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

The calculation of sparticle and Higgs decays in the minimal and next-to-minimal supersymmetric standard models: SOFTSUSY4.0

We describe a major extension of the SOFTSUSY spectrum calculator to include the calculation of the decays, branching ratios and lifetimes of sparticles into lighter sparticles, covering the next-to-minimal supersymmetric standard model (NMSSM) as well as the minimal supersymmetric standard model (MSSM). This document acts as a manual for the new version of SOFTSUSY, which includes the calculation of sparticle decays. We present a comprehensive collection of explicit expressions used by the program for the various partial widths of the different decay modes in the appendix

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

Wγ production at NNLO+PS accuracy in GENEVA

We present an event generator for the process pp→ℓνℓγ at next-to-next-to-leading order (NNLO) in QCD and matched to the PYTHIA8 parton shower. The calculation makes use of the GENEVA framework, which combines a resummed calculation obtained via Soft-Collinear Effective Theory (SCET) with the fixed-order result. We validate the NNLO accuracy of our results by comparing predictions for inclusive quantities with an independent fixed-order calculation, and then present the resummed partonic 0-jettiness spectrum at next-to-next-to-leading logarithmic (NNLL′) accuracy. Finally, we compare our predictions against data collected by the ATLAS experiment at the Large Hadron Collider during its 7 TeV run, finding good agreement

Organisational culture and its role in developing a sustainable science communication platform

© 2015 Informa UK Limited, trading as Taylor & Francis Group. There is an ongoing tension for scientists when deciding to engage with the public about their research as many scientists view direct participation as peripheral to their role. Pressures of time, lack of support by management and a lack of communicative skills are identified by scientists as reasons for not committing to communicative initiatives. We aimed to explore and explain the organizational culture of a research community that activity communicates with the public and has an international research culture. The Centre for Brain Research (CBR) was identified as a model and was analyzed using the concept of Complex Adaptive Systems (CAS). Twelve participants (scientists (8), clinicians (1), community liaison people (2)) and an identified director of the organization were interviewed. Direct quotes from interview were used to provide examples of the characteristics of CAS for example a variety of agents interacting, adapting the learning within the organization, non-linear dynamic behavior that is a result of aggregates of groups with actions emerging from self-organizing behavior and the development of an emergent culture. This analysis showed that complexity theory was a suitable framework for analyzing the sustainable communicative organization within CBR

The role of founder experience in industrial development: Firm entry, growth and diversification in Pakistan's textile industry during trade liberalisation.

Firm entry, growth and diversification are central drivers of industrial development. However, firms often perform very differently when facing the same institutional environment. Using original data from field research in Pakistan, I find evidence of diverging firm performance in Pakistan's textile industry during trade liberalisation in which only two thirds of Pakistan's textile firms maintain their pre-liberalisation level of exports and market share is gained by better performers. Using data on firm origins and growth, I show how firm performance is related to pre-founder (or Director) experience which includes education, industry-related employment and industry exposure. Representative case studies show that this experience is manifested in the firm's entry strategy, its initial production and organisational capabilities, and persists via its procedures to improve productivity, quality and marketing. In particular, higher managerial quality results in effective recruitment and incentives which enable workers to improve shop-floor performance. Further, I analyse Pakistan's broader industrial diversification to date and show that an increase in competition during trade liberalisation encouraged firm diversification as profitability of the textile sector fell. However, I find that most textile firms and business groups enter protected domestic industries while, in contrast, the founders of firms in higher value-added sectors such as pharmaceuticals and information technology have greater industry-specific education and experience. This further highlights the role of founder experience in shaping industrial diversification and the firm-level roots of growth. In conclusion, I suggest how policy measures to accumulate industry-related experience and increase firm competition could enable low-income countries to break out of the equilibrium of poor industrial development

Germ cell specification and ovary structure in the rotifer Brachionus plicatilis

<p>Abstract</p> <p>Background</p> <p>The segregation of the germline from somatic tissues is an essential process in the development of all animals. Specification of the primordial germ cells (PGCs) takes place via different strategies across animal phyla; either specified early in embryogenesis by the inheritance of maternal determinants in the cytoplasm of the oocyte ('preformation') or selected later in embryonic development from undifferentiated precursors by a localized inductive signal ('epigenesis'). Here we investigate the specification and development of the germ cells in the rotifer <it>Brachionus plicatilis</it>, a member of the poorly-characterized superphyla Lophotrochozoa, by isolating the <it>Brachionus </it>homologues of the conserved germ cell markers <it>vasa </it>and <it>nanos</it>, and examining their expression using <it>in situ </it>hybridization.</p> <p>Results</p> <p><it>Bpvasa </it>and <it>Bpnos </it>RNA expression have very similar distributions in the <it>Brachionus </it>ovary, showing ubiquitous expression in the vitellarium, with higher levels in the putative germ cell cluster. <it>Bpvas </it>RNA expression is present in freshly laid eggs, remaining ubiquitous in embryos until at least the 96 cell stage after which expression narrows to a small cluster of cells at the putative posterior of the embryo, consistent with the developing ovary. <it>Bpnos </it>RNA expression is also present in just-laid eggs but expression is much reduced by the four-cell stage and absent by the 16-cell stage. Shortly before hatching of the juvenile rotifer from the egg, <it>Bpnos </it>RNA expression is re-activated, located in a subset of posterior cells similar to those expressing <it>Bpvas </it>at the same stage.</p> <p>Conclusions</p> <p>The observed expression of <it>vasa </it>and <it>nanos </it>in the developing <it>B. plicatilis </it>embryo implies an epigenetic origin of primordial germ cells in Rotifer.</p

An investigation of the αS and heavy quark mass dependence in the MSHT20 global PDF analysis

We investigate the MSHT20 global PDF sets, demonstrating the effects of varying the strong coupling αS(M2Z) and the masses of the charm and bottom quarks. We determine the preferred value, and accompanying uncertainties, when we allow αS(M2Z) to be a free parameter in the MSHT20 global analyses of deep-inelastic and related hard scattering data, at both NLO and NNLO in QCD perturbation theory. We also study the constraints on αS(M2Z) which come from the individual data sets in the global fit by repeating the NNLO and NLO global analyses at various fixed values of αS(M2Z), spanning the range αS(M2Z)=0.108 to 0.130 in units of 0.001. We make all resulting PDFs sets available. We find that the best fit values are αS(M2Z)=0.1203±0.0015 and 0.1174±0.0013 at NLO and NNLO respectively. We investigate the relationship between the variations in αS(M2Z) and the uncertainties on the PDFs, and illustrate this by calculating the cross sections for key processes at the LHC. We also perform fits where we allow the heavy quark masses mc and mb to vary away from their default values and make PDF sets available in steps of Δmc=0.05 GeV and Δmb=0.25 GeV, using the pole mass definition of the quark masses. As for varying αS(M2Z) values, we present the variation in the PDFs and in the predictions. We examine the comparison to data, particularly the HERA data on charm and bottom cross sections and note that our default values are very largely compatible with best fits to data. We provide PDF sets with 3 and 4 active quark flavours, as well as the standard value of 5 flavours

reSolve — A transverse momentum resummation tool

In this note, we introduce the new tool reSolve, a Monte Carlo differential cross-section and parton-level event generator whose main purpose is to add transverse momentum resummation to a general class of inclusive processes at hadron colliders, namely all those which do not involve hadrons or jets in the measured final state. This documentation refers to the first main version release, which will form the basis for continued developments, consequently it only implements the key features of those we plan to ultimately include. This article acts as a manual for the program; describing in detail its use, structure, validation and results; whilst also highlighting key aspects of the resummation formalism applied. It details the two classes of processes so far included; these are diphoton production and Drell–Yan production. A main concept behind the development of the tool is that it is a hands-on white box for the user: significant effort has been made to give the program a modular structure, making the various parts which comprise it independent of each other as much as possible and ensuring they are transparently documented, customisable and, in principle, replaceable with something that may better serve the user's needs. reSolve is a new C++ program, based on an evolution of the private Fortran code 2gres, it is also influenced by the DYRes Fortran code. This initial version calculates the low transverse momentum contribution to the fully differential cross-section for two main categories of processes; the inclusive production of two photons, and inclusive Drell–Yan production. In all cases resummation up to Next-to-Next-to-Leading Logarithm (NNLL) is included. We aim to extend the program to several more processes in the near future. The program is publicly available on Github. Program summary: Program title: reSolve Program Files doi: http://dx.doi.org/10.17632/4djmkmy69c.1 Licensing provisions: GNU General Public License 3 Programming language: C++, fortran External routines: minuit and Cuba Nature of problem: Calculating the transverse momentum spectrum, including resummation, for a general process at hadron colliders. Solution method: Monte Carlo generation of the phase space points and phase space integration to allow the production of differential distributions, each phase space point itself has to be inverse Fourier transformed and double inverse Mellin transformed to allow the resummation, following the usual transverse momentum resummation impact parameter space formalism. reSolve performs up to Next-to-Next-to-Leading Logarithm resummation (NNLL). Restrictions: So far only diphoton production in the Standard Model (background, not including Higgs) and Drell–Yan production are included, nonetheless the program is designed to allow further extensions to additional processes, including by the user. The limitations on the processes possible to implement are that they must be hadron–hadron collisions producing a non-strongly interacting measured final state system. This first main implementation of reSolve calculates only the resummed part of the differential cross-section, which is dominant at low transverse momentum, this has to be matched with the usual finite contributions to obtain the spectrum over the whole transverse momentum range.This research has been partially supported by STFC consolidated grant ST/L000385/1 and by STFC consolidated grant ST/P000681/1, and also in part by the National Science Foundation under Grant No. NSF PHY-1748958 along with the Gordon and Betty Moore Foundation

Updates of PDFs using the MMHT framework

We summarise recent developments in the path towards the "MMHT19" parton distribution functions. We concentrate on the extraction of the strange quark upon the improvement of theoretical calculations for NNLO charged current cross sections; the effect of an extension of our parameterisation; and the role of correlated uncertainties in some data sets which prove difficult to fit