62691127
Computing for the next generation flavour factories
The next generation of Super Flavor Factories, like SuperB and SuperKEKB, present significant computing challenges. Extrapolating the BaBar and Belle experience to the SuperB nominal luminosity of 1036 cm−2s−1, we estimate that the data size collected after a few years of operation is 200 PB and the amount of CPU required to process them of the order of 2000 KHep-Spec06. Already in the current phase of detector design, the amount of simulated events needed for estimating the impact on very rare benchmark channels is huge and has required the development of new simulation tools and the deployment of a worldwide production distributed system. With the collider is in operation, very large data set have to be managed and new technologies with potential large impact on the computational models, like the many core CPUs, need to be effectively exploited. In addition SuperB, like the LHC experiments, will have to make use of distributed computing resources accessible via the Grid infrastructures while providing an efficient and reliable data access model to its final users. To explore the key issues, a dedicated R&D program has been launched and is now in progress. A description of the R&D goals and the status of ongoing activities is presented.
110445306
The distributed production system of the SuperB project: description and results
The SuperB experiment needs large samples of MonteCarlo simulated events in order to finalize the detector design and to estimate the data analysis performances. The requirements are beyond the capabilities of a single computing farm, so a distributed production model capable of exploiting the existing HEP worldwide distributed computing infrastructure is needed. In this paper we describe the set of tools that have been developed to manage the production of the required simulated events. The production of events follows three main phases: distribution of input data files to the remote site Storage Elements (SE); job submission, via SuperB GANGA interface, to all available remote sites; output files transfer to CNAF repository. The job workflow includes procedures for consistency checking, monitoring, data handling and bookkeeping. A replication mechanism allows storing the job output on the local site SE. Results from 2010 official productions are reported.
62980375
ATLAS detector simulation: status and outlook
The simulation program for the ATLAS experiment at CERN is currently in a full operational mode and integrated into the ATLAS's 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 needs to tackle, in a common way, different full ATLAS simulations setups, test beams and cosmic ray studies. 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
118593923
Magnetic Fields at First Order Phase Transition: A Threat to Electroweak Baryogenesis
The generation of the observed baryon asymmetry may have taken place during the electroweak phase transition, thus involving physics testable at LHC, a scenario dubbed electroweak baryogenesis. In this paper we point out that the magnetic field which is produced in the bubbles of a first order phase transition endangers the baryon asymmetry produced in the bubble walls. The reason being that the produced magnetic field couples to the sphaleron magnetic moment and lowers the sphaleron energy; this strengthens the sphaleron transitions inside the bubbles and triggers a more effective wash out of the baryon asymmetry. We apply this scenario to the Minimal Supersymmetric extension of the Standard Model (MSSM) where, in the absence of a magnetic field, successful electroweak baryogenesis requires the lightest CP-even Higgs and the right-handed stop masses to be lighter than about 127 GeV and 120 GeV, respectively. We show that even for moderate values of the magnetic field, the Higgs mass required to preserve the baryon asymmetry is below the present experimental bound. As a consequence electroweak baryogenesis within the MSSM should be confronted on the one hand to future measurements at the LHC on the Higgs and the right-handed stop masses, and on the other hand to more precise calculations of the magnetic field produced at the electroweak phase transition.
119185656
Conditional probabilities in the excursion set theory: generic barriers and non-Gaussian initial conditions
The excursion set theory, where density perturbations evolve stochastically with the smoothing scale, provides a method for computing the dark matter halo mass function. The computation of the mass function is mapped into the so-called first-passage time problem in the presence of a moving barrier. The excursion set theory is also a powerful formalism to study other properties of dark matter haloes such as halo bias, accretion rate, formation time, merging rate and the formation history of haloes. This is achieved by computing conditional probabilities with non-trivial initial conditions, and the conditional two-barrier first-crossing rate. In this paper we use the path integral formulation of the excursion set theory to calculate analytically these conditional probabilities in the presence of a generic moving barrier, including the one describing the ellipsoidal collapse, and for both Gaussian and non-Gaussian initial conditions. While most of our analysis associated with Gaussian initial conditions assumes Markovianity (top-hat in momentum space smoothing, rather than generic filters), the non-Markovianity of the random walks induced by non-Gaussianity is consistently accounted for. We compute, for a generic barrier, the first two scale-independent halo bias parameters, the conditional mass function and the halo formation time probability, including the effects of non-Gaussianities. We also provide the expression for the two-constant-barrier first-crossing rate when non-Markovian effects are induced by a top-hat filter function in real space.
27622380
Supersymmetric Leptogenesis with a Light Hidden Sector
Supersymmetric scenarios incorporating thermal leptogenesis as the origin of the observed matter-antimatter asymmetry generically predict abundances of the primordial elements which are in conflict with observations. In this paper we propose a simple way to circumvent this tension and accommodate naturally thermal leptogenesis and primordial nucleosynthesis. We postulate the existence of a light hidden sector, coupled very weakly to the Minimal Supersymmetric Standard Model, which opens up new decay channels for the next-to-lightest supersymmetric particle, thus diluting its abundance during nucleosynthesis. We present a general model-independent analysis of this mechanism as well as two concrete realizations, and describe the relevant cosmological and astrophysical bounds and implications for this dark matter scenario. Possible experimental signatures at colliders and in cosmic-ray observations are also discussed.
109930494
Interpretation of AMS-02 results: correlations among dark matter signals
The AMS-02 collaboration has recently released data on the positron fraction e+/(e−+e+) up to energies of about 350 GeV. If one insists on interpreting the observed excess as a dark matter signal, then we find it is best described by a TeV-scale dark matter annihilating into τ+τ−, although this situation is already severely constrained by gamma-ray measurements.The annihilation into μ+μ− is allowed by gamma-rays more than τ+τ−, but it gives a poorer fit to AMS-02 data. Moreover, since electroweak corrections induce correlations among the fluxes of stable particles from dark matter annihilations, the recent AMS-02 data imply a well-defined prediction for the correlated flux of antiprotons. Under the assumption that their future measurements will not show any antiproton excess above the background, the dark matter interpretation of the positron rise will possibly be ruled out by only making use of data from a single experiment. This work is the first of a program where we emphasize the role of correlations among dark matter signals.
9467477
Benchmarks for dark matter searches at the LHC
A bstractWe propose some scenarios to pursue dark matter searches at the LHC in a fairly model-independent way. The first benchmark case is dark matter co-annihilations with coloured particles (gluinos or squarks being special examples). We determine the masses that lead to the correct thermal relic density including, for the first time, strong Sommerfeld corrections taking into account colour decomposition. In the second benchmark case we consider dark matter that couples to SM particles via the Z or the Higgs. We determine the couplings allowed by present experiments and discuss future prospects. Finally we present the case of dark matter that freezes out via decays and apply our results to invisible Z and Higgs decays.