1,721,255 research outputs found
Tracking and flavour tagging selection in the ATLAS High Level Trigger
Full text linkIn high-energy physics experiments, track based selection in the online environment is crucial for the efficient real time selection of the rare physics process of interest. This is of particular importance at the Large Hadron Collider (LHC), where the increasingly harsh collision environment is challenging the experiments to improve the performance of their online selection. Principal among these challenges is the increasing number of interactions per bunch crossing, known as pileup. In the ATLAS experiment the challenge has been addressed with multiple strategies. Firstly, specific trigger objects have been improved by building algorithms using detailed tracking and vertexing in specific detector regions to improve background rejection without loosing signal efficiency. Secondly, since 2015 all trigger areas have benefited from a new high performance Inner Detector (ID) software tracking system implemented in the High Level Trigger. Finally, performance will be further enhanced in future by the installation and commissioning of a hardware based Fast TracKer (FTK) throughout 2017.\\ This presentation will focus on the performance of the ID tracking software as well as looking ahead to projected improvements from FTK. Specific focus will be given to the case of flavour tagging of b-jets, as an example of the implementation of novel algorithms to improve vertexing and light-jet rejection in real time
Integration and Commissioning of the Fast TracKer system
Full text linkThe Fast TracKer (FTK) system is a track reconstruction processor able to perform full event tracking synchronously with the ATLAS Level 1 trigger acceptance rate. The high quality tracks produced by the system will be used by the High Level Trigger algorithms to improve the iden- tification of physics objects such as b-jets and taus, as well as to help mitigating the effects of pile-up. The combinatorial challenge of global track fitting requires the use of a custom designed track processor. The idea behind the Fast TracKer system is to simulate all possible tracks before an ATLAS data taking run. During the actual data-taking, the hits coming from the detector are compared with the hits expected from the simulated tracks. This comparison or ‘pattern match- ing’ is then followed by a two step linearized track fit. This task is executed by a system of seven custom electronics board types that will process data from the Inner Detector at the 100 kHz rate of the Level 1 trigger. Currently, the FTK system is under installation and commissioning into the ATLAS Data Acquisition System. The status of the system integration is presented and a review of the first data collected by the FTK system is shown
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Studies on H-->bb decay and VH production with the ATLAS detector
No full textThe ATLAS experiment physics program can be summarized into two goals: the test of the Standard Model and the search for Beyond the Standard Model (BSM) physics signatures. Both aspects are tackled in this thesis as the first part of the work is dedicated to the measurement of the Higgs boson decay to a couple of b-quarks as predicted by the SM, while another part addresses the search for deviations in the Higgs boson production and decay in a phase space highly sensitive to BSM effects. In this thesis, the Higgs boson decay into two b-quarks is studied in the associated production with a vector boson (W or Z) decaying into leptons. Two complementary strategies have been developed and they are indicated as resolved and merged analysis. In the resolved analysis the Higgs boson decay products are reconstructed as two separate objects (b-jets) while in the merged analysis, designed for the high energy phase space, the two b-jets produced by the highly boosted Higgs boson tend to coalesce and are reconstructed as a single large jet. The resolved analysis search led to the first observation of the Higgs boson decay into two b-quarks and to the first observation of the VH production.
The data sample used for the H-->bb search has also been used to perform measurements of the VH cross-section in bins of the V-boson transverse momentum. This measurement, exploiting the so-called Simplified Template Cross Section framework, is designed to investigate possible BSM effects
Measurement of the diboson pp-->WW+WZ production cross section in the semileptonic decay channel at sqrt{s}=8 TeV with the ATLAS detector
No full textThe Large Hadron Collider (LHC) is a particle accelerator designed as a high energy, high intensity proton-proton collider. The study of the diboson production at LHC provides an important test of the electroweak interaction structure at high energies. The goal of this thesis is to measure the diboson production cross section in the semileptonic decay channel using the data collected by the ATLAS detector at LHC at a center-of-mass energy TeV.\\
Beside providing an important test of the Standard Model structure the diboson measurement also stands as a mean to detect new physics signals that could be unravelled through the measurement of an anomalous Triple Gauge Coupling. The study of the and processes is also important for the searches of new physics or Higgs physics where the diboson production may stand as irreducible backgrounds.\\
In the semileptonic decay channel a W decays into a lepton and a neutrino and the other boson (W or Z) decays into hadrons.
This final state is typically reconstructed by one lepton, large missing transverse energy, and two separate jets produced from the hadronically decayed boson. At sufficiently high transverse momentum, the decay products of the hadronically decaying boson become too close to each other and it is difficult to resolve them as two separate jets. This thesis focuses on events where the hadronically decaying boson has high transverse momentum and is reconstructed as a single jet with a large cone. The properties of the substructure of such a jet are used to enhance the discrimination between signal jets, having a two prong structure, and background jets. This is the first time the diboson production cross-section is measured in the boosted regime using experimental techniques based on the large cone jets.\\
The final measurement of the cross section is the result of a joint effort among the components of the `` Analysis Team''. In the following paragraph I depict the structure of the thesis highlighting my personal contribution to the analysis.
During the preparation of this thesis work I benefited of the suggestions of my supervisor and of the Analysis Team members, with whom I have been constantly in contact through frequent meetings.\\
The structure of the thesis is as follows: in Chapter 1 I give an overview of the theoretical framework and I summarise the recent results of massive diboson cross section measurements obtained using the ATLAS and CMS detectors. In Chapter 2 I illustrate the ATLAS experimental apparatus. In Chapter 3 I give a description of the reconstruction of the particle objects. Chapter 4 is focused on the description of the event selection of the candidate events. Candidate events are required to have exactly one lepton, large missing transverse energy and a single jet. The first tasks during my Master's thesis work has been to implement the event selection and to validate it. I have also studied the jet reconstruction techniques and the substructure variables, arriving to the implementation in my code and in a new event selection. Once obtained the full selection, I have measured the signal yield by performing a binned maximum-likelihood fit to the jet mass distribution of the data using templates based on Monte Carlo simulations. In Chapter 5 I summarise how I obtained the final Monte Carlo templates and how they are used in the fit to extract the production cross section.\\
The main background processes in the boosted regime are W+jet, and and single top production. I have developed two selections as close as possible to the signal selection to define two control regions, each one enriched of one of the two main background processes. The definition of these control regions is described in Chapter 6. These regions allow to understand the level of agreement between data and simulated events. I dedicated a particular study to optimize the selection cuts to reduce the top background and I describe it in Chapter 7. The sources of systematic uncertainties that affect the measurement of the production cross section are discussed in Chapter 8. I have personally prepared the templates of most of the systematic uncertainties that are relevant for this analysis. In Chapter 9 the preliminary results on the cross-section measurement and on the limit on the anomalous triple gauge couplings are described. I personally performed the fit procedure to extract the signal cross-section
Studies on decay and production with the ATLAS detector
No full textThe ATLAS experiment physics program can be summarized into two goals: the test of the Standard Model and the search for Beyond the Standard Model (BSM) physics signatures. Both aspects are tackled in this thesis as the first part of the work is dedicated to the measurement of the Higgs boson decay to a couple of b-quarks as predicted by the SM, while another part addresses the search for deviations in the Higgs boson production and decay in a phase space highly sensitive to BSM effects. In this thesis, the Higgs boson decay into two b-quarks is studied in the associated production with a vector boson ( or ) decaying into leptons. Two complementary strategies have been developed and they are indicated as resolved and merged analysis. In the resolved analysis the Higgs boson decay products are reconstructed as two separate objects (b-jets) while in the merged analysis, designed for the high energy phase space, the two b-jets produced by the highly boosted Higgs boson tend to coalesce and are reconstructed as a single large jet. The resolved analysis search led to the first observation of the Higgs boson decay into two b-quarks and to the first observation of the VH production. The data sample used for the search has also been used to perform measurements of the VH cross-section in bins of the V-boson transverse momentum. This measurement, exploiting the so-called Simplified Template Cross Section framework, is designed to investigate possible BSM effects
Commissioning of the Laser II of the TileCal Calorimeter CERN summer student report
No full textThe Tile calorimeter is the central hadronic calorimeter of ATLAS. It is a sampling calorimeter allowing the detections of hadrons, jets and hadronic decays of tau leptons contributing also to the missing transverse energy determination. It includes about 10k PhotoMultipliers (PMT’s) to detect the light produced by particles showering in the detector. The role of the Laser II system is to control the stability of the gains of such PMT’s. Before the installation of the laser in the pit to replace the old system a long commissioning phase has been done. My task was to participate to the measurements and to the analysis of the collected data
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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