abstract

Positronium is a suitable leptonic system to test Charge-Parity (CP) discrete symmetry involving the correlations of photons momenta originating from ortho-positronium (o-Ps) annihilation. The photon–photon interaction in the final state due to the vacuum polarization may mimic CP symmetry violation of the order of \(10^{-9}\), while weak interaction effects lead to a violation of the order of \(10^{-14}\) according to the Standard Model prediction. So far, the experimental limits on CP symmetry violation in the o-Ps decay are set at the level of \(10^{-4}\). One of the unique features of the J-PET detector is its ability to measure the polarization direction of the annihilation photons without the magnetic field. The J-PET detector can be used to explore discrete symmetry by looking for probable non-zero expectation values of the symmetry-odd operators, constructed from spin of ortho-Positronium and momentum, and polarization vectors of gamma (\(\gamma \)) quanta resulting from o-Ps annihilation. In this work, the J-PET detector experimental and analysis method to improve the sensitivity level at least by one order for CP discrete symmetry studies in the o-Ps decay via symmetry odd operator \((\vec {\epsilon }_{i} \cdot \vec {k}_{j})\), where \(\vec {\epsilon }_{i}\) and \(\vec {k}_{j}\) are reconstructed polarization and momentum vectors of photons from the o-Ps decays, respectively, will be presented.

abstract

Cosmic ray muon scattering tomography is a non-invasive screening technique that can provide three-dimensional images of the internal structure of large objects such as shipping containers, allowing for comprehensive searches for hidden illicit items. Cosmic ray muons possess substantially higher energies compared to typical X-rays, which gives them the ability to penetrate large and dense materials. This unique characteristic makes muon scattering tomography a valuable tool for identifying materials hidden inside shielding that may be too thick or deep for other imaging methods such as X-rays or conventional gamma-ray scanning. We report a Geant4 simulation study for the detection of low- and high-\(Z\) illicit objects hidden inside a legal cargo in a shipping container. We have used the Point of Closest Approach (PoCA) reconstruction algorithm to create the three-dimensional image of a shipping container and have applied image processing tools to improve signal-to-noise ratio for detection of illicit objects inside the legal cargo. Simulation and reconstruction results showed that the applied method can detect illicit materials within a minute time scale.

abstract

This paper deals with summarizing available results to indirectly observe a bound dineutron in the (\(n\), \(^{2}n\)) nuclear reactions on \(^{159}\)Tb and \(^{197}\)Au and its properties to characterize the dineutron as a unique nucleus with the magic number 2. Upon its full-scope discovery, this could open the row with \(N=2\) in the interactive chart of nuclides. To finalize the existence of a bound dineutron, its decay products must be observed. Therefore, a Geant4 model has been developed to simulate the decay of bound dineutrons and detect electrons as one of the decay products of the dineutron. The results obtained demonstrate that a thoroughly planned experiment could provide a positive assurance for observation of a bound dineutron within the \(E_\beta = 190\)–560 keV energy region of the instrumental beta spectrum.

abstract

Spin-polarized surface positronium (Ps) spectroscopy is a new method to characterize the spin-polarized electronic states associated with the top-surface of solid. We have been developing this method based on the Ps time-of-flight technique with a transversely spin-polarized positron beam generated with a \(^{22}\)Na source. Although the spin-polarized density of states (DOS) of Ni(111) and Co(0001) surfaces were successfully obtained, there was still room for improvement in the energy resolution and count rate. Subsequently, we inserted a Ps quencher (Kapton) at the detector position so that more Ps atoms were captured in a reduced time (and hence energy) window. Consequently, the energy resolution and count rate were improved by an order of magnitude, giving rise to much better spin-polarized DOS profile. In the future, to obtain further information about the band dispersion and the Fermi surface of solid top-surface, this method needs to be extended to the angle-resolvable version. In this respect, we discuss the possibility of positron emission tomography technology.

abstract

The positronium, a bound state of electron and positron, is a unique system to perform highly precise tests, due to no hadronic background and precise Quantum Electrodynamics (QED) predictions. Being a system of lepton and antilepton, its properties are precisely described by QED in the Standard Model (SM). The final events topology can be simulated using Monte Carlo techniques. The J-PET detector is a multi-purpose, large acceptance system that is very well-suitable to the studies of positronium decay due to its excellent angular (\(1^\circ \)) and timing resolutions. We present preliminary results on the feasibility of searching for Dark Matter (DM) candidates in the decay o-Ps \(\rightarrow \) invisible with the J-PET, which is well-suited for the detection of positronium-decay products. Toy Monte Carlo simulations have been prepared to incorporate DM decay models to the o-Ps decay expectations in order to assess the detector capabilities to search for such an elusive component of our Universe.

abstract

The PANTHEON project aims to test the Pauli Exclusion Principle (PEP) in nuclear reactions by searching for nuclear transitions prohibited by PEP in processes respecting the Messiah–Greenberg super-selection rule. The project aims at using the proton beam from the 3.5 MV Singletron accelerator of the Bellotti facility located at the Gran Sasso Underground Laboratory, to perform a measurement based on a test setup able to disentangle protons coming from the PEP-prohibited processes. The goal is to prepare a dedicated setup for future measurements to improve by orders of magnitude the limit on PEP violation established in previous studies and challenge theories beyond the Standard Model at a precision level presently unattained.

abstract

In the framework of a scalar QFT, we evaluate the decay of an initial massive state into two massless particles through a triangle-shaped diagram in which virtual fields propagate. Under certain conditions, the decaying state can be seen as a bound state, thus it is analogous to the neutral pion (quark–antiquark pair) and to the positronium (electron–positron pair), which decay into two photons. While the pion is a relativistic composite object, the positronium is a non-relativistic compound close to the threshold. We examine similarities and differences between these two types of bound states.

abstract

This article presents the results of the kaonic helium-4 measurement conducted by the SIDDHARTA-2 experiment, aiming to provide crucial insights into the low-energy strong interaction in the strangeness sector. High-precision X-ray spectroscopy is used to examine the interaction between negatively charged kaons and nuclei in atomic systems. The SIDDHARTA‑2 setup was optimized through the kaonic helium-4 measurement in preparation for the challenging kaonic deuterium measurement. The kaonic helium-4 measurement at a new density of 2.25 g/l is reported, providing the absolute and relative yields for the \(L\)-series transitions, which are essential data for understanding kaonic atom cascade processes.

abstract

The positronium system, a bound state of an electron and a positron, is suitable for testing the predictions of quantum electrodynamics (QED) as well as symmetry invariance. The Ps triple state, the ortho-Positronium (o-Ps), which mainly decays to three photons, is further studied to search for decays into \(4\gamma \) and \(5\gamma \), the former C-violating decay and the latter never observed. The J-PET is a multi-purpose detector optimized for the detection of photons from positron–electron annihilation and can be used in a broad scope of interdisciplinary investigation. The large acceptance and high angular resolution of the J-PET detector will push the present limits in these forbidden and rare decays. The aim is to reach a sensitivity below \(O(10^{-6})\) while reducing the uncertainties, thus increasing the sensitivity.