We present a measurement of the top anti-top quark (ttbar)production cross section in the dilepton final states from proton-proton collisions at a center of mass energy at 7 TeV at the LHC. A b-tagging algorithm based on tracks displaced from the event interaction vertex is applied to identify bottom quark jets from top quark decay and reject background events. Given the relatively pure sample of bottom quark jets in ttbar dilepton final states, a new technique to measure in-situ the b-tagging efficiency is introduced that uses the distribution of the number of observed b-tagged jets. We present results with data collected at the ATLAS detector in 2010 with an integrated luminosity of 35 pb-1. The measured ttbar cross section is 176 +22/-21 (stat.) ± 20 (syst.) ± 6 (lum.) pb in the dilepton channel. We will also discuss the future prospects of this measurement.

We present a measurement of the top anti-top quark (ttbar)production cross section in the dilepton final states from proton-proton collisions at a center of mass energy at 7 TeV at the LHC. A b-tagging algorithm based on tracks displaced from the event interaction vertex is applied to identify bottom quark jets from top quark decay and reject background events. Given the relatively pure sample of bottom quark jets in ttbar dilepton final states, a new technique to measure in-situ the b-tagging efficiency is introduced that uses the distribution of the number of observed b-tagged jets. We present results with data collected at the ATLAS detector in 2010 with an integrated luminosity of 35 pb-1. The measured ttbar cross section is 176 +22/-21 (stat.) ± 20 (syst.) ± 6 (lum.) pb in the dilepton channel. We will also discuss the future prospects of this measurement.

Després de 20 anys de preparació, el LHC s'encendrà a finals del 2009, col.lisionant protons a energies de 14TeV, per recrear els primers moments del Big Bang. Les partícules s'acceleraran al llarg del túnel circular de 27 km de circumferència fins a velocitats properes a la de la llum. El túnel, situat prop de Ginebra, i els seus experiments formen un dels més grans esforços de la història per estudiar l'estructura fonamental de la matèria. S'espera que a aquestes altes energies de col.lisió nous fenòmens físics puguin esdevenir i siguin descoberts. Entre les restes resultants de les col.lisions entre protons, evidències de dimensions extres, de la misteriosa matèria fosca que inunda el nostre univers o de la partícula de Higgs que dona massa a les partícules elementals, podran ser observades. ATLAS és un dels experiments del LHC. A més a més del descobriment de nova Física en el seu programa, també està inclosa la investigació de la Física ja coneguda. Un millor coneixement de la teoria pertorbativa de Quantum Chromodynamics és un dels objectius d'ATLAS. QCD és la teoria que descriu les interaccions fortes entre quarks i gluons. Aquesta teoria encara roman sense resoldre, ja que no exiteix un mètode d'aproximació vàlid per qualsevol escala d'energies. La teoria pertorbativa de QCD pot descriure un gran nombre d'interaccions a altes energies. El seu formalisme ha donat una eina molt valuosa dins l'estudi de les interaccions fortes. La signatura més notable dels processos QCD en col.lisionadors d'hadrons és la producció de jets de partícules col.limats. La mesura d'aquests jets en associació amb un bosó vector, W o Z, proporciona un test estricte dels càlculs de la teoria pertorbativa de QCD. A més, alguns dels processos de la nova Física, com la producció del bosó Higgs o de partícules supersimètriques, poden ser imitats per la producció dels bosons vectros en associació amb jets, que constitueixen un background irreduïble a l'investigació d'aquests nous processos. Aquesta tesi presenta la mesura de la "inclusive jet cross section" en events amb un bosó Z(e,e,) o Z(mu,mu), comparant les prediccions teòriques amb les dades "real", i.e. events Monte Carlo "fully-reconstructed", pel primer 1fb-1 de dades obtingudes amb el detector ATLAS. Les dades reconstruïdes i corregides es comparen amb les prediccions de la teoria pertorbativa de QCD a nivell NLO i LO. Aquestes prediccions pertorbatives es corregeixen amb les contribucions de processos no pertorbatius, com l'underlying event o la fragmentació dels partons dins dels jets d'hadrons. Aquests processos no poden ser descrits per la teoria pertorbativa, i s'estimen amb models fenomenològics. S'han utilitzat dos tipus diferents de dades reconstruides Monte Carlo, ALPGEN i PYHTIA. S'han estudiat les comparacions entre les prediccions d'ambdós generadors. Els processos background han estat estimats utilitzant diferents mètodes "data-driven". Per la recerca dels jets, s'ha utilitzat l'algoritme ATLAS Cone 0.4, després d'identificar la presència d'un bosó Z mitjançant la reconstrucció del seu decaiment (electrons o muons). Les dades reconstruides han estat corregides pels efectes del detector, utilitzant factors independents. Aquest anàlisi ha estat realitzat abans que ATLAS recollís les primeres dades reals, abans de l'inici del LHC, per aquest motiu aquesta tesi es basa en dades simulades amb generadors Monte Carlo. Mentres dura la preparació d'un experiment de Física d'altes energies com ATLAS, aquestes simulacions són molt importants pel desenvolupament d'estratègies eficaces d'anàlisi de dades i reconstrucció d'objectes físics mesurats pel detector. / Después de 20 años de preparación, el LHC va a encenderse a finales del 2009, colisionando protones a una energia de 14 TeV, para recrear los primeros momentos después del Big Bang. Las partículas serán aceleradas a lo largo del tunel circular de 27 km de circumferencia hasta velocidades próximas a la de la luz. El túnel, situado cerca de Ginebra, y sus experimentos forman uno de los más grandes esfuerzos de la história para estudiar la estructura fundamental de la materia. Se espera que a estas elevadas energías de colisión, nuevos fenómenos físicos puedan ocurrir y sean descubiertos. Entre los resultantes escombros de las colisiones entre protones, evidencias de dimensiones extras, de la misteriosa materia oscura que inunda nuestro universo o de la partícula de Higgs que da masa a las partículas elementales serán observadas. ATLAS es uno de los experimentos del LHC. Además del descubrimiento de nueva Fisica en su programa, también está la investigación de la Fisica ya descubierta. Un mejor conocimiento de la teoría perturbativa de Quantum Chromodynamics es uno de los objetivos de ATLAS. Quantum Chromodynamics es la teoria de campos que describe las interacciones fuertes entre quarks y gluones. Esta teoría todavia permanece sin resolver, ya que no existe un método de aproximación válido para cualquier escalada de energía. La teoría perturbativa de QCD puede describir un gran numero de interacciones a altas energías. Su formulismo ha dado una herramienta muy valiosa en el estudio de las interacciones fuertes. La signatura más notable de procesos QCD en collisionadores de hadrones es la producción de jets colimados de hadrones. La medición de estos jets en asociación con un bosón vector, W o Z, proporciona un test severo de los cálculos de la teoría perturbativa de QCD. Además, algunos de los procesos de nueva Física en los colisionadores de hadrones, como la production del boson de Higgs o de partículas supersimétricas, pueden ser imitados por la producción de bosones vectores en asociación con jets, que constituyen un background irreducible a la investigación de estos nuevos procesos. Esta tesis presenta la medida de la "inclusive jet cross section" en sucesos con un boson Z (ee) o Z(mu,mu), comparando las prediciones teoricas con los datos "reales", i.e. sucesos Monte Carlo "fully-reconstructed", para el primer 1fb-1 de datos obtenidos con el detector ATLAS. Los datos reconstruidos y corregidos son comparados a las predicciones de la teoria perturbativa de QCD a nivel NLO y LO. Estas predicciones perturbativas se corrigen con las contribuciones de procesos no perturbativos, como el underlying event o la fragmentación de los partones en jets de hadrones. Estos procesos no pueden ser descritos por la teoria perturbativa, y son estimados con modelos fenomenologicos. Se han ultilizado dos tipos distintos de datos reconstruidos Monte Carlo, ALPGEN y PYTHIA. Comparaciones entre las predicciones de ambos generadores Monte Carlo han sido estudiadas. Los procesos background han sido estimados usando distintos métodos "data-driven". Para la búsqueda de jets se ha usado el algoritmo ATLAS Cone 0.4 jet, después de identificar la presencia de un bosón Z a través de la reconstrucción de su decaimiento (electrones o muones). Los datos reconstruidos son corregidos por los efectors del detector, usando factores independientes. Este analisis ha sido realizado antes que ATLAS recogiera los primeros datos reales, antes del inicio del LHC, por este motivo esta tesis esta basada en datos simulados con generadores Monte Carlo. Mientras dura la preparación de un experimento de fisica de altas energías como ATLAS, estas simulaciones son de vital importancia para el desarrollo de estrategias eficaces de analisis de datos y reconstrucción de objetos físicos medidos por el detector. / After 20 years of preparation, the Large Hadron Collider is going to be switched on in late 2009, smashing protons at an energy of 14 (10) TeV, to recreate the first moments after the Big Bang. Particles will whizz around a circular tunnel of 27 km in circumference at near light speed. The tunnel, built near Geneva, and its experiments constitute one of the largest coordinated efforts ever made to study the fundamental structure of nature. It is expected that at the energies reached in the proton-proton collisions at the LHC, unknown physical phenomena will have to occur and will be observable. Among the particle debris may lie evidence for extra dimensions, mysterious dark matter that pervades the universe or the Higgs boson, which gives mass to elementary particles. ATLAS is one of the LHC experiments. Besides the new phenomena goals in its physics program, there is the understanding of the already known physics. The better understanding of perturbative Quantum Chromodynamics theory is one of the aims of ATLAS. Quantum Chromodynamics is the field theory which describes the strong interaction between quarks and gluons. It remains an "unsolved" theory, since no single approximation method can be used to all length scales. Perturbative QCD naturally describes a large set of high-energy, large-momentum-transfer cross sections and its formalism has provided an invaluable tool in the study of the strong interactions. The most prominent signature of QCD at hadron colliders is the production of collimated jets of hadrons. The measurement of the production of such jets in association with a vector boson, W or Z, provides a stringent test of perturbative QCD (pQCD) calculations. Furthermore, some of new physics processes at hadron colliders, such as the production of Higgs bosons and supersymmetric particles, can be mimicked by the production of vector bosons in association with jets that constitute irreducible backgrounds to these searches. This PhD. thesis presents the measurement of the inclusive jet cross section in Z → e+e− and in Z → μ+μ− events, comparing theory predictions with "real data", i.e. Monte Carlo fully-reconstructed events, for the first 1fb−1 of data at the ATLAS detector. Reconstructed corrected data is compared to next-to-LO (NLO) and LO pQCD predictions. Perturbative predictions are corrected for the contributions of the non-perturbative processes, like the underlying event and the fragmentation of the partons into jets of hadrons. These processes are not described by perturbation theory and must be estimated using phenomenological models. Two different reconstructed data are used, PYTHIA and ALPGEN Monte Carlo data. Comparisons of both Monte Carlo predictions are studied. Background processes are estimated proposing different data-driven methods to be applied to real data. ATLAS Cone 0.4 algorithm is used to look for jets in the events after identifying the presence of a Z boson through the reconstruction of its decay (electrons or muons). Reconstructed data is corrected for detector effects, using independent factors. As this work was carried out before the "physics-data" start of the LHC, the presented studies are based on Monte Carlo simulations. During the preparation of a high-energy collider experiment, such simulations are important to develop efficient strategies for data analysis and for the reconstruction of the physics objects observed with the detectors.

This master thesis is Atlas Copco Craelius’ first step in incorporating numericalmethods in load case analysis during the development process. Atlas Copco needs toconstantly evolve and refine their methods in the design process to remain as thenumber one manufacturer of mining and construction equipment. Poor knowledge ofloads results either in structural failures or in oversized structures, both very costlyfor Atlas Copco.The main goal of this thesis is to examine the potential in MBS software by using it toidentify extreme load cases in one of Atlas Copco Craelius’ surface drill rigs, Mustang5. The MBS-software ADAMS View is used to build a model of the Mustang 5 drill rigand evaluate simulation results. The rig model is subject to motions which representreal case scenarios. The feed positioning possibilities are examined thoroughly since it was expected that the positioning has impact on the load levels. 25 different feedpositioning are simulated.The main conclusion is that the load levels are highly dependent on the feedpositioning. For example, the load levels in the boom raising cylinder can increaseseven times, if the rig is operated with the most unfavorable positioning compared tothe recommended. It could also be concluded that not only one positioning isextreme in terms of loads; it depends on which part of the boom system is beingobserved. Thus, several positioning cases have to be taken into consideration in orderto optimize the design of parts in the boom system.

In the ATLAS experiment software plays a central role in data taking, reconstruction, and analysis. This thesis presents a set of analysis algorithms written for the ATLAS software framework Athena, towards H+ searches in the τ+jets channel. Data recorded by the ATLAS experiment for 900 GeV proton-proton collisions from 2009 and 7 TeV proton-proton collisions from 2010 are analyzed with these algorithms and compared to Monte Carlo. A search for top quarks is performed on 36 pb-1 of data, and the results are found to agree well with Monte Carlo.

This research has been done on a mission from Atlas Copco Secoroc AB, DTH department. The focus and purpose of the study is to acknowledge the important factors you need to take advantage of when it comes to offering bundles. There is also a theoretical purpose, which is to investigate if communication together with bundles can create loyalty and, how this three factors affect each other. This is a somewhat overlooked research area within the bundles theory and is therefore of keen interest for this case. The research has been conducted through seven in-depth interviews with people related to Atlas Copco Secoroc and the sell-buy transactions.  The interviewed people were customers, sales persons, service technician, distributions co-ordinator and price department personnel. There was also investigative quantitative research done, where nineteen customer centres were asked to reveal competitor’s customers net price on different products. The interviews could not have been conducted without a literature review done within the subjects of bundles, communication, loyalty and price strategies. These four topics together with how the order works and the contact between different instances worked as the base for the interviews. The literature review plus learned information on Secoroc was the basis of the knowledge needed to conduct the interviews. The key factors found in the research that Secoroc needs to take advantage of are communication within the company, and with the customer and also the importance of relationship building. This is something a majority of the interviewed persons believe is missing, or hard to have time for, and something that theory puts a lot of pressure on. Better communication will lead to easier sales, better relationships and through that, increased loyalty. It will facilitate the sales of bundles and the communication will help in the creation of bundles. The findings include a suggestion where the mission is to involve Secoroc deeper with their customers. The findings suggested that a reason for the missing contact is because lack of resources. Therefore the solution is to employee service technicians in high-loaded areas. Through that a more regular and close contact will be established. Customers can concentrate on the drilling and Atlas Copco Secoroc will take care of the administrative work. Further research has to be done within subject of how to divide the invoice when more then one product company is involved in the bundle. Connected to this is how the reward should be divided between involved sales persons. A redevelopment of the system is needed and therefore more knowledge and research over how that can be accomplished must be acquired.

Thèse de doctorat : Géosciences : INPL : 2007. / Titre provenant de l'écran-titre. Bibliogr.

<p>A simultaneous measurement of three Standard Model cross-sections using 4.7 inverse femtobarns of proton-proton collision data at a center-of-mass energy of 7 TeV is presented. Collision data were collected using the ATLAS detector at the Large Hadron Collider. The signal production cross-sections studied are for top quark pair production, charged weak boson pair production, and Drell-Yan production of tau lepton pairs with invariant mass greater than 40 GeV. A data sample is defined from events with isolated high-energy electron-muon pairs arranged in a phase space defined by missing transverse momentum and jet multiplicity. A binned maximum likelihood fit is employed to determine signal yields in this phase space. Signal event yields are in turn used to measure full cross-section values and cross-section values within a fiducial region of the detector, and unlike conventional measurements the signal measurements are performed simultaneously. This is the first such simultaneous measurement of these cross-sections using the ATLAS detector. Measured cross-sections are found in good agreement with the most precise published theoretical predictions.</p> / Dissertation

The Large Hadron Collider (LHC) at the international particle physics laboratory CERN in Switzerland is currently the most powerful particle accelerator on earth. This thesis presents analyses of proton-proton collisions at the energy √s = 7 TeV, recorded by ATLAS, one of the detectors at the LHC. The goal of the LHC and its detectors is to find new phenomena not described by the Standard Model (SM) of particle physics.The top quark is the heaviest known elementary particle and it is produced in very large numbers at the LHC. Measuring the production cross-section of top pairs (ttbar) is important for many reasons: for validating the strong production mechanism of the SM, for commissioning and calibration of the detector and analysis software and because several scenarios for physics beyond the SM predict changes to the ttbar production cross-section.Five different measurements of the ttbar cross-section will be presented in this thesis. The first three are measurements of the total cross-section, the fourth is a simultaneous measurement of the ttbar, Zττ and WW cross-sections and the fifth is a measurement of the relative differential ttbar cross-section. The most accurate measurement of the total cross-section is 176 pb with a total uncertainty of 9%, and the relative differential cross-section for ttbar-masses above ~ 1 TeV is 0.007 1/TeV with an uncertainty of 43%. Both values agree with the SM predictions.Measurements or searches in particle physics often have to be conducted in the presence of uninteresting background processes.  Reducing and providing estimates of these backgrounds is one of the main analysis tasks. Many backgrounds can be simulated with sufficiently good accuracy. However, the background due to mis-identified leptons cannot be accurately simulated. This thesis presents and evaluates a method for estimating this background from data, and this is then used in the total ttbar cross-section measurements. / LHC (Large Hadron Collider) vid det internationella partikelfysiklaboratoriet CERN i Schweiz är för närvarande världens mest kraftfulla partikleaccelerator. I den här avhandlingen presenteras anlyser av proton-protonkollisioner vid $\sqrt{s}=7\TeV{}$, registrerade med ATLAS som är en av detektorerna vid LHC. Målet med LHC och dess detektorer är att upptäcka nya fenomen som inte kan beskrivas av partikelfysikens nuvarande standardmodell (SM). Toppkvarken är den tyngsta elementarpartikeln man känner till och den produceras i stort antal vid LHC. Att mäta produktionstvärsnittet för par av topkvarkar (\ttbar{}) är viktigt av flera skäl: för att validera den starka produktionsmekanismen i SM, och för att testa och kalibrera detektorn och analysverktygen. Dessutom förutsäger flera teoretiska utvidgningar av SM ändringar av tvärsnittet för \ttbar{}. Fem olika mätningar av tvärsnittet för \ttbar{} presenteras i den här avhandlingen. De första tre är mätningar av det totala tvärsnittet, den fjärde är en simultan mätning av tvärsnitten för produktion av \ttbar{}, $WW$ och \Ztt{} och den femte är en mätning av det \emph{relativa differentiella} tvärsnittet. Det mest noggranna mätningen av det totala tvärsnittet är $176 $ pb med $9 \%$ total osäkerhet, och det relativa differentiella tvärsnittet för \ttbar{}-massor över $\sim 1 \TeV{}$ är $0.007 \TeV^{-1}$ med $43\%$ osäkerhet. Båda mätresultaten stämmer med respektive förutsägelse från standardmodellen. Mätningar eller sökningar inom partikelfysiken måste ofta utföras i närvaro av ointressanta bakgrundsprocesser. Att reducera och skatta dessa bakgrunder är en av huvuduppgifterna inom en dataanalys. Många bakgrunder kan simuleras med tillräcklig precision. Men bakgrunden av felidentifierade leptoner kan däremot inte simuleras tillräckligt noggrant. Den här avhandlingen presenterar och utvärderar en metod för att skatta bakgrunden av felidentifierade leptoner från data, och resultatet används i mätningarna av det totala tvärsnittet för \ttbar{}. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.</p>

First measurements are made of the underlying event in calorimeter jet events at the LHC, using 37 pb-1 of pp collisions at √s = 7TeV, recorded during 2010 by the ATLAS detector. Results are compared for an assumed di-jet topology based on a single identified jet, and an exclusive di-jet requirement. The number of charged particles in the azimuthal region transverse to the jet axis is recorded, as well as their total and average transverse momentum. The total energy carried by all particles - charged and neutral - is also calculated, using the full calorimeter acceptance |η| < 4:8. Distributions are constructed to show the variation of these quantities versus the transverse momentum of the selected jet, over the range 20 - 800 GeV. Additional jets in the transverse region are shown to dramatically influence the measured activity. Software is developed to perform Bayesian iterative unfolding, testing closure of the process and stability with respect to the number of iterations performed. Pseudo-experiments are used to propagate systematic errors, and the intrinsic error due to unfolding is estimated. Although the correction relies on a prior probablitity distribution, model-dependence is reduced to an uncertainty comparable to or smaller than experimental systematic errors. The software is used to correct underlying event measurements for effects introduced by the ATLAS detector. Unfolded results are compared to predictions from different Monte Carlo event generators used in LHC analyses, showing general agreement in the range |η| < 2:5, but discrepancies in the forward region. Comparison with other ATLAS results shows compatible behaviour in events defined by any high-momentum charged particle, or by leptonic Z-boson decays.