8883161
Study of a neutrino mass texture generated in supergravity with bilinear R-parity violation
Abstract.We study a particular texture of the neutrino mass matrix generated in supergravity with non-universal bilinear R-parity violation parameters. The relatively high value of $\tan\beta$ makes the one-loop contribution to the neutrino mass matrix as important as the tree-level one. The atmospheric angle is nearly maximal, and its deviation from maximal mixing is related to the small size of the ratio between the solar and atmospheric mass scales. There is also a common origin for the small values of the solar and reactor angles, but the latter is much smaller due the large mass ratio between the heaviest two neutrinos. There is a high dependence of the neutrino mass differences on the scalar mass m0 and the gaugino mass M1/2, but a smaller dependence of the mixing angles on the same Sugra parameters. Measurements of branching ratios for the neutralino decays can give important information on the parameters of the model. There are good prospects at a future linear collider for these measurements, but a more detailed analysis is necessary for the LHC.
10821211
Commissioning of the ATLAS electron, photon and tau trigger selection
Since March 2010, the ATLAS experiment has been recording proton-proton collisions of the Large Hadron Collider (LHC) at a center of mass energy of 7 TeV. At low instantaneous luminosity, data were selected by the hardware based Level-1 trigger and processed by the software based High Level Trigger (HLT) without active rejection; as the luminosity increased, the HLT rejection has been gradually activated. Since then, electrons from J/ψ, bottom, charm, W and Z decays, prompt photons and a first sample of tau hadronic decays from W have been efficiently selected. This paper gives an overview of the implementation of the electron, photon and tau trigger selection algorithms and of the first experience running these triggers online. The performance of the three trigger levels is discussed and a set of comparisons of the online discriminating variables with offline reconstruction is shown, as well as the comparison of data with the Monte Carlo simulation on which the current selection was tuned.
55245440
Gamma ray bursts : observations and theoretical conjectures
Gamma Ray Bursts (GRBs) are short bursts of very high energy photons which were discovered in the late 1960s. Ever since their discovery, scientists have wondered about their origin. Nowadays it is known that they originate outside the Milky Way because of their high red shift first measured in the afterglows thanks to the Beppo-SAX satellite and ground-based observations. However, theoreticians still do not agree about the mechanism that generates the bursts, and different competing models are animatedly debated. Current GRB experiments include the Swift satellite and the Pierre Auger Observatory that could detect GRBs with an increase of the background. A forthcoming dedicated experiment is GLAST, a satellite observatory for detecting gamma rays with energies up to 300 GeV, whose launch is scheduled for early 2008. 1 Observational progress Gamma Ray Bursts (GRBs) were discovered by the US military satellite Vela in 1967 while monitoring for clandestine tests of nuclear weapons. This information was not released to the scientific community until the following decade. GRBs are among the most energetic known objects ever measured and their origin and mechanism became a puzzle to the community [1, 2]. Fig. 1: GRBs measured by BATSE in Galactic coordinates [3] In the early 1990s the Compton Gamma Ray Observatory (CGRO) was launched and started to unravel these questions. It included four different detectors to measure gamma rays, one of which was BATSE with a 4π sr field of view, 0.3–1.2 MeV energy range, and a precision of 2 degrees. At that moment, not only was the origin of GRBs unknown, but also their location in space, and many scientists speculated that they were explosions occurring within our Galaxy. When the map showing an isotropical distribution of the GRBs as measured by BATSE was published (Fig. 1), it was clear *Work performed as a student project under the supervision of E. Nardi.
126043268
Composition studies of Ultra High Energy Cosmic Rays using Data of the Pierre Auger Observatory
The subject of this work is to estimate the mass composition of Ultra High Energy Cosmic Rays recorded by the surface detector of the Pierre Auger Observatory. The time traces of the surface detector stations are explored to obtain a new observable sensitive to the mass composition. This observable is based on the time it takes for the integrated signal recorded by each one of the stations of the surface detector, to rise from 10% to 50% of the final value, which is known as the risetime, t1/2. The new observable, called ∆1000 is calculated for high quality hybrid events and calibrated with the most mass-sensitive observable recorded by the fluorescence detector, namely the depth of the shower maximum, Xmax. This is the depth in the atmosphere at which the maximum number of particles in the shower is reached. It is demonstrated that with this method one takes advantage of the high statistics provided by the surface detector (100% duty cycle) to obtain a new estimation for the depth of the shower maximum, XSD max. The details of the calibration method, estimations of systematic uncertainties and discussions about fluctuations of the data are presented. Deductions on mass composition, based on comparisons with simulations are presented as well. The results on mass composition obtained by the fluorescence detector (around 13% duty cycle) are corroborated by the surface detector on average basis, pointing to an increase of the mass composition with the energy. Due to the large statistics of the surface detector, the energy range of the Observatory for measuring Xmax could be extended to energies of 80 EeV, i.e. by a factor of 2.3 with respect to the range reached with the analysis of fluorescence data. The mass composition corresponding to energies above 1019.6 eV is found to get heavier but still remains in a mixed mass composition.