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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

A study of missing transverse energy in minimum bias events with in-time pile-up at the Large Hadron Collider using the ATLAS Detector and √s=7 TeV proton-proton collision data

Wang, Kuhan 03 August 2011 (has links)
A sample of $ L dt = 3.67 pb{-1} of minimum bias events observed using the ATLAS detector at the Large Hadron Collider at $\s=7 TeV is analyzed for Missing Transverse Energy (MET) response in the presence of in-time pile-up. We find that the MET resolution ($\sigma_\text{X,Y}$) is consistent with a simple model of the detector response for minimum bias events, scaling with respect to the sum of the scalar energy ($\sum E_\text{T}$) as $\sigma_\text{X,Y}=A\sqrt{\sum E_\text{T} }$. This behavior is observed in the presence of in-time pile-up and does not vary with global calibration schemes. We find a bias in the mean ($\mu_\text{X,Y}$) of the MET that is linear with respect to $\sum E_\text{T}$, leading to an asymmetry in the $\phi_\text{X,Y}$ distribution of the MET. We propose an explanation for this problem in terms of a misalignment of the nominal center of the ATLAS detector with respect to its real center. We contrast the data with a Monte Carlo sample produced using PYTHIA. We find that the resolution, bias and asymmetry are all approximately reproduced in simulation. / Graduate
72

The cosmic muon flux in the ATLAS Detector at the Large Hadron Collider

Hill, Ewan Chin 01 September 2011 (has links)
Many ATLAS analyses study events with muons in them including those searching for the Higgs boson and new physics. Cosmics muons, however, can also occasionally enter the detector and mimic the trajectory of a muon from one of the collisions produced by CERN’s Large Hadron Collider. By understanding the different ways ATLAS triggers on, collects, reconstructs, and analyses data from cosmic rays and collisions, the flux of cosmic muons with transverse momenta above 20 GeV in the central region of the detector was measured to be 1.34 ± 0.06 (stat.) s^−1 m^−2 . At the same time the cosmic muon charge ratio has been measured to be 1.3 ± 0.1 (stat.). This measurement of the cosmic muon flux in ATLAS is the first step in quantifying the sizes of the cosmic muon backgrounds to various physics analyses that look for events with muons. / Graduate
73

The design and construction of the beam scintillation counter for CMS

Bell, Alan James January 2008 (has links)
This thesis presents the design qualification and construction of the Beam Scintillator Counter (BSC) for the CMS Collaboration at CERN in 2007 - 2008. The BSC detector is designed to aid in the commissioning of the Compact Muon Solenoid (CMS) during the first 2 years of operation and provide technical triggering for beam halo and minimum-bias events. Using plastic scintillator tiles mounted at both ends of CMS, it will detect minimum ionizing particles through the low-to-mid luminosity phases of the Large Hadron Collider (LHC) commissioning. During these early phases, the BSC will provide probably the most interesting and widely used data of any of the CMS sub-detectors and will be employed in the track based alignment procedure of the central tracker and commissioning of the Forward Hadron Calorimeter.
74

The design & construction of the beam scintillation counter for CMS : a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Physics at the University of Canterbury /

Bell, Alan J. January 2008 (has links)
Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. [167]-170). Also available via the World Wide Web.
75

Probing supergravity unified theories at the Large Hadron Collider a dissertation /

Lin, Zuowei. January 1900 (has links)
Thesis (Ph. D.)--Northeastern University, 2008. / Title from title page (viewed March 9, 2009). Graduate School of Arts and Sciences, Dept. of Physics. Includes bibliographical references (p. 114-123).
76

TeV scale leptogenesis, primordial monopoles, and supersymmetry at LHC

Dar, Shahida. January 2008 (has links)
Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisor: Qaisar Shafi, Dept. of Physics & Astronomy. Includes bibliographical references.
77

Physics beyond the standard model supersymmetry, dark matter, and LHC phenomenology.

Essig, Rouven. January 2008 (has links)
Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Physics and Astronomy." Includes bibliographical references.
78

A search for neutral high-mass Higgs bosons decaying into pairs of hadronically decaying tau leptons in 13 TeV collisions recorded by the ATLAS detector

Pickering, Mark Andrew January 2016 (has links)
This thesis outlines the search for neutral Higgs bosons in a mass range of m<sub>H/A</sub> = 200 GeV − 1.2 TeV, decaying to a pair of hadronically decaying tau leptons. The search is performed using &radic;s = 13 TeV proton-proton collision data, corresponding to an integrated luminosity of 3.21 fb<sup>-1</sup>, recorded by the ATLAS detector. No excess over the predicted Standard Model background is observed and upper limits are placed on the production cross section times branching fraction as a function of the mass of the scalar resonance. When combined with the results of the analysis where one of the tau leptons decays to either a muon or electron, the 95% confidence level upper limit on the cross section times branching fraction ranges from 1.4 pb at m<sub>H/A</sub> = 200 GeV to 0.025 pb at m<sub>H/A</sub> = 1.2 TeV for a scalar boson produced via gluon-gluon fusion, and 1.6 pb at m<sub>H/A</sub> = 200 GeV to 0.028 pb at m<sub>H/A</sub> = 1.2 TeV for a scalar boson produced via b-associated production. The results are interpreted in the Minimal Supersymmetric extension to the Standard Model (MSSM) as a limit on the value of tan&beta;, as a function of the mass of the neutral CP-odd MSSM Higgs boson. In the mmod+ scenario, the 95% confidence level upper limit is tan&beta; &LT; 7.6 for m<sub>A</sub> = 200 GeV, and tan&beta; &LT; 47 for m<sub>A</sub> = 1 TeV. For the mass range m<sub>A</sub> &GT; 500 GeV, the upper limit on tan&beta; is improved in comparison to previous ATLAS searches.
79

A study of longitudinal Hadronic shower leakage and the development of a correction for its associated effects at √s = 8 TeV with the ATLAS detector

Gupta, Shaun January 2015 (has links)
In the high energy environment of the Large Hadron Collider, there is a finite probability for the longitudinal tail of the hadronic shower represented by a jet to leak out of the calorimeter, commonly referred to as longitudinal hadronic shower leakage, or jet 'punchthrough'. This thesis prescribes a method for identifying such 'punch-through' jets via the use of muon activity found behind a jet in the ATLAS muon spectrometer, finding an occurrence rate of up to 18% in the worst affected regions. 'Punch-through' jets were found to degrade the measured jet energy scale by up to 30%, and jet energy resolution by a factor of 3. A correction to remove these effects was developed in Monte Carlo and validated in data, with associated systematic uncertainties derived. The correction was found to negate the degradation of the measured jet energy scale, improving the jet energy resolution by up to 10% in the worst affected regions, and up to 1.6% overall. The correction was integrated into the final 2012 ATLAS jet energy calibration scheme as the fifth step of the Global Sequential corrections. The prescription developed in this thesis to derive the correction is currently being used by ATLAS in Run II of the Large Hadron Collider.
80

Calculation of webs in non-Abelian gauge theories using unitarity cuts

Waelkens, Andries Jozef Nicolaas January 2017 (has links)
When calculating scattering processes in theories involving massless gauge bosons, such as gluons in Quantum Chromodynamics (QCD), one encounters infrared (IR), or soft, divergences. To obtain precise predictions, it is important to have exact expressions for these IR divergences, which are present in any on-shell scattering amplitude. Due to their long wavelength, soft gluons factorise with respect to short-distance, or hard, interactions and can be captured by correlators of semi-infinite Wilson lines. The latter obey a renormalisation group equation, which gives rise to exponentiation. The exponent can be represented diagrammatically in terms of weighted sums of Feynman diagrams, called webs. A web with L external legs, each with ni gluon attachments, is denoted (n1; n2; : : : ; nL). In this way all soft gluon interactions can be described by a soft anomalous dimension. It is currently known at three loops with lightlike kinematics, and at two loops with general kinematics. Our work is a step towards a three-loop result in general kinematics. In recent years, much progress has been made in understanding the general physical properties of scattering amplitudes and in exploiting these properties to calculate specific amplitudes. At the same time, we have discovered a lot of structure underpinning the space of multiple polylogarithms, the functions in terms of which most known amplitudes can be written. General properties include analyticity, implying that scattering amplitudes are analytic functions except on certain branch cuts, and unitarity, or conservation of probability. These two properties are both exploited by unitarity cuts. Unitarity cuts provide a diagrammatic way of calculating the discontinuities of a Feynman diagram across its branch cuts, which is often simpler than calculating the diagram itself. From this discontinuity, the original function can be reconstructed by performing a dispersive integral. In this work, we extend the formalism of unitarity cuts to incorporate diagrams involving Wilson-line propagators, where the inverse propagator is linear in the loop momenta, rather than the quadratic case which has been studied before. To exploit this for the calculation of the soft anomalous dimension, we first found a suitable momentum-space IR regulator and corresponding prescription, and then derived the appropriate largest time equation (LTE). We find that, as in the case of the scalar diagrams, most terms contributing to the LTE turn out to be zero, albeit for different reasons. This simplifies calculations considerably. This formalism is then applied to the calculation of webs with non-lightlike Wilson lines. As a test, we first looked at webs that have been previously studied using other methods. It emerges that, when using the correct variables, the dispersive integrals one encounters here are trivial, illustrating why unitarity cuts are a particularly useful tool for the calculation of webs. We observe that our technique is especially efficient when looking at diagrams involving three-gluon vertices, such as the (1; 1; 1) web and the Y diagram between two lines. We then focus on three-loop diagrams connecting three or four external non-lightlike lines and involving a three-gluon vertex. We calculate the previously unknown three-loop three-leg (1; 1; 3) web in general kinematics. We obtain a result which agrees with the recently calculated lightlike limit. We also develop a technique to test our results numerically using the computer program SecDec, and we find agreement with our analytical result. The result for the (1; 1; 3) web can then be exploited to gain insight into the more complicated three-loop four-leg (1; 1; 1; 2) web. Indeed, the (1; 1; 1; 2) web reduces to the (1; 1; 3) web in a certain collinear limit. We propose an ansatz for the (1; 1; 1; 2) web in general kinematics, based on a conjectured basis of multiple polylogarithms. The result for the (1; 1; 3) web, together with the known result for the lightlike limit of the (1; 1; 1; 2) web, imposes strong constraints on the ansatz. Using these constraints, we manage to fix all but four coefficients in the ansatz. We fit the remaining coefficients numerically, but find that the quality of the fit is not good. We find possible explanations for this poor quality. This calculation is still a work in progress. Our results provide a major step towards the full calculation of the three-loop soft anomalous dimension for non-lightlike Wilson lines. We calculated new results for three-loop webs, and also deepened the understanding of webs in general. We confirm a conjecture about the functional dependence of the soft anomalous dimension on the cusp angles. We also confirm earlier findings about the symbol alphabet of the relevant functions. This confirms the remarkable simplicity found earlier in the expressions for the soft anomalous dimension.

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