Research

Postdoctoral researcher at AGH University of Kraków, Faculty of Physics and Applied Informatics

Since October 2021 I have been involved in the study of relativistic heavy-ion collisions as a member of the AGH Heavy-Ion Collision Physics group from the ATLAS collaboration. One of the main tasks was to optimize the reconstruction and identification of photons with low $p_T$ values in ultraperipheral lead-lead collisions (UPC). Events were reconstructed using lower thresholds and looser selection criteria in the reconstruction. It will be important, for instance in measuring light-by-light scattering, where two photons with low $p_T$ are present in the detector without any other activity above noise thresholds. The efficiency of cluster and photon reconstruction has been significantly improved for photon $p_T < 5$ GeV for UPC HI events. For example, for photon $p_T = 1.5$ GeV, the efficiency was 15\% with default photon thresholds and is now about 70\% with optimized requirements. A dedicated working point for the identification of very loose photons has been developed for Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.36$ TeV. It is based on the ``cut-based’’ method. As a result, a constant photon identification efficiency of 95% was achieved.

Also, I am taking part in the analysis of measurements of top quark pair production in proton-lead collisions at $\sqrt{s_{\mathrm{NN}}} = 8.16$ TeV in the ATLAS experiment. The data set was recorded in 2016 and corresponds to an integrated luminosity of 165 nb$^{-1}$. Top quarks are reconstructed in the lepton+jet and dilepton decay channels with electrons and muons in the final state. The dilepton channel is being studied in heavy-ion collisions for the first time. My main task was to estimate the background contribution to the signal sample. Using the Matrix Method, the efficiencies of fake leptons and two components of real leptons for proton-lead collisions were measured. These efficiencies are input data for the matrix method to determine distributions for non-prompt and fake lepton background in $t\bar{t}$ production. The method uses regions in the transverse momentum space of leptons enriched with fake and non-prompt leptons from MC simulation. The background from $W$ boson decay, $Z$ boson decay, and $t\bar{t}$ production have been determined and subtracted. The efficiency of fake leptons is measured for electrons and muons for transverse momenta $p_T > 18$ GeV and absolute pseudorapidity $\left\lvert \eta < 2.5 \right\rvert$.

Last but least, I am working with the inter-experimental group HonexComb as part of the STRONG-2020 project, of which AGH is a member, consisting of experimenters and theorists from LHC. My task aims to average the existing measurements of lepton pair production in ultra-peripheral lead-lead collisions, $ Pb+Pb \rightarrow Pb(\gamma \gamma \rightarrow \tau\tau)Pb $, at $\sqrt{s_{\mathrm{NN}}}=5.02 $ TeV in LHC. I am working on combining results from the ATLAS and CMS experiments regarding the anomalous magnetic moment of the tau lepton using an extended maximum likelihood method. This analysis is ongoing.

PhD studies at Jagiellonian University, Faculty of Physics, Astronomy and Applied Computer Science

In 2021 I finished my doctoral thesis at Jagiellonian University under the supervision of dr hab. Roman Skibi{'n}ski. My doctoral dissertation deals with the theoretical study of the three-nucleon observables for the nucleon elastic and inelastic scattering on the deuteron. This is also supplemented by the study of other selected quantities in few-nucleon systems using nucleon-nucleon (NN) nuclear potentials for which statistical properties (the expected values and covariance matrix) of parameters are known. For my research work the most important examples of such models are the new generation of the chiral interaction derived up to fifth-order (N$^{4}$LO$^{+}$) of the chiral expansion using the semilocal regularization in momentum space (SMS) by the Bochum-Bonn group and the One-Pion-Exchange-Gaussian (OPE-Gaussian) potential. These models are dictated by the availability of the covariance matrix for the potential parameters. Knowledge of the covariance matrix of NN potential parameters opens possibilities in studies of few-nucleon systems.

My doctoral dissertation concerns the application of the covariance matrix of the nucleon-nucleon interaction potential parameters in the study of proton scattering reactions on a neutron and, first of all, an elastic neutron scattered by a deuteron. In addition, I showed several results related to the deuteron breakup reaction by the nucleon and the binding energy of the deuteron and triton. In addition, I demonstrated several results related to the deuteron breakup reaction by a nucleon and the binding energy of a deuteron and a triton. I used modern nuclear force potentials, such as the One-Pion-Exchange Gaussian potential, as an example of a semi-phenomenological model of nuclear forces and nucleon-nucleon SMS (semi-local moment space regularized) potential obtained by the chiral approach. The latter model is currently the best model available for theoretical research between two nucleons. The version of the chiral potential I used contains all the elements up to the fifth order of the chiral expansion (N$^4$LO) and is even supplemented by the selected elements of the next order (N$^4$LO$^+$ force). Both of the models used were derived in the recent past (2014 and 2018, respectively) and one of their advantages is the availability of the covariance matrix for free parameters of these forces. The use of this matrix is the main topic of the presented doctoral dissertation for the investigated processes.

The most important scientific result presented in the dissertation on theoretical uncertainties is the estimation of the uncertainty of theoretical predictions, which arises due to the uncertainty of the nucleon-nucleon potential parameters, the source of which is the uncertainty of experimental data used to determine the values of these parameters. In addition to this type of theoretical uncertainty (so-called statistical uncertainty), I compared it with other types, i.e. the truncation error arising from neglecting corrections to the nuclear potential coming from higher orders of the chiral expansion, estimated, among other things, within Bayesian statistics and the cutoff dependence of chiral predictions — uncertainty resulting from the dependence of theoretical predictions on the value of the chiral potential regularization parameter. It was found that the resulting statistical uncertainty is smaller than the truncation errors for the chiral force at lower orders of the chiral expansion. At the higher orders of the chiral expansion and at low energies the statistical error exceeds the truncation one but at intermediate and higher energies truncation error is more important.

The second problem examined in the dissertation concerned the study of the correlation among observables in the reactions of elastic proton-neutron or neutron-deuteron scattering. Correlation coefficients were estimated among many observables and investigated their dependence on the scattering angle, reaction energy, and nuclear potential. Thus, it was possible to identify pairs of observables that remain linearly correlated with each other, or for which the correlation coefficient remains close to zero. The results of these studies significantly expanded the knowledge about the correlations that occurred, previously limited to only two or three cases of pairs of observables. I comprehensively examined all pairs of observables in the elastic neutron-deuteron scattering, obtaining information about their correlation. For example, I showed that the pair of the neutron-vector and the deuteron-tensor analyzing powers maintain a strong mutual correlation even at higher energies ($E$ = 135 MeV). On the other hand, most observables show a linear dependence only at low energies, which is most likely due to the sensitivity of these observables to selected potential parameters only. Knowing if some observables are or are not correlated, will influence future methods of fixing free parameters of the two- and many-body potentials. It is hoped that the results of this study will help to improve the efficiency of the fitting procedure used to determine nucleon-nucleon potential parameters by improving the accuracy of determining potential parameters and our understanding of the three-nucleon Hamiltonian.

During my summer 2021 fellowship, I had the opportunity to work remotely with the BAND (Bayesian Analysis of Nuclear Dynamics) team, collaborating with members from Northwestern and Michigan State University (USA). The primary focus of our work involved developing an interface that bridged a physics code with the BAND/surmise framework (written in python). Our main goal was to address how uncertainty quantification can be integrated into nuclear physics at every level from theoretical modeling and simulations, to experimental analysis and control. In particular, we focused on addressing nucleon-nucleon and nucleon-deuteron scattering problems while constructing this interface. Results were presented at the Quark Matter 2022 conference (Krakow).