352,942 research outputs found

    Impact of Theory Uncertainties on the Precision of the Top Quark Mass in a Threshold Scan at Future e+e- Colliders

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    Future energy-frontier electron-positron colliders will be capable of high-precision studies of top quark properties. The measurement of the top-pair production cross section around the threshold provides access to the mass of the top quark in theoretically well-defined schemes, with statistical uncertainties of 20 MeV or less, depending on the assumed integrated luminosity of the measurement. At this level of precision, experimental and theory systematics are likely to become important or even dominant. This contribution presents a first analysis of the impact of the remaining uncertainties of the recently completed calculation of the top pair production cross section at NNNLO QCD including the exchange of Higgs bosons on the extraction of the top quark mass from a threshold scan. The analysis is based on reconstruction efficiencies and background levels obtained in full simulation studies for CLIC, combined with signal cross sections from the higher-order calculations. To assess possible differences between different collider options, the study is performed in the context of CLIC, ILC and FCC-ee by considering the differences in the luminosity spectra.Comment: 5 pages, 3 figures, proceedings ICHEP 201

    A Study of Direct Photon Production in Hadronic Interactions

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    This thesis presents results on direct photon production in pi--p and pi+-p interactions at an incident beam momentum of 280 GeV/c, using data recorded by CERN experiment WA70 at the Omega Prime Spectrometer. The direct photon cross-section, and the ratio of direct photon and pi cross-sections, is measured over the Pt range 4-7 GeV/c and the Feynman X range -0.4 to 0.4. Chapter 1 gives an account of the theoretical framework used to describe direct photon production, together with a brief review of recent experimental results. Chapter 2 describes the experimental apparatus used by WA70, with particular emphasis on the high-granularity electromagnetic calorimeter constructed specifically for the experiment. Chapter 3 discusses the reconstruction programs used to process the raw data from the Omega Prime Spectrometer and calorimeter prior to performing any physics analysis. Chapter 4 describes the sequence of cuts used to isolate the pi0 and direct photon signals in the experimental data. In Chapter 5, the efficiencies of detection of pi0s and direct photons, and the residual backgrounds in the direct photon signal, are determined. The simulation programs used to measure these efficiencies and backgrounds are described, together with the methods used when the simulation programs could not be applied. Finally, in Chapter 6 the cross-sections for direct photon and pi0 production and the ratio of the cross-sections are presented. The pi0 cross-sections are compared to the parametrised results from other experiments, and the direct photon cross-sections are compared with the predictions of next-to-leading order perturbative quantum chromodynamics

    Direct Photon and pi0 Production in pi-p, &pi+p and pp Interactions at 280 GeV/C

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    This thesis presents results on direct photon and pi0 production in pi-p, pi+p and pp interactions at an incident beam momentum of 280 GeV/c, using data recorded by CERN experiment WA70 at the Omega Prime Spectrometer. Chapter 1 discusses the theoretical background for direct photon production and presents results from previous experiments. Chapter 2 describes the experimental apparatus used by WA70, with particular emphasis on the high-granularity electromagnetic calorimeter constructed specifically for the experiment. Chapter 3 discusses the reconstruction programs used to process the raw data from the Omega Prime Spectrometer and calorimeter prior to performing any physics analysis. Chapter 4 presents a detailed account of the method, developed by the author, to calculate the efficiencies of the individual planes of the 4m wire chamber, and presents these efficiencies for the two experimental runs. Chapter 5 discusses some of the methods used in offline calibration of the electromagnetic calorimeter, referring particularly to two separate studies performed by the author, (i) the detection of a discontinuity in the online calibration for the 1984 data taking run, and (ii) the search for a J/ps signal in the 1985 run, which would be particularly useful, since the e+e- pair can be detected in both the wire chambers and photon detector. In Chapter 6 an analysis of the 1985 data is performed to provide the cross- sections for direct photon and pi production and the ratio of the cross-sections. This chapter gives a description of the procedures involved in producing the raw signals, calculating the various cuts and contaminations, and evaluating the detection efficiencies for pi and direct photons. The pi cross-sections are compared to the parametrised results from other experiments, and the direct photon cross-sections are compared with the predictions of next-to-leading order QCD

    Glare, a GIS tool to reconstruct the 3D surface of palaeoglaciers

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    Acknowledgements This research has been supported by the Leverhulme Trust International Network Grant IN-2012-140. Processing and collecting of ground penetrating data in Forgefonna was part of Elend Førre's master's project that was completed in 2009 at the Department of Geography, University of Bergen. We also acknowledge Dr Andreas Bauder for providing the subglacial topography data for Griessgletscher and Simone Tarquini for granting access to the high resolution TIN of Italy, a cut of which is provided to the reader to practice the tools (see Appendix). Referees Dr. Iestyn Barr, Dr. Jeremy Ely and Dr. Marc Oliva are thanked for their constructive comments and tool testing, which significantly improved the final output.Peer reviewedPostprin

    Charm, Beauty and Top at HERA

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    Results on open charm and beauty production and on the search for top production in high-energy electron-proton collisions at HERA are reviewed. This includes a discussion of relevant theoretical aspects, a summary of the available measurements and measurement techniques, and their impact on improved understanding of QCD and its parameters, such as parton density functions and charm- and beauty-quark masses. The impact of these results on measurements at the LHC and elsewhere is also addressed.Comment: 103 pages, 60 figures, to be published in Prog. Part. Nucl. Phy

    Diboson Production in Proton-Proton Collisions at s=7\sqrt{s}=7 TeV

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    This review article summarizes results on the production cross section measurements of electroweak boson pairs (WWWW, WZWZ, ZZZZ, WγW\gamma and ZγZ\gamma) at the Large Hadron Collider (LHC) in pppp collisions at a center-of-mass energy of s=7\sqrt{s}=7 \TeV. The two general-purpose detectors at the LHC, ATLAS and CMS, recorded an integrated luminosity of 5fb15fb^{-1} in 2011, which offered the possibility to study the properties of diboson production to high precision. These measurements test predictions of the Standard Model (SM) in a new energy regime and are crucial for the understanding and the measurement of the SM Higgs boson and other new particles. In this review, special emphasis is drawn on the combination of results from both experiments and a common interpretation with respect to state-of-the-art SM predictions.Comment: 60 page

    Closing the Wedge: Search Strategies for Extended Higgs Sectors with Heavy Flavor Final States

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    We consider search strategies for an extended Higgs sector at the high-luminosity LHC14 utilizing multi-top final states. In the framework of a Two Higgs Doublet Model, the purely top final states (ttˉ,4tt\bar t, \, 4t) are important channels for heavy Higgs bosons with masses in the wedge above 2mt2\,m_t and at low values of tanβ\tan\beta, while a 2b2t2 b 2t final state is most relevant at moderate values of tanβ\tan \beta. We find, in the ttˉHt\bar t H channel, with HttˉH \rightarrow t \bar t, that both single and 3 lepton final states can provide statistically significant constraints at low values of tanβ\tan \beta for mAm_A as high as 750\sim 750 GeV. When systematics on the ttˉt \bar t background are taken into account, however, the 3 lepton final state is more powerful, though the precise constraint depends fairly sensitively on lepton fake rates. We also find that neither 2b2t2b2t nor ttˉt \bar t final states provide constraints on additional heavy Higgs bosons with couplings to tops smaller than the top Yukawa due to expected systematic uncertainties in the ttˉt \bar t background.Comment: Added a Fig. and updated references. Matches journal version. 31 pages, 11 figure

    Jets in Hadron-Hadron Collisions

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    In this article, we review some of the complexities of jet algorithms and of the resultant comparisons of data to theory. We review the extensive experience with jet measurements at the Tevatron, the extrapolation of this acquired wisdom to the LHC and the differences between the Tevatron and LHC environments. We also describe a framework (SpartyJet) for the convenient comparison of results using different jet algorithms.Comment: 68 pages, 54 figure
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