Aspects of GMSB Phenomenology at TeV Colliders

The status of two on-going studies concerning important aspects of the phenomenology of gauge-mediated supersymmetry breaking (GMSB) models at TeV colliders is reported. The first study deals with the characteristics of the light Higgs boson spectrum allowed by the (minimal and non-minimal) GMSB framework. Today's most accurate GMSB model generation and two-loop Feynman-diagrammatic calculation of m_h have been combined. The Higgs masses are shown in dependence of various model parameters at the messenger and electroweak scales. In the minimal model, an upper limit on m_h of about 124 GeV is found for m_t = 175 GeV. The second study is focused on the measurement of the fundamental SUSY breaking scale sqrt(F) at the LHC in the GMSB scenario where a stau is the next-to-lightest SUSY particle (NLSP) and decays into a gravitino with c*tau_NLSP in the range 0.5 m to 1 km. This implies the measurement of mass and lifetime of long lived sleptons. The identification is performed by determining the time of flight in the ATLAS muon chambers. Accessible range and precision on sqrt(F) achievable with a counting method are assessed.Comment: 22 pages, 9 figures (12 eps files). Report of the GMSB SUSY Working Group, Workshop "Physics at TeV Colliders", Les Houches, 7-18 June 1999. Revised version v3: A few typos correcte

Signature of Sub GeV Dark Matter particles at LHC and TEVATRON

In this letter, we investigate the production of light dark matter particles at LHC in light of the model (N = 2 SUSY inspired) proposed in Ref. [1] and demonstrate that they will be copiously produced if the colored messengers Fq are lighter than 1 TeV. We expect up to a million events if the Fq mass is about 500 GeV, assuming a ~1 inverse fb luminosity. In addition, we show that, even if the Fq mass is above a few TeV, searches for Fq production at LHC are promising because a kinematical signature can be used to separate the signal from background. This signature is similar to that expected in supersymmetric scenarios. Hence, our study shows that most of the Fq mass range could be constrained using LHC data. This should encourage further studies since they could infirm/confirm the MeV DM scenario.Comment: 4 page

Measuring the SUSY Breaking Scale at the LHC in the Slepton NLSP Scenario of GMSB Models

We report a study on the measurement of the SUSY breaking scale sqrt(F) in the framework of gauge-mediated supersymmetry breaking (GMSB) models at the LHC. The work is focused on the GMSB scenario where a stau is the next-to-lightest SUSY particle (NLSP) and decays into a gravitino with lifetime c*tau_NLSP in the range 0.5 m to 1 km. We study the identification of long-lived sleptons using the momentum and time of flight measurements in the muon chambers of the ATLAS experiment. A realistic evaluation of the statistical and systematic uncertainties on the measurement of the slepton mass and lifetime is performed, based on a detailed simulation of the detector response. Accessible range and precision on sqrt(F) achievable with a counting method are assessed. Many features of our analysis can be extended to the study of different theoretical frameworks with similar signatures at the LHC.Comment: 28 pages, 12 figures (18 eps files). Revised version v2(published in JHEP): Some important corrections and additions to v

Fast shower simulation in the ATLAS calorimeter

The time to simulate pp collisions in the ATLAS detector is largely dominated by the showering of electromagnetic particles in the heavy parts of the detector, especially the electromagnetic barrel and endcap calorimeters. Two procedures have been developed to accelerate the processing time of electromagnetic particles in these regions: (1) a fast shower parameterisation and (2) a frozen shower library. Both work by generating the response of the calorimeter to electrons and positrons with Geant 4, and then reintroduce the response into the simulation at runtime. In the fast shower parameterisation technique, a parameterisation is tuned to single electrons and used later by simulation. In the frozen shower technique, actual showers from low-energy particles are used in the simulation. Full Geant 4 simulation is used to develop showers down to ~1 GeV, at which point the shower is terminated by substituting a frozen shower. Judicious use of both techniques over the entire electromagnetic portion of the ATLAS calorimeter produces an important improvement of CPU time. We discuss the algorithms and their performance in this paper

ATLAS Simulation readiness for first data at LHC

The commissioning phase for the ATLAS experiment, in preparation for the new LHC machine to switch on, has presented challenges to nearly every aspect of the software development. The ATLAS simulation program, as a part of this phase, is now operational and fully functional within the ATLAS common software framework, Athena. The latest developments are directed towards enhanced versatility to cope with the increasing needs of developers and users and ease of use for the large ATLAS community, now with more than 2000 potential users. Emphasis in this talk is on recently added functionality recently added, validation and production strategy, and improved robustness and maintainability

Propiedades de la membrana y viabilidad celular: Importancia de la fluidez

Numerosos estudios sugieren que las vías de señalización y por ende la funcionalidad celular dependen de la organización de dominios en la membrana, que a su vez está determinada por la composición lipídica de la misma. El colesterol (Col) interviene en la regulación de la fluidez al particionar de manera selectiva en dominios específicos de la membrana, y se ha demostrado que su homeostasis es crucial para la viabilidad celular. Además, se sabe que el exceso de Col puede resultar citotóxico. Este lípido no puede ser degradado o utilizado como combustible, por lo que su exceso debe ser removido por aceptores o almacenado en compartimientos intracelulares. Las lipoproteínas de alta densidad (HDL) y en particular su apolipoproteína mayoritaria, la apoA-I, cumplen un rol fundamental en el transporte reverso del Col, que consiste en transportar el excedente desde los tejidos periféricos hacia el hígado para su eliminación en forma de sales biliares, o para ser redirigido desde los hepatocitos hacia los tejidos esteroidogénicos

Heterogeneity of resting and hyperemic myocardial blood flow in healthy humans

Objective: Absolute myocardial blood flow (MBF) is not well-defined in large normal populations, and appears to be heterogeneous in both humans and animals. These factors contribute to the difficulties in defining resting MBF to hibernating myocardium. We therefore assessed absolute baseline and hyperemic MBF in a large population of normal humans. Methods: MBF was quantified by positron emission tomography with oxygen-15-labeled water at baseline and during hyperemia induced by either adenosine or dipyridamole in 131 men and 38 women, aged 21-86 (mean 46±12) years. MBF was corrected for workload using the rate-pressure product (RPP). Results: Uncorrected baseline MBF ranged from 0.590 to 2.050 (mean 0.985±0.230) ml/min/g (coefficient of variation=27%), and corrected MBF from 0.736 to 2.428 (mean 1.330±0.316) ml/min/g (coefficient of variation=24%). MBF in the inferior region was significantly (P<0.0001) lower than either the anterior or lateral regions. Baseline MBF in females was significantly (P<0.001) higher than in males. Conclusions: These results confirm the heterogeneity of MBF in normals and highlight the difficulty in establishing the lower limit of normal MB

Interactions of Heavy Hadrons using Regge Phenomenology and the Quark Gluon String Model

The search for stable heavy exotic hadrons is a promising way to observe new physics processes at collider experiments. The discovery potential for such particles can be enhanced or suppressed by their interactions with detector material. This paper describes a model for the interactions in matter of stable hadrons containing an exotic quark of charges $\pm {1/3}e$ or $\pm {2/3}e$ using Regge phenomenology and the Quark Gluon String Model. The influence of such interactions on searches at the LHC is also discussed

The ATLAS Simulation: an LHC Challenge

The simulation program for the ATLAS experiment at CERN is currently in a full operational mode and integrated into the ATLAS common analysis framework, Athena. The OO approach, based on GEANT4, and in use during the DC2 data challenge has been interfaced within Athena and to GEANT4 using the LCG dictionaries and Python scripting. The robustness of the application was proved during the DC2 data challenge. The Python interface has added the flexibility, modularity and interactivity that the simulation tool requires in order to be able to provide a common implementation of different full ATLAS simulation setups, test beams and cosmic ray applications. Generation, simulation and digitization steps were exercised for performance and robustness tests. The comparison with real data has been possible in the context of the ATLAS Combined Test Beam (2004) and ongoing cosmic ray studies