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1
Nolten, Martin Richard. "Electroweak corrections to hadronic processes at TeV energy colliders." Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434092.
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Kallweit, Stefan. "Precision calculations for Gauge-Boson pair production with a hadronic jet at Hadron colliders." Diss., kostenfrei, 2008. http://edoc.ub.uni-muenchen.de/9362/.
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Rontsch, Raoul Horst. "Higher order QCD corrections to diboson production at hadron colliders." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:5c4c3e7e-5c2a-4878-9fad-d9e5e0535d30.
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Hadronic collider experiments have played a major role in particle physics phenomenology over the last few decades. Data recorded at the Tevatron at Fermilab is still of interest, and its successor, the Large Hadron Collider (LHC) at CERN, has recently announced the discovery of a particle consistent with the Standard Model Higgs boson. Hadronic colliders look set to guide the field for the next fifteen years or more, with the discovery of more particles anticipated. The discovery and detailed study of new particles relies crucially on the availability of high-precision theoretical predictions for both the signal and background processes. This requires observables to be calculated to next-to-leading order (NLO) in perturbative quantum chromodynamics (QCD). Many hadroproduction processes of interest contain multiple particles in the final state. Until recently, this caused a bottleneck in NLO QCD calculations, due to the difficulty in calculating one-loop corrections to processes involving three or more final state particles. Spectacular developments in on-shell methods over the last six years have made these calculations feasible, allowing highly accurate predictions for final state observables at the Tevatron and LHC. A particular realisation of on-shell methods, generalised unitarity, is used to compute the NLO QCD cross-sections and distributions for two processes: the hadroproduction of W+ W-jj, and the hadroproduction of W+ W-jj. The NLO corrections to both processes serve to reduce the scale dependence of the results significantly, while having a moderate effect on the central scale choice cross-sections, and leaving the shapes of the kinematic distributions mostly unchanged. Additionally, the gluon fusion contribution to the next-to-next-to-leading order (NNLO) QCD corrections to W+ W-j productions are studied. These contributions are found to be highly depen- dent on the kinematic cuts used. For cuts used in Higgs searches, the gluon fusion effect can be as large as the NLO scale uncertainty, and should not be neglected. All of the higher-order QCD corrections increase the accuracy and reliability of the theoretical predictions at hadronic colliders.
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Medley, Jack James. "High energy resummation and electroweak corrections in dijet production at hadronic colliders." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/25429.
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Coloured final states are ubiquitous at hadron colliders such as the Large Hadron Collider (LHC). Therefore understanding high energy perturbative quantum chromodynamics (QCD) at these experiments is essential not only as a test of the Standard Model, but also because these processes form the dominant background to many searches for new physics. One such `standard candle' is the production of a dilepton pair in association with dijets. Here we present a new description of this final state (through the production of a Z⁰ boson and γ*). This calculation adds to the fixed-order accuracy the dominant logarithms in the limit of large partonic centre-of-mass energy to all orders in the strong coupling αs. This is achieved within the framework of High Energy Jets. This calculation is made possible by extending the high energy treatment to take into account the multiple t-channel exchanges arising from Z⁰ and gamma* -emissions off several quark lines. The correct description of the interference effects from the various t-channel exchanges requires an extension of the subtraction terms in the all-order calculation. We describe this construction and compare the resulting predictions to a number of recent analyses of LHC data. The description of a wide range of observables is good, and, as expected, stands out from other approaches in particular in the regions of large dijet invariant mass and large dijet rapidity spans. In addition we also present the application of the High Energy Jets framework to two new experimental scenarios. Firstly, we show a comparison of High Energy Jets matched to the ARIADNE parton shower to an ATLAS study of gap activity in dijet events. We see that our description agrees well with the data throughout and in many distributions gives the best theoretical description. This shows the extra logarithmic corrections are essential to describe data already in LHC Run I. Secondly, we present a study of Z⁰/γ* plus dijets at 100 TeV. We compare the behaviour of the high energy logarithmic enhancements to the QCD perturbative series at 7 TeV and 100 Tev and see that at any high energy hadronic Future Circular Collider (FCC) the effects described by our resummation become significantly more important.
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Gaunt, Jonathan. "Double parton scattering in proton-proton collisions." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243945.
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Double hard parton-parton interactions are expected to occur frequently in proton-proton (p-p) collisions at the LHC. They can give rise to significant backgrounds to certain rare single scattering (SPS) signals, and are an interesting signal process in their own right. In this thesis, we discuss the theoretical description of the double parton scattering (DPS) cross section in the context of Quantum ChromoDynamics (QCD). After an overview of QCD and an introduction to DPS in Chapter 1, we describe in Chapter 2 a framework for calculating the p-p DPS cross section introduced by Snigirev et al., in which this cross section is expressed in terms of double PDFs D_p {ij}(x_1,x_2,Q_A 2,Q_B 2) (dPDFs). We show that the equal-scale dPDFs are subject to momentum and number sum rule constraints, and use these in the construction of an explicit set of leading order (LO) equal-scale dPDFs (the 'GS09' dPDFs). The leptonic same-sign WW DPS signal obtained using GS09 dPDFs is compared with that obtained using simple factorised forms, and the prospects of observing this signal taking into account SPS backgrounds are analysed. We discuss two ways in which the dPDF framework for describing p-p DPS is deficient in Chapter 3. We discuss interference and correlated parton effects in flavour, spin, colour, and parton type, which are ignored by the dPDF framework. We then study DPS-type graphs in which the parton pairs from both protons have arisen from a perturbative 1->2 branching, derive an expression for the part of such graphs associated with the particles arising from the 1->2 branchings being almost on-shell, and use this to demonstrate that the treatment of these graphs by the the dPDF framework is unsatisfactory. In Chapter 4, we study DPS-type graphs in which the parton pair from only one proton has arisen from a perturbative 1->2 branching. We discover that such graphs contribute to the LO p-p DPS cross section, and that crosstalk between partons in the 'nonperturbatively generated' pair is allowed provided that it occurs at a lower scale than that of the perturbative 1->2 branching in the other proton. The result of this analysis is combined with that of the previous chapter to propose a formula for the LO total DPS cross section, and our proposal is compared with those from other authors. We finish in Chapter 5 with some conclusions and suggestions for further work.
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Winter, Jan-Christopher. "QCD jet evolution at high and low scales." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1208912443778-27732.
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This thesis deals with a broad range of aspects that concern the simulation of QCD jet physics by Monte Carlo event generators. Phenomenological work is presented in validating the CKKW approach for merging tree-level matrix elements and parton showers. In the second part the main project is documented comprising the definition, realization and verification of a new QCD colour-dipole cascade. Finally, a new cluster-hadronization model is introduced.
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Fletcher, Gregory. "A Measurement of W+jets Z+jets with the ATLAS Detector." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8047.
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A study is presented on the production of vector boson (W and Z0) events in association with recoiling hadronic activity in the form of hadronic jets, using proton-proton collisions at the LHC. The dataset was taken by the ATLAS detector during the 2011 data-taking run, at a centre of mass energy p s = 7 TeV, and corresponds to an integrated luminosity of 4.6 fb 1. A measurement of the cross-section ratio of W+jets Z+jets events is de ned, reducing the large systematic uncertainties inherent in the experimental measurement of such events. Inclusive and di erential cross-sections are presented for W+jets Z+jets , as a function of a range of kinematic variables, and are compared to state-of- the-art theoretical predictions.
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Winter, Jan-Christopher. "QCD jet evolution at high and low scales." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23602.
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This thesis deals with a broad range of aspects that concern the simulation of QCD jet physics by Monte Carlo event generators. Phenomenological work is presented in validating the CKKW approach for merging tree-level matrix elements and parton showers. In the second part the main project is documented comprising the definition, realization and verification of a new QCD colour-dipole cascade. Finally, a new cluster-hadronization model is introduced.
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Schälicke, Andreas. "Event generation at hadron colliders." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1122466458074-11492.
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Diese Arbeit befasst sich mit der Simulation von hochenergetischen Hadron-Kollisionsexperimenten, wie sie im Moment am Tevatron (Fermilab) durchgeführt werden und in naher Zukunft am Large Hadron Collider (LHC) am CERN zu erwarten sind. Für die Beschreibung dieser Experimente wird ein Algorithmus untersucht, der es ermöglicht, exakte Multijet-Matrixelemente auf Baumgraphenniveau in die Simulation einzubeziehen und so die Qualität der Vorhersage deutlich zu verbessern. Die Implementierung dieses Algorithmus in den Eventgenerator "SHERPA" und die Erweiterung des Parton Showers in diesem Programm ist das Hauptthema dieser Arbeit. Die Ergebnisse werden mit experimentellen Daten und mit anderen Simulationen verglichenThis work deals with the accurate simulation of high energy hadron-hadron-collision experiments, as they are currently performed at Fermilab Tevatron or as they are expected at the Large Hadron Collider at CERN. For a precise description of these experiments an algorithm is investigated, which enables the inclusion of exact multi-jet matrix elements in the simulation. The implementation of this algorithm in the event generator "SHERPA" and the extension of its parton shower is the main topic of this work. The results are compared with those of other simulation programs and with experimental data
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Jouttenus, Teppo T. (Teppo Tapani). "Jet production at hadron colliders." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76979.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 101-104).
Hadronic jets feature in many final states of interest in modern collider experiments. They form a significant Standard Model background for many proposed new physics processes and also probe QCD interactions at several different scales. At high energies incoming protons produce beam jets. Correctly accounting for the beam and central jets is critical to precise understanding of hadronic final states at the Large Hadron Collider. We study jet cross sections as a function of the shape of both beam and central jets. This work focuses on measuring jet mass but our methods can be applied to other jet shape variables as well. Measuring jet mass introduces additional scales to the collision process and these scales produce large logarithms that need to be resummed. Factorizing the cross section into hard, jet, beam, and soft functions enables such resummation. We begin by studying jet production at e + e- collisions in order to focus on the effects of jet algorithms. These results can be carried over to the more complicated case of hadron collisions. We use the Sterman-Weinberg algorithm as a specific example and derive an expression for the quark jet function. Turning to hadron colliders, we show how the N-jettiness event shape divides phase space into N +2 regions, each containing one central or beam jet. Thus, N-jettiness works as a jet algorithm. Using a geometric measure gives central jets with circular boundaries. We then give a factorization theorem for the cross section fully differential in the mass of each jet, and compute the corresponding soft function at next-to-leading order (NLO). We use a method of hemisphere decomposition, which can also be applied to calculate N-jet soft functions defined with other jet algorithms. Our calculation of the N-jettiness soft function provides the final missing ingredient to extend NLO cross sections to resunmmed predictions at next-to-next-to-leading logarithmic order. We study the production of an exclusive jet together with a Standard Model Higgs boson. Based on theoretical reasons and agreement between our calculation and data from the ATLAS collaboration, we argue that our results for the jet mass spectrum are a good approximation also for inclusive jet production and other hard processes.
by Teppo T. Jouttenus.
Ph.D.
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Pruna, Giovanni Marco. "Phenomenology of the minimal B-L Model : the Higgs sector at the Large Hadron Collider and future linear colliders." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/199955/.
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This thesis is devoted to the study of the phenomenology of the Higgs sector of the minimal B −L extension of the Standard Model at present and future colliders. Firstly, the motivations that call for the minimal B −L extension are summarised. In addition, the model is analysed in its salient parts. Moreover, a detailed review of the phenomenological allowed Higgs sector parameter space is given. Finally, a complete survey of the distinctive Higgs boson signatures of the model at both the Large Hadron Collider and the future linear colliders is presented
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Phaf, Lukas Kaj. "Top quark production at hadron colliders." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2004. http://dare.uva.nl/document/77187.
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Duran, Delgado Rosa Maria. "Infrared QCD resummations at hadron colliders." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/infrared-qcd-resummations-at-hadron-colliders(aedf38f2-aa9c-45bc-a39f-dc660759dc91).html.
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In this thesis we study two different processes at hadron colliders: Z-boson production and dijet production with a jet veto. Our calculations focus on the resummation of logarithmically enhanced contributions coming from soft and/or collinear gluon emission. For Z-boson production, we calculate the cross-section distribution in aT , a novel variable proposed by Vesterinen and Wyatt as a more accurate probe of the Z at low transverse momentum pT . The observable aT is defined as the component of pT perpendicular to an experimentally convenient axis: the axis with respect to which the two final-state leptons (from a Z leptonic decay) have equal transverse momenta. Our study involves the resummation of large logarithms in aT /pT up to next-to-leading accuracy. We then compare the resulting distributions in aT to the well-known pT distribution, identifying important physical differences between the two cases. We also test our resummed result at the two-loop level by comparing its expansion with a fixed-order calculation and find agreement with our expectations. Besides, we study dijet production with a veto in the inter-jet rapidity region in proton-proton collisions. We resum the leading logarithms in the ratio of the transverse momentum of the leading jets and the veto scale and we match this result to leading-order QCD matrix elements, taking into account energy-momentum conservation effects. We compare our theoretical predictions to experimental data measured by the ATLAS collaboration and find good agreement, although our results are affected by large theoretical uncertainties.
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Davies, Eleanor Lucy. "Electron and hadronic recoil calibration for the first measurement of the mass of the W boson by the ATLAS experiment at the Large Hadron Collider." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:61c91234-837d-4462-9e29-c317f90001ed.
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This thesis presents work towards the first measurement of the mass of the W boson (mW) at ATLAS at the Large Hadron Collider using √s = 7 TeV collision data taken in 2011. The electron energy calibration is presented, including a detailed study of the linearity of the ATLAS electromagnetic calorimeter. Separately, the measurement of the W boson recoil is calibrated using Z boson events. Recoil corrections for the underlying event, pileup, recoil magnitude resolution, recoil angular resolution and recoil response mismodelling are determined, with statistical uncertainties on these corrections corresponding to an estimated uncertainty on mW of 3.9 MeV. The corrections for calorimeter non-linearity and recoil modelling improve the description of the data, though systematic biases remain. To achieve a precision commensurate with the statistics of the data, these biases will need to be understood.
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Elkhalii, Amine [Verfasser]. "Analog Hadronic Calorimeter for a Future Linear Collider / Amine Elkhalii." Wuppertal : Universitätsbibliothek Wuppertal, 2020. http://d-nb.info/1221970275/34.
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Adamson, Katherine Louise. "Vector boson pair production at hadron colliders." Thesis, Durham University, 2002. http://etheses.dur.ac.uk/3965/.
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We calculate the contribution of gluon-gluon induced processes to vector boson pair production at hadron colliders, specifically the production of WZ, Wγ and Zγ pairs. We calculate the tree level processes gg → WZqq, gg → Wγqq and gg → Zγqq, and the one loop process gg → Zγ. We use the helicity method and include the decay of the W and Z bosons into leptons in the narrow width approximation. We include anomalous triple gauge couplings in all of our vector boson pair production calculations. In order to integrate over the qq final state phase space we use an extended version of the subtraction method to NNLO and cancel collinear singularities ex-plicitly. The general subtraction terms that are obtained apply to all vector boson pair production processes. Due to the large gluon density at low z, the gluon induced terms of vector boson pair production are expected to be the dominant NNLO QCD correction, relevant at LHC energies. However, we show that due to a cancellation they turn out to provide a rather small contribution, anticipating good stability for the perturbative expansion. This contribution remains small even when anomalous couplings are added, and when one considers energies far above the energies of currently planned hadron colliders.
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Savine, Alexandre Yurievich 1962. "Forward calorimetry at hadron collider." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/288749.
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Calorimeter has been an essential element of High Energy Physics Experiment for decades. As beam energies of hadron colliders reached the multi-TeV range, hermeticity of the calorimetric system became a high priority issue. Additional requirements arose from increased luminosity. The Forward Calorimeter (covering rapidity η >3) must to provide high quality measurements of hadronic jets (energy and position) at extremely high rate and at the same time withstand a harsh radiation environment. The Liquid Argon Tube Forward Calorimeter was developed at the University of Arizona to fulfill those requirements. Prototypes of the electromagnetic section (15X₀, later 25X₀) were tested at BNL and CERN secondary beams in 1993 and 1995. Data acquired in those tests allowed us to study such vital parameters of the calorimeter as response uniformity, energy and position resolution. An energy range from 2 GeV to 200 GeV and angles from 0.6° to 5.6° were covered. Observed results (together with extensive Monte-Carlo simulation studies of the Forward Region) allowed the Liquid Argon Tube Calorimeter to be chosen among several competing designs as the Baseline for the Forward Calorimeter of the ATLAS multi-purpose detector at the LHC (CERN).
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Kahawala, Dilani S. "Topics on Hadron Collider Physics." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10806.
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In this dissertation we present four techniques that could be used at the Large Hadron Collider (LHC) to improve the efficiency with which collected data is utilized, and to help detect signals of physics beyond the Standard Model. We present an extension of the Qjets algorithm which allows us to exploit the different possibilities for reconstructing an event at the LHC to produce multiple interpretations for each event. For example, using this approach on a Higgs plus Z boson sample, with h → bb we find a 28% improvement in significance can be realized at the 8 TeV LHC. We also propose a measurement of the bottom quark forward-central asymmetry at the LHC in order to gain further insight into the Tevatron t tbar anomaly. Using a toy axigluon model we find that if the relevant new-physics couplings to the bottom quark are similar to those of the top, then the effects should be visible at the 2 σ level in less than 10 fb-1 of 7 TeV LHC data. Finally we develop two techniques to measure fundamental quantum numbers of new particles at the LHC, with the goal of distinguishing between different theories beyond the Standard Model. In the first case we consider long lived colored particles and in the second case we consider bound states of new colored particles which annihilate into Standard Model particles.Physics
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Skottowe, Hugh Philip. "Studies of RICH detectors and the Bd→K*μ⁺[mu]⁻ decay at the LHCb experiment." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609041.
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Zhou, Jia. "Precision Calculations for Electroweak Physics at Hadron Colliders." Thesis, State University of New York at Buffalo, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10163882.
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Electroweak (EW) corrections can be enhanced at high energies due to the soft or collinear radiation of virtual and real W and Z bosons that result in Sudakov-like corrections of the form α Wllogn(Q2/MV 2), where αW = α/(4πsin2&thetas; W) and n ≤ 2l – 1. Here MV denotes the W or Z boson mass, &thetas; w the weak mixing angle and Q2 a typical energy scale of the hard process under consideration. The inclusion of EW corrections in predictions for the CERN Large Hadron Collider (LHC) is therefore especially important when searching for signals of possible new physics in distributions probing the kinematic regime Q2 » MV 2. Next-to-leading order (NLO) EW corrections should also be taken into account when their size (O(α)) is comparable to that of QCD corrections at next-to-next-to-leading order (NNLO) (O(αs2)). To this end we have calculated and implemented in the parton-level Monte-Carlo program MCFM the NLO weak corrections to three key processes at the LHC: the Neutral-Current Drell-Yan process, top-quark pair production and di-jet production. This enables a study of their effects on LHC observables combined with the already available QCD corrections at NLO and NNLO. We provide both the full NLO weak corrections and their Sudakov approximation, since the latter is often used for a fast evaluation of weak effects at high energies and can be extended to higher orders. With both the exact and approximate results at hand, the validity of the Sudakov approximation can be readily quantified. In the case of top-quark pair production at the LHC we also calculated the NLO QED corrections.
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Ciccolini, Mariano L. "Standard Model Higgs boson phenomenology at hadron colliders." Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/13398.
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In this thesis two different aspects of Standard Model Higgs boson phenomenology at hadron colliders are addressed. A precise theoretical knowledge of production cross sections is needed in order to assist in the Higgs boson search efforts of the experimental community. Consequently, the next-to-leading-order electroweak corrections to Higgs boson production in association with a vector boson at hadron colliders have been calculated. Significant corrections were found, and theoretical uncertainties were analysed. In addition to production cross sections, a deep knowledge of background processes is also needed, especially at hadron colliders. The gluon-induced contributions to offshell W-boson pair production have been calculated. The invariant amplitude has been used to calculate the contribution from gluon initiated processes to the non-resonant W-boson pair production background to the Higgs boson search channel at the CERN LHC. These contributions are evaluated in the approximation of massless quarks circulating the loops. These results were used to study the effect of experimental cuts proposed to increase the signal to background ratio of the above mentioned search channel.
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Nordström, Karl Anders Mattias. "Phenomenology for the Large Hadron Collider." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8388/.
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The search for physics Beyond the Standard Model is the underlying motivation for the physics programme of the Large Hadron Collider at CERN. In this thesis we will present studies into the Large Hadron Collider phenomenology of dark matter inspired extensions to the Standard Model, di-Higgs + 2 jet (hhjj) production, CP violating effects in the Higgs sector, and the use of shape information from top polarisation measurements in searches for new physics. Full scans of the parameter space of Simplified Dark Matter models are demonstrated to be viable and allow for intriguing comparisons to relic density constraints. Strongly self-interacting dark sectors are shown to leave a potentially measurable imprint on the energy scaling of mediator production. The weak boson fusion induced production of hhjj turns out to be sensitive to a number of new physics effects, including CP violation in the Higgs sector. The use of top polarisation measurements to discover new physics which predicts polarised resonances is shown to be an effective way to ameliorate the loss of shape information for kinematically challenging regions of parameter space.
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Melbéus, Henrik. "Phenomenology of Hyperbolic Large Extra Dimensions for Hadron Colliders." Thesis, KTH, Teoretisk partikelfysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-79541.
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The subject of extra dimensions has experienced a renewed interest in recent years. Arkani-Hamed, Dimopoulos, and Dvali (ADD) have pointed out that it is possiblethat there exist extra dimensions that are as large as micrometer sized, if theStandard Model fields are restricted to a four-dimensional brane. In the ADD model, only the graviton is able to probe the extra dimensions. The main motivation for this model is that it could solve the hierarchy problem between the electroweak scale and the Planck scale by lowering the Planck scale to 1 TeV. However, in the ADD model, the radius of the extra dimensions is large, giving a new hierarchy problem between this radius and the electroweak scale. In addition, there are significant constraints on the model coming from astrophysics. To improve on the ADD model, it is possible to consider a model with curved extra dimensions. An interesting scenario is provided by extra dimensions of hyperbolic geometry. In this case, it is possible to bring the Planck scale down to 1 TeV without the need of a large radius. Also, the constraints that are important for the ADD model can be completely avoided. The most efficient probe of large extra dimensions is particle physics. In particular, it is possible to study their phenomenology in high-energy particle accelerators such as the Large Hadron Collider, which will be completed in 2008. The phenomenology of the ADD model has been extensively studied. In this thesis, we consider the phenomenology of a model where the internal space is a hyperbolic disc. We obtain the Kaluza-Klein spectrum approximately and study the Kaluza-Klein modes. The results are cross sections for production of a graviton together with a photon or a hadronic jet, which are the most important reactions for LHC physics.
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Ahrens, Valentin [Verfasser]. "Top-quark pair production at hadron colliders / Valentin Ahrens." Mainz : Universitätsbibliothek Mainz, 2011. http://d-nb.info/1018559884/34.
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Zhao, Zhijie [Verfasser]. "Multi-Higgs production at future hadron colliders / Zhijie Zhao." Siegen : Universitätsbibliothek der Universität Siegen, 2019. http://d-nb.info/1177366355/34.
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Tripathee, Aashish. "Jet substructure at the Large Hadron Collider." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/111882.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 57-60).
In this thesis, we use the CMS Open Data to study the 2-prong substructure of jets. We use CMS's particle flow reconstruction algorithm to obtain jet constituents, which we then use to perform various jet substructure studies. After validating our basic kinematics and substructure results through a comparison to results from parton shower generators, we extract the 2-prong substructure of the leading jet using the soft drop algorithm. We find good agreement between the results from the Open Data and those obtained from parton shower generators. For the 2-prong substructure, we also compare to analytic calculations performed to modified leading-logarithmic accuracy. To our best knowledge, this is the first ever physics analysis based on the CMS Open Data.
by Aashish Tripathee.
S.B.
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Dreyer, Frédéric. "Precision physics at the large hadron collider." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066170/document.
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L'avènement du LHC marque le début d'une ère de haute précision en physique des particules. Dans cette thèse de doctorat, nous abordons avec des outils innovants deux processus clés des collisionneurs de hadrons: la production inclusive de jets, et la production du boson de Higgs par fusion de bosons vecteurs (VBF). Dans la première partie de cette thèse, nous montrons comment resommer les premiers ordres logarithmiques de rayon de jet R, et appliquons ce formalisme à une étude approfondie du spectre inclusif des jets. Nous étudions les termes dépendant de R au troisième ordre non-nul (next-to-next-to-leading-order, NNLO), et les intégrons dans notre calcul. Nous examinons les éliminations dans la dépendance d'échelle, conduisant à une nouvelle prescription pour l'évaluation des incertitudes, et vérifions l'impact d'effets non-perturbatifs. Dans la deuxième partie de cette thèse, nous étudions les corrections de chromodynamique quantique dans la production de Higgs par VBF. En utilisant l'approche des fonctions de structure, nous calculons les corrections de quatrième ordre non-nul (NNNLO) à la section efficace inclusive. Nous calculons ensuite les corrections NNLO entièrement différentielles à la production de Higgs par VBF. Nous montrons que ces contributions sont significatives après coupures VBF, se trouvant en dehors des bandes d'incertitude d'échelle NLOWith the advent of the LHC, particle physics has entered an era where high precision is required. In this thesis, we tackle two of the key processes at hadron colliders using innovative tools: inclusive jet production and Higgs production through vector-boson fusion (VBF). In the first part of this thesis, we show how to resum leading logarithmic terms of the jet radius R, and apply this formalism to a detailed study of the inclusive jet spectrum. We study subleading R-dependent terms at next-to-next-to-leading order (NNLO), and incorporate them into our calculation. We investigate cancellations in the scale dependence, leading to new prescriptions for evaluating uncertainties, and examine the impact of non-perturbative effects. In the second part of the thesis, we study QCD corrections in VBF-induced Higgs production. Using the structure function approach, we compute the next-to-next-to-next-to-leading order (NNNLO) corrections to the inclusive cross section. We then calculate the fully differential NNLO corrections to VBF Higgs production. We show that these contributions are substantial after VBF cuts, lying outside the NLO scale uncertainty bands
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Tripathee, Aashish. "Jet substructure at the Large Hadron Collider." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111882.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 57-60).
In this thesis, we use the CMS Open Data to study the 2-prong substructure of jets. We use CMS's particle flow reconstruction algorithm to obtain jet constituents, which we then use to perform various jet substructure studies. After validating our basic kinematics and substructure results through a comparison to results from parton shower generators, we extract the 2-prong substructure of the leading jet using the soft drop algorithm. We find good agreement between the results from the Open Data and those obtained from parton shower generators. For the 2-prong substructure, we also compare to analytic calculations performed to modified leading-logarithmic accuracy. To our best knowledge, this is the first ever physics analysis based on the CMS Open Data.
by Aashish Tripathee.
S.B.
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Rauch, Michael. "Quantum effects in Higgs-boson production processes at hadron colliders." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980300681.
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Papanastasiou, Andrew Sofronis. "Off-shell effects for top quark production at hadron colliders." Thesis, Durham University, 2012. http://etheses.dur.ac.uk/6350/.
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A good description of processes involving the production and decay of top quarks is crucial to phenomenology at the Tevatron and LHC. In this thesis, a general method constructed using ideas from Effective Theories is presented, allowing predictions to be made for differential observables that importantly include the effects of non-zero top quark virtuality. Calculations using this method can be significantly simpler than those in standard perturbation theory and its use enables the identification of potentially important structures in the amplitudes. The method is applied to the example of top-pair production for a realistic experimental setup at the Tevatron. A number of observables are studied and an evaluation of off-shell effects is given. The latter tend to be small in general but do become enhanced in regions near kinematical boundaries for distributions that are sensitive to the invariant mass of top quarks.
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Macey, Tom. "An algorithm to measure parton fragmentation at large hadron colliders." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8657.
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The Standard Model of particle physics is discussed with emphasis on light quark QCD, and existing data on light quark fragmentation from e+e annihilation and deep inelastic scattering experiments. A method is developed to measure the directionally correlated pionic scaled momentum distribution, or partonic fragmentation function, in large hadron collider conditions. Jet algorithms are used to provide partonic momentum estimates, which in turn scale the hadronic momenta. The associated resolution is unfolded. Hadronic profiles about the parton are examined at Monte Carlo "truth" level. There is found to be a uniform uncorrelated background, which may be estimated event-by-event in regions away from jets and then subtracted statistically from the final distributions. A variable radius cone sampling method is used to count correlated charged hadrons and this also provides a method of coping with any poor directional resolution of jet algorithms. Extrapolation techniques make an estimated measurement possible when the largest safe sampling radius is not large enough to include all correlated hadrons. A novel method to calculate jet mass using jet collimation information available from the FAPS method is demonstrated. The algorithm was tested over an order of magnitude in hard scale ( 100GeV ! 1TeV) with two standard ATLAS reconstructed level Monte Carlos, Pythia and HERWIG, and the calculated fragmentation function is found to be in agreement with the trend of previous data at the hard scale overlap. These models have very different hadronisation models, so may be used to estimate systematic error and test feasibility for a possible full large scale measurement in data. Such work could support the concept of quark universality by establishing propagator invariance.
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Vryonidou, Eleni. "Phenomenology of the standard model and beyond at hadron colliders." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648273.
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Khelifa, Kerfa Kamel. "QCD resummation for high-pT jet shapes at hadron colliders." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/qcd-resummation-for-highpt-jet-shapes-at-hadron-colliders(16fdf645-238d-4979-8239-155f9ba07001).html.
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Exploiting the substructure of jets observed at the LHC to better understand and interpret the experimental data has recently been a very active area of research. In this thesis we study the substructure of high-pt QCD jets, which form a background to many new physics searches. In particular, we explore in detail the perturbative distributions of a certain class of observables known as non-global jet shapes. More specifically, we identify and present state-of-the-art calculations, both at fixed-order and to all-orders in the perturbative expansion, of a set of large logarithms known as non-global logarithms. Hitherto, these logarithms have been largely mis-treated, and in many cases ignored, in the literature despite being first pointed out more than a decade ago. Our work has triggered the interest of many groups, particularly Soft and Collinear Effective Theory (SCET) groups, and led to a flurry of papers on non-global logarithms and related issues. Although our primary aim is to provide analytical results for hadron-hadron scattering environments, it is theoretically instructive to consider the simpler case of e+e- annihilation. We thus examine, in chapters 4, 5 and 6, the the said jet shapes in the latter environment and compute the full next-to-leading logarithmic resummation of the large logarithms present in the distribution for various jet definitions. We exploit the gained experience to extend our calculations to the more complex hadronic environment in chapter 7. We provide state-of-the-art resummation of the jet mass observable in vector boson + jet and dijet QCD processes at the LHC up to next-to-leading logarithmic accuracy. The resultant distribution of the former (vector boson + jet) process agrees well, after accounting for hadronisation corrections, with standard Monte Carlo event generators and potential comparisons to data from the LHC will be made soon.
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Papaefstathiou, Andreas. "Phenomenological aspects of new physics at high energy hadron colliders." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/239399.
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This thesis contains studies of phenomenological aspects of new physics at hadron colliders, such as the Large Hadron Collider (LHC). After a general introduction in chapter 1, in chapter 2 we outline the main features of the Standard Model (SM) of particle physics and the theoretical motivations for going beyond it. We subsequently provide brief descriptions of a few popular models that aim to solve the issues that arise within the SM. In chapter 3 we describe the general Monte Carlo method for evaluating multidimensional integrals and show how it can be used to construct a class of computational tools called Monte Carlo event generators. We describe the main generic features of event generators and how these are implemented in the HERWIG++ event generator. By applying resummation techniques, we provide, in chapter 4, analytical calculations of two types of hadron collider observables. The first, global inclusive variables, are observables that make use of all measured particle momenta and can provide useful information on the scale of new physics. The second observable is the transverse energy of the QCD initial state radiation (ET ), associated with the either Drell-Yan gauge boson production or Higgs boson production. In both cases we provide comparisons to results obtained from Monte Carlo event generators. In chapter 5 we examine two well-motivated models for new physics: one of new heavy charged vector bosons (W prime), similar to the SM W gauge bosons, and a model motivated by strong dynamics electroweak symmetry breaking that contains new resonances, leptoquarks, that couple primarily to quarks and leptons of the third generation. In the prior model, we improve the current treatment of the W' by considering interference effects with the SM W and construct an event generator accurate to next-to-leading order which we use to conduct a phenomenological analysis. For the leptoquark model, starting from an effective Lagrangian for production and decay, we provide an implementation in the HERWIG++ event generator and use it to form a strategy for mass reconstruction. The thesis ends with some conclusions and suggestions for extensions of the work presented. Further details and useful formulæ are given in the appendices.
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Tevlin, Christopher. "Top quark phenomenology at the large hadron collider." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506278.
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Kukla, Romain. "Probes of top compositeness at theLarge Hadron Collider." Thesis, KTH, Partikel- och astropartikelfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-143540.
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Rafique, Haroon. "MERLIN for high luminosity large hadron collider collimation." Thesis, University of Huddersfield, 2017. http://eprints.hud.ac.uk/id/eprint/32605/.
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The large hadron collider (LHC) uses the most energetic and highest luminosity man made proton beams on Earth. The high luminosity (HL-LHC) [1] upgrade aims to increase the levelled luminosity of the LHC by a factor of five, to 5 · 1034cm−2 s −1 , by increasing the bunch population from 1 to 2.22·1011 protons, and decreasing emittance, and β ∗ . Thus the stored beam energy increases from ≈ 362 MJ to ≈ 675 MJ per beam. All synchrotrons encounter unavoidable proton losses. Protons that populate the beam halo pose a threat to the performance and lifetime of certain hardware, such as superconducting magnets, which in the LHC may be quenched by an impact of ≈ 1 · 106 protons [2]. A multi stage collimation system must operate at an efficiency such that no more than 2 · 10−5% of protons incident on collimators may escape and impact upon these magnets [3]. To predict and protect against proton losses in the HL-LHC, collimation simulations must be performed. MERLIN, a C++ accelerator physics library, has been updated to carry out such simulations for the HL-LHC. Novel materials such as molybdenum graphite have been investigated as collimator materials, and a novel technique - collimation enhancement via a hollow electron lens (HEL) - has been studied. Using detailed simulations the performance and operation of possible collimation upgrades are explored.
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Morris, Adam Benjamin. "Measurements of charmless B⁰s meson decays at LHCb." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28878.
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Using 3 fbˉ1 of proton-proton collisions, collected at centre-of-mass energies of √s = 7 and 8 TeV by the LHCb detector, several measurements of charmless B⁰s meson decays are made. A search is also performed for a highly suppressed B⁰ decay. First, the branching fraction of the B0⁰s→ ØØ decay is measured to be B(B⁰s→ ØØ) = (1.84 ± 0.05(stat) ± 0.07(syst) ± 0.11(fs=fd) ± 0.12(norm))X10ˉ⁵; where the third and fourth uncertainties arise from the fragmentation fraction fs/fd and the branching fraction of the normalisation mode. This represents a factor of five reduction in the statistical uncertainty compared to the previous best measurement. An upper limit on the branching fraction of the mode B⁰→ ØØ is set at B(B⁰→ ØØ) < 2.8 X 10ˉ⁸ (90% CL). This is a factor of seven improvement over the previous best measurement. An amplitude analysis of the B⁰s→ ØK+Kˉ decay is performed, wherein first observations of the decay modes B⁰s→ Øf´2(1525) and B⁰s→ ØØ(1680) are made. The branching fraction of the B⁰s→ Øf´2(1525) decay is measured to be B(B⁰s→ Øf´2 (1525)) = (1.63 ± 0.18(stat) ± 0.12(syst) ± 0.29(model) ± 0.17(norm)) X 10ˉ⁶; where the 'model' uncertainty arises from the choice of amplitude model. The longitudinal polarisation fraction of the decay B⁰s→ Øf´2(1525) is measured to be F0 = (86.6 ± 3.4 ± 0.8 ± 2.0 (model))%.
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Ellis, K. V. "TRAPS : Topological Reconstruction Algorithm for Parton Scatters." Thesis, Queen Mary, University of London, 2012. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8556.
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There is strong motivation to study standard model physics using the highest-energy data provided by the Large Hadron Collider. This is aided by the process of defining clusters of hadrons to form ‘jets’. Existing jet-finders are dependent on pre-defined parameters which, to some extent, influence their properties. This thesis introduces a novel algorithm which aims to reconstruct partons outgoing from hard interactions, prior to any splitting, by concentrating solely on the highest momentum transfer scale. In this way parton properties such as fragmentation and structure functions from hadron colliders may be compared directly with results from DIS and e+e− annihilation. This original, standalone tool is named ‘traps’ - the Topological Reconstruction Algorithm for Parton Scatters. The algorithm was developed using Pythia Monte Carlo QCD events, under a pragmatic approach that assumes the model provides a good approximation to reality at both hadronic and partonic level. Various tests were made to gauge the performance of the algorithm against standard jet-finders. The infrared safety and algorithm speed were also assessed. The objective of traps is to have low sensitivity to parameters, and to be fast and robust. A high event acceptance is necessary, as maximum statistics are required where cross-sections are at their lowest. A chapter of this thesis is dedicated to a description of the author’s studies in calibration and monitoring of the timing of the ATLAS Level-1 Calorimeter Trigger system. Pulses from triggered energy are sent via largely η× φ = 0.1 × 0.1 granularity ‘trigger towers’. Synchronous triggering with 1-2 ns precision is required for the system to make an accurate energy estimate.
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Cockburn, James David. "Subleading corrections to hadronic cross-sections at high energies." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/29519.
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The Large Hadron Collider (LHC) has provided, and will continue to provide, data for collisions at the highest energies ever seen in a particle accelerator. A strong knowledge of the properties of amplitudes for Quantum Chromodynamics in the High Energy Limit is therefore important to interpret this data. We study this limit in the context of the High Energy Jets (HEJ) formalism. This formalism resums terms in the perturbative expansion of the cross-section that behave like αn/s log (s/-t)ⁿ¯¹, which are enhanced in this limit. Understanding this region is particularly important in certain key analyses at the LHC: for example, Higgs-boson- plus-dijet analyses where cuts are applied to pick out events with a large mjj and in many searches for new physics. In this thesis, we discuss two directions in which HEJ's accuracy has been improved. Firstly, we look at adding descriptions of partonic subprocesses which are formally sub-leading in the jet cross-section but Leading Logarithmic (LL) in the particular subprocess itself. This required the derivation of new effective vertices that describe the emission of a quark/anti-quark pair in a way that is consistent with the resummation procedure. The inclusion of such processes reduces HEJ's dependence on fixed-order calculations and marks an important step towards full Next-to-Leading Logarithmic (NLL) accuracy in the inclusive dijet cross-section. The second extension was to improve our description of events involving the emission of a Higgs boson along with jets. Specifically, we derive new effective vertices which keep the full dependence on the quark mass that appears in the loops that naturally arise in such amplitudes. The formalism is also simple enough to allow for any number of extra nal state jets in the process. Therefore, HEJ is unique in its ability to provide predictions for high-multiplicity Higgs-plus-jets processes with full nite quark mass e ects. Such a calculation is far beyond the reach of any xed order approach.
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Brensing, Silja Christine [Verfasser]. "Resummation for supersymmetric particle production at hadron colliders / Silja Christine Brensing." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2011. http://d-nb.info/1018187073/34.
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Brooks, Helen Marguerite. "Multi-jet phenomenology for hadron colliders in the high energy limit." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12313/.
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We have incorporated next-to-leading logarithmic corrections into the High Energy Jets (HEJ) formalism and parton-level Monte Carlo generator for $W$ plus inclusive dijet production. This has involved an analytic demonstration of factorisation for the relevant configurations, an extraction of the effective current and proof of its gauge invariance. We have thoroughly validated our numerical implementation and matching of the cross section to leading order accuracy. We have studied the impact of these corrections upon transverse momentum distributions and found a significant improvement in the description of data. We also present a new merging algorithm, inspired by the CKKW-L method, for combining high energy and soft-collinear logarithms. This has been implemented for HEJ+\textsc{Pythia}. Multiple parton interactions and hadronisation effects are also accounted for, allowing for an accurate description of jets shapes. We find good agreement with data for observables such as the average number of jets and gap fractions which are relevant for understanding the impact of jet vetoes.
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Llodra-Perez, Jérémie. "Modèles effectifs de nouvelle physique au Large Hadron Collider." Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00610216.
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Grâce à l'exploitation du Large Hadron Collider, débutée en 2010, le monde de la physique des particules espère enfin avoir une compréhension plus précise du mécanisme de brisure de la symétrie électrofaible et résoudre certaines questions expérimentales et théoriques que soulèvent encore le modèle standard. S'inscrivant dans cette effervescence scientifique, nous allons présenter dans ce manuscrit une paramétrisation largement indépendante des modèles afin de caractériser les effets d'une éventuelle nouvelle physique sur les mécanismes de production et de désintégration du bosons de Higgs. Ce nouvel outil pourra aisément être utilisé dans les analyses des grandes expériences généralistes comme CMS et ATLAS afin de valider ou d'exclure de manière significative certaines théories au delà du modèle standard. Ensuite, dans une approche différente, fondée sur la construction de modèles, nous avons considéré un scenario où les champs du modèle standard peuvent se propager dans un espace plat possédant six dimensions. Les nouvelles directions spatiales supplémentaires sont compactifiées sur un Plan Projectif Réel. Cet orbifold original est l'unique géométrie à six dimensions qui présente des fermions chiraux et un candidat de matière noire dit naturel. Le photon scalaire, particule la plus légère du premier mode de Kaluza-Klein, est en effet stabilisé par une symétrie résiduelle de l'invariance de Lorentz à six dimensions. En utilisant les contraintes actuelles fournies par les observations cosmologiques, nous avons déterminé l'ordre de grandeur de la masse de cette particule aux alentours d'une centaine de GeV. De ce fait les nouveaux états présents dans cette théorie sont suffisamment légers pour produire des signatures claires et observables au Large Hadron Collider. Avec une étude plus poussée du spectre de masses et des couplages du modèle, incluant les corrections radiatives à une boucle, nous avons pu ainsi donner les premières prédictions et contraintes sur la phénoménologie attendue au Large Hadron Collider.
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Russell, Michael. "Top quark physics in the Large Hadron Collider era." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8314/.
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We explore various aspects of top quark phenomenology at the Large Hadron Collider and proposed future machines. After summarising the role of the top quark in the Standard Model (and some of its well-known extensions), we discuss the formulation of the Standard Model as a low energy effective theory. We isolate the sector of this effective theory that pertains to the top quark and that can be probed with top observables at hadron colliders, and present a global fit of this sector to currently available data from the LHC and Tevatron. Various directions for future improvement are sketched, including analysing the potential of boosted observables and future colliders, and we highlight the importance of using complementary information from different colliders. Interpretational issues related to the validity of the effective field theory formulation are elucidated throughout. Finally, we present an application of artificial neural network algorithms to identifying highly-boosted top quark events at the LHC, and comment on further refinements of our analysis that can be made.
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Love, Jeremy R. "A search for technicolor at the Large Hadron Collider." Thesis, Boston University, 2012. https://hdl.handle.net/2144/31586.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
The Standard Model of particle physics provides an accurate description of all experimental data to date. The only unobserved piece of the Standard Model is the Higgs boson, a consequence of the spontaneous breaking of electroweak symmetry by the Higgs mechanism. An alternative to the Higgs mechanism is proposed by Technicolor theories which break electroweak symmetry dynamically through a new force. Technicolor predicts many new particles, called Technihadrons, that could be observed by experiments at hadron colliders. This thesis presents a search for two of the lightest Technihadrons, the ρT and ωT . The Low-Scale Technicolor model predicts the phenomenology of these new states. The ρT and ωT are produced through qq annihilation and couple to Standard Model fermions through the Drell-Yan process, which can result in the dimuon final state. The ρT and ω T preferentially decay to the πT and a Standard Model gauge boson if kinematically allowed. Changing the mass of the πT relative to that of the ρT and ωT affects the cross section times branching fraction to dimuons. The ρT and ωT are expected to have masses below about 1 TeV. The Large Hadron Collider (LHC) at CERN outside of Geneva, Switzerland, produces proton-proton collisions with a center of mass energy of 7 TeV. A general purpose high energy physics detector ATLAS has been used in this analysis to search for Technihadrons decaying to two muons. We use the ATLAS detector to reconstruct the tracks of muons with high transverse momentum coming from these proton-proton collisions. The dimuon invariant mass spectrum is analyzed above 130 GeV to test the consistency of the observed data with the Standard Model prediction. We observe excellent agreement between our data and the background only hypothesis, and proceed to set limits on the cross section times branching ratio of the ρT and ωT as a function of their mass using the Low-Scale Technicolor model. We combine the dielectron and dimuon channels to exclude masses of the ρT and ωT between 130 GeV - 480 GeV at 95% Confidence Level for masses of the πT between 50 GeV - 480 GeV. In addition for the parameter choice of m(π T ) = m(ρT /ω T )- 100 GeV, 95% Confidence Level limits are set excluding masses of the ρT and ωT below 470 GeV. This analysis represents the current world's best limit on this model.
2031-01-01
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Hendricks, Khalida. "Jets + Missing Energy Signatures At The Large Hadron Collider." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563367019906869.
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Crispin, Ortuzar Mireia. "High jet multiplicity physics at the Large Hadron Collider." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:68af3867-1488-48d1-9738-73397ba3399d.
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The Large Hadron Collider at CERN completed its first data-taking phase in 2013, after three years of remarkable performance. The high-energy proton-proton collisions recorded by the ATLAS experiment provide a gateway to the world of subatomic particles. This thesis presents two analyses of the full 8 TeV dataset taken by ATLAS, inspired by two of the major physics goals of the experiment. The first analysis is a search for new phenomena that could explain the nature of Dark Matter and solve the hierarchy problem. In particular, the search is optimised to look for heavy supersymmetric particles decaying to large numbers (7 to ≥10) of jets. The events are further classified according to the number of jets identified as originating from a b quark. No evidence is found for physics beyond the Standard Model, so the results are interpreted in terms of exclusion limits on various simplified supersymmetry-inspired models where gluinos are pair produced, as well as a mSUGRA/CMSSM model. The main background to the search is due to multi-jet production via the strong force. This motivates the second analysis presented in this thesis, which is a measurement of the cross section of four-jet events. The measurement is performed differentially in a series of variables which describe the kinematics and spatial configuration of the events. The results are compared to existing theoretical predictions.
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Edelhäuser, Lisa [Verfasser], and Werner [Akademischer Betreuer] Porod. "Model Independent Spin Determination at Hadron Colliders / Lisa Edelhäuser. Betreuer: Werner Porod." Würzburg : Universitätsbibliothek der Universität Würzburg, 2012. http://d-nb.info/1022790897/34.
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Kollár, Monika. "Top-quark and top-squark production at hadron colliders at electroweak NLO." kostenfrei, 2007. http://mediatum2.ub.tum.de/doc/616927/document.pdf.
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Mellor, Paul. "Off-shell effects for single top-quark production processes at hadron colliders." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/3210/.
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We present a calculation of s- and t-channel single top-quark production and decay at next-to-leading order in QCD for the Tevatron and for the LHC. The calculation includes the off-shell effects of the intermediate top-quark and the non-factorisable corrections arising from interferences between the production and decay subprocesses, extending the results beyond the narrow-width approximation. A general method for including such effects is outlined. The method comprises a simultaneous expansion in the coupling constants, as in a standard perturbative approach, along with an expansion in the virtuality of the intermediate heavy-particle. This expansion makes it possible to identify the contributions relevant to the calculation, up to a desired accuracy, before computation of the amplitudes, allowing significant simplifications to be made to the final calculation. Results obtained using this method are presented, along with results obtained using both the standard and improved narrow-width approximations. This enables us to investigate the impact of both off-shell and spin-correlation effects on the cross section and various kinematic distributions. In general, both effects are found to be small except close to kinematic boundaries or for specific distributions, such as the top-quark invariant-mass, where their effects can become sizeable.