Nuclear Experiment·nucl-ex

Tue·Aug 4, 2026Tuesday·August 4, 2026

12 papers—4 primary·8 cross-listed

01
Modification of $Υ$ production in $p$ O and OO collisions at LHCb
LHCb collaboration: R. Aaij🇳🇱 · M. Abdelfatah🇺🇸 · A.S.W. Abdelmotteleb🇬🇧 · C. Abellan Beteta🇨🇭 · F. Abudinén🇬🇧 · T. Ackernley🇬🇧 · A.A. Adefisoye🇺🇸 · B. Adeva🇪🇸 · M. Adinolfi🇬🇧 · P. Adlarson🇵🇱 · C. Agapopoulou🇫🇷 · C.A. Aidala🇺🇸 and 1178 other authors
The production rates of $Υ (2 S)$ and $Υ (3 S)$ mesons relative to that of the $Υ (1 S)$ state are measured in $pp$ , $p$ O, and OO collisions by the LHCb collaboration. The ratios measured in $pp$ data are consistent with previous LHCb measurements at different center-of-mass energies. Only slight relative suppression of the $Υ (2 S)$ and $Υ (3 S)$ states is found in $p$ O collisions, while in OO collisions the $Υ (2 S)$ is suppressed by a factor of $\sim 2$ , with evidence for suppression of the $Υ (3 S)$ . The significant suppression in OO data, compared to the small effect in $p$ O data, shows the emergence of additional suppression mechanisms in the relatively small OO collision system. Models incorporating quark-gluon plasma formation in OO collisions successfully describe the data. Implications for the interplay between cold nuclear matter effects and color screening in a deconfined quark-gluon plasma are discussed.
nucl-exhep-ex0 citations
02
Collision energy and system size dependence of $p_{T}$ -differential radial flow fluctuations $v_{0} (p_{T})$ at RHIC
Zaining Wang🇨🇳
We report the first RHIC measurements of $v_{0} (p_{T})$ in Au+Au collisions at $s_{NN} = 7.7$ -- $200$ GeV and O+O collisions at $s_{NN} = 200$ GeV. The integral fluctuation $v_{0}$ follows a common $N_{ch}$ dependence in large and small systems, suggesting that the fluctuation magnitude is predominantly controlled by event-by-event fluctuations of the initial transverse size. The normalized response $v_{0} (p_{T}) / v_{0}$ factorizes across centralities and systems, revealing a universal hydrodynamic response $κ_{0} (p_{T}) / κ_{0}$ largely independent of the fluctuation amplitude. Identified-hadron mass ordering and viscous model comparisons demonstrate sensitivity to bulk viscosity ( $ζ / s$ ). These results establish $v_{0} (p_{T})$ as a probe of the radial hydrodynamic response, collectivity across large and small collision systems, and QGP transport properties.
nucl-ex0 citations
03
Hadron Spectroscopy: Experimental Overview
Volker Crede🇺🇸
One of the most fascinating phenomena in nuclear and particle physics is the formation of light hadrons -- strongly interacting particles -- out of massless gluons and almost massless quarks. These particles exhibit rich excitation spectra due to their complex quark-gluon structures. Short-lived pairs of virtual quarks and antiquarks are continually formed and annihilated inside hadrons. Every physics student probably knows that the proton consists of three quarks. This statement is misleading, though. For example, the proton only shows a constant excess of three quarks versus antiquarks from the outside, and these three quarks are not even well defined. Understanding hadrons goes well beyond explaining their properties in terms of three quarks for baryons and a quark-antiquark pair for mesons. Much like atomic spectroscopy revealed the structure of atoms through discrete energy levels, hadron spectroscopy seeks the mapping of the spectrum of hadronic states and to use that information to better understand the underlying theory of the strong force -- Quantum Chromodynamics (QCD). Over the past few decades, hadron spectroscopy has entered an exciting new era with the discovery of many exotic hadrons that do not fit neatly into the traditional quark model classification of ordinary baryons and mesons. Many of the discoveries come from the heavy-flavor sector. As experimental techniques and computational methods continue to advance, hadron spectroscopy will remain a vital tool for probing the deepest layers of matter and understanding the fundamental structure of the universe.
nucl-exhep-exhep-ph1 citation
04
Charm-quark collectivity from small to large systems with ALICE
Marcello Di Costanzo🇮🇹
In these proceedings, the elliptic flow ( $v_{2}$ ) measurement of prompt charm hadrons in lead-lead (Pb-Pb) and oxygen-oxygen (OO) collisions at $s_{NN} = 5.36$ TeV, using the data collected during LHC Run 3 by the ALICE detector, is presented. The analysis is performed at midrapidity ( $∣ y ∣ < 0.8$ ) and hadronic decay channels are used to reconstruct the signal candidates. The $v_{2}$ coefficient is measured via the Scalar Product (SP) technique. The $v_{2}$ of prompt D $^{0}$ , D $^{+}$ , D $_{s}^{+}$ mesons, and $Λ_{c}^{+}$ baryons in semicentral Pb-Pb collisions is reported. These results achieve unprecedented precision and low- $p_{T}$ reach for the D mesons and highlight the first observation of the splitting of baryon and meson elliptic flow at intermediate $p_{T}$ in the charm sector. The prompt D-meson $v_{2}$ is also measured in peripheral Pb-Pb collisions and central OO collisions, probing the degree of thermal equilibration reached by charm quarks propagating in progressively smaller quark-gluon plasma media.
nucl-exhep-ex0 citations
05
Rethinking Total Absorption Gamma Spectroscopy Deconvolution: Supervised Machine Learning vs Response-Matrix Methods
J. Balibrea-Correa🇪🇸 · E. N{á}cher · C. Fonseca-Vargas · J. L. Tain🇪🇸
The extraction of $β$ -feeding distributions in Total Absorption $γ$ -ray Spectroscopy constitutes a challenging inverse problem, particularly in nuclei with complex decay schemes involving a large number of excited states. In such cases, the measured spectrum arises from the superposition of many detector response functions, making the determination of the individual feedings intrinsically ill-posed and highly sensitive to the methodology employed. In this work, we present a systematic comparison between supervised Machine-Learning techniques and Response-Matrix methods using realistic Monte Carlo simulations of an experimental Total Absorption Spectrometer. Supervised Machine-Learning approaches construct a non-parametric estimator that infers level feedings from the measured spectrum after a training stage, whereas Response-Matrix methods determine the feeding distribution by directly minimizing the difference between measured and reconstructed spectra. Our results show that supervised Machine-Learning techniques achieve superior accuracy in the reconstruction of individual feeding intensities, whereas Response-Matrix methods provide robust and physically consistent initial solutions. These findings support a hybrid strategy in which a Response-Matrix method is first used to obtain an initial feeding estimate, which is then refined using a supervised Machine-Learning approach to achieve improved overall accuracy.
↳ physics.data-ancs.LGnucl-ex0 citations
06
Nuclear $γ$ -Ray Cascades as Markov Processes
A. Psaltis
A framework for computing $γ$ -ray feeding probabilities in nuclear decay schemes based on absorbing Markov chains is presented. In this approach, excited nuclear states are treated as transient states and long-lived levels as absorbing states, allowing feeding fractions to be obtained exactly from the transition matrix. Experimental uncertainties are propagated via Monte Carlo sampling from Dirichlet distributions, which naturally maintains the physical constraint of unit normalization for branching-ratio vectors. This framework is applied to the key $E_{r} = 92$ keV resonance in the $^{25}$ Mg(p, $γ$ ) $^{26}$ Al reaction ( $E_{x} = 6398$ keV), which governs the production of $^{26}$ Al in hydrogen-burning environments. Combining multiple experimental datasets within a Hierarchical Bayesian framework, a ground-state feeding probability of $f_{0} = 0.68 \pm 0.06 (1 σ) \pm 0.13 (2 σ)$ is found, and for the first time the dominant $γ$ -decay transitions contributing to its uncertainty are identified. The formalism reproduces traditional cascade calculations while providing analytic sensitivity information and a transparent uncertainty decomposition. This approach offers a general and computationally efficient tool for propagating nuclear-structure uncertainties to astrophysical reaction rates and can be readily extended to other nuclei.
↳ nucl-thnucl-exPRC(2026)·0 citations
07
Constraining tensor force terms with the charge radii difference of mirror-pair nuclei
Yan Ya · Na Tang · Rong An🇨🇳
Charge radii differences of mirror partner nuclei provide an alternative probe to pin down the interaction components in asymmetric nuclear matter. In this work, the differences in the charge radii of almost spherical mirror-paired nuclei $^{54}$ Ni- $^{54}$ Fe and $^{36}$ Ca- $^{36}$ S are used to constrain the magnitude of tensor terms in the Skyrme interactions. The calculated results suggest that a linear correlation can be found between the difference of charge radii of mirror partner nuclei and the adopted strengths of the triplet-odd and triplet-even tensor components. Besides, it suggests that charge radii differences of mirror-paired nuclei are more sensitive to the adopted strengths of the triplet-odd parameter $U$ rather than the triplet-even parameter $T$ . Combining the quantitative constraint strengths of the triplet-even tensor part obtained from the magnetic dipole (M1) excitations, the charge-exchange Gamow-Teller (GT) states, and the spin-dipole (SD) excitations, the triplet-odd strengths are further constrained for the SLy5 as well as SGII effective interactions. This provides an alternative approach to constrain the appropriate magnitude of tensor force.
↳ nucl-thnucl-exPRC(2026)·0 citations
08
Proton-proton Femtoscopy as a Probe of Short-range Structure in High-Energy O+O Collisions
Baoshan Xi🇨🇳 · Pei Li🇨🇳 · Chunjian Zhang🇨🇳 · Jinhui Chen🇨🇳 · Su-Ya-La-Tu Zhang🇨🇳 · Yu-Gang Ma🇨🇳
Short-range nucleon-nucleon correlations are a defining feature of the nuclear many-body wave function, yet they are invisible in the one-body density and therefore inaccessible to observables that measure a nuclear size. We show that proton-proton femtoscopy supplies the missing sub-femtometer sensitivity. In $^{16}$ O+ $^{16}$ O collisions at $s_{NN} =$ 200 GeV, we compare three nuclear-structure inputs spanning mean-field, low-resolution cluster, and short-range-correlated descriptions. The $p$ - $p$ correlation function separates all three, most sharply in peripheral collisions, where the \textit{ab initio} input suppresses the extracted source radius by $\sim 5%$ relative to the mean-field baseline. Under identical conditions $π^{+}$ - $π^{+}$ correlations respond an order of magnitude more weakly, and the $C_{pp} / C_{π^{+} π^{+}}$ double ratio retains the full effect, pointing to the short-distance weighting of the $^{1} S_{0}$ pair rather than to an overall rescaling of the source. The signal survives the leading theoretical systematic, the choice of strong-interaction potential, which we quantify explicitly. These results identify $p$ - $p$ femtoscopy as a short-distance-resolved probe of light-nucleus structure, complementary to flow observables that constrain only the low-order moments of the initial geometry.
↳ nucl-thnucl-ex1 citation
09
A femtoscopic tale of two $C$ -parities: the $Z_{c} (3900)$ and the isovector partner of the $X (3872)$
Pan-Pan Shi🇪🇸 · Miguel Albaladejo🇪🇸 · Feng-Kun Guo🇨🇳 · Juan Nieves🇪🇸
Understanding the nature of the exotic $Z_{c} (3900)$ and $Z_{cs} (3985)$ states, and searching for the predicted isovector partner $W_{c 1}$ of the $X (3872)$ , remain central challenges in exotic-hadron spectroscopy. We investigate the femtoscopic correlation functions (CFs) of the $D^{(*) 0} D_{(s)}^{(*) -}$ systems. Since these charm-meson--antimeson pairs are not $G$ -parity eigenstates, their CFs contain contributions from both the $C$ -odd and $C$ -even sectors, providing direct access to the dynamics underlying the $Z_{c}$ , $Z_{cs}$ , and the predicted isovector exotic $W_{c 1}$ . Within a heavy-quark-spin-symmetric coupled-channel framework, we show that the $C$ -even admixture enhances the low-momentum CFs by more than $2.5 σ$ in the vicinity of their thresholds. Free from Coulomb distortions and accessible in high-multiplicity $pp$ collisions at the LHC, these channels offer the first direct femtoscopic probe of the isovector $C$ -even sector and of the elusive $W_{c 1}$ state.
↳ hep-phhep-exnucl-exnucl-th1 citation
10
Necessary and sufficient conditions of nonlinear causality in viscous anisotropic hydrodynamics
Kento Yoshida🇯🇵 · Shujun Zhao🇯🇵 · Tetsufumi Hirano🇯🇵
We derive the necessary and sufficient conditions for nonlinear causality in viscous anisotropic hydrodynamics (VAH) within the approximation that neglects small correction terms. Relativistic hydrodynamics provides a successful description of the space-time evolution of the matter produced in relativistic heavy-ion collisions, yet the earliest stage at which a hydrodynamic description becomes valid remains an open question. VAH has been proposed as an extension of conventional viscous hydrodynamics (VH) that can accommodate the large pressure anisotropies of the early-time dynamics. However, in such far-from-equilibrium regimes, the nonlinear causality of the theory is not guaranteed. By analyzing the characteristic velocities of the VAH equations of motion, we derive a set of inequalities that ensures causal signal propagation in all directions. The resulting conditions take a remarkably simple form and admit a clear physical interpretation in terms of the characteristic modes of the anisotropic medium. These results establish the regime of validity of VAH and provide a foundation for its application to the early-time dynamics of relativistic heavy-ion collisions.
↳ nucl-thhep-phnucl-ex0 citations
11
Mass Spectrometry Studies of Hydrogen Ions Energy Distributions in an ECR- based Large Volume Plasma Source
Bibekananda Naik · Ramesh Narayanan · Debaprasad Sahu · Mainak Bandyopadhyay · Ashish Ganguli🇺🇸
Plasma is produced in a Large Volume Plasma Source (LVPS; dia. = 1 m, height = 1m) using CW microwaves (= 400 - 600 W, 2.45 GHz), in a compact ECR plasma source (CEPS) attached to LVPS, at hydrogen gas pressures = 1 - 3 mTorr. Plasma expands along the CEPS magnetic field into LVPS. A Hiden Analytical HPR 60 molecular beam mass spectrometer (MBMS) is used to measure the H^- ion energy distribution functions (IEDFs) in the downstream plasma. Previous plasma characterization studies in LVPS indicated favourable downstream plasma conditions for volume production of H^- ions. Measurements conducted with the MBMS probe aligned facing the plasma flow = 80 cm downstream, gave typical H^- count rates = 3 x 10^5 counts /s, at = 400 W, = 1 mTorr, along with a distinct high energy tail (<= 20 eV). These and other results are analyzed in detail. The positive ion spectrum showed the H_3^+ count to be consistently high in all cases (= 60-70 %); the counts for H_2^+ and H^+ were =30-35 % and a =few %. Combining the Langmuir probe (LP) and MBMS data it is possible to determine the approximate densities in front of the MBMS probe aperture. At = 500 W and = 2 mTorr, one finds: n_(H^+) = 9.6 x 10^9 cm^(-3), n_(H_2^+) = 1.7 x 10^10 cm^(-3) and n_(H_3^+) = 4.3 x 10^10 cm^(-3). The corresponding H^- density, = 80 cm downstream is n_(H^-) = 3.9 x 10^8 cm^(-3). Accounting for all H^- losses due to scattering and destruction, one finds the effective mean free path for H^- loss to be = 12.4 cm. Noting that H^- formation takes place about = 10 - 30 cm downstream of the source exit, the approximate average H^- density in the formation zone is determined as = 5.5 x 10^10 cm^(-3). This value is remarkably encouraging for H^- production in volume mode, considering the large chamber volume and area, as well as the very moderate power used for the experiments.
↳ physics.plasm-phnucl-exphysics.acc-phphysics.atm-clus0 citations
12
Effects of light-cluster degrees of freedom on collective flows in heavy-ion collisions at FOPI energies
Xin Li🇨🇳 · Si-Pei Wang🇨🇳 · Rui Wang🇨🇳 · Zhen Zhang🇨🇳 · Jie Pu🇨🇳 · Chun-Wang Ma🇨🇳 · Lie-Wen Chen🇨🇳
Within a lattice Boltzmann-Uehling-Uhlenbeck transport model coupled to a kinetic approach for light-cluster formation, we investigate the impact of explicit light-cluster degrees of freedom on collective flows in Au+Au collisions at FOPI energies with beam energies $E_{beam}$ = $120$ -- $1500 A$ MeV by using a density-, momentum-, and isospin-dependent N $5$ LO Skyrme pseudopotential. We first benchmark the kinetic approach by comparing the calculated light-cluster yields with FOPI data in central Au+Au collisions. We then analyze the collective flows of protons and light nuclei (deuterons, tritons, $^{3} He$ , and $^{4} He$ ) in mid-central collisions. For protons, calculations with and without dynamical light-cluster degrees of freedom are compared to quantify the influence of dynamical cluster formation on proton directed ( $v_{1}$ ), elliptic ( $v_{2}$ ), triangular ( $v_{3}$ ), and quadrangular ( $v_{4}$ ) flows. We find that the dynamical light-cluster effect appreciably modifies proton $v_{1}$ -- $v_{4}$ flows at $E_{beam} = 120$ -- $150 A$ MeV, remains visible at $E_{beam} = 250$ -- $400 A$ MeV, and gradually weakens at $E_{beam} ≳ 600 A$ MeV. For light nuclei, the kinetic approach captures the overall beam-energy dependence of the FOPI flow data, with better agreement for $E_{beam} \geq 400 A$ MeV. We further examine the nucleon-number scaling of $v_{2} / A$ in both model calculations and experimental data, finding that the kinetic light-cluster formation approach qualitatively reproduces the observed scaling behavior. These results highlight the importance of a dynamical treatment of light-cluster formation for interpreting collective flows in heavy-ion collisions below about $600 A$ MeV, although the clustering effects on proton flows are minor at higher collision energies.
↳ nucl-thhep-exhep-phnucl-ex0 citations

Affiliations

first authorsco-authorsvia INSPIRE