Nuclear Experiment·nucl-ex

Wed·Aug 12, 2026Wednesday·August 12, 2026

10 papers—2 primary·8 cross-listed

01
First measurement of kaonic deuterium X-ray transitions
Massimiliano Bazzi🇮🇹 · Francesco Clozza🇮🇹 · Carlo Guaraldo🇮🇹 · Mihail Antoniu Iliescu🇮🇹 · Alessandro Scordo🇮🇹 · Francesco Sgaramella🇮🇹 · Diana Sirghi🇮🇹 · Florin Sirghi · Johann Zmeskal🇮🇹 · Leonardo Abbene · Claude Amsler🇦🇹 · Francesco Artibani🇮🇹 and 29 other authors
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 $1 s$ level to be $ε_{1 s} = - 810.9 \pm 24.5 (stat) \pm 2.1 (syst) eV$ and $Γ_{1 s} = 812 \pm 97 (stat) \pm 33 (syst) eV$ , 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-exphysics.atom-ph0 citations
02
Anisotropic Flow in Ultra-Central Pb $-$ Pb Collisions at $s_{NN} = 5.36$ TeV with ALICE
Iris Likmeta🇺🇸
Anisotropic flow measurements in heavy-ion collisions are sensitive to the spatial distribution of the initial state, and quark-gluon plasma transport properties such as the shear viscosity to entropy density ratio $(η / s)$ . State-of-the-art relativistic hydrodynamic models successfully describe such flow measurements over a wide centrality range. However, the hydrodynamic description of anisotropic flow deviates from the experimental data in ultra-central collisions (UCC), where the average geometric anisotropy of the system becomes small and fluctuations dominate the initial-state geometry. This discrepancy constitutes the UCC puzzle, as the expected hierarchy of flow harmonics is not fully reproduced by current modeling approaches. Probing towards ultra-central collisions, effects on flow fluctuations due to the initial spatial anisotropies are suppressed. The measured flow can be explained by quantum fluctuations on the energy distribution of $^{208}$ Pb nuclei. An octupole deformation of the $^{208}$ Pb nuclei has been proposed as a remedy to improve the modeling of the measured $v_{3} {2} / v_{2} {2}$ ratio. In this contribution, we present measurements of $v_{3} {2} / v_{2} {2}$ ratio in ultra-central Pb\textendash Pb collisions at $s_{NN} = 5.36$ TeV with ALICE Run 3 detector and compare them with recent hydrodynamic model calculations.
nucl-exhep-ex0 citations
03
The iSTORM Instrument for Airborne Measurements of Gamma-Ray Emissions from Thunderstorms
Daniel Shy🇺🇸 · J. Eric Grove🇺🇸 · Bernard Phlips🇺🇸 · Alena Schell · Mary Johnson-Rambert · Mason Quick · David Corredor · Scott Podgorny · Roy Salinas🇵🇱 · Mitch Davis
The in-Situ Thunderstorm Observer for Radiation Mechanisms (iSTORM) is a gamma-ray spectrometer to study gamma-ray transients originating from thunderstorms, such as glows and terrestrial gamma-ray flashes (TGFs). It is designed and built by the U.S. Naval Research Laboratory for deployment aboard a NASA ER-2 aircraft. Using an array of 32 one-inch-diameter $CeBr_{3}$ scintillators read out with silicon photomultipliers (SiPMs), the instrument achieves an energy range of $\sim 250 keV$ to $5 MeV$ under flight conditions, with a total geometrical area of $157 c m^{2}$ . One of two gamma-ray instruments in the ALOFT campaign, iSTORM recorded glows, terrestrial gamma-ray flashes (TGFs), and the newly discovered flickering gamma-ray flashes (FGFs).
↳ physics.ao-phastro-ph.EPastro-ph.IMnucl-ex0 citations
04
Extraction of baryon number susceptibilities at finite density from heavy-ion collisions
Grégoire Pihan🇺🇸 · Roman Poberezhniuk🇺🇸 · Volodymyr A. Kuznietsov🇺🇸 · Volodymyr Vovchenko🇺🇸
We present, to our knowledge, the first Bayesian extraction of baryon number susceptibilities of QCD matter at finite baryon density from heavy-ion collision data on proton number cumulants. The framework embeds arbitrary equation-of-state susceptibilities $χ_{n}^{B}$ into realistic hydrodynamic particlization hypersurfaces through maximum-entropy freeze-out, maps the resulting (anti)baryon fluctuations onto protons, applies the experimental kinematic acceptance, and accounts for exact baryon number conservation. Applying the framework to measurements of (net-)proton number fluctuations in 0--5\% central Au-Au collisions from the RHIC Beam Energy Scan in the collider mode, we extract, at each collision energy, the second-order susceptibility normalized by the hadron resonance gas value, $χ_{2}^{B} / χ ˉ_{2}^{B}$ , and the higher-order susceptibility ratios $χ_{3}^{B} / χ_{1}^{B}$ and $χ_{4}^{B} / χ_{2}^{B}$ . We obtain tight constraints on $χ_{2}^{B}$ , with extracted values in quantitative agreement with lattice QCD based estimates along the chemical freeze-out line for $μ_{B} ≲ 300$ ~MeV. At larger $μ_{B}$ , the extracted values indicate an enhancement of baryon number fluctuations relative to the noncritical lattice-based extrapolation and HRG baseline considered here. The third- and fourth-order susceptibilities are only weakly constrained. In particular, we find that the observed nonmonotonic collision-energy dependence of the proton factorial cumulant ratio $C^_{3} / C^_{1}$ can be described without irreducible three- or four-baryon correlations. This behavior emerges from the interplay between the energy dependence of $χ_{2}^{B}$ and exact baryon number conservation.
↳ hep-phnucl-exnucl-th0 citations
05
Position Resolution of a Scintillator Hodoscope Employing Triangular Counters with Embedded Wavelength Shifting Fibers
E. Craig Dukes🇺🇸 · Ralf Ehrlich🇺🇸 · Daniel Lee🇺🇸 · Luke Watson🇺🇸 · Alan Bross🇺🇸 · Sten Hansen🇺🇸 · Paul Rubinov🇺🇸
Scintillator counters employing embedded wavelength-shifting fibers have been used in particle physics experiments for several decades. Such counters have been produced with square, rectangular, and triangular profiles. An advantage of arrays of triangular counters is that their position resolution can be greatly enhanced by interpolation between adjacent counters using their relative light yields. We report here on a testbeam study of the position resolution of such a scintillator hodoscope and compare the results to a simulation. We find an order of magnitude improvement in the position resolution over that found by simply using the fiber separation.
↳ physics.ins-dethep-exnucl-ex0 citations
06
Probing vorticity and fluctuations in a rotating hadron resonance gas at LHC energy
S. Ipsita Sahoo🇮🇳 · Sanjeebani Biswal🇮🇳 · D. Dutta🇮🇳 · D. K. Mishra🇮🇳
A large vorticity produced in non-central ultra-relativistic heavy-ion collisions induces an effective chemical potential in both partonic and hadronic matter, thereby influencing the quark-hadron transition and its associated properties. In this work, we investigate the influence of rotation on hadron yields within the framework of Hadron Resonance Gas (HRG) model. Our results show that vorticity significantly modifies hadron yields and their ratios. Most notably, rotation enhances the $p / π^{+}$ ratio while suppressing the $K^{+} / π^{+}$ ratio, suggesting that these observables may serve as sensitive probes of the rotational properties of the medium created in heavy-ion collisions. To quantify the effect of rotation, the calculated dependence of the $p / π^{+}$ ratio on vorticity is compared with the centrality dependence of the $p / π$ ratio measured by the ALICE collaboration in Pb+Pb collisions at $s_{_{N N}}$ = 5.02 TeV. From this comparison, we estimate the maximum vorticity produced at freeze-out for different collision centralities. In case of peripheral collisions, the freeze-out vorticity ( $ω$ ) is found to reach an upper bound value of approximately 0.088 GeV, whereas for central collisions it is about 0.028 GeV. Furthermore, we investigate the effect of rotation on fluctuations of conserved quantities and their correlations. This study provides a quantitative framework for assessing the role of rotation in the thermodynamics of hadronic matter and its phenomenological consequences for heavy-ion collisions.
↳ hep-phnucl-exnucl-th0 citations
07
Probing Gluon Linear Polarization with Dihadron Fragmentation in $χ_{b}$ Decays
Zhi-Guo He🇨🇳 · Guanghui Li🇨🇳 · Yang Liu🇨🇳 · Yu-Jie Tian🇨🇳 · Xin-Kai Wen🇨🇳 · Bin Yan🇨🇳
The dihadron fragmentation function (DiFF) of a linearly polarized gluon has not yet been accessed experimentally, leaving an important aspect of spin-dependent gluon hadronization unexplored. We show that, at leading order, the color-singlet decay channel of the $P$ -wave bottomonium state $χ_{b 0}$ produces two energetic gluons with correlated linear polarizations. Within collinear factorization, their fragmentation into separate dihadron pairs generates an Artru--Collins-type angular correlation that provides the first direct probe of the linearly polarized gluon DiFF, while the corresponding semi-inclusive decay rate constrains the unpolarized gluon DiFF. A spectator-model benchmark indicates percent-level asymmetries, potentially within reach of existing Belle data. A dedicated Belle~II data set would substantially improve the statistical precision, enabling more stringent constraints on the kinematic dependence of the linearly polarized gluon DiFF.
↳ hep-phhep-exnucl-exnucl-th1 citation
08
Evolution of the underlying event and non-extensive thermodynamics in pp collisions from RHIC to LHC energies
Suraj Prasad🇭🇺 · Aditya Nath Mishra🇮🇳 · Guy Paić🇭🇺 · Gergely Gábor Barnaföldi🇭🇺
We investigate the geometrical and thermodynamical aspects of particle production in pp collisions over a broad center-of-mass energy, ranging from $s = 62.4$ GeV to 13 TeV using PYTHIA8. We study the azimuthal dependence of charged-particle production relative to the leading particle. This includes the study of the Tsallis--Pareto parameters extracted from the charged-particle transverse-momentum spectra in fixed $Δ ϕ$ intervals relative to the leading charged particle. The simultaneous analysis of charged-particle multiplicity and event topology demonstrates that the underlying event (UE) dominated region can be extended beyond the conventional transverse side region across RHIC and LHC energies. To further disentangle effects from soft and hard particle production mechanisms, the study is performed in different transverse spherocity and charged-particle flattenicity classes. We demonstrate that the UE region extends beyond the conventional transverse region, validating an enlarged angular interval of $4 0^{\circ} ≲ ∣Δ ϕ ∣ ≲ 14 0^{\circ}$ from RHIC to LHC energies. Event-shape selections reveal that jetty events consistently exhibit larger $q$ and lower $T_{s}$ than isotropic events. The $Δ ϕ$ profiles of charged-particle multiplicity and transverse spherocity remain universal in shape across collision energies despite the strong increase in overall event activity, whereas the Tsallis parameters retain a residual, leading-particle-driven energy dependence in the near- and away-side regions.
↳ hep-phhep-exhep-thnucl-ex+10 citations
09
Nucleon electromagnetic form-factors in a minimal Gari-Krümpelmann model including the explicit two-pion continuum
Wulf Krümpelmann🇩🇪 · Yong-Hui Lin🇩🇪 · Ulf-G. Meißner🇩🇪
The Gari--Krümpelmann (GK) model provided one of the first semiphenomenological descriptions of the electromagnetic nucleon form-factors over a wide range of momentum transfer. It combined vector-meson dominance at low and intermediate momentum transfer with perturbative-QCD constraints at large momentum transfer. The present work extends this framework by including the dispersive two-pion continuum explicitly in the isovector channel. The two-pion contribution is taken from modern dispersive analyses and embedded into the intrinsic high- $Q^{2}$ structure of the GK ansatz. The physical $ρ$ dynamics is then interpreted as part of the correlated two-pion spectral function. The direct coupling terms remain essential for the transition to the asymptotic regime. This gives a cleaner separation between long-range continuum dynamics, coherent vector-meson contributions, and direct quark-current dynamics. With just 5 parameters, we can describe the large body on form-factor data and differential cross sections from electron-proton scattering in the space-like region.
↳ nucl-thhep-exhep-phnucl-ex1 citation
10
An improved direct limit on the muon electric dipole moment
The Muon g-2 Collaboration: D. P. Aguillard (32)🇺🇸 · T. Albahri (29)🇬🇧 · D. Allspach (7)🇺🇸 · J. Annala (7)🇺🇸 · K. Badgley (7)🇺🇸 · S. Baeßler (34)🇺🇸 · L. Bailey (26)🇬🇧 · E. Barlas-Yucel (27 and a)🇺🇸 · T. Barrett (6)🇺🇸 · E. Barzi (7)🇺🇸 · F. Bedeschi (10)🇮🇹 · M. Berz (16)🇺🇸 and 182 other authors
A limit on the permanent electric dipole moment (EDM) of the positive muon is presented based on data from the Fermilab Muon g-2 Experiment taken between 2019 and 2020. The tracking detectors measure the average vertical decay angle of positrons from muon decays, enabling a search for an interaction between a possible muon EDM $d_{μ}$ and the lab-frame magnetic field. The result, $d_{μ} = (- 0.35 \pm 0.1 9_{stat} \pm 0.3 4_{sys}) \times 1 0^{- 19} e \cdot$ cm, is consistent with zero and sets a new direct limit on the muon EDM of $∣ d_{μ} ∣ < 1.10 \times 1 0^{- 19} e \cdot$ cm at the 95 percent confidence level.
↳ hep-exnucl-ex0 citations

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