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The \textsc{Atlas} discovery potential for the hadronic decay of a heavy charged Higgs boson, H , is presented. A new matched production algorithm for the processes ggtbH and gbtH is used allowing to span the investigated mass range from mHmt up to mHmt with a consistent treatment of the transition region. For the considered charged Higgs boson masses from 165 to 600 GeV, H is the most relevant decay channel together with Htb . Whereas the latter suffers from large irreducible backgrounds, the decay channel offers a decisively cleaner signature. This is the first \textsc{Atlas} Full Simulation study of the H channel. For the background, \textsc{Atlas} Fast Simulation is used for the investigation of a greater variety of channels than in previous studies, emphasizing the need for new selection cuts with additional discriminating power between signal and background. Such cuts are introduced and it is shown that current limits from direct charged Higgs boson searches can be substantially extended already with a few years of LHC data.

The discovery of a charged Higgs boson would be tangible proof of physics beyond the Standard Model. This note presents the ATLAS potential for discovering a charged Higgs boson, utilizing five different final states of the signal arising from the three dominating fermionic decay modes of the charged Higgs boson. The search covers the region below the top quark mass, taking into account the present experimental constraints, the transition region with a charged Higgs boson mass of the order of the top quark mass, and the high-mass region with a charged Higgs boson mass up to 600 GeV. All studies are performed with a realistic simulation of the detector response including all three trigger levels and taking into account all dominant systematic uncertainties. Results are given in terms of discovery and exclusion contours for each channel individually and for all channels combined, showing that the ATLAS experiment is capable of detecting the charged Higgs boson in a significant fraction of the (tanb, mH±) parameter space with its first 10 fb−1 of data. The so-called intermediate tanb region (around tanb = 7) is experimentally hard to reach but exclusion sensitivity is given in this area.

Charged Higgs bosons are predicted in models beyond the Standard Model, for example in two-Higgs-doublet models and specifically in Minimal Supersymmetric extensions of the Standard Model (MSSM). We have applied an Iterative Discriminant Analysis (IDA) method with the aim to study how the use of this multivariate method can improve on the sequential-cut-based method. The IDA method has been used to optimize the signal efficiency and background rejection in a charged Higgs boson discovery analysis for Higgs masses in the range 165 GeV to 600 GeV. The analysis is based on high-statistics Monte Carlo data and a fast detector simulation. The performance of the IDA results is compared with that of a recent sequential-cut-based analysis.

The tau identification in two distinct high-multiplicity environments, pile-up and ttbar events, is investigated. The tau ID performance in such environments is known to be degraded. It is shown that it is necessary to adjust the tau ID quality cut in order to reach a working point in terms of tau efficiency versus jet rejection comparable to more frequently investigated and cleaner types of events like Z->tautau and W->taunu. Three different ways of recovering performance and robustness are investigated: Firstly, the usage of dedicated probability density functions as input to the tau likelihood method is tested, obtained from Z->tautau events with pile-up and ttbar events. Effects are generally small, except for high-pT tau jets in ttbar events. Secondly, it is investigated whether likelihood input variables can be removed without reducing performance (to increase robustness and reduce systematic uncertainties), and thirdly, whether adding new variables or replacing existing variables with new variables can lead to increased performance in terms of jet rejection at fixed tau efficiency. It is shown that several variables are redundant for tau identification in high-multiplicity environments. At least one variable is identified which can efficiently replace one of the existing variables in high-multiplicity events, namely the fraction of energy deposited in a wider isolation cone than used by the default tau identification.

Standard Model-like decays of a top quark pair with tau leptons are the dominant background for most charged Higgs boson searches. It is shown that the background can be emulated starting from a pure ttbar->bmunu bW sample by replacing tracks and calorimeter cells on an ESD (Event Summary Data) level in close vicinity to the muon with those of a simulated tau lepton. ATLAS reconstruction algorithms are then re-run to provide higher-level objects, eliminating the need of ad-hoc corrections to the missing energy. Relevant distributions like top quark invariant masses, tau jet properties and missing transverse energy can be reproduced within a 10% level.

A grid is defined as being 'coordinated resource sharing and problem solving in dynamic, multi-institutional virtual organizations'. Over recent years a number of grid projects, many of which have a strong regional presence, have emerged to help coordinate institutions and enable grids. Today, we face a situation where a number of grid projects exist, most of which are using slightly different middleware. Grid interoperation is trying to bridge these differences and enable Virtual Organizations to access resources at the institutions independent of their grid project affiliation. Grid interoperation is usually a bilateral activity between two grid infrastructures. Recently within the Open Grid Forum, the Grid Interoperability Now (GIN) Community Group is trying to build upon these bilateral activities. The GIN group is a focal point where all the infrastructures can come together to share ideas and experiences on grid interoperation. It is hoped that each bilateral activity will bring us one step closer to the overall goal of a uniform grid landscape. A fundamental aspect of a grid is the information system, which is used to find available grid services. As different grids use different information systems, interoperation between these systems is crucial for grid interoperability. This paper describes the work carried out to overcome these differences between a number of grid projects and the experiences gained. It focuses on the different techniques used and highlights the important areas for future standardization.