Dr Ulla Blumenschein Project Abstract
BSc projects
Search for Supersymmetry at the LHC
The search for a fundamental theory of matter and forces in the universe has ever since attracted the interest of physicists. The large success of the gauge theories in the description of low-energy phenomena nourishes the hope that gauge symmetries are the clue to a unified description of all fundamental processes at high energy scales. Particle collision experiments of the past decades have probed the structure of matter with increasing resolution. The phenomena observed in collision experiments at current energy scales are described with a large precision by the Standard Model of particle physics. Nevertheless, many open questions in the Standard Model suggest that it is an effective low-energy theory of a more fundamental theory: the numbers of free parameters of the model, the numbers of generations, the hierarchy between the electroweak scale and the Planck scale, the pending integration of gravity and the evolution of the strengths of the fundamental forces at large energy regimes. In addition, recent cosmological data suggest that the density of ordinary matter which is described by the Standard Model, corresponds only to a small fraction of the matter density in the universe.
Many of the above mentioned problems are addressed by an extension of the Standard Model that is based on an additional internal symmetry, the Supersymmetry of fermions and bosons. It predicts the existence of a partner for each known fundamental particle with the same quantum numbers but different spin. Supersymmetry must be broken at the energy regime of present collider experiments which leads to different masses of Standard Model particles and their super-partners.
Supersymmetric particles have been searched for at various colliders with increasing energy coverage. In the past years, the Large Hadron Collider at CERN has opened new mass regimes to the search for these particles.
In this project, you are expected to review the motivation and fundamental structure of supersymmetric theories and the outcome of the search for Supersymmetry in the past years at the Large Hadron Collider.
Measurement of the strength of quartic gauge-boson couplings at the high-luminosity Large Hadron Collider.
The non-Abelian nature of the electroweak SU(2)L× U(1)Y gauge structure in the Standard Model of particle physics leads to triple and quartic couplings between gauge bosons. The strength of these gauge boson self-interactions is predicted by the Standard-Model. These interactions contribute directly to diboson and triboson production at particle colliders. Studies of triboson production can test in particular the quartic interactions and any possible observed deviation from the theoretical prediction would provide hints of new physics at a higher energy scale. Compared with triple gauge couplings, quartic gauge couplings are usually harder to study due to the, in general, smaller production cross sections of the relevant processes. Many of these rare processes are expected to barely be discovered in the coming years at the Large-Hadron-Collider (LHC). The upgraded version of this collider, the high-luminosity Large-Hadron-Collider, HL-LHC, which is expected to start in 2024, will be able to increase the amount of data by a factor of hundred compared to our current records. With this large amount of data, it will be possible to measure quartic gauge-boson couplings at a high precision and maybe even discover hints for new physics at higher energy regimes.
In this project, you will investigate how to select final-states with three W bosons or a combination of W and Z bosons, via their decays into leptons using simulations of the new HL-LHC. You will derive estimates of how precisely we can measure the rate of such processes and hence the strength of the quartic gauge couplings. The analysis will be performed using the modular scientific software framework ROOT.
Requirement: C++ programming skills.
MSci projects
Study of the production of b or c quarks in association with Z bosons in the ATLAS experiment.
The production of Z bosons with leptonic decays has become a standard candle in the hadron collider experiments. The production rate is known to high precision. A subset of these Z bosons is produced together with heavy bottom and charm quarks, usually due to a heavy quark in the initial state or due to final-state radiation. These processes are of highest interest, as they can be used to study both the proton structure and perturbative Quantum Chromo Dynamics. In addition, they constitute a major background for both Higgs-boson and top-quark physics. Bottom and charm quarks can be selected based on the feature that they evolve into B and D mesons which travel a tiny distance through the detector before they decay, such that the decay vertex of these particles is displaced with respect to the primary interaction vertex.
In this project, you will use recent fully calibrated ATLAS data to first select Z bosons decaying to electrons or muons and then select bottom or charm quarks produced in association with the Z bosons. You will compare the measured rate with theoretical predictions built into Monte-Carlo Generators or QCD calculations. The analysis will be performed using the modular scientific software framework ROOT.
Requirement: C++ programming skills.
Measurement of quartic gauge-boson couplings and search for new physics at the high-luminosity Large Hadron Collider.
The non-Abelian nature of the electroweak SU(2)L× U(1)Y gauge structure in the Standard Model of particle physics leads to triple and quartic couplings between gauge bosons. The strength of these gauge boson self-interactions is predicted by the Standard-Model. These interactions contribute directly to diboson and triboson production at particle colliders. Studies of triboson production can test in particular the quartic interactions and any possible observed deviation from the theoretical prediction would provide hints of new physics at a higher energy scale. Compared with triple gauge couplings, quartic gauge couplings are usually harder to study due to the, in general, smaller production cross sections of the relevant processes. Many of these rare processes are expected to barely be discovered in the coming years at the Large-Hadron-Collider (LHC). The upgraded version of this collider, the high-luminosity Large-Hadron-Collider, HL-LHC, which is expected to start in 2024, will be able to increase the amount of data by a factor of hundred compared to our current records. With this large amount of data, it will be possible to measure quartic gauge-boson couplings at a high precision and maybe even discover hints for new physics at higher energy regimes.
In this project, you will select final-states with three W bosons or a combination of W and Z bosons, via their decays into leptons using simulations of the new HL-LHC. You will derive estimates of how precisely we can measure the rate of such processes and hence the strength of the quartic gauge couplings. You will also investigate the sensitivity to generic new physics models, which would introduce anomalous quartic gauge couplings which increase the rate of this process at high energy regimes.
The analysis will be performed using the modular scientific software framework ROOT.
Requirement: C++ programming skills.
