arXiv subjects

Ivica Friščić

Publications and source records attributed to Ivica Friščić.

12 recordsLinked to original sources

arXiv2026

Pulse-shape discrimination with machine learning for CZT detectors at the DA$Φ$NE beam test facility

Cadmium zinc telluride (CZT) detectors offer versatility, operational simplicity, and room-temperature X- and gamma-ray spectroscopy, making them attractive for collider applications, yet their use under high-flux conditions remains limited. Here, we present a preliminary feature-based pulse-shape analysis employing machine learning, on data acquired with a quasi-hemispherical CZT detector at the DA$\Φ$NE beam test facility of the National Laboratory of Frascati of INFN. A 300-MeV electron beam impinging on a lead target produced characteristic Pb X-rays together with a broad background extending up to the electron-positron annihilation region. Physically motivated temporal and morphological features were extracted from the recorded waveforms and used to distinguish nominal photon-like pulses from anomalous events. An XGBoost classifier trained and validated on 10,000 labeled waveforms achieved an accuracy of approximately 97%, with most of its classification performance reached using only a few hundred labeled examples. The trained model was applied to more than 700,000 events, substantially reducing the spectral continuum and coincidence peaks, while preserving the characteristic Pb X-ray lines up to the 511-keV annihilation peak. These preliminary results demonstrate the potential of machine-learning-assisted pulse-shape discrimination for improving CZT spectroscopy in collider environments.

physics.ins-det↗

arXiv2026

A stop to field line misconceptions

For two hundred years - ever since Faraday's first conception of the field lines - hearts and minds of students have been pervaded by erroneous and unsubstantiated claims about these well defined mathematical objects. The most prominent misconceptions include: (1) a notion of the field lines as of 'lines of force'; (2) a notion that the field lines coincide with particle trajectories; (3) a notion that a field line density measures a magnitude of a vector field; (4) a notion that the field lines of a divergence-free field always form closed loops. Even the modern day literature systematically perpetuates some of these claims. We compile here the trivial counterexamples to these claims, providing physics instructors with an efficient and effective way of dispelling these misconceptions.

physics.class-ph↗

arXiv2026

First measurement of kaonic deuterium X-ray transitions

The study of the strong interaction among hadrons at low energies remains one of the key challenges in fundamental physics because of its non-perturbative nature, which makes theoretical descriptions strongly dependent on experimental input. Although substantial progress has been made for systems involving up and down quarks, theoretical models in the strangeness sector continue to face limitations due to the lack of experimental data. Kaonic atoms provide a powerful tool to study the low-energy strong interaction with strangeness through the energy shifts and widths induced on their lowest atomic levels. In this context, kaonic deuterium X-ray spectroscopy has long represented one of the major open challenges in hadronic-atom physics because of its extremely low X-ray yield. This measurement is particularly important because it gives access to the experimentally inaccessible $K^-n$ interaction at threshold energy. Here, we report the first observation of kaonic deuterium X-ray transitions, performed with the SIDDHARTA-2 experiment at the DA$Φ$NE collider. We determine the strong-interaction shift and width of the $1s$ level to be $\varepsilon_{1s}=-810.9\pm24.5\,(\mathrm{stat})\pm2.1\,(\mathrm{syst})\,\mathrm{eV}$ and $Γ_{1s}=812\pm97\,(\mathrm{stat})\pm33\,(\mathrm{syst})\,\mathrm{eV}$, respectively. This measurement constitutes the most precise experimental determination of the $K^-d$ strong interaction at threshold and allows discrimination among competing theoretical models. Combined with the kaonic hydrogen measurement, this result provides the experimental input required to determine the isospin-dependent $K^-N$ scattering lengths, with implications for the description of the nature of the first predicted hadronic molecular state, the $Λ(1405)$, and neutron-rich matter.

nucl-ex↗

arXiv2026

Probing Nuclear Structure with Kaonic Atoms through E2 Resonance Mixing

Kaonic atoms provide a unique laboratory to investigate the interplay between atomic, nuclear, and strong-interaction physics. In heavy nuclei, atomic transitions can couple to low-lying collective nuclear excitations via the electric quadrupole interaction. When the energy difference between two kaonic atomic levels approaches that of a nuclear $2^+$ excitation, a resonant configuration mixing may occur, known as the E2 nuclear resonance effect. In this work, we investigate the conditions for E2 resonance in kaonic molybdenum isotopes. We describe the mixing using state-of-the-art Dirac-Fock calculations combined with updated nuclear structure inputs, including recent electric quadrupole transition strength values and excitation energies. We evaluate the sensitivity of the effect to key parameters, assess its observability in future experiments such as the EXKALIBUR program, and discuss its impact on cascade dynamics. Our results demonstrate the potential of kaonic atoms as a probe of nuclear structure, complementary to conventional nuclear spectroscopy.

nucl-ex↗

arXiv2026

A reconciliation of the Pryce-Ward and Klein-Nishina statistics for semi-classical simulations of annihilation photons correlations

Two photons from the ground state para-positronium annihilation are emitted in a maximally entangled singlet state of orthogonal polarizations. In case of the Compton scattering of both photons the phenomenon of quantum entanglement leads to a measurable increase in the azimuthal correlations of scattered photons, as opposed to a classical description treating the two scattering events as independent. The probability of the scattering of the system of the entangled photons is described by the Pryce-Ward cross section dependent on a difference of the azimuthal scattering angles in the fixed coordinate frame, while the independent scattering of single photons is described by the Klein-Nishina cross section dependent on the azimuthal angle relative to each photon's initial polarization. Since the singlet state of orthogonal polarizations is rotationally invariant, it does not carry any physical information on the initial polarizations of the single annihilation photons. In such bipartite state the angular origin for the Klein-Nishina cross section is undefined, making the Pryce-Ward and Klein-Nishina descriptions mutually exclusive. However, semi-classical simulations of the joint Compton scattering of entangled photons - implementing the Pryce-Ward cross section, but still treating the two photons as separate entities - can reconcile the Pryce-Ward correlations with the Klein-Nishina statistics for single photons by implementing a modified version of a scattering cross section presented in this work.

quant-ph↗

arXiv2026

Extended X-ray energy characterization of SIDDHARTA-2 large-area Silicon Drift Detectors up to 50 keV

The SIDDHARTA-2 experiment at the DA$Φ$NE collider of INFN-LNF performs high precision light kaonic atoms X-ray spectroscopy to investigate the kaon-nucleon(s) strong interaction in the low-energy (O(10 keV)) regime. A large area Silicon Drift Detectors (SDDs) system has been developed to carry out these measurements. The collaboration aims to extend the measurements campaign to higher mass kaonic atoms, which exhibit transition lines at increased X-ray energies. In this context, the spectroscopic response of the SIDDHARTA-2 SDD system was investigated in terms of linearity and energy resolution up to 50 keV. An accuracy of the energy calibration procedure $ΔE/E < 10^{-3}$ was achieved.

physics.ins-det↗

arXiv2025

EXKALIBUR: Towards a Kaonic Atoms Periodic Table to test Fundamental Interactions

Kaonic atoms, formed when a negatively charged kaon replaces an electron, provide a unique laboratory to test fundamental interactions at low energies. EXKALIBUR (EXtensive Kaonic Atoms research: from LIthium and Beryllium to URanium) is a program to perform systematic, high-precision X-ray spectroscopy of selected kaonic atoms across the periodic table at the DA$Φ$NE accelerator at the National Laboratory of Frascati (INFN-LNF). Here, we outline its detector-driven strategy: Silicon Drift Detectors for 10-40 keV transitions in light targets (Li, Be, B, O), CdZnTe detectors for 40-300 keV lines in intermediate-$Z$ systems (Mg, Al, Si, S), and a High-Purity Germanium detector for high-$Z$ atoms (Se, Zr, Ta, Mo, W, Pb), complemented by VOXES, a high-resolution crystal spectrometer for sub-eV studies. EXKALIBUR plans to (i) reduce the charged-kaon mass uncertainty below 10 keV, (ii) produce a database of nuclear shifts and widths to constrain multi-nucleon K$^{-}$-nucleus interaction models, and (iii) provide precision data for testing bound-state QED in strong fields. We summarize the planned measurements and expected sensitivities within DA$Φ$NE luminosities.

nucl-ex↗

arXiv2023

Closing the Door on the "Puzzle of Decoherence'' of Annihilation Quanta

In para-positronium annihilation, exploration of the polarization correlations of the emerging gamma quanta has gained interest, since it offers a possibility to improve signal-to-background in medical imaging using positron emission tomography. The annihilation quanta, which are predicted to be in an entangled state, have orthogonal polarizations and this property may be exploited to discriminate them from two uncorrelated gamma photons contributing to the background. Recent experimental studies of polarization correlations of the annihilation quanta after a decoherence process induced by a prior Compton scattering of one of them, had rather different conclusions regarding the strength of the correlation after the decoherence, showing its puzzling nature. In the present work, we perform for the first time, a study of the polarization correlations of annihilation quanta after decoherence via Compton scattering in the angular range $0^\circ-50^\circ$ using single-layer gamma ray polarimeters. In addition, we compare the measured polarization correlations after Compton scattering at $30^\circ$ with an active and a passive scatterer element. The results indicate that the correlation, expressed in terms of the polarimetric modulation factor, shows no significant difference at small scattering angles ($0^\circ-30^\circ$) compared to the correlation measured for direct photons, while lower modulation was observed for $50^\circ$ scattering angle.

quant-ph↗

arXiv2021

Measurements of the electron-helicity asymmetry in the quasi-elastic ${\rm A}(\vec{e},e' p)$ process

We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from $^{2}$H and $^{12}$C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle $ϕ_{pq}$, with a polar angle $θ_{pq}$ coverage up to about 8 degrees. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual $^{11}$B system. We find that the helicity asymmetry for $p$-shell knockout from $^{12}$C depends on the final state of the residual system and is relatively large (up to $\approx 0.16$), especially at low missing momentum. It is considerably smaller (up to $\approx 0.01$) for $s$-shell knockout from both $^{12}$C and $^2$H. The data for $^2$H are in very good agreement with theoretical calculations, while the predictions for $^{12}$C exhibit differences with respect to the data.

nucl-ex↗

arXiv2020

Measurements of the induced polarization in the quasi-elastic $A(e,e'\vec p\,)$ process in non-coplanar kinematics

We report measurements of the induced polarization $\vec P$ of protons knocked out from $^2$H and $^{12}$C via the $A(e,e'\vec p\,)$ reaction. We have studied the dependence of $\vec P$ on two kinematic variables: the missing momentum $p_{\rm miss}$ and the "off-coplanarity" angle $ϕ_{pq}$ between the scattering and reaction planes. For the full 360$\degree$ range in $ϕ_{pq}$, both the normal ($P_y$) and, for the first time, the transverse ($P_x$) components of the induced polarization were measured with respect to the coordinate system associated with the scattering plane. $P_x$ vanishes in coplanar kinematics, however in non-coplanar kinematics, it is on the same scale as $P_y$. We find that the dependence on $ϕ_{pq}$ is sine-like for $P_x$ and cosine-like for $P_y$. For carbon, the magnitude of the induced polarization is especially large when protons are knocked out from the $p_{3/2}$ shell at very small $p_{\rm miss}$. For the deuteron, the induced polarization is near zero at small $|p_{\rm miss}|$, and its magnitude increases with $|p_{\rm miss}|$. For both nuclei such behavior is reproduced qualitatively by theoretical results, driven largely by the spin-orbit part of the final-state interactions. However, for both nuclei, sizeable discrepancies exist between experiment and theory.

nucl-ex↗

arXiv2019

Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

We present measurements of the polarization-transfer components in the $^2$H$(\vec e,e'\vec p)$ reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, $p_{\rm miss}$, up to 220 MeV$/c$, and $Q^2=0.65$ $({\rm GeV}/c)^2$. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components $P_x$ and $P_z$ and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio $G_E/G_M$ at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for $^2$H to those of a free (moving) proton. We find that the universal behavior of $^2$H, $^4$He and $^{12}$C in the double ratio $\frac{(P_x/P_z)^A}{(P_x/P_z)^{^1\rm H}}$ is maintained in the positive missing-momentum region.

nucl-ex↗

arXiv2019

The proton charge radius extracted from the Initial State Radiation experiment at MAMI

We report on a comprehensive reinterpretation of the existing cross-section data for elastic electron-proton scattering obtained by the initial-state radiation technique, resulting in a significantly improved accuracy of the extracted proton charge radius. By refining the external energy corrections we have achieved an outstanding description of the radiative tail, essential for a detailed investigation of the proton finite-size effects on the measured cross-sections. This development, together with a novel framework for determining the radius, based on a regression analysis of the cross-sections employing a polynomial model for the form factor, led us to a new value for the charge radius, which is $(0.870 \pm 0.014_\mathrm{stat.}\pm 0.024_\mathrm{sys.} \pm 0.003_\mathrm{mod.})\,\mathrm{fm}$.

nucl-ex↗