Nuclear Experiment·nucl-ex

Tue·Sep 22, 2026Tuesday·September 22, 2026

8 papers—2 primary·6 cross-listed

01
Electromagnetic transition strength in $^{53}$ Ca: the lifetime of the $5/ 2^{-}$ state
S. Chen · M. Petri · S. Paschalis · H. L. Crawford · P. Doornenbal · R. Taniuchi · K. Wimmer · B. A. Brown · J. D. Holt · B. S. Hu · T. Miyagi · T. Otsuka and 27 other authors
High-resolution in-beam $γ$ -ray spectroscopy of $^{53}$ Ca was performed at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. Excited states in $^{53}$ Ca were populated via one-neutron and one-proton removal reactions from a $^{55}$ Sc radioactive beam, and the emitted $γ$ rays were detected using the HiCARI hybrid germanium detector array. The lifetime of the first excited $5/ 2^{-}$ state in $^{53}$ Ca was measured for the first time through an analysis of Doppler-roadened $γ$ -ray line shapes arising from relativistic recoil velocities. A lifetime of $τ = 11. 3_{- 11.3}^{+ 5.3 (s t a t) + 3 (sy s)}$ ps was deduced, corresponding to a reduced transition probability of $B (E 2; 5/ 2^{-} \to 1/ 2^{-}) > 2.6 e^{2} f m^{4}$ at the 1 $σ$ level, with a best-fit value of $4.5 e^{2} f m^{4}$ . The measured transition strength is compared with state-of-the-art shell-model and ab initio calculations, providing a stringent benchmark for shell-model Hamiltonians and effective charges and modern ab initio descriptions of the neutron-rich calcium isotopes approaching the potential $N$ = 40 shell closure.
nucl-exnucl-th
02
Jet-like di-hadron correlations in pO, OO, and Ne--Ne collisions
Suraj Prasad for the ALICE Collaboration
Heavy-ion collisions are primarily studied to investigate the properties of hot and dense nuclear matter, known as the quark--gluon plasma (QGP). However, recent observations of hydrodynamic flow-like behaviour in pp and p--Pb collisions at the LHC suggest the possible formation of QGP droplets even in small collision systems. To bridge the multiplicity gap between small and large systems and to examine the applicability of hydrodynamic descriptions, light-ion collisions were performed for the first time at the LHC in 2025. This contribution presents measurements of the near-side peak width of di-hadron correlations in pO, OO, and Ne--Ne collisions with ALICE, used to search for medium effects. The width of the near-side correlation peak is studied as a function of the average charged-particle multiplicity at midrapidity. At low transverse momentum ( $p_{T}$ ), the near-side peak is broader in OO and Ne--Ne collisions than in pp and pO collisions, and in central collisions its width approaches that measured in Pb--Pb collisions. At higher $p_{T}$ the peak narrows modestly with increasing multiplicity. The results are compared with PYTHIA, AMPT, and JETSCAPE calculations, none of which reproduces the measured widths over the full kinematic range.
nucl-exhep-ex
03
Kinematic Fitting of electromagnetic calorimeter data - an improved method
Nicolas Kolanus · Jonas Kohlen · Ulrike Thoma
Kinematic fitting is widely used in particle physics experiments as a powerful tool to improve experimental resolutions, to suppress background and to provide selection criteria for the identification of specific reactions. Kinematic fitting methods, however, typically assume that the fitted quantities follow Gaussian distributions; an assumption which does not always hold. This is particularly true for energy measurements from electromagnetic calorimeters. This issue can largely be overcome by performing a transformation of the non-Gaussian variables into variables which follow a Gaussian distribution. The new adapted kinematic fitting procedure allows to better account for the non-Gaussian nature of the measured calorimeter energies, at the same time improving the accuracy and robustness of the kinematic fit. This leads to improved pull and confidence-level distributions of the kinematic fit as well as improved invariant mass distributions and signal-to-background ratios in the final event sample.
↳ physics.ins-dethep-exnucl-exphysics.data-an
04
Coherent deeply virtual Compton scattering on helium-4 beyond the leading twist approximation
V.Martínez-Fernández · B.Pire · P.Sznajder · J.Wagner
Coherent hard exclusive reactions on light nuclei offer access to their quark and gluon structure and provide a framework for three-dimensional nuclear tomography. We analyze deeply virtual Compton scattering on a helium-4 target, including leading-twist contributions as well as kinematical twist-3 and twist-4 effects. We present numerical estimates of cross sections and asymmetries for kinematic regimes relevant to JLab experiments. We emphasize the importance of next to leading order (NLO) and kinematical twist 3 and 4 contributions to interpret data in the JLab kinematics. We deduce a first tomographic image of quarks and gluons in the helium-4 nucleus.
↳ hep-phnucl-exnucl-th
05
Probing the nucleon axial form factor via the $e^{+} +^{2} H \to ν ˉ_{e} + p + p$ reaction below the pion-production threshold
A. M. Ankowski · J. Golak · E. Pérez del Rio · S. Sharma · R. Skibiński · K. Topolnicki · H. Witała · W. N. Polyzou · H. Kamada · D. Dutta
The nucleon axial form factor $F_{A} (Q^{2})$ is a primary source of systematic uncertainty in charged-current quasielastic interactions, of critical importance for long-baseline neutrino-oscillation studies. Its low- $Q^{2}$ behavior is particularly problematic to pin down in neutrino measurements. To address this limitation, we investigate the weak process of polarized positron capture on the deuteron, $e^{+} +^{2} H \to ν ˉ_{e} + p + p$ . Employing a relativistic momentum-space formalism, we present predictions for the total cross section. Focusing on the kinematic regime free from pion-production backgrounds, we analyze various differential cross sections and their sensitivity to the $F_{A} (Q^{2})$ variation. Our results demonstrate that thanks to the positron upgrade, Jefferson Lab will gain a unique position to make inroads into determining the low- $Q^{2}$ behavior of the axial form factor.
↳ nucl-thnucl-ex
06
Machine Learning for Invisible Dark Boson Searches at the Electron-Ion Collider
Rojae Mighty · Ankush Reddy Kanuganti
We investigate whether adding $t$ , the positive magnitude of the squared nuclear four-momentum transfer, enables boosted decision trees (BDTs) to improve invisible-dark-boson selection relative to optimized rectangular cuts at the Electron-Ion Collider. We model coherent exclusive scalar and vector production at generator level in electron-gold collisions at 18 GeV by 100 GeV per nucleon. Both methods use identical weighted samples, inputs, preselection, and optimization objectives. Using only electron information, the BDT provided no consistent advantage over optimized cuts for signal selection across 11 masses for each boson type. When both methods also use $t$ , the BDT distinguishes signal from background slightly better than optimized cuts at 10 GeV for both boson types. These results motivate further investigation of machine learning in EIC dark-boson searches through exclusive processes where $t$ can be reconstructed.
↳ hep-phcs.LGnucl-ex
07
Benchmarking Nucleon Production in Hadron Interactions Relevant for GeV-scale Neutrino Experiments
Richard Diurba · Steve Dytman · Matthew King · Yinrui Liu
In neutrino scattering experiments, the emitted final state particles are essential for identifying interaction channels and reconstructing neutrino energies. During intranuclear propagation, neutrino-induced hadrons can interact with surrounding nucleons, altering both the number of final state particles and detectable energy depositions. As a result, neutrino experiments rely on hadron-nucleus scattering models to simulate these nuclear effects. This paper explores nucleon production predicted by hadron scattering models for common hadrons in neutrino experiments, specifically nucleons and pions. We investigate these models with simulations from the \textsc{GENIE} neutrino event generator, which includes implementations of \textsc{Geant4} Bertini Cascade and \textsc{INCL++}. For popular target nuclei, we find that the number of emitted nucleons for mesonless hadron interactions can be parameterized by simple Gaussian and exponential decay functions. We present these relationships and provide reweighting tools for addressing the hadron scattering model spread in both visible energy and final state nucleon multiplicities.
↳ hep-exnucl-ex
08
Dynamical Coulomb effects on charged-pion HBT-radius splitting in central Au+Au collisions at few-GeV energies
Pengcheng Li · Yongjia Wang · Qingfeng Li
The pair transverse momentum ( $k_{T}$ ) and collision-energy ( $s_{N N}$ ) dependent difference between $π^{+} π^{+}$ and $π^{-} π^{-}$ femtoscopic correlations was observed by the HADES and STAR Collaborations. We investigate how much of the observed splitting can be accounted for by Coulomb dynamics in 0-10\% central Au+Au collisions at $s_{N N} = 2.42$ -5.2 GeV. Using the UrQMD model and the CRAB programme, three transport scenarios that successively include baryon-baryon, baryon-meson, and meson-meson Coulomb interactions are considered. In a separate calculation based on the baryon-baryon reference, we reconstruct the time-dependent effective charge $Z_{eff} (t)$ and radius $R_{eff} (t)$ of the residual charged source and propagate each pion from its individual last strong-interaction point through the evolving field. The calculations reproduce the main $k_{T}$ and $s_{N N}$ dependences of the radii. Baryon--meson Coulomb interactions generate most of the additional charge splitting in the microscopic calculation. The residual-source treatment also enhances the longitudinal and sideward radius ratios relative to the reference, whereas the outward ratio changes little, and the enhancement generally decreases with increasing $s_{N N}$ . Within the present framework, this contribution does not fully account for the data, motivating further investigation of the charged-source geometry and its interplay with strong-interaction dynamics.
↳ nucl-thnucl-ex