Seminars 2020/2021

Scheduled talks

10 December 2020

Speaker: Nora Salone (Studium Doktoranckie NCBJ)

Title: Electromagnetic transition form factors and Dalitz decays of hyperons

Abstract: This project aims to gain information about the hyperon structure through the study of Dalitz decays of a hyperon resonance to a ground-state hyperon and an electron-positron pair. The usual framework of fixed target experiments, albeit very suitable for nucleons, is not as effective for hyperon resonances. One should consequently change the explored kinematical region, from space-like to time-like $q^2$, with the aid of crossing symmetry.

After parametrizing the corresponding baryon-photon-baryon vertex through the use of electromagnetic transition form factors, we formulate double differential decay rates for different spin-parity combinations of the initial state resonance ($J^P = \frac{1}{2}^\pm, \frac{3}{2}^\pm$) transitioning to a ground-state hyperon ($J^P = \frac{1}{2}^+$). Such decay rates are then computed at $q^2=0$ (“QED-type” approximation) and compared to the original quantities where a “radius” structure has been implemented through a low-energy approximation of the form factors. This parallelism can give a rough estimate for the measurement accuracy needed to distinguish between a structure-less and a composite hyperon, namely the minimum requirements for the hyperon internal structure to be “seen”.

Further information on electromagnetic transition form factors can be acquired through the self-analyzing weak decay of the ground-state hyperon: computing the respective multi-differential four-body decay width results  in an additional term containing a relative phase between combinations of the original form factors.

3 December 2020

Speaker: Yashwanth Prabhu (Studium Doktoranckie NCBJ)

Title: On the Determination of 𝛿CP with Accelerator Neutrinos

Abstract: One of the most important open questions in particle physics is whether the CP symmetry is violated in the leptonic sector- more specifically in the neutrino sector. It is well known the CP symmetry is violated in the quark sector. Discovery of CP violation in the neutrino sector will have implications on the observed matter and antimatter asymmetry in the Universe. The leptonic CP violation arises through the phase 𝛿CP which is a parameter in the neutrino mixing matrix. If 𝛿CP takes a non-conserving value, it will result in CP violation.

In my thesis, I studied the effect of 𝛿CP on neutrino and anti-neutrino oscillation probabilities and extended the same to the study of event rates at long baseline neutrino experiments. In this talk, I will discuss the results obtained from my analysis of accelerator neutrinos that travel 1,300 km before detection.

26 November 2020

Speaker: Michał Jędrzejczyk (Studium Doktoranckie NCBJ)

Title: Establishment of reasonable model to simulate emergency passive coolant system in HTTR reactor

Abstract: International Atomic Energy Agency (IAEA) Coordinated Research Program (CRP) on “Heat Transport and Afterheat Removal for Gas-cooled Reactors under Accident Conditions” started in November 1993. In this program, benchmark tasks were proposed for the analysis of passive afterheat removal from gas-cooled reactors (GCR) under accident conditions. The specific objective of the benchmark program is to capture the essential heat transfer features of reactor-to-reactor vessel cooling system (VCS) and provide useful information applicable to a wide variety of designs, operating conditions and model parameters.

In the present study, a 1/6 scale model of VCS for High-Temperature Test Reactor (HTTR) was used to develop a reasonably accurate thermal-hydraulics model of a passive cooling system. HTTR is a graphite-moderated gas-cooled research reactor in Oarai, Ibaraki, Japan, operated by the Japan Atomic Energy Agency (JAEA). The reasonable 2D model was established by using ANSYS Fluent software. In the study temperature profiles of the outside of the scaled reactor vessel for three experiment configurations were obtained numerically and compared with experimental results. The numerical results showed good agreement with the experimental ones. Moreover, a simplified numerical approach has been proposed and new heat transfer coefficients were determined. The approach allows for a two-fluid system simulation with significantly reduced computational costs.

19 November 2020

Speaker: Luis Eduardo Suelves (Studium Doktoranckie NCBJ)

Title: Anisotropic multiplicative bias in weak lensing shear estimates

Abstract: Gravitational weak lensing, the weak regime of gravitational lensing phenomena, arises in the sky as a slight shape distortion of observed galaxies, quantified as a change in their ellipticity. As the only information of a galaxy’s ellipticity that we have is in the observation itself, the gravitational effect has to be extracted statistically. Simply speaking, the intrinsic shape of a set of galaxies at an astronomical frame would stack to that of a circle, therefore, any deviation from this stacked shape would be produced by some mass distribution.

This Master Thesis project was dedicated to characterize the systematic effects that can bias the measurements in weak lensing and cosmic shear surveys of the shear, a main quantity to characterize weak lensing studies. We produced highly simplified simulations of astronomical frames, with a uniform shear applied to the galaxies, using the Stuff/SkyMaker package, and then applied the KSB shear estimation method. The formalism used to calibrate the measurement systematics, called calibration bias, differs from the one found usually in the literature by the introduction of extra cross-components.

12 November 2020

Speaker: Mateusz Kmieć (Studium Doktoranckie NCBJ)

Title: Feasibility Studies of CPT Violation Measurement in Flavour Oscillations of the Neutral D Meson

Abstract: Mesons are bound quark-antiquark pairs. Flavoured neutral mesons are defined as mesons with no electric charge and non-zero strangeness, charm or beauty content. The weak interactions mix neutral-mesons with their antiparticles
leading to spontaneous transitions between meson and  antimeson  quantum  states, which  can  serve  as  a  sensitive  interferometer  facilitating precision testing of CPT invariance.

The main objective of my master’s thesis was to perform feasibility studies of the CPT violation (CPTV) measurement in the system of the neutral D meson. CPT symmetry is one of the fundamental symmetries of the Standard Model (SM). The measurement of CPTV would mean that there exists physics beyond the SM. My goal was to probe the level of sensitivity of testing CPTV in the system of the neutral D meson. For this purpose, I created a Monte Carlo (MC) generator of neutral meson decays, where CPTV was controlled by a complex phenomenological parameter z. The MC generator was used to simulate the CPT violation effect at the level of z=0.1 for an ensemble of 100 pseudo-experiments. Each experiment consisted of N=6.5*107 of MC generated events corresponding to the number of D0 -> K+pi decays collected by the LHCb (2011-2012). For such statistics, the CPT violation effect would be seen at seven standard deviations level. This can be contrasted with the best experimental limit for the parameter z of order O(1) provided by the FOCUS collaboration.

5 November 2020

Speaker: Victor Martínez-Fernández (Studium Doktoranckie NCBJ)

Title: CP violation in the Minimal Linear sigma Model

Abstract: In this seminar we review the generalities of composite Higgs (CH) models that aim to solve the Standard Model hierarchy problem with the introduction of the Higgs as a Nambu-Goldstone boson as well as a new strong sector with new heavy particles. In particular we work with a renormalizable CH model, the Minimal Linear sigma model (MLsM). The phenomenology of this model is extended with the study of the electron electric dipole moment (eEDM) in accordance with the experimental constraints furnished by the ACME Collaboration in order to set limits on the MLsM CP-violating phases.

Our interest in the eEDM stems from the fact that a non-zero value implies CP violation. Since it is a low-energy observable, we perform an integration-out of the heavy fields, obtaining an effective field theory that at 2 loop describes an eEDM (Barr-Zee diagram).

29 October 2020

Speaker: Maitrayee Mandal (Studium Doktoranckie NCBJ)  

Title: Improving the Tau Appearance Study in Atmospheric Neutrinos with Neutron Capture Information at the Super-Kamiokande Experiment

Abstract: The Super-Kamiokande (SK) experiment is dedicated to the detection and understanding of neutrino physics. Currently, few experiments constrain the tau neutrino sector and therefore, improving the detection of the appearance of tau neutrinos in atmospheric neutrino flux at SK is an interesting problem. To identify the tau signal from the background, a neural network is utilised at SK. The predominant background consists of neutral current interactions of neutrinos of all flavors. Lesser neutron captures per event are expected in case of the tau signal than in the predominant background, however the present neural network does not include an input of neutron capture information. The recent SK-Gd upgrade will result in 90% of the neutrons produced in the detector being detected and recognised. In the presented study, we show that adding a new input corresponding to the number of neutron captures per event allows for better classification of the tau-signal. We also observe a positive correlation of initial kinetic energy of the event with the separation of signal and background due to neutron captures.

22 October 2020

Speaker: Paritosh Verma (Studium Doktoranckie NCBJ)  

Title: Searching for gravitational waves from pulsars in Jordan Brans Dicke theory

Abstract: I shall talk about gravitational waves in Jordan Brans Dicke (JBD) theory. There are two tensor polarization states in the General theory of relativity (GR) but there can also be vector and scalar polarization states in alternative theories of gravity. The JBD theory is one of the attempts to modify the general theory of relativity by varying gravitational constant G and it has three polarization states. The first two states are the same as in GR and the third one is the scalar polarization. We have extracted these three polarizations for a particular case of a rotating neutron star with a mountain and then calculated the F-statistic. Finally, we have developed a simulation to estimate the amplitudes from quadrupole as well as dipole emission.