The Development of Computational Tools for Theoretical Predictions in Particle Physics at the Large Hadron Collider

The Large Hadron Collider (LHC) experiments are an excellent tool for the improvement of our knowledge of the Standard Model and the examination of Beyond Standard Model theories. Nonetheless, to maximise the learning-potential of the LHC, clear and precise theoretical predictions are needed, for both the Standard Model and its extensions, to allow critical comparison of these models with data. In particular, given the complexity of the collision environment at the LHC, and the expansive nature of many parameter spaces of Beyond Standard Model theories, computational programs to perform theoretical calculations are increasingly required. The work presented in this thesis fits this role, it is focused on two computational programs developed with the aim of producing such theoretical predictions for LHC phenomenology in two key areas. These are the precision Standard Model predictions of transverse momentum spectra for a wide class of processes at the LHC, and Beyond Standard Model predictions for the decay widths of as-yet undiscovered particles in the context of supersymmetry. Chapter 1 presents a brief chronology and review of the Standard Model. Fol- lowing this, the work reported in this thesis is split into two parts, focused on the two main projects undertaken. Chapters 2, 3 and 4 describe the development of the SoftSusy decay calculator program to determine the partial widths and branching ratios of supersymmetric and Higgs particles in the Minimal Supersymmetric Standard Model and the Next-to-Minimal Supersymmetric Standard Model. The theoretical and phenomenological background, methodology, assumptions, and the vast array of decay modes calculated by the program are described. This is followed by details of the extensive validation of the decay calculator program and a selection of results. Chapter 5 begins the second part of the thesis, providing theoretical background for Chapters 6 and 7, which discuss the newly-developed reSolve program, designed to undertake the theoretically-demanding calculations associated with transverse momentum resummation for a wide range of LHC processes. Details of the methods, assumptions, validation and results for channels so far included are all provided, these show excellent agreement with previous theoretical results and experimental data. Both projects are then summarised in Chapter 8. Further information is provided in the appendices; Appendix A presents explicitly all formulae incorporated into the SoftSusy decay calculator pro- gram; whilst Appendix B provides further details on the theoretical underpinning of the transverse momentum resummation calculations performed by the reSolve program.This work was supported mainly by an STFC PhD Studentship. This work has been partially supported by STFC consolidated grant ST/L000385/1, with further help from the Department of Applied Mathematics and Theoretical Physics and the Cambridge Philosophical Society. In addition a portion of this work was completed whilst supported by a KITP Graduate Fellowship from The Kavli Institute for Theoretical Physics, University of California Santa Barbara via the National Science Foundation under Grant No. NSF PHY-1748958 along with the Gordon and Betty Moore Foundation

Constraining the top-quark mass within the global MSHT PDF fit

We examine the ability of experimental measurements of top-quark pair production to constrain both the top-quark mass and the strong coupling within the global MSHT parton distribution function (PDF) fit. Specifically, we consider ATLAS and CMS measurements of differential distributions taken at a centre-of-mass energy of 8 TeV, as well as $t\bar{t}$ total cross section data taken at a variety of experiments, and compare to theoretical predictions including next-to-next-to-leading order corrections. We find that supplementing the global fit with this additional information results in relatively strong constraints on the top-quark mass, and is also able to bound the strong coupling in a limited fashion. Our final result is $m_t=173.0\pm0.6~\mathrm{GeV}$ and is compatible with the world average pole mass extracted from cross section measurements of $172.5\pm0.7~\mathrm{GeV}$ by the Particle Data Group. We also study the effect of different top-quark masses on the gluon parton distribution function, finding changes at high $x$ which nonetheless lie within the large PDF uncertainties in this region.Comment: 35 pages, 13 figures, 3 table

Impact of Inclusive Electron Ion Collider Data on Collinear Parton Distributions

A study is presented of the impact of simulated inclusive Electron Ion Collider Deep Inelastic Scattering data on the determination of the proton and nuclear parton distribution functions (PDFs) at next-to-next-to-leading and next-to-leading order in QCD, respectively. The influence on the proton PDFs is evaluated relative to the HERAPDF2.0 set, which uses inclusive HERA data only, and also relative to the global fitting approach of the MSHT20 PDFs. The impact on nuclear PDFs is assessed relative to the EPPS21 global fit and is presented in terms of nuclear modification ratios. For all cases studied, significant improvements in the PDF uncertainties are observed for several parton species. The most striking impact occurs for the nuclear PDFs in general and for the region of high Bjorken $x$ in the proton PDFs, particularly for the valence quark distributions.Comment: 20 pages, 10 figures, 1 Tabl

Quantifying the interplay of experimental constraints in analyses of parton distributions

Parton distribution functions (PDFs) play a central role in calculations for the LHC. To gain a deeper understanding of the emergence and interplay of constraints on the PDFs in the global QCD analyses, it is important to examine the relative significance and mutual compatibility of the experimental datasets included in the PDF fits. Toward this goal, we discuss the L2 sensitivity, a convenient statistical indicator for exploring the statistical pulls of individual datasets on the best-fit PDFs and identifying tensions between competing datasets. Unlike the Lagrange multiplier method, the L2 sensitivity can be quickly computed for a range of PDFs and momentum fractions using the published Hessian error sets. We employ the L2 sensitivity as a common metric to study the relative importance of datasets in the recent ATLAS, CTEQ-TEA, MSHT, and reduced PDF4LHC21 PDF analyses at next-to-next-to-leading-order and approximate next-to-next-to-next-to-leading-order. We illustrate how this method can aid the users of PDFs to identify datasets that are important for a PDF at a given kinematic point, to study quark flavor composition and other detailed features of the PDFs, and to compare the data pulls on the PDFs for various perturbative orders and functional forms. We also address the feasibility of computing the sensitivities using Monte Carlo error PDFs. Together with the article, we present a companion interactive website with a large collection of plotted L2 sensitivities for eight recent PDF releases and a C++ program to plot the L2 sensitivities

The PDF4LHC21 combination of global PDF fits for the LHC Run III

A precise knowledge of the quark and gluon structure of the proton, encoded by the parton distribution functions (PDFs), is of paramount importance for the interpretation of high-energy processes at present and future lepton-hadron and hadron-hadron colliders. Motivated by recent progress in the PDF determinations carried out by the CT, MSHT, and NNPDF groups, we present an updated combination of global PDF fits: PDF4LHC21. It is based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either its Hessian reduction or its replica compression. Extensive benchmark studies are carried out in order to disentangle the origin of the differences between the three global PDF sets. In particular, dedicated fits based on almost identical theory settings and input datasets are performed by the three groups, highlighting the role played by the respective fitting methodologies. We compare the new PDF4LHC21 combination with its predecessor, PDF4LHC15, demonstrating their good overall consistency and a modest reduction of PDF uncertainties for key LHC processes such as electroweak gauge boson production and Higgs boson production in gluon fusion. We study the phenomenological implications of PDF4LHC21 for a representative selection of inclusive, fiducial, and differential cross sections at the LHC. The PDF4LHC21 combination is made available via the LHAPDF library and provides a robust, user-friendly, and efficient method to estimate the PDF uncertainties associated to theoretical calculations for the upcoming Run III of the LHC and beyond.Comment: 87 pages, 44 figures, 11 table

The genomes of two key bumblebee species with primitive eusocial organization

Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation

A bacterial genome in transition - an exceptional enrichment of IS elements but lack of evidence for recent transposition in the symbiont Amoebophilus asiaticus

<p>Abstract</p> <p>Background</p> <p>Insertion sequence (IS) elements are important mediators of genome plasticity and are widespread among bacterial and archaeal genomes. The 1.88 Mbp genome of the obligate intracellular amoeba symbiont <it>Amoebophilus asiaticus </it>contains an unusually large number of transposase genes (n = 354; 23% of all genes).</p> <p>Results</p> <p>The transposase genes in the <it>A. asiaticus </it>genome can be assigned to 16 different IS elements termed ISCaa1 to ISCaa16, which are represented by 2 to 24 full-length copies, respectively. Despite this high IS element load, the <it>A. asiaticus </it>genome displays a GC skew pattern typical for most bacterial genomes, indicating that no major rearrangements have occurred recently. Additionally, the high sequence divergence of some IS elements, the high number of truncated IS element copies (n = 143), as well as the absence of direct repeats in most IS elements suggest that the IS elements of <it>A. asiaticus </it>are transpositionally inactive. Although we could show transcription of 13 IS elements, we did not find experimental evidence for transpositional activity, corroborating our results from sequence analyses. However, we detected contiguous transcripts between IS elements and their downstream genes at nine loci in the <it>A. asiaticus </it>genome, indicating that some IS elements influence the transcription of downstream genes, some of which might be important for host cell interaction.</p> <p>Conclusions</p> <p>Taken together, the IS elements in the <it>A. asiaticus </it>genome are currently in the process of degradation and largely represent reflections of the evolutionary past of <it>A. asiaticus </it>in which its genome was shaped by their activity.</p

MSHT20aN3LO- Approximate N3LO PDFs withTheoretical Uncertainties

I will discuss our recent paper within the MSHT PDF collaboration on the inclusion of theoretical uncertainties and higher order (N3LO) terms into the MSHT PDFs, producing the MSHT20aN3LO (approximate N3LO) set. This represents the first global analysis of parton distribution functions (PDFs) at approximate N3LO as well as simultaneously the inclusion of theoretical uncertainties into the MSHT PDFs from missing higher order terms beyond NNLO. I will review the formalism, higher orders and theoretical uncertainties included, and their effects on both the fit quality and PDFs before examining indicative N3LO predictions

MSHT20aN3LO- Approximate N3LO PDFs withTheoretical Uncertainties

I will discuss our recent paper within the MSHT PDF collaboration on the inclusion of theoretical uncertainties and higher order (N3LO) terms into the MSHT PDFs, producing the MSHT20aN3LO (approximate N3LO) set. This represents the first global analysis of parton distribution functions (PDFs) at approximate N3LO as well as simultaneously the inclusion of theoretical uncertainties into the MSHT PDFs from missing higher order terms beyond NNLO. I will review the formalism, higher orders and theoretical uncertainties included, and their effects on both the fit quality and PDFs before examining indicative N3LO predictions

MSHT20 - Inclusion of Theoretical Uncertainties and Higher Order Effects into PDFs

I will discuss our recent paper within the MSHT PDF collaboration on the inclusion of theoretical uncertainties and higher order (N3LO) terms into the MSHT PDFs, producing the MSHT20aN3LO (approximate N3LO) set. This represents the first global analysis of parton distribution functions (PDFs) at approximate N3LO as well as the first inclusion of theoretical uncertainties from missing higher orders beyond NNLO. I will review the formalism, higher orders and theoretical uncertainties included, and their effects on both the fit quality and PDFs before examining indicative N3LO predictions