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31رسالة جامعية
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32رسالة جامعية
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33رسالة جامعية
المؤلفون: Li, Ji
المساهمون: Bartolini, Riccardo, Burrows, Philip
مصطلحات موضوعية: 539.7
الوصف: After more than a decade of operation, the Diamond Light Source (DLS) is planning an upgrade to the next generation of diffraction limited synchrotron light sources based on an ultra-low emittance accelerator lattice design. The optimisation of the photon beam properties like flux, brilliance and coherence of the light generated in the storage ring (SR), is a key driver for the storage ring design. The key performance parameters (KPP) characterizing the photon beamlines (BL) define the requirements on the electron beam and on the storage ring design. The storage ring design is supported by the development of optimisation tools that allow the simultaneous modelling of the photon and the electrons beams. A strategy has been developed to bridge the gap between storage ring lattice and beamline needs, based on an integrated approach of accelerator physics tracking codes (ELEGANT) and of radiation codes (SRW, SHADOW). Python is the interface for these codes. This thesis presents the integrated approach used to track electron beams and propagate the synchrotron radiation wavefronts through the beamline. The optimisation of the performance of the beamline is achieved by using multi-objective genetic algorithms. Such an integrated approach is new and promises to achieve the best exploitation of the beamlines, by tailoring the photon beams to the need of the applications.
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34رسالة جامعية
المؤلفون: Taylor, Robert
المساهمون: Vacheret, Antonin
مصطلحات موضوعية: 539.7
الوصف: The groundbreaking observation of neutrino oscillations indicates that the elusive neutrino is massive, providing tantalising evidence for physics beyond the standard model. However, given that neutrinos cannot obtain mass through the same mechanism as the charged leptons, unsolved problems still remain. Neutrinoless double beta decay (0νββ) is a hypothetical process that, if discovered, may shine light on the origins of neutrino mass. It would also confirm that Majorana fermions exist in nature, and that the neutrino is its own anti-particle, demonstrating that lepton number is not conserved through a fundamental symmetry of the universe. In this thesis, the capability of past, present and future dual-phase xenon time projection chambers to search for 136Xe 0νββ is demonstrated. A search for this process is performed in a short 19 kg·yr exposure of the LUX experiment, with the goal of illustrating the reconstruction of O(MeV) events in such detectors, and demonstrating the techniques required for future experiments. Next, the sensitivity of the LUX-ZEPLIN (LZ) experiment to the 0νββ half-life T1/2 is studied, revealing that after 1,000 days of exposure, LZ can exclude T1/2 < 1.06 × 1026 yr at 90% CL. A similar sensitivity projection is also performed for a hypothetical, large scale future detector that utilises O(100 tonnes) of xenon. It is shown that at this scale it is possible to exclude T1/2 < 1.0 × 1028 yr, and probe almost the entire inverted neutrino mass hierarchy at 90% CL. Finally, a machine learning method for fast simulation of the detector response using a generative adversarial network is studied. It is demonstrated that this technique can accurately generate the digitised photomultiplier signals resulting from interactions in a dual-phase detector. This technique may provide a computationally inexpensive method for fast simulation in future detectors.
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35رسالة جامعية
المؤلفون: Trovato, Fabrizio
مصطلحات موضوعية: 539.7, QC0770 Nuclear and particle physics. Atomic energy. Radioactivity
الوصف: Searches for production of charginos and neutralinos as predicted by Supersymmetry in three-lepton final states are presented. The analyses use data collected by the ATLAS detector at 13-TeV proton-proton collisions between 2015-2018 for a total of 139 fb-1. The targeted simplified models are those for the production of the lightest chargino and the next-to-lightest neutralino decaying to the lightest neutralino and Standard Model bosons, W Z or W h, subsequently decaying leptonically to yield three leptons in the final states. No significant deviation with respect to the Standard Model predictions is observed, and results are interpreted as exclusion limits on the considered simplified models. Masses of the lightest chargino and the next-to-lightest neutralino up to 640 GeV are excluded at 95% CL for the W Z model, while in the case of W h model, masses up to 180 GeV are excluded.
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36رسالة جامعية
المؤلفون: Tee, Amy
مصطلحات موضوعية: 539.7
الوصف: This thesis describes a study into Transverse-Momentum-Dependent (TMD) distributions of gluons inside a proton, through a J/ψ meson plus γ final state. The analysis was performed using 2.57 fb−1 of data collected by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV in 2015. A measurement of the continuum J/ψ+γ cross section is carried out, in order to give access to the TMD function fg1(k2T), which describes the distribution of unpolarised gluons in an unpolarised proton. Assuming a Gaussian shape of the TMD distribution, with dependence on the intrinsic transverse momentum of a gluon, kT, a measurement of the mean transverse momentum was achieved at three different invariant mass ranges, Q, of the J/ψ−γ system. The invariant mass ranges, and measured values of ⟨k2T⟩−−−−√ are summarised as follows: for 15 ≤Q< 22 GeV, the mean gluon transverse momentum was found to be ⟨k2T⟩−−−−√ = 1.99 ± 0.25 GeV. For the second invariant mass range considered 22 ≤Q< 31 GeV giving ⟨k2T⟩−−−−√ = 3.63 ± 0.41 GeV. For the last (upper) invariant mass range considered 31 ≤Q< 44 GeV, it was found that 4.08 ± 0.74 GeV. It is shown that between the lowest and highest invariant mass ranges considered, the intrinsic mean transverse momentum of gluons inside an unpolarised proton increases by a factor of 2. The second measurement was an attempt to measure the contribution of the TMD function h⊥g1(k2T), which describes the distribution of linearly polarised gluons inside an unpolarised proton. By measuring the induced angular azimuthal modulations expected from interacting polarised gluons no statistically significant modulation was found with the dataset used.
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37رسالة جامعية
المؤلفون: Montella, Marco
مصطلحات موضوعية: 539.7
الوصف: A search is presented for single-produced vector-like B quark decaying to a Standard Model b-quark and a Higgs boson, itself decaying into a b-quark pair. The B decay system is reconstructed as an association of a large-radius jet and a small-radius jet, respectively taken to reflect the secondary Higgs decay system and the b quark produced in the immediate resonance decay. The search is the first at ATLAS to probe the Higgs to b-quark pair final state in Run-2, and aims at extending the region of the M(B) phase space the current exclusion limits, set by the pair production combination search at 1220 GeV for a Vector-Like B quark occurring as an isospin singlet. For this purpose, a newly designed and optimised event selection was implemented for maximal sensitivity in the 1000-2000 GeV invariant mass region, and a particular effort was dedicated in researching and implementing data-driven modelling techniques to provide a reliable estimation of the main, QCD-Driven, background source to the search. A binned likelihood fit is set up for the statistical interpretation of the results, which are presented in the form of mass- and coupling-dependent 95% CLs exclusion limits on the production cross section of a VLQ-like signal.
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38رسالة جامعية
المؤلفون: Senes, Eugenio
المساهمون: Burrows, Philip, Wendt, Manfred, Krupa, Michal
مصطلحات موضوعية: 539.7, Instrumentation, Physics
الوصف: Novel acceleration technologies promise a large improvement in particle accelerator performance, but pose a number of technical challenges due to the use of several beams and the beam parameters involved. To exploit these new technologies, these technical challenges need to be addressed. Innovative beam instrumentation is to be devised, to allow these acceleration experiments to become operational accelerators. The AWAKE experiment at CERN aims to develop proton beam-driven plasma wakefield acceleration, with the aim of producing high brightness and high energy particle beams for particle physics research. At AWAKE, plasma wakefields are excited by means of a 400 GeV proton beam driver, and used to accelerate an electron witness beam. The plasma is formed by ionising a Rubidium gas with a terawatt laser pulse. The laser, electron and proton beams co-propagate in the same beampipe for metres before entering the plasma. The electron beam diagnostic is obfuscated by the presence of the more intense proton beam. Consequently, the electron beam position cannot be measured in the presence of the proton beam. To drive the acceleration efficiently, a precise positioning of the three beams is crucial. Therefore, a technique to measure the electron beam position in the presence of the stronger proton beam has to be studied. This work addresses the beam position measurement when more than one beam is present in the beampipe. For the case of AWAKE, a technique to measure the electron-beam position exploiting the bunch-length difference with the proton beam is described. It is shown that the electron-position measurement can be carried out, provided that the detection frequency is sufficiently high. In the second part, a novel beam-position-measurement device, capable of working in the required frequency regime, is developed. Such a device is based on the emission of Cherenkov Diffraction Radiation from dielectric inserts in the beampipe. Electromagnetic simulations of the device are shown, together with the results of experimental tests on a prototype. Further developments to produce an operational instrument are discussed. The potential applications of this technology are not only in plasma-acceleration schemes, but also in any accelerator that uses short bunches, e.g. Free Electron Lasers.
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39رسالة جامعية
المؤلفون: Scharmberg, Nicolas
المساهمون: Peters, Yvonne
مصطلحات موضوعية: 539.7
الوصف: In this thesis a novel method for quality control of the cooling half-rings in the pixel endcaps is described. The half rings are used to provide the cooling for pixel modules in the new Inner Tracker of the ATLAS experiment that will operate during the runs of the High Luminosity LHC. In the quality control, they are analysed using infrared measurements during cooling processes. Defective half rings can be found and rejected during the serial production. The sensitivity of this method is shown for small ring pieces with known implanted defects, as well as for a half ring prototype. The measurement of the ttH production cross section with H! bb decays for the full Run II data set, corresponding to an integrated luminosity of 139.0 fb-1 at a centre of mass energy of p s = 13 TeV, is discussed. The signal strength with respect to the Standard Model expectation is measured to be: (ttH = 0.84(+0.49-0.44) (+0.21-0.21 stat.)(+0.44 -0.39 sys.) , which corresponds to an observed (expected) significance of 1.9 sigma (2.2sigma). Additionally, a new analysis strategy to measure the CP-nature of the t-H-coupling in the ttH production is described. This analysis is expected to exclude the purely CP-odd scenario at almost 95% confidence level.
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40رسالة جامعية
المؤلفون: Price, Alan Colm
مصطلحات موضوعية: 539.7
الوصف: Future particle colliders will usher in a new era of precision physics. It will be crucial that the theory community can provide highly precise predictions forthese experiments. In particular, for future e+e− colliders the theoretical calculations will need to improve by a factor 2-100, depending on the observable. In this thesis,we will present the theoretical improvements implemented in the SHERPA event generator for e+e− physics. We will concentrate on the treatment of QED radiation within the framework of Yennie, Frautschi and Suura resummation and discuss its impact on future colliders. In particular, we shall show how initial state radiation can be resummed in a process-independent manner to all orders in the QED coupling. We find that the resummation alone is not sufficient, and the inclusion of fixed-order corrections improves the perturbative description substantially. We will apply these corrections to the study of e+e−→ff,e+e−→W+W− and e+e−→ZH processes at a future lepton-lepton collider, and discuss the impact of the QED corrections. In the second part of this thesis we will consider precision calculation of W/Z+jet at a future hadron-hadron colliders, namely the HE-LHC/FCC-hh. The theoretical modelling of these processes is crucial for controlling the background in many beyond the standard model searches. The processes are calculated up to next-to-next-to-leading order in the QCD coupling αs. A detailed and robust study of the associated scale and shape uncertainties is presented.
