## The Faculty of Mathematics and Natural Sciences: Search

Now showing items 1-10 of 38

#### Probing the Standard Model of particle physics with **t<span style="text-decoration:overline;">t</span>H, WWZ **and** WZZ** multilepton final states

(2020-01-13)

The Standard Model of particle physics elegantly describes the fundamental constituents of matter and their interactions. The electroweak gauge and top-quark Yukawa couplings can be directly probed in the associated ...

#### Probing new physics with boosted **H → b<span style="text-decoration:overline">b</span>** decays with the **ATLAS** detector at 13 TeV

(2020-01-27)

The discovery of the Higgs boson by the ATLAS and CMS collaborations at the Large Hadron Collider was a major success in particle physics. Even though studies of the Higgs boson suggest that its properties are in agreement with the Standard Model (SM) expectations, there are still many open questions connected to the physics of the Higgs sector. New physics extensions of the SM attempt to answer these questions. Many new physics models predict heavy resonances which decay into final states with a SM Higgs boson. In this thesis a search for a heavy resonance

**V′**decaying via a**W**or**Z**boson and a Higgs boson into a final state with leptons and**b**-quark jets with the ATLAS detector is presented. One of the main challenges in this analysis is the reconstruction of Higgs bosons with a high Lorentz-boost decaying into**b**-quark jets. In this thesis, reconstruction algorithms for boosted**H → b<span style="text-decoration:overline">b</span>**<span style="text-decoration:overline"></span> decays are discussed, laying emphasis on the identification of**b**-jets (**b**-tagging) in boosted topologies. A new method for a data-based double-**b**-tagging calibration using gluon splitting (**g→ b<span style="text-decoration:overline">b</span>**<span style="text-decoration:overline"></span>) events is presented for the first time for the ATLAS experiment....#### Probing the Interstellar Medium and Dark Matter with Pulsars

(2020-03-05)

Pulsars are rapidly rotating, highly magnetised neutron stars which emit electromagnetic radiation from their magnetic poles in the form of highly collimated beams. Pulsars are known as a powerful tool to probe the ...

#### Hadron-Hadron Interactions from **N<sub>f</sub> = 2+1+1** Lattice QCD: The **ρ**-resonance

(2020-01-07)

In this work the calculation of the

**ρ**resonance's decay parameters with**N<sub>f</sub> = 2+1+1**flavour lattice QCD is presented. The calculation is performed based on gauge configuration ensembles produced by the ETM collaboration which were generated with three different lattice spacing values and pion masses ranging from**230**MeV to**500**MeV. The calculation of resonance parameters with Lattice QCD requires correlation functions of all relevant decay channels in multiple moving reference frames. In this work operators resembling a**ρ**meson as well as a p<sup>+</sup>p<sup> </sup> system are used. The boost to moving frames breaks rotational symmetry and thereby causes a level splitting. Operators which transform like basis states of the reduced symmetry groups' irreducible representations are constructed to determine each energy level individually. Aided by the stochastic Laplacian Heaviside method correlation functions are calculated for all lattice momenta up to**(0, 0, 2)**and all irreducible representations that emerge. <br /> From these correlation functions energy levels are determined under consideration of systematic error sources. Most notably the effect of thermal pollutions and bias from fit range selection are taken into account. By applying the Lüscher method the energy spectra are translated into phase shift curves on each ensemble separately. From a Breit-Wigner fit to the phase shift curves the**ρ**meson mass and width on all ensembles are determined. The results are fed into a combined fit of mass and width and extrapolated to the chiral and continuum limit. <br /> The main result of this thesis are the continuum extrapolated values of**M<sub>ρ</sub>**and**Γ<sub>ρ</sub>**at the physical point which were determined to <center>**M<sub>ρ</sub> = 769(19)**MeV and**Γ<sub>ρ</sub> = 129(7)**MeV. </center> <br /> Lattice artefacts could not be resolved within the statistical uncertainties of this work. While the**ρ**meson mass is in very good agreement with experiment the corresponding decay width differs by about two standard deviations from its experimental counterpart....#### Disconnected Contributions to Hadronic Processes

(2020-01-06)

Lattice quantum chromodynamics (QCD) is a powerful tool to calculate the dynamics of low-energy, non-perturbative QCD. It has made great strides in numerically evaluating hadronic observables by simulating the interactions ...

#### Λ(1405) photoproduction with the BGO-OD experiment

(2020-05-14)

The Λ(1405) has been considered for many years a candidate for an unconventional hadronic state.
Being difficult to understand within the framework of a three valence quark, constituent quark model,
models explicitly ...

#### Jacobi No-Core Shell Model for P-shell Hypernuclei

(2020-06-19)

Understanding baryon-baryon (BB) interactions in the non-zero strangeness sectors is a crucial step toward one of the ultimate goals of nuclear physics - a unified theory describing interactions among baryons. Due to the scarcity of hyperon-nucleon (YN) and practically complete lack of hyperon-hyperon (YY) scattering data, BB interactions in the strangeness <var> S=-1 </var> and <var> S=-2 </var> sectors are poorly constrained and must be additionally confronted to hypernuclear observables such as the binding energies and the energy level splittings. The purpose of this thesis is to develop a many-body method that can accurately calculate observable properties of the light p-shell hypernuclei (with single and double strangeness) and unambiguously connect these properties to that of the underlying YN and YY interactions. For that, we advance the J-NCSM approach that has been a successful tool for describing ordinary nuclei up to the p-shell. The approach is an

**ab initio**method that is based on an expansion in a many-body HO basis depending on relative Jacobi coordinates. We have generalized the J-NCSM formalism so that the extension to strangeness sectors other than <var>S=-1 </var> and <var>S=-2 </var> will be straightforward....#### Halo bias renormalisation

(2020-06-09)

Modern galaxy redshift surveys provide a wealth of information about the evolution of our Universe. They allow to measure both the two-dimensional position on the sky and the distance (given by the cosmological redshift) ...

#### Study of Excited Ξ Baryons in Anti-Proton Proton Collisions with the <span style="text-decoration: overline">P</span>ANDA Detector

(2020-02-11)

Understanding the excitation pattern of baryons is indispensable for the understanding of non-perturbative QCD. Up to now only the nucleon excitation spectrum has been subject to systematic experimental studies, in contrast ...

#### Lepton Flavor Violation Phenomenology Beyond the Standard Model

(2020-03-12)

Historically, experimental searches for flavor violating processes have been essential for the theoretical developments in Particle Physics. After the detection of neutrino oscillations, the most clear experimental evidence ...