4 simulation studies of electromagnetic showers in the energy range 1-100 GeV in CsI have been performed. When sampled in layers of 1.99 cm thickness, corresponding to 1.08 radiation lengths, the energy fluctuations in the samples show distributions that vary significantly with depth. The energy distributions are similar for incident electrons and photons and were found to change systematically along the shower, varying little with the initial energy. Three probability distributions have been fitted to the data: negative binomial, log-normal and Gaussian distributions, none of which gives a good fit over the full shower length. The obtained parameterizations might be useful in the use of the maximum likelihood method for estimating the energy. Two methods for estimating the energy have also been studied. One method is based on fitting individual longitudinal shower profiles with a Gamma-function, the other one corrects the measured energy for leakage by utilizing the energy deposited in the last layer. Our simulations indicate that the last-layer correction method applied to photons and electrons of 1 and 10 GeV gives about a factor of 2 improvement in the energy resolution.
120082547
Fermi Gamma-ray Space Telescope sees first light
With exceptional resolution and sensitivity, the latest orbiting gamma-ray telescope based on detection techniques from particle physics is opening a new window on the high-energy universe.
119757503
A review of experimental results on neutrino oscillations
21221936
Neutrino Scattering at High Energies
The construction of a high energy (∼100 GeV), sign‐selected neutrino beam opens exciting opportunities to search for beyond‐standard‐model physics as well as to make valuable QCD measurements. Such a beam can be produced at the Tevatron or, potentially, at the CERN SPS+. The resulting physics would be unique and complementary to the present neutrino program. Here we use neutrino‐electron scattering as an example.
20950520
Photodegradation mechanisms of tetraphenyl butadiene coatings for liquid argon detectors
We report on studies of degradation mechanisms of tetraphenyl butadiene (TPB) coatings of the type used in neutrino and dark matter liquid argon experiments. Using gas chromatography coupled to mass spectrometry we have detected the ultraviolet-blocking impurity benzophenone. We monitored the drop in performance and increase of benzophenone concentration in TPB plates with exposure to ultraviolet (UV) light, and demonstrate the correlation between these two variables. Based on the presence and initially exponential increase in the concentration of benzophenone observed, we propose that TPB degradation is a free radical-mediated photooxidation reaction, which is subsequently confirmed by displaying delayed degradation using a free radical inhibitor. Finally we show that the performance of wavelength-shifting coatings of the type envisioned for the LBNE experiment can be improved by 10-20%, with significantly delayed UV degradation, by using a 20% admixture of 4-tert-Butylcatechol.
208856461
Search for core-collapse supernovae using the MiniBooNE neutrino detector
We present a search for core-collapse supernovae in the Milky Way galaxy, using the MiniBooNE neutrino detector. No evidence is found for core-collapse supernovae occurring in our Galaxy in the period from December 14, 2004 to July 31, 2008, corresponding to 98% live time for collection. We set a limit on the core-collapse supernova rate out to a distance of 13.4 kpc to be less than 0.69 supernovae per year at 90% C.L.
13999234
Recent Results on Neutrino Oscillations
This article reviews the many new results from neutrino oscillation searches which were presented at ICHEP '98. Exciting indications of neutrino oscillations have been seen in the solar neutrino deficit, atmospheric neutrino deficit and LSND excess. These indications and reported limits on oscillations are considered. Attempts to develop a theory which addresses all of the neutrino oscillation data are discussed. Some of the remaining questions and the future experiments which will help answer these questions are described.