abstract

Recently, when examining the differential internal pair creation coefficients of \(^8\)Be, \(^4\)He, and \(^{12}\)C nuclei, we observed peak-like anomalies in the angular correlation of the \(e^+e^-\) pairs. This was interpreted as the creation and immediate decay of an intermediate bosonic particle with a mass of \(m_{X}c^2\approx 17\) MeV, receiving the name X17 in subsequent publications. In this paper, I will give a mini-review of the experiments related to X17 the results of which are already published, and the ones closest to being published.

abstract

The JEF program aims at performing precision measurements of various \(\eta \) and \(\eta ^{\prime }\) decays with emphasis on rare neutral decays. Since the production rates of \(\eta \) and \(\eta ^{\prime }\) are similar under the JEF experimental conditions, the same data set will offer sensitive probes for decay modes. Compared to the existing and planned \(\eta \)/\(\eta ^{\prime }\) experiments worldwide, the unique feature of the JEF program is to offer a clean data set in the rare neutral decays of both \(\eta \) and \(\eta ^{\prime }\) with a significant reduction in background. The JEF data will offer significantly different systematics compared to other \(\eta ^{(\prime )}\) programs.

abstract

The PADME experiment at Laboratori Nationali di Frascati is designed to study possible dark matter explanations relying on the presence of a light particle that acts as a mediator between the visible and the hidden sectors. Three data-taking runs have resulted in the collection of more than \(10^{13}\) positrons-on-target. The experimental setup was initially designed to the search for associate dark photon production and later modified for the search for resonant production of a new \(X17\) particle, originally proposed by the ATOMKI Institute. The setup for the different runs, the data taking, and background studies are presented, as well as the first physics results and the prospects for the next run of PADME.

abstract

We analyze the sensitivity of the \(\eta \to \pi ^{0}\gamma \gamma \) decays to a leptophobic \(B\) boson in the sub-GeV mass range and provide branching ratio predictions for the single ALP \(\eta /\eta ^{\prime }\to \pi \pi a\) decays as a function of the ALP mass.

abstract

The REDTOP experiment is a proposed super-\(\eta \)/\(\eta '\) factory aimed at exploring physics beyond the Standard Model in the MeV–GeV range and rare \(\eta \)/\(\eta '\) meson decays. With projected production rates exceeding \(10^{13}\) \(\eta \)/year and \(10^{12}\) \(\eta '\)/year, REDTOP will enable studies of symmetry violations and all four portals to the dark sector. preliminary studies show sensitivity, which could open a broad possibility for exploring New Physics and contribute to a deeper understanding of fundamental interactions within the Standard Model. Such high-statistics experiments and the required sensitivity can only be achieved with a high-intensity proton or pion beam, available at several accelerator facilities worldwide. This article discusses the physics potential of the REDTOP experiment, the detector design, and the future beam requirements.

abstract

We discuss the role of gluon dynamics in \(\eta '\) physics and in nucleon resonances where excitations of gluonic potentials may also be important. Interesting phenomenology includes a possible narrow near-threshold resonance in \(\eta '\) photoproduction and whether the parity doublets observed in the higher-mass nucleon resonance spectrum might be hinting at a possible second minimum in the confinement potential corresponding to supercritical confinement.

abstract

We discuss the exclusive production of \(\eta \) meson in proton–proton collisions in order to learn about the relevant production mechanism at the GSI-FAIR energies. The nucleon and baryonic-resonance amplitudes are derived within an effective Lagrangian approach. Assuming that for the \(pp \to pp \eta \) reaction the dominant contribution is due to an excitation of \(N(1535)\) via the \(\rho ^{0}\) exchange, the present model reproduces data for both total and differential cross sections, for instance, the distributions of the polar angle of the \(\eta \) meson in the center-of-mass system. The role of vector-meson-fusion processes \(\omega \omega , \rho ^{0} \rho ^{0} \to \eta \) is specified. Comparisons with currently existing data from the DISTO and HADES experiments are made, and predictions for higher energies (HADES, PANDA, SIS100) are given.

abstract

The performance of the kinematic fit analysis tool (KinFit) has been tested in reconstructing the \(\eta /\omega \) mesons in the simulated data of \(pp \rightarrow pp\eta /\omega \ (\rightarrow \pi ^{+}\pi ^{-}\pi ^{0})\) reactions at \(\sqrt {s} = 3.46\) GeV with a missing mass constraint. For the fitting procedure, the detector resolutions were calculated based on the simulations, and the goodness of fit was studied. The results show a significant improvement in the mass resolution and the mesons mass values.

abstract

This study presents the exclusive analysis of the \(pp\rightarrow ppK^{+}K^{-}\) reaction with data taken with the HADES detector in February 2022 at a center-of-mass energy of 3.47 GeV. A neural network-based particle identification was developed that compensates for simulation-experiment discrepancies through domain adversarial technique. The background was suppressed by means of kinematic refit with 4 overconstraints corresponding to the conservation of 4-momentum, which allowed us to obtain a high-purity sample of data with \(S/B\approx 15\). Clear signals from \(\phi (1020) \to K^{+}K^{-}\) and \({\mit \Lambda }(1520) \to pK^{-}\) decays were observed with their parameters consistent with those published by the PDG. Moreover, the importance of \(K^{+}K^{-}\) non-resonant final-state interactions was confirmed. This paper discusses the details of our event selection, efficiency corrections, and presents a number of intermediate results.