abstract

We have designed and fabricated a research brain time-of-flight PET scanner for in vivo range verification for the proton therapy. Featuring state-of-the-art spatial, timing, and energy resolutions, this scanner can also serve as a precision tool for positronium imaging. We present initial studies using our scanner to search for ortho-positronium (o-Ps) \(3\gamma \) self-annihilation events within the plastic casing of a Na-22 button source. By detecting triple coincidences and filtering out false events, such as those produced by the Compton scattering of back-to-back 511 keV gammas, we have successfully observed the signature of true o-Ps formation. This was achieved through four filtering techniques based on energy, decay plane orientation, time-of-flight, and momentum. The experimental results are guided by Geant4 simulations. Additionally, a control study was conducted using a metal-encased Ge-68 line source, demonstrating the expected quenching of o-Ps\(\,\rightarrow 3\gamma \) events in metals compared to plastics.

abstract

The deviations from combined Charge, Parity, and Time (CPT) symmetry could indicate the presence of new physics beyond the current theoretical framework. The positronium (Ps), the lightest bound state of an electron–positron pair, offers a unique probe for such investigations because it is an eigenstate of charge conjugation (C) and parity (P). This work explores the potential of the Jagiellonian Positron Emission Tomography (J-PET) detector for sensitive tests of CPT symmetry in the three-photon decay of ortho-Ps (o-Ps) atom. The CPT symmetry invariance in o-Ps decays has been previously tested using the J-PET detector, measuring the CPT-violating angular correlation between the o-Ps spin and its annihilation photon momenta, achieving a precision of \(0.00067 \pm 0.00095\). However, a range of five orders of magnitude is still unexplored to test its exactness. A Monte Carlo simulation study is presented to distinguish between the o-Ps signal and background events using Multivariate Data Analysis (TMVA). We discuss the impact of improving the sample purity in enhancing the sensitivity of the CPT symmetry test.

abstract

The Jagiellonian-Positron Emission Tomography (J-PET) is distinguished by its ability to determine the polarization plane of photons emitted during the positronium annihilation. According to the Standard Model prediction, photon–photon interactions in its final state due to vacuum polarization can mimic CP symmetry violation at a magnitude of approximately \(10^{-9}\), which is significantly larger than the predicted value of the order of \(10^{-14}\) for weak interactions. Currently, with the help of the J-PET detector, experimental limits on CP symmetry violation in o-Ps decay are set at a precision value of the order of \(10^{-4}\). The J-PET detector measures the polarization direction of annihilation photons without a magnetic field and can investigate discrete symmetry by examining non-zero expectation values of symmetry-odd operators, constructed from the momentum and polarization-related vectors of gamma (\(\gamma \)) quanta coming from the o-Ps annihilation. This work focuses on studying the CP symmetry in o-Ps decay and the initial operator plot derived from data collected over 250 days using the J-PET detector. The primary objective of this experiment is to enhance statistical significance in fundamental symmetry studies and refine the precision of CP symmetry tests. The study utilizes the CP symmetry-odd operator \((\vec {\epsilon }_{i} \cdot \vec {k}_{j})\), where \(\vec {\epsilon }_{i}\) and \(\vec {k}_{j}\) represent the reconstructed polarization-related and momentum vectors of the photons emitted from o-Ps decay.

abstract

Pairs of neutral kaons produced at the DA\(\Phi \)NE collider allowed to perform the first model-independent direct test of T, CP, and CPT symmetries utilizing the oscillations between the flavor and CP eigenbases. The analysis of \(1.7 \ \mathrm {fb^{-1}}\) data collected in 2004–2005 in the KLOE experiment led to the determination of ratios and double ratios of kaons’ decay rates, establishing a few percent precision of the measurement in a model-free manner.

abstract

Since its inception in 1967, the International Physics Olympiad (IPhO) has played a pivotal role in promoting physics and fostering global educational links. This paper provides an overview of IPhO’s history, structure, and impact on the physics community, with a focus on the recent IPhO2023 held in Tokyo. The challenges and successes of organizing an IPhO event are also discussed.

abstract

Due to the high linear energy transfer (LET) and a Bragg peak, proton radiation therapy enables targeted radiation treatment focused on cancer cells while reducing exposure to normal tissues. However, various studies are needed to measure proton energy accurately, as uncertainties can arise depending on the energy of the proton beam and the characteristics of human tissue. In this work, we developed an optical dosimeter to verify the range of the proton beam using a PMMA (poly-methyl methacrylate)-based tissue-equivalent plastic scintillator with a CMOS (complementary metal-oxide-semiconductor) camera. The Bragg peak position was confirmed through image processing after photographing the scintillation light generated during proton beam irradiation with the camera. Additionally, the correct Bragg peak was measured by correcting for the quenching effect of the scintillator. The proton beam’s energy was adjusted using an aluminum degrader, and the experimental results were verified by comparing them with the Geant4 simulation. The relationship between the simulated and measured proton beam ranges was \(R^2=0.99\), confirming the validity of KOMAC’s (Korea Multi-purpose Accelerator Complex) 102 MeV proton beam for range verification.

abstract

This work presents a comparative study of point defects in three \(\mathrm {TiO_2}\) polymorphs: anatase, rutile, and brookite. Open volume point defects were characterized using the positron annihilation spectroscopy combined with ab initio calculations of positron lifetimes. The \(\mathrm {TiO_2}\) polymorphs have been investigated in the form of polycrystalline powders and nanopowders. Polycrystalline and nanocrystalline \(\mathrm {TiO_2}\) powders contain vacancies, vacancy clusters, and nanoscopic pores in which positronium forms. Anatase has the most open structure and exhibits the longest positron lifetimes. In contrast, the shortest positron lifetimes were observed for rutile.

abstract

Positronium (Ps), governed by Quantum Electrodynamics (QED), provides a rich domain for exploring fundamental physics. Monte Carlo simulations of its decay provide insights into various aspects of particle physics. The development of J-PET, an innovative tomography system at the Jagiellonian University using high-resolution scintillator detectors, facilitates interdisciplinary studies encompassing fundamental physics tests, medical research, and quantum entanglement measurements but also enhances our capacity to investigate positronium decays in pursuit of potential dark matter (DM) candidates, a lingering enigma within the current Standard Model (SM) framework. In our research, we employ the J-PET detector to study ortho-positronium (o-Ps) decays as a part of our ongoing quest for the discovery of DM. Our primary goal is to explore mirror matter, which seeks to restore parity invariance and is proposed as a candidate for the Universe’s DM. Our study aims to push the boundaries of precision measurement in the decay width of o-Ps to three gamma quanta, contributing to our understanding of the elusive nature of dark matter. The article presents the preliminary lifetime distribution of o-Ps as a search for mirror matter obtained from data collected during a portion of a long-term measurement conducted with the J-PET detector in 2020. The long-term aim of the study is to achieve \(10^{-6}\) lifetime sensitivity.

abstract

The SiFi-CC group is developing a scintillating-fiber-based Compton camera for high-efficiency gamma-ray imaging, specifically tailored for online range verification in particle therapy. After thorough optimization studies, including the development of neural-network approaches for event selection, the capability of the prototype for detecting range deviations is being studied by using realistic Monte Carlo simulations. We have implemented a spectral-spatial reconstruction based on the LM-MLEM algorithm and spectral analytical models for the system matrix and the sensitivity. In this work, we show the reconstructed images obtained from the irradiation of PMMA phantoms with \(4\times 10^9\) protons at therapeutic energies. The results show the capability of the SiFi-CC detector prototype to recover the \(4.44\) MeV prompt-gamma line and to detect \(5\) mm Bragg peak shifts.

abstract

Based on plastic scintillators, Jagiellonian PET (J-PET) is a multi-discipilinary PET scanner having a wide range of applications. With the potential of J-PET to register multiphotons, we aim at exploring the rare and forbidden decay channels of the Positronium triplet state, the ortho-Positronium (o-Ps). The o-Ps decaying into a higher number of photons than the predominant mode (o-Ps \(\rightarrow 3\gamma \)) is six orders of magnitude smaller than expected from the Quantum Electrodynamics (QED) calculations. In this article, we intend to present the status of the preliminary studies of the multi-photon decays of ortho-Positronium. We will explain toy Monte Carlo simulations involving 4- and 5-gamma decays of the o-Ps, together with a preliminary estimation of a J-PET-like detector efficiencies for these channels.

abstract

A substantial amount of scattered data is rejected in a conventional Positron Emission Tomography (PET). We propose a novel algorithm for PET image reconstruction from single-scattered (inside tissue) events with a known Time of Flight (TOF) and without energy information, particularly useful for plastic scintillator. Previous single scatter reconstruction algorithms relied on both energy and time information of detected events which is applicable only for inorganic scintillators. We discuss the framework of our reconstruction algorithm with the GATE simulated data where we achieved a resolution of 1.8 cm approximately for a line source. Currently, our work is demonstrated for 2D images and the algorithm accurately predicts the source location.