Physics thesis topics (for October 2021)

  1. Gravitational lensing of the cosmic microwave background
    • Supervisor: dr. hab. Paweł Bielewicz
    • Description: Gravitational lensing of the cosmic microwave background (CMB) is a relativistic effect caused by the gravitational interaction of the CMB photons with matter inhomogeneities encountered during their travel from the last scattering surface to an observer. Reconstructed from correlated CMB photon deflection angles gravitational potential of the lensing structures projected along the line-of-sight gives a unique image of the formation of the large scale structure at high redshifts and enables testing cosmological models at large scales. On the other hand, generated by the lensing effect divergence-free component of CMB polarisation has to be precisely estimated and corrected to be able to detect primordial gravitational waves produced during the inflationary epoch. This PhD project will involve research on different aspects of the CMB gravitational lensing effect including developing and implementation of algorithms for estimation of the gravitational lensing potential, modelling and simulations of the effect, cross-correlations with galaxy and radio surveys and correcting CMB maps for the lensing effect. The PhD student will analyse publicly available data from the Planck satellite and other ongoing and near future CMB experiments. The cross-correlation studies will be also realized within the framework of the Large Synoptic Survey Telescope experiment expected to begin observations in 2022. We seek strongly motivated PhD candidates with interest in cosmology who can demonstrate ability in programming and have experience in numerical methods.
    • Funding: NCBJ Fellowship
  2. Search for new physics with displaced tau leptons and muons with the CMS experiment at LHC
    • Supervisor: dr hab. Michał Bluj
    • Description: The scientific goal of this doctoral Project is to search for phenomena beyond by the Standard Model (BSM) of elementary particles in final states with pairs of tau leptons and muons. The search will be conducted using data from proton-proton (pp) collisions at 13TeV, which will be collected by the Compact Muon Solenoid (CMS) experiment at CERN during the Run-3 of the LHC collider (2022-2024). The study will focus on the search for non-standard signatures with tau leptons and muons produced far from the pp collision vertex, so-called displaced tau leptons and muons. Such final states may arise from the decay of the hypothetical long-lived particles (LLPs) predicted by a number of extensions of the Standard Model. To date, a number of searches for long-lived particles have been performed, some with the CMS detector, but one of the still unexplored signatures are the final states with displaced tau leptons. Among models where such signatures are expected are those in which the LLP couples to particles of the Standard Model by mixing with the Higgs boson, or in which the LLP is a heavy neutral lepton, i.e. a heavy neutrino. The results of the search proposed in the Project may significantly contribute to setting strict limits to the proposed BSM scenarios or to the discovery of new particles. One of the challenges of the Project is a demanding reconstruction of tau leptons. Tau leptons decay in about 1/3 of the cases into lighter charged leptons, electrons or muons, (and neutrinos) or into hadrons (and a tau neutrino) in the remaining 2/3 cases. Charged leptons from tau lepton decays are generally indistinguishable from directly produced leptons, while decays to hadrons can be effectively used to identify tau. The difficulty in reconstructing tau decays into hadrons is the background from hadrons copiously produced in pp collisions. This background must be suppressed as much as possible while maintaining high efficiency of identifying tau. On the other hand, leptonic tau decays, due to the relatively low production rate of leptons in pp collisions, are helpful (in conjunction with hadronic tau decays) in the selection of events containing tau-tau pairs. The first stage of the planned research is to develop algorithms for the reconstruction of the signal characteristic for hadronic decays of tau leptons produced outside the interaction point as such algorithms are currently not available in the CMS experiment. The next step is to build efficient algorithms for triggering based on newly developed tau reconstruction algorithms in combination with similar muon algorithms. The next step is to construct the analysis, i.e. define the event selection, background estimation methods and statistical analysis of the results. A particularly demanding step is the background estimation, which we expect is largely due to instrumental effects that are difficult to simulate. This requires the development of methods to determine the background with the use of control samples of pp collision data. The exact definition of these methods and samples with estimation of related systematic uncertainties are important parts of the Project.
    • Funding: NCBJ Fellowship
  3. Alpha-particle clustering in medium mass nuclei
    • Supervisor: dr hab. Nicholas Keeley
    • Description: The degree of alpha-particle clustering in medium mass nuclei, e.g. Ca and Ar isotopes, is a topic of considerable current interest. Sophisticated large-scale modern shell model calculations are able to predict the structure of these nuclei and can quantify the probability of formation of alpha-particle clusters through the medium of the alpha-particle spectroscopic factors, Sα, quantities which can be extracted from experimental measurements and thus compared with the theory, providing an important validation of the calculations. Unfortunately, the Sα are not observables, that is to say they cannot be directly measured, and must be extracted from direct reaction data using a model of the reaction process. This makes the empirical Sα extracted from data “model dependent” quantities and, despite over 40 years of effort, they remain notoriously poorly determined. This project aims to use new data to be obtained at the Heavy Ion Laboratory of the University of Warsaw to carry out comparative studies of different heavy-ion induced alpha-particle transfer reactions – (12C,8Be), (16O,12C), (20Ne,16O) and (24Mg,20Ne) – to attempt to establish a coherent, consistent picture of the alpha-particle clustering in the ground states of stable Ca isotopes. The successful candidate will be expected to carry out all aspects of the setting up and running of the experiments and the data reduction. A major part of the work will consist in modelling the reaction data using state-of-the-art direct reaction codes to extract the Sα. These will be compared with the results of modern large scale shell model calculations. Part of the goal of this work will be to attempt to establish whether one of the reactions in particular is best suited to these studies. Opportunities to participate in experiments at radioactive ion beam facilities elsewhere will also be available, in particular at GANIL, France, and possibly also ISOLDE, CERN, Switzerland, TRIUMF, Vancouver, Canada, and EXOTIC/SPES, Legnaro, Italy.
    • Funding: NCBJ Fellowship
  4. Search for super-stable super-heavy high-K isomers.
    • Supervisor: dr. hab. Michał Kowal
    • Description: Superheavy elements are extremely unstable systems with very low production cross sections. Existing experimental facilities limit the possibilities for discovery of new nuclides to those synthesized with the cross sections above 100 fb what is possible currently in selected laboratories, actually only in two of them, i.e. in DUBNA and in RIKEN. As the creation of new elements is a very difficult task as a parallel or additional line of study one could try a search for new, long-lived metastable states of already known heavy nuclei. Evaluation of probability of synthesis such heavy nuclei in high-K states via fusion evaporation reactions will be the main topic of this thesis – never done before! Due to small structural overlap and strong centrifugal effect transition between non-analogical states are excluded. Different excitation energies of a high-K configuration in parent and daughter nucleus seem than particularly important for a hindrance of the alpha-decay. This, together with their relatively low excitation suggests a possibility that they could be isomers with an extra stability – five and more orders of magnitude longer-lived than the ground states. This in turn would mean that chemical studies of such exotic high-K sates would be more likely than for quite unstable ground states. In this thesis, for the first time, we plan to include into two- and four-quasi particle states additional odd particle effect with this we are going to discuss the influence of the odd nucleons on the hindrance mechanism in alpha decay process.
    • Funding: NCBJ Fellowship
  5. Quantum groups from quantum gravity
    • Supervisor: prof. dr hab. Jerzy Kowalski-Glikman
    • Description: The quest for quantum gravity is one of the most important unfinished challenges of modern high energy theoretical physics. Its solution will presumably provide us, among others, with an understanding of very early stages of the evolution of the universe and physics of black holes. Unfortunately, in the construction of this theory we not only encounter enormous technical problems, but also, we seem to be guided by only few experimental hints. This is due to the fact that the energy scale where quantum gravity effects become dominant is about 15 orders of magnitude higher that the highest energies seen at LHC. It is of major importance therefore to investigate possible traces that quantum gravity generically leaves at lower energies, changing slightly the theories that we know well and for which we can try to experimentally observe minute departures from the expected behavior. For example, the influence of quantum gravity may modify the early universe cosmological scenarios and the theory of quantum fields, used in the construction of the Standard Model of elementary particle physics. One of the possible ways to organize these possible quantum gravity corrections is to take as a starting point the hypothesis that they are captured by a subtle modification of our low energy theories associated with the emergence of quantum groups that become necessary to properly describe the spacetime symmetries. The aim of the research project the PhD student is supposed to undertake would be to to find out how quantum groups emerge as an effective description of symmetries of fields and particles when quantum gravity effects are considered. Literature: J.Kowalski-Glikman, “A short introduction to kappa-deformation”, Int. J. Mod. Phys. A 32 (2017) no.35, 1730026, doi:10.1142/S0217751X17300265 [arXiv:1711.00665 [hep-th]].
    • Funding: NCBJ Fellowship
  6. Deep and machine learning methods for searching for optical counterparts to gravitational wave events
    • Supervisor: prof. dr hab. Andrzej Królak
    • Auxiliary supervisor: dr Adam Zadrożny
    • Description: One of the hottest topics in today’s astronomy is searching and analyzing optical counterparts to gravitational wave events. Still there is only one such event observed, which is GW170817 / AT 2017gfo. It was observed during LIGO-Virgo Observing Run O2, which lasted 6 months and had one event that might plausibly produce optical counterpart. During O3 the third observing run there were more than 10 event that might have optical counterpart, but yet none was found. In order to make search more successful in upcoming LIGO-Virgo O4 science run (2022+) we would like to develop a strain of machine learning/deep learning methods for optical follow-up. The developed methods would be tested on TOROS collaboration telescopes during LIGO-Virgo O4 Observing Run. There is a possibility to expand scope of the project to electromagnetic data from POLAR-2 and LSST.
    • Funding: NCBJ Fellowship
  7. Studies of eta’ meson decays at BESIII experiment
    • Supervisor: dr hab. Andrzej Kupść
    • Description: The standard model of particle physics (SM) is not complete since it leaves out several questions unanswered, such as why there is more matter than antimatter in the universe. Therefore there should be new paricles not included in the SM. In addition to the direct searches for such particles at high-energy accelerators, a complementary method is to search for indirect effects they have on quantum fluctuations in vacuum. Such effects can be detected in precision low energy experiments such as muon anomalous moment (g-2) measurement or studies of violation patterns of fundamental symmetries such as charge conjugation (C) and parity (P). All low energy tests must include effects from light-hadron interactions (especially from the light mesons) which are difficult to calculate directly from the SM, since they involve strong forces at low energies. At the same time search for violation of the combined CP symmetry outside the known sources in the weak processes can be done using decays of light neutral mesons such as eta and eta’. The aim of the proposed PhD project is experimental study of eta’ meson decays using data collected at electron-positron experiment BESIII in China. The data set of 50 million of eta’ mesons allows one e.g. to improve determination of light meson interactions effects for g-2 value and to perform novel CP symmetry tests. The specific focus of the application are eta’ decay processes with four charged particles. The successful candidate will join new BESIII group at NCBJ.  
    • Funding: NCBJ Fellowship
  8. Modelling dust around evolved stars and its infrared emission for spatially unresolved galaxies
    • Supervisor: dr hab. Katarzyna Małek
    • Auxiliary supervisor: Dr Ambra Nanni
    • Description: Evolved stars (asymptotic giant branch and red super giants) lose mass at high rates enriching the interstellar medium with elements processed in their interiors. The resulting dense circumstellar envelope and relative low temperature make evolved stars the ideal site for the build-up of dust grains from the available metals. Such dust grains absorb the light from stars and re-emit it mainly in the mid-infrared bands. Given they large luminosity, evolved stars shape the spectral energy distribution (SED) of spatially unresolved galaxies in the mid-infrared. The aim of this PhD thesis is to model the observed mid-infrared emission and features of spatially resolved evolved stars as a function of the stellar parameters, to include the results in stellar population synthesis models, and in the code CIGALE in order to model the SED of spatially unresolved galaxies. The PhD student is expected to work in the framework of the NCN SONATA BIS project DINGLE: Dust IN Galaxies: Looking through its Emission.
    • Funding: NCN grant
  9. UV-complete BSM extensions with flavor and dark matter signatures
    • Supervisor: dr hab. Enrico Maria Sessolo
    • Description: The fundamental constituents of matter are described by the Standard Model of particle physics, one of the most successful theories in the history of science. Yet, there exist phenomena that are not predicted in this framework so that developing a theory “beyond” the Standard Model (BSM) and a sound strategy for its detection have become crucial endeavors. The energy scale of the new theory is unknown. It could be the extremely high energy of quantum gravity, which is well-motivated but very difficult to explore experimentally. Much closer to the energies we can probe, however, we sense the presence of particles possibly responsible for some of the signals that recently appeared in the LHCb detector, which are connected to the theory of “flavor.” And many theorists believe that just before our eyes may stretch a world of invisible, feebly interactive light particles, which could be at the origin of dark matter. The goal of this project is to draw connections between these different scales, from the UV to the IR, using modern techniques in quantum field theory, like the idea of asymptotic safety, and a systematic treatment of empirical data based on the latest numerical programs. By combining a variety of multi-scale inputs, the PhD candidate will participate in deriving unique predictions that can be tested in current and future experiments in particle and astro-particle physics.
    • Funding: NCN grant
  10. Direct photon production in relativistic heavy-ion collisions measured in the Alice experiment at the CERN Large Hadron Collider
    • Supervisor: prof. dr hab. Teodor Siemiarczuk
    • Description: The direct photons are the unique probes carrying information about the structure of hadrons and characteristics of the hot partonic matter – the quark-gluon plasma (QGP). The latter is a special state of matter consisting of quarks and gluons no longer confined into hadrons. The QGP was presumably the state of matter existing in the Universe some tiny fraction of a second after the Big Bang. After subsequent cooling, the QGP changed to hadrons which we observe today. The QGP can be created artificially in the laboratory in the small Big Bangs in high- energy heavy-ion collisions when the hadronic matter is heated to the temperature of about 150 MeV. The ALICE experiment, one of the four large CERN experiments, is the only one dedicated to the study of the QGP. ALICE consists of 18 detectors. One of them is the unique highly granulated photon spectrometer with high spatial and energy resolution in a wide dynamical range. The photons interact via the electromagnetic force and, due to the weakness of the electromagnetic interaction compared to the strong interaction between hadrons, their free path in the strongly interacting medium is relatively large. They escape from those hot-spots of the hadronic matter with their momenta unchanged providing us with the „snapshots” of the matter in the moment of their production. The aim of this PhD Thesis will be to single out the direct photons from those stemmed from the particles decay, compare their production with the perturbative QCD predictions for hard interactions of partons and seek for the direct thermal photons emitted from the hot fireball of the quark-gluon plasma.
    • Funding: NCBJ Fellowship
  11. Search for physics beyond the Standard Model in Vector Boson Scattering processes at the CMS experiment
    • Supervisor: dr hab. Michał Szleper
    • Description: Vector Boson Scattering (VBS) processes belong to the most important tests of the Standard Model of particle physics.  They probe Higgs couplings to vector bosons W and Z, as well as triple and quartic couplings between W and Z bosons.  In addition, scattering of longitudinally polarized vector bosons provides a direct insight into the mechanism of electroweak symmetry breaking.  In recent years the CMS and ATLAS experiments at CERN have observed for the first time the VBS processes at a level roughly consistent with Standard Model expectations, but more data is crucial in order to look for possible new physics effects or to place better limits.  The successful applicant will participate in the analysis of CMS data collected during Run 3 of the LHC.  He/she is expected to work on the implementation of the “clipping” technique to derive limits interpretable in the language of Effective Field Theories, development of techniques to tag W/Z polarizations in the final state, and the combination of different channels.  The project will also involve technical work on the CMS muon trigger system as part of the Warsaw CMS group activities.
    • Funding: NCBJ Fellowship
  12. Gluon saturation in Quantum Chromodynamics at high-energy
    • Supervisor: dr hab. Tolga Altinoluk
    • Auxiliary supervisor: dr. Guillaume Beuf
    • Description: Our understanding of protons and neutrons, or nucleons—the building blocks of atomic nuclei—has advanced dramatically, both theoretically and experimentally, in the past half century. It is known that nucleons are made of fractionally charged “valence” quarks, as well as dynamically produced quark-antiquark pairs, all bound together by gluons, the carrier of the strong force. A central goal of modern nuclear physics is to understand the structure of the proton and neutron directly from the dynamics of their quarks and gluons governed by the theory of their interactions, quantum chromodynamics (QCD). The designed Electron Ion Collider (EIC)  is the instrument that can answer many of these fundamental questions. The topics of this PhD project focus on either theoretical or phenomenological investigation of some processes which will play a key role on EIC physics studies and on the interpretation of the results of the ongoing experiments at LHC, JLAB, RHIC and COMPASS. Successful candidate will have the opportunity to collaborate with world-known physicists from France, Spain and USA.
    • Funding: NCBJ Fellowship