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Physics Nuclear Experiment

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Thursday 20 August

Nuclear Experiment · Cross-listed from hep-ph

QED radiative effects in semi-inclusive deep-inelastic scattering: traditional and factorized approaches

Igor Akushevich, Haiyan Gao, Alexander Ilyichev et al. (+5 more)

Semi-inclusive deep-inelastic scattering (SIDIS) of leptons is a vital tool for probing the three-dimensional momentum space partonic structure of the nucleon. Reliable extraction of the intrinsic collinear or transverse momentum dependent parton distributions from SIDIS data requires careful treatment of QED radiative effects beyond the Born level. In this work we perform a detailed comparative analysis of QED effects in SIDIS using the traditional Bardin-Shumeiko approach, augmented by the electron structure function method, and a more recent factorized approach that treats QED and QCD radiation on equal footing. We compare analytical and numerical results of these approaches for the unpolarized $\pi^+$ electroproduction cross sections off the proton and the Collins and Sivers transverse single-spin asymmetries, and identify the sources of discrepancies between the calculations, which for the cross sections can reach up to $\approx 2\%$, $\approx 7\%$, and $\approx 5\%$ at Jefferson Lab, HERMES, and EIC kinematics, respectively. To provide a unified approach for reliably extracting partonic information from future SIDIS measurements, we propose a hybrid framework that employs the salient features of both frameworks in their respective regions of applicability.
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All authors Igor Akushevich, Haiyan Gao, Alexander Ilyichev, Shuo Jia, Vladimir Khachatryan, Youjie Lin, Tianbo Liu, W. Melnitchouk

Nuclear Experiment · Cross-listed from hep-ex

Heavy-flavour production and correlations in pp collisions: precision tests of pQCD and hadronisation with ALICE

Deependra Sharma and for the ALICE Collaboration

Heavy quarks (charm and beauty) are predominantly produced in hard partonic scatterings, making their cross sections in proton–proton (pp) collisions calculable in perturbative quantum chromodynamics (pQCD) and thus providing stringent tests of pQCD. Furthermore, the associated production of two charm hadrons in a single collision offers a sensitive probe of multiparton interaction dynamics, distinguishing between single parton scattering (SPS) and double parton scattering (DPS) processes. In this contribution, preliminary measurements of prompt D-meson production are reported, together with the final results of the $\rm B^{0}$-meson production cross section down to $p_{\rm T}$ = 1 GeV/$c$ at midrapidity. The rapidity dependence of B-meson production is investigated by computing the ratio with respect to LHCb measurements at forward rapidity. The associated production of $\rm D^{0}$–$\mathrm{J}/\psi$ pairs in pp collisions at $\sqrt{s} = 13.6$ TeV is presented as well, where $\rm D^{0}$ mesons are reconstructed at midrapidity, while $\mathrm{J}/\psi$ candidates are measured at forward rapidity. These measurements are compared with pQCD calculations and phenomenological models, providing crucial constraints on heavy-quark production, hadronisation, and multiparton interaction dynamics.
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Nuclear Experiment · Cross-listed from hep-ph

Tracing Vacuum Hadronization with Conserved Currents

Weiyao Ke, Hai Tao Li, Wanchen Li et al. (+2 more)

We show that color triality constrains the nonperturbative states that screen a Wilson-line endpoint, allowing the joint flows of net electric charge, baryon number, and strangeness to probe QCD vacuum hadronization. Whether evaluated from resolved hadrons in a jet initiated by a quark of flavor $f$ or from the corresponding charge correlators, these flows satisfy the Gell-Mann–Nishijima relation $\langle Q_{\rm flow}\rangle_f \simeq I_{3,f} +\frac{1}{2}\left( \langle S_{\rm flow}\rangle_f +\langle B_{\rm flow}\rangle_f \right)$, where $I_{3,f}$ is the third component of the initiating-quark isospin. The net jet baryon number, $\langle B_{\rm flow}\rangle_f\simeq \frac{r_{qq}}{1+r_{qq}}$, directly probes the relative probability of a diquark–antidiquark vacuum excitation, with $r_{qq}$ the diquark-to-quark production ratio. Thus, for $r_{qq}\ll1$, the baryon number carried by the jet is substantially suppressed relative to the initiating-quark value $B_f=1/3$. Likewise, the strange-to-light pair-production ratio, defined by $u\bar u:d\bar d:s\bar s=1:1:r_s$, is encoded in the measured jet strangeness $\langle S_{\rm flow}\rangle_f \simeq S_f+\frac{3r_s}{2+r_s} \left(\frac{1}{3}- \langle B_{\rm flow}\rangle_f\right)$, predicting a nonzero mean net strangeness even in $u$- and $d$-initiated jets. The conserved-current moments appearing in these relations are independent of the renormalization scale. Their simultaneous measurement therefore provides a direct, flavor-resolved probe of vacuum pair production and quantum-number transport during hadronization.
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All authors Weiyao Ke, Hai Tao Li, Wanchen Li, Xiaohui Liu, Ding Yu Shao

Wednesday 19 August

Nuclear Experiment · Cross-listed from hep-lat

The QCD crossover temperature and curvature coefficient from unbiased exponential resummation at physical quark masses in (2+1)-flavor lattice QCD

Sabarnya Mitra

We present the first application of the unbiased exponential resummation method to the determination of the QCD pseudocritical temperature $T_{\rm pc}$ at vanishing baryon chemical potential $\mu_B$. By reconstructing the finite-density baryon number susceptibility $\chi_2^B$, we define two thermal-derivative observables whose peak positions yield $T_{\rm pc}^T=160.2(4)(3)$ MeV and $T_{\rm pc}^C=158.1(5)(3)$ MeV. We also show that the pseudocritical temperature, $T_{\rm pc}^\chi$ obtained from the peak of the fourth-order baryon number susceptibility $\chi_4^B$ is consistent with these determinations and with previous lattice-QCD results based on Taylor expansions \cite{Bollweg:2022Pade}. Further, we demonstrate that scaling relations \cite{Bollweg:2022fqq} between $\chi_4^B$ and the thermal derivatives of $\chi_2^B$ yield mutually consistent estimates of the leading second order curvature coefficient $\kappa_2^B$ at the corresponding pseudocritical temperatures. A direct analysis of the $\mu_B$ dependence of the pseudocritical temperatures provides an independent but substantially less constrained determination of the curvature, which remains statistically consistent with the scaling-based estimates. These results demonstrate the consistency of unbiased exponential resummation with the expected scaling behavior and establish it as a complementary approach for probing the QCD crossover at small finite baryon density.
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Nuclear Experiment

Improved $^{94}$Mo neutron resonance parameters from neutron capture and transmission measurements at n_TOF and GELINA

R. Mucciola, S. Cristallo, S. Kopecky et al. (+140 more)

We report high-resolution measurements of the $^{94}\mathrm{Mo}(\mathrm{n},\gamma)^{95}\mathrm{Mo}$ cross section in the neutron energy range from a few eV up to about 250 keV, performed at the n_TOF facility (CERN), and of the $^{94}\mathrm{Mo}(\mathrm{n},\mathrm{tot})$ cross section up to 32 keV, measured at GELINA (JRC Geel). A combined R-matrix analysis of capture and transmission data yields significantly improved neutron-resonance parameters for $^{94}$Mo. A total of 186 resonances were observed in this analysis of which 127 reported here for the first time. The resulting Maxwellian-averaged cross section at stellar temperatures relevant to the slow neutron-capture process (s-process) is approximately 25% lower than previous evaluations and literature values. To assess the astrophysical impact of the revised cross section, we performed s-process nucleosynthesis calculations for low-mass asymptotic giant branch stars. Despite the substantial reduction in the $^{94}\mathrm{Mo}(\mathrm{n},\gamma)^{95}\mathrm{Mo}$ rate, the final yields vary by only 3-4%. This demonstrates that the isotopic budget of $^{94}$Mo in AGB stars is primarily governed by the branching flow at $^{94}\mathrm{Nb}$ rather than by the neutron-capture destruction on $^{94}$Mo itself. The new cross section thus helps disentangle nuclear cross-section uncertainties from branching-flow effects in the s-process production of $^{94}$Mo.
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All authors R. Mucciola, S. Cristallo, S. Kopecky, N. Liu, C. Massimi, A. Mengoni, A. Manna, C. Paradela, P. Schillebeeckx, G. Sibbens, D. Vescovi, O. Aberle, V. Alcayne, S. Altieri, S. Amaducci, J. Andrzejewski, V. Babiano-Suarez, M. Bacak, J. Balibrea-Correa, C. Beltrami, S. Bennett, A. P. Bernardes, E. Berthoumieux, R. Beyer, M. Boromiza, D. Bosnar, M. Caamano, F. Calvino, M. Calviani, D. Cano-Ott, A. Casanovas, D. M. Castelluccio, F. Cerutti, G. Cescutti, S. Chasapoglou, E. Chiaveri, P. Colombetti, N. Colonna, P. Console Camprini, G. Cortes, M. A. Cortes-Giraldo, L. Cosentino, S. F. Dellmann, M. Diakaki, M. Di Castro, M. Dietz, S. Di Maria, C. Domingo-Pardo, R. Dressler, E. Dupont, I. Duran, Z. Eleme, S. Fargier, B. Fernandez, B. Fernandez-Dominguez, P. Finocchiaro, S. Fiore, V. Furman, F. Garcia-Infantes, A. Gawlik-Ramiega, G. Gervino, S. Gilardoni, E. Gonzalez-Romero, S. Goula, C. Guerrero, F. Gunsing, C. Gustavino, J. Heyse, W. Hillman, D. G. Jenkins, E. Jericha, A. Junghans, Y. Kadi, K. Kaperoni, G. Kaur, A. Kimura, I. Knapova, M. Kokkoris, Y. Kopatch, M. Krticka, N. Kyritsis, I. Ladarescu, S. Lanzi, C. Lederer-Woods, J. Lerendegui-Marco, G. Lerner, T. Martinez, A. Masi, P. Mastinu, M. Mastromarco, E. A. Maugeri, A. Mazzone, E. Mendoza, V. Michalopoulou, P. M. Milazzo, F. Murtas, E. Musacchio Gonzalez, A. Musumarra, A. Negret, N. Patronis, J. A. Pavon, M. G. Pellegriti, P. Perez-Maroto, A. Perez de Rada Fiol, J. Perkowski, C. Petrone, L. Piersanti, E. Pirovano, J. Plaza del Olmo, S. Pomp, I. Porras, J. Praena, J. M. Quesada, R. Reifarth, D. Rochman, Y. Romanets, C. Rubbia, A. Sanchez-Caballero, M. Sabate-Gilarte, D. Schumann, A. Sekhar, A. G. Smith, N. V. Sosnin, M. E. Stamati, A. Sturniolo, G. Tagliente, A. Tarifeno-Saldivia, D. Tarrio, P. Torres-Sanchez, S. Urlass, E. Vagena, S. Valenta, V. Variale, P. Vaz, G. Vecchio, V. Vlachoudis, R. Vlastou, A. Wallner, P. J. Woods, T. Wright, R. Zarrella, P. Zugec, The n_TOF Collaboration

Nuclear Experiment · Cross-listed from physics.ins-det

Study of the intrinsic resolution of LaBr3(Ce,Sr) and NaI(Tl) crystals

Peiyi Feng, Xilei Sun, Zhenghua An et al. (+4 more)

The Gravitational wave burst high-energy Elec?tromagnetic Counterpart All-sky Monitor (GECAM) utilizes a large number of LaBr3 and NaI(Tl) crystals as sensitive materials for its gamma-ray detectors. To address the fitting issues of the energy resolution curves in the ground calibration of the GECAM detectors, this work conducts a comprehensive testing and comparative study of the energy resolution of 1-inch LaBr3(Ce,Sr) and NaI(Tl) crystals produced from the same batch. We employed a Hard X-ray Calibration Facility (HXCF), a PMT single-photoelectron calibration system, and Geant4 Monte Carlo simulation tools to quantify seven factors influencing energy resolution. The results indicate that the contributions of various components to energy resolution differ, with pho?toelectron statistical fluctuations and intrinsic resolution being predominant. For 100 keV X-rays, the total energy resolution of the LaBr3(Ce,Sr) crystal is 3.71% \pm 0.03% (expressed as 1-{\sigma}), with a contribution from photoelectron statistical fluctuations of 2.69% \pm 0.00% and an intrinsic resolution of 2.45% \pm 0.05%. For 100 keV X-rays, the total energy resolution of the NaI(Tl) crystal is 4.41% \pm 0.14% (expressed as 1-{\sigma}), with a contribution from photoelectron statistical fluctuations of 3.20% \pm 0.00% and an intrinsic resolution of 2.90% \pm 0.21%. We discussed the sources of intrinsic resolution, and the results indicate that the intrinsic resolution of the LaBr3(Ce,Sr) crystal primarily arises from luminescence non-proportionality, while that of the NaI(Tl) crystal mainly stems from fluctuations during energy transfer. This study emphasizes precise and specific experimental measurements and comparative research, demonstrating that both factors are important contributors to intrinsic resolution.
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All authors Peiyi Feng, Xilei Sun, Zhenghua An, Dali Zhang, Xinqiao Li, Shaolin Xiong, Hong Lu

Nuclear Experiment · Cross-listed from nucl-th

Toward testing antinucleon$\unicode{x2013}$nucleus optical potentials with antineutron scattering lengths

Hiroyuki Fujioka and Sayaka Ishii

The antineutron$\unicode{x2013}$nucleus scattering length is currently known only indirectly, via antiproton$\unicode{x2013}$nucleus optical potentials fitted to level shifts and widths of antiprotonic atoms. The antineutron$\unicode{x2013}$nucleus and antiproton$\unicode{x2013}$nucleus potentials are related to each other through charge symmetry. We calculate the scattering length from optical potentials proposed for antiprotonic atoms using nucleon density distributions as input. We find that the scattering length for an $N>Z$ nuclide is largely affected by the poorly constrained neutron density distribution and by a possible isovector interaction, one of the mechanisms introduced to reproduce the isotope dependence of antiprotonic $^{40,48}\mathrm{Ca}$ data. For $^{48}\mathrm{Ca}$, the isovector term modifies the scattering length by $0.3\unicode{x2013}0.4\,\mathrm{fm}$ ($0.4\unicode{x2013}0.5\,\mathrm{fm}$) for the real (imaginary) part, an order of magnitude beyond the uncertainty propagated from the isoscalar potential. As no antineutron$\unicode{x2013}$nucleus scattering data are available below $76\,\mathrm{MeV}/c$, a direct measurement with recently proposed low-energy antineutron beams would provide the first access to the antinucleon$\unicode{x2013}$nucleus interaction in the $s$-wave regime.
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Tuesday 18 August

Nuclear Experiment

Observation of enhanced baryon production using strange hadrons in oxygen-oxygen collisions

CMS Collaboration

A hot deconfined medium known as the quark-gluon plasma (QGP) is created in collisions of ultrarelativistic heavy nuclei. In these systems, hadron production is strongly modified relative to proton-proton (pp) interactions. In the hadron transverse momentum region 2 $\lt$ $p_\mathrm{T}$ $\lt$ 5 GeV, collective radial flow and quark coalescence are important mechanisms that can produce such modifications. While these effects are well-established for collisions of large ions, such as lead, it is unknown if they are present in systems produced using smaller ions. To address this question, the $p_\mathrm{T}$ spectra of two strange hadrons, K$^0_\mathrm{S}$ and $\Lambda$, are measured in oxygen-oxygen (OO) and pp collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The measurements are performed using the CMS detector at the LHC, and the OO and pp datasets correspond to integrated luminosities of 6.8 nb$^{-1}$ and 1.1 pb$^{-1}$, respectively. The spectral modification of K$^0_\mathrm{S}$ mesons in OO collisions relative to pp collisions is found to be similar to that of inclusive charged hadrons. Conversely, the $\Lambda$-to-K$^0_\mathrm{S}$ cross section ratio exhibits a pronounced enhancement in OO collisions when compared to pp collisions. The results provide the first observation of a baryon-to-meson enhancement in OO collisions and suggest the formation of a deconfined medium, offering insight into the roles of strangeness, radial flow, and quark coalescence in QGP.
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Nuclear Experiment · Cross-listed from physics.atom-ph

Probing the electroweak structure of nuclei with rare atoms and molecules

Silviu-Marian Udrescu, Antoine Belley, Jason D. Holt et al. (+2 more)

Precision experiments of atoms and molecules have become a powerful probe of the electroweak structure of atomic nuclei and of physics beyond the Standard Model. We review how the interaction between a nucleus and its surrounding bound electrons can be exploited to precisely measure the electromagnetic, parity-violating, and CP-violating properties of nuclei and their fundamental constituents. We focus on rare, unstable isotopes, surveying the experimental techniques and facilities developed in recent years that have extended these measurements to the most exotic regions of the nuclear chart. Recent advances in the precision control and interrogation of single molecules, together with direct laser excitation of nuclear transitions, are opening new frontiers in nuclear and particle physics. At the same time, progress in nuclear theory, machine learning, and high-performance computing is strengthening the connection between our microscopic description of nature and laboratory observables. In many cases, the precision with which nuclear and particle physics properties can be extracted is now limited not by experiment, but by the molecular, atomic, or nuclear theory required to interpret the measurements. This challenge presents a major opportunity for combined theoretical and experimental advances that will enable future discoveries.
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All authors Silviu-Marian Udrescu, Antoine Belley, Jason D. Holt, Gilad Perez, Ronald F. Garcia Ruiz

Nuclear Experiment · Cross-listed from nucl-th

Symbolic Regression for Interpretable Emulation of Proton Collective Flow in Intermediate-Energy Heavy-Ion Collisions

Nicholas Cox, Xavier Grundler and Bao-An Li

Symbolic regression provides an interpretable machine-learning approach for constructing explicit analytic relations between physical inputs and observables. In this work, we develop symbolic-regression emulators for the isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model and compare their performance with deep neural network (DNN) emulators. Using the same transport-model data employed in our previous emulator studies, we show that symbolic regression can reproduce the proton mid-rapidity slope $F_1$ of transverse flow $v_1$ and elliptic flow $v_2$ with accuracy comparable to that of DNNs, while providing explicit analytic expressions and substantially faster prediction once trained. We further demonstrate the use of symbolic regression in the reverse direction by constructing analytic relations that predict the in-medium nucleon-nucleon cross-section modification factor $X$ from the flow observables. Although the symbolic-regression models require substantially longer training times and exhibit greater run-to-run variation than DNNs, their analytic form and rapid evaluation make them promising tools for future transport-model sensitivity and uncertainty analyses.
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Nuclear Experiment

Revised $^{45}$V($p,\gamma$)$^{46}$Cr reaction rate and its impact on the production of $^{44}$Ti in core-collapse supernovae

R.S. Sidhu, Y. Luo, C. Sarma et al. (+2 more)

The thermonuclear $^{45}$V($p,\gamma$)$^{46}$Cr reaction is the primary leakage pathway from the $^{44}$Ti–$^{45}$V quasi-equilibrium cluster during $\alpha$-rich freeze-out in core-collapse supernovae (CCSN), governing the final abundance of the $\gamma$-ray-emitting isotope $^{44}$Ti. A recent high-resolution $\gamma$-ray study [C. Cousins et al., Phys. Rev. Lett. 136, 252701 (2026)] identified ten previously unknown low-spin proton-unbound states in $^{46}$Cr, enabling the first experimentally constrained $^{45}$V($p,\gamma$)$^{46}$Cr reaction rate using the AME2020 mass excess, $\text{ME}(^{46}\text{Cr}) = -29472(11)$~keV. Here, we adopt the four-fold more precise CSRe mass excess $\text{ME}(^{46}\text{Cr}) = -29477.2(2.6)$~keV [M.~Wang et al., Phys. Rev. C 106, L051301 (2022)] to recalculate the reaction rate. Including proton capture on the ground and first two excited states of $^{45}$V alongside new shell-model proton spectroscopic factors, we reduce mass-related rate uncertainties to a subdominant level. The revised rate is up to 69% higher than that of Cousins et al. at $\alpha$-rich freeze-out temperatures ($T \simeq 1.5$–$2$~GK). CCSN nucleosynthesis calculations show this revised rate increases the ejected $^{44}$Ti yield by $\sim$26% in a $20\,M_\odot$ model compared to The et al. [ApJ 504, 500 (1998)], while causing negligible changes for the SN~1987A trajectory. We demonstrate that $^{44}$Ti production sensitivity is dictated by the ejecta electron fraction ($Y_e$): the reaction significantly affects proton-rich ejecta ($Y_e \approx 0.50$) but has little impact on neutron-rich ejecta ($Y_e \approx 0.496$), where lower free-proton abundances suppress reaction flow. This reconciles conflicting results from past sensitivity studies.
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All authors R.S. Sidhu, Y. Luo, C. Sarma, M. Wiescher, X. Xu

Nuclear Experiment · Cross-listed from hep-ph

Bound-state spectra of $\chi_{cJ}$ in finite nuclei and the universal pattern of mass levels

Tian-Le Gao, Ze-Hua Zhang and Xiang Liu

In this work, we investigate possible $\chi_{cJ}$–nuclear bound states with $J=0,1,2$ using in-medium mass shifts generated by virtual $D^{(*)}\bar{D}^{(*)}$ loops within an unquenched framework. The resulting $\chi_{cJ}$–nucleus potentials are constructed in the local density approximation, and the bound state spectra are calculated for $^{12}{\rm C}$, $^{16}{\rm O}$, $^{40}{\rm Ca}$, $^{90}{\rm Zr}$, $^{197}{\rm Au}$, and $^{208}{\rm Pb}$. Bound states are obtained for all systems considered. The $\chi_{c0}(1P)$ and $\chi_{c1}(1P)$ spectra are nearly degenerate, whereas the larger in-medium mass shift of $\chi_{c2}(1P)$ leads to deeper binding. Although the absolute bound state energies depend appreciably on the cutoff parameter, the energy differences relative to the $1s$ level are considerably less sensitive to it and exhibit a regular pattern that decreases approximately as $A^{-2/3}$ with increasing nuclear mass number. A cosh-type potential with a common nuclear geometry provides a compact description of these spectra. The predicted bound-state structures and level-spacing systematics could be investigated in future high-statistics near-threshold photoproduction experiments at the upgraded JLab facility.
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Nuclear Experiment · Cross-listed from nucl-th

Generative artificial intelligence for reconstructing neutron-star matter

Julia Yu. Panteleeva, Herzallah Alharazin and Evgeny Epelbaum

Neutron-star cores hold the only known matter in the universe that is simultaneously cold and strongly interacting, compressed beyond nuclear density into a state of unknown composition. The equation of state links stellar masses, radii and tidal deformabilities to this regime, but recovering this key quantity from sparse observations is an ill-posed inverse problem. Existing analyses bury a prior in a fixed functional form, unevenly weighting admissible solutions and biasing the result. We reconstruct the equation of state with a denoising diffusion model that keeps prior, physics and data separate: it learns an inspectable, physically motivated prior anchored to first-principles nuclear theory, while perturbative-QCD and astrophysical constraints are imposed exactly. Future measurements therefore will update the posterior by reweighting alone, without retraining or resampling. The inferred radius of 12.6 km and tidal deformability of 469 at 1.4 solar masses reproduce Gaussian-process and heavy-ion-informed inferences despite a far broader prior. We find near-conformal but still stiff matter in the heaviest stars, consistent with a gradual hadron-quark crossover and disfavouring a strong first-order phase transition. More broadly, coupling a learned prior to exactly enforced physics establishes a template for ill-posed inverse problems where theory and data constrain different regions.
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Monday 17 August

Nuclear Experiment · Cross-listed from hep-ph

Closed-form expressions for tree-level gluon-gluon scattering: a framework for obtaining theoretical systematic uncertainties for jet-medium Monte Carlo simulations

Lukas Opitz, Hemanth Regi and Gojko Vujanovic

Modern Bayesian theory-to-data comparisons for jet-medium interactions, such as [Phys. Rev. C 111,054913 (2025)], are lacking the careful accounting of theoretical systematic uncertainties included within their uncertainty budget. Tree-level gluon-gluon scattering is revisited to establish a framework capable of quantifying theoretical systematic uncertainties to be used in Bayesian jet-medium constraints. The behavior of tree-level scattering in thermal QCD is examined in detail, finding deviations away from the commonly used approximations. Deviations in the scattering rate affect jet-medium transport coefficients at the partonic level, leading to a more intricate kinematic dependence for $\hat q$ and $\hat e$ than, say, the well-known logarithmic behavior. These deviations away from well-known behavior are used to estimate theoretical systematic uncertainties in Bayesian analysis.
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Nuclear Experiment · Cross-listed from hep-ph

The high-energy behavior of tree-level scattering in finite-temperature QCD: estimates of theoretical systematic uncertainty in jet-medium Monte Carlo simulations

Lukas Opitz, Hemanth Regi and Gojko Vujanovic

We examine the behavior of tree-level scattering in thermal QCD at high energies and find significant deviations away from the commonly used approximations [Phys. Rev. D 44, 1298 (1991), Phys. Rev. D 44, R2625 (1991), Phys. Rev. D.77, 014015 (2008), Phys. Rev. D. 77.114017 (2008)]. These deviations in the scattering rate also affect jet-medium transport coefficients at the partonic level, leading to a different kinematic dependence of the transverse momentum broadening per unit length $\hat{q}$. As scattering rates and $\hat{q}$ are used by large-scale Monte Carlo simulations of jets in the quark-gluon plasma (QGP), such as [Phys. Rev. C 111,054913 (2025)], current constraints on $\hat q$ are biased owing to the approximations used therein. Besides theoretically improving $\hat q$, the differences between the $\hat q$ herein and the approximate $\hat q$ used in jet Monte Carlo simulations are used to construct a theoretical systematic uncertainty, which in turn can be employed to devise a covariance matrix for $\hat q$ and enables updating the uncertainty bands on $\hat q$ obtained by Bayesian analysis.
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Nuclear Experiment

Determination of Tritium Content in D2 Gas and Heavy Water

Sandeep Puri, Noah D'Amico, Ian Jones et al. (+4 more)

A simple experimental method for the determination of tritium concentration in natural hydrogen and deuterium gas down to the femtomole level is described. Palladium and platinum catalysts were used to react hydrogen and oxygen, creating water that could be analyzed in a Revvity Quantulus GCT 6220. This analysis produced sub-femtomole detection limits of tritium present in hydrogen gas or heavy water. A contamination level of $\sim 1\text{ femtomole/SL}$ was found in the $\text{D}_2$ gas sample that was analyzed. A contamination level of $\sim 0.025\text{ femtomole/SL}$, which is below the noise level of the Quantulus, was found in the standard hydrogen gas sample that was analyzed. The choice of palladium or platinum catalyst did not significantly affect the resulting tritium measurement. By showing that common $\text{D}_2$ samples can be contaminated with trace amounts of tritium orders of magnitude above natural abundance, this test demonstrates that a baseline tritium measurement for deuterium samples is highly important for determining the validity of results in nuclear fusion yield experiments.
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All authors Sandeep Puri, Noah D'Amico, Ian Jones, Sonny Alaniz, Andrew Gillespie, Cuikun Lin, R. V. Duncan

Nuclear Experiment

Accurate Charge Radius Measurement of $^{14}$C Confronts Ab Initio Theory

Kristian König, Patrick Müller, Tobias Gesser et al. (+11 more)

Located at the neutron shell closure $N = 8$, the long-lived radioactive isotope $^{14}$C plays a critical role in geochronology and nuclear structure studies. Despite its widespread use, the nuclear charge radius of $^{14}$C has remained less precisely known compared to its stable counterpart $^{12}$C. Here, we report a high-precision determination of the $^{14}$C charge radius using collinear laser spectroscopy at the COALA setup at TU Darmstadt, improving upon the precision of previous muonic measurements by a factor $5$ and revealing a $1.9\sigma$ discrepancy of combined uncertainty, indicating a likely underestimated uncertainty in the muonic determination. This measurement challenges state-of-the-art ab initio nuclear theory calculations, including auxiliary field diffusion Monte Carlo, the valence-space in-medium similarity renormalization group, and the no-core shell model, augmented by neural-network techniques. With $^{12}$C and $^{14}$C now forming one of the most precisely characterized even-even isotope pairs, these results also enable improved QED tests.
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All authors Kristian König, Patrick Müller, Tobias Gesser, Emily Burbach, Stefano Gandolfi, Matthias Heinz, Phillip Imgram, Alessandro Lovato, Pieter Maris, Takayuki Miyagi, Wilfried Nörtershäuser, Robert Roth, Julien Spahn, Achim Schwenk

Nuclear Experiment · Cross-listed from nucl-th

Nuclear Drip Line and the Composition of Supernova Matter

S. Maity and S. Mallik

The nuclear drip line plays a crucial role in determining the composition of matter under extreme astrophysical conditions. In core-collapse supernovae and neutron-star crusts, matter is driven far from saturation density and nuclear stability; nuclei coexist with a sea of free neutrons, an effect that is present even at zero temperature in neutron-star crusts and becomes more pronounced in the hotter, neutron-rich supernova environment. This makes a careful treatment of drip-line physics essential for a realistic description of the equation of state and composition. In this work, the influence of the nuclear drip line on the baryonic composition of supernova matter is investigated within the framework of nuclear statistical equilibrium (NSE). The composition is evaluated in terms of free nucleons, light clusters, and heavy nuclei at finite temperature and global sub-saturation densities. The results indicate that, at low proton fractions and higher densities, the inclusion of nuclei beyond the drip line enhances the formation of extremely neutron-rich light clusters, leading to a significant reduction in the free-neutron density and the charge fraction of heavy nuclei. These findings demonstrate that drip-line physics has a significant impact on the composition of supernova matter and should be carefully incorporated in supernova modeling and nucleosynthesis studies.
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Nuclear Experiment

Probing the Size of Neutron and Proton Single-Particle Orbitals from Nucleon Knockout Reactions

M. Enciu, A. Obertelli, P. Doornenbal et al. (+83 more)

The size of neutron and proton single-particle orbitals of $^{52}$Ca, $^{53}$Ca, $^{54}$Ca, and $^{55}$Sc were investigated via nucleon knockout reactions at $\sim$ 230 MeV/nucleon. The determination method is based on the measured fragment momentum distributions in $(p,pn)$ and $(p,2p)$ reactions, which are shown to be sensitive to the spatial extension of the wave function of the knocked-out nucleon, interpreted within the distorted wave impulse approximation (DWIA) framework. A systematic sensitivity study is carried out for the $(p,pn)$ recoil-momentum distribution method and is presented in this work. The experimental momentum distributions are compared to state-of-the-art mean field and $ab$ $initio$ in-medium similarity renormalization group and self-consistent Green's function calculations in combination with DWIA reaction theory calculations. Based on this work, the 1$p$ neutron orbitals are consistently found $0.48-0.78$ fm larger than the $0f_{7/2}$ neutron orbitals in $^{52-54}$Ca, while the size evolution of the valence proton orbitals remains inconclusive due to the large associated statistical uncertainties.
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All authors M. Enciu, A. Obertelli, P. Doornenbal, C. Barbieri, S. Brolli, M. Heinz, W. Horiuchi, T. Inakura, W. H. Long, T. Miyagi, F. Nowacki, K. Ogata, A. Poves, A. Schwenk, K. Yoshida, N. L. Achouri, H. Baba, F. Browne, D. Calvet, F. Château, S. Chen, N. Chiga, A. Corsi, M. L. Cortés, A. Delbart, J-M. Gheller, A. Giganon, A. Gillibert, C. Hilaire, T. Isobe, T. Kobayashi, Y. Kubota, V. Lapoux, H. N. Liu, T. Motobayashi, I. Murray, H. Otsu, V. Panin, N. Paul, W. Rodriguez, H. Sakurai, M. Sasano, D. Steppenbeck, L. Stuhl, Y. L. Sun, Y. Togano, T. Uesaka, K. Wimmer, K. Yoneda, O. Aktas, T. Aumann, L. X. Chung, F. Flavigny, S. Franchoo, I. Gasparic, R.-B. Gerst, J. Gibelin, K. I. Hahn, D. Kim, Y. Kondo, P. Koseoglou, J. Lee, C. Lehr, P. J. Li, B. D. Linh, T. Lokotko, M. MacCormick, K. Moschner, T. Nakamura, S. Y. Park, D. Rossi, E. Sahin, P-A. Söderström, D. Sohler, S. Takeuchi, H. Toernqvist, V. Vaquero, V. Wagner, S. Wang, V. Werner, X. Xu, H. Yamada, D. Yan, Z. Yang, M. Yasuda, L. Zanetti

Nuclear Experiment · Cross-listed from hep-ph

Rotation modified QCD equation of state across crossover at finite chemical potential

S. Ipsita Sahoo, Sanjeebani Biswal, Dipanwita Dutta et al. (+1 more)

It is well-established that at low baryon chemical potential, the transition from the confined hadronic phase to the deconfined partonic phase is a smooth crossover rather than a first or second-order phase transition. We develop a thermodynamically consistent hybrid equation of state to study the effect of global rotation on the equation of state across the QCD crossover that interpolates the hadronic and partonic phases. The temperature dependence of normalized thermodynamic observables, such as entropy density ($s/T^3$), pressure ($P/T^4$), energy density ($\varepsilon/T^4$), specific heat ($C_V/T^3$), and the square of speed of sound ($c_s^2$) in presence of rotation are investigated. The effect of non-zero chemical potential on thermodynamic quantities in presence of rotation is also studied. Our results show that increasing chemical potential enhances the thermodynamic quantities, whereas rotation suppresses them in the crossover region. Further, we investigate the effect of rotation on the conserved numbers susceptibilities and their correlations as a function of temperature. The susceptibilities and their correlations exhibit a systematic enhancement with increase in rotation in both the hadronic and partonic phases. These findings provide new insights into the interplay between rotation and QCD thermodynamics, which can have important implications for rapidly rotating strongly interacting matter produced in ultra-relativistic heavy-ion collisions.
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All authors S. Ipsita Sahoo, Sanjeebani Biswal, Dipanwita Dutta, Dipak Kumar Mishra

Saturday 15 August

Nuclear Experiment · Cross-listed from physics.ins-det

Development of a 10 mol% Rubidium-doped CsI Crystal for $^{87}$Rb Beta-Spectroscopy and Sterile Neutrino Searches

W. K. Kim, K. W. Kim, L. T. Truc et al. (+3 more)

The third-forbidden non-unique beta-decay of $^{87}$Rb to $^{87}$Sr (Q$_\beta = 282.275(6)$ keV) has long served as an important benchmark for understanding forbidden beta-decay. To investigate this, we have developed a novel CsI scintillator with a 10 mol% Rb concentration using the Bridgman method. The incorporated $^{87}$Rb serves as an intrinsic radioactive source, enabling a source-in-detector configuration with high detection efficiency and minimal energy loss for low-energy electrons from beta-decay. We investigated both Rb doped and Tl co-doped CsI crystals and characterized their scintillation properties, including light yield, energy resolution, and non-linear response. We report distinct scintillation characteristics for the CsI:Rb and CsI:Tl,Rb crystals, with light yields of $1.38\pm0.01$ and $4.73\pm0.13$ PE/keV, respectively. Using the measured $^{87}$Rb beta-spectrum, we search for a keV-scale sterile neutrino admixture through the characteristic kink-like distortion induced by a heavy neutrino mass eigenstate. This study provides a basis for future sterile neutrino searches using rubidium doped CsI crystal.
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All authors W. K. Kim, K. W. Kim, L. T. Truc, H. S. Lee, H. J. Kim, Y. D. Kim

Nuclear Experiment

Best Reaction Target To Determine Proton Distribution Radii of Atomic Nuclei

Jun-Yao Xu, Bao-Hua Sun, Isao Tanihata et al. (+29 more)

We found that a heavy target such as Pb is most suitable for determining the proton distribution radii of unstable nuclei through charge-changing cross-section ($\sigma_\text{cc}$) measurements. As a heavy ion probe, low-$Z$ targets are routinely used to determine nucleon distribution radii of unstable isotopes. This approach has recently been extended to study proton distribution radii from $\sigma_\text{cc}$ measurements. However, empirical scaling factors have to be introduced to apply the Glauber models. In the present work, we systematically investigated the scaling factor using 39 new $\sigma_\text{cc}$ data of 18 $p$-shell nuclei on hydrogen, carbon, silver, and lead targets at around 240 MeV/nucleon. Together with the existing data, we reveal a universal dependence of the scaling factor on both the masses of target nuclei and the separation energies of projectile nuclei. The scaling factors decrease with increasing target-nucleus mass and converge to 1 for the highest-$Z$ target, making the scaling unnecessary. We conclude that instead of a low-$Z$ target, employing a heavy target such as Pb in $\sigma_\text{cc}$ measurements is the best option to determine the proton distribution radii of unstable nuclei.
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All authors Jun-Yao Xu, Bao-Hua Sun, Isao Tanihata, Satoru Terashima, Jian-Wei Zhao, Ji-Chao Zhang, Ge Guo, Shi-Tao Wang, Lei Shen, Jun Su, Xiao-Dong Xu, Andrej Prochazka, Guang-Shuai Li, Xiu-Lin Wei, Chang-Jian Wang, Feng Wang, Meng Wang, Jing Wang, Liu-Chun He, Chuan-Ye Liu, Wen-Jian Lin, Wei-Ping Lin, Zhong Liu, Pei-Pei Ren, Yu Zhang, Mei-Xue Zhang, Ya-Zhou Sun, Zhi-Yu Sun, Chen-Gui Lu, Xue-Heng Zhang, Jin-Rong Liu, Tian-Yu Wu

Friday 14 August

Nuclear Experiment · Cross-listed from physics.data-an

Statistical validation of calorimeter inpainting with generative diffusion priors

Himanshu Raj and Roli Esha

Localized detector inefficiencies produce incomplete calorimeter data that limit the ability to perform precision measurements. We address this problem in relativistic heavy-ion collisions from a Bayesian perspective using pretrained calorimeter diffusion models as priors to reconstruct the missing signal conditioned on surrounding measurements. In this work, we conduct a systematic comparison of several diffusion-based inpainting algorithms, whose performance is evaluated using Bayesian posterior diagnostics of energy response, spatial bias, and uncertainty calibration. The reconstruction fidelity is also analyzed across collision centralities and masked region sizes. This study establishes a general validation strategy for probabilistic reconstruction of missing detector information.
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Nuclear Experiment

Extraction of Neutron-Skin Parameters in Zr+Zr and Ru+Ru Collisions at $\sqrt{s_{\text{NN}}}$ = 200 GeV

Junjian Zhou, Dongsheng Li, Fan Si et al. (+2 more)

The initial nuclear geometry of colliding nuclei, manifested in proton and neutron density profiles, plays a key role in determining final-state effects in high-energy heavy-ion collisions. We study ${^{96}\text{Ru}}+{^{96}\text{Ru}}$ and ${^{96}\text{Zr}}+{^{96}\text{Zr}}$ collisions at $\sqrt{s_{\text{NN}}}=200$ GeV incorporating an isospin-dependent Woods-Saxon distribution to account for neutron-skin effects in the UrQMD model. By systematically scanning the proton surface diffuseness parameter $a_{\text{p,Zr}}$ of the $^{96}\text{Zr}$ nucleus and performing a $\chi^2$ analysis by comparing with STAR experimental data, we extract the relative neutron-skin thickness difference $0.278 \pm 0.018$ fm between the two isobaric systems using the net-charge yield difference $\Delta Q$. We further show that the neutron-skin effect evidently modifies the baryon-to-charge transport ratio $R_{B/Q}=\langle B \rangle/\Delta Q \times \Delta Z/A$, and substantially influences the observed $R_{B/Q}>1$ behavior in central collisions. This work indicates that nuclear structure effects contribute non-negligibly to baryon transport observables without a baryon junction hypothesis, and underscores the importance of precise initial-state geometry constraints for exploring novel QCD phenomena in relativistic heavy-ion collisions.
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All authors Junjian Zhou, Dongsheng Li, Fan Si, Xiujun Li, Yifei Zhang

Nuclear Experiment

Observing the effects of numbers of valence nucleons on $0_{gs}^+ \rightarrow 2_1^+$ transitions in deformed nuclei by comparing proton and neutron transition matrix elements

P. D. Cottle, L. A. Riley, A. Gade et al. (+2 more)

We examined the ratios of neutron and proton transition matrix elements, $M_n/M_p$, for the $0_{gs}^+ \rightarrow 2_1^+$ transitions in 48 even-even stable nuclei with $N>20$ for which electromagnetic matrix elements were compiled by Pritychenko et al. and for which high-quality inelastic proton scattering data were available. Several deformed rare earth nuclei have $(M_n/M_p)/(N/Z)$ values significantly below 1.0, which is not consistent with a simple liquid drop picture. However, this phenomenon can be explained using a schematic picture in which $M_p$ reaches a maximum at proton mid-shell ($Z=66$) and $M_n$ reaches its maximum at neutron mid-shell ($N=104$). Several mid-mass vibrational nuclei have $M_n/M_p$ values significantly below $N/Z$, which is not consistent with the expectation that $M_n/M_p = N/Z$ in such nuclei. A shell model investigation of these observations might yield insights about this behavior.
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All authors P. D. Cottle, L. A. Riley, A. Gade, K. W. Kemper, M. Spieker

Thursday 13 August

Nuclear Experiment · Cross-listed from physics.chem-ph

Comparative measurements of DC electrical breakdown distributions in liquid nitrogen, liquid helium, and liquid argon

N. S. Phan, S. M. Clayton, R. Gautam et al. (+4 more)

We present a comparative study of DC electrical breakdown in liquid nitrogen, liquid helium, and liquid argon using a common cryostat, electrode assembly, voltage-ramp protocol, and analysis procedure. This common experimental configuration minimizes systematic differences that often complicate comparisons among cryogenic liquids, including variations in electrode geometry, stressed area, surface finish, and gap spacing. For each liquid, breakdown was characterized as a statistical distribution rather than by a single characteristic voltage, allowing the stochastic nature of the process to be examined. Measurements were performed both near saturated vapor pressure and under modest pressurization to assess the influence of bubble formation and related thermodynamic effects. Liquid argon exhibited a non-stationary "turn-on" behavior, with breakdown voltage increasing over repeated discharges, consistent with evolution of the local impurity environment or electrode surface state. Near saturated vapor pressure, liquid helium showed a bimodal breakdown distribution, with a lower-field component consistent with bubble-mediated processes. Liquid nitrogen exhibited higher breakdown fields than liquid argon and fields comparable to those measured in pressurized liquid helium, within the observed run-to-run variation associated with surface state. Taken together, these results support a comparative framework in which breakdown strength reflects both thermodynamic stability against bubble formation and the transport properties of the dominant negative charge carrier.
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All authors N. S. Phan, S. M. Clayton, R. Gautam, T. M. Ito, L. Kadlec, C. M. O'Shaughnessy, T. J. Schaub

Nuclear Experiment · Cross-listed from physics.ins-det

Optical Characterization Measurements of Commercial Polyvinyltoluene Scintillators for Accurate Geant4 Detector Modeling

Fergus Martin Huggins, Micah S. Johnson and Matthew Quinn Buckner

Accurate Monte Carlo simulation of plastic scintillator detectors requires precise wavelength-dependent optical properties. We present the first comprehensive measurements of wavelength-dependent refractive index $n(\lambda)$ and bulk absorption length $L_{\mathrm{abs}}(\lambda)$ for six commercial polyvinyltoluene (PVT)-based scintillators (Saint Gobain BC-400, BC-404, BC-408, BC-418, BC-422, and BC-430) across the 370-660 nm range. Using a precision refraction apparatus and variable-thickness transmission measurements, we characterize material-specific dispersion that deviates substantially from both the manufacturer specification and literature values for pure PVT. Validation simulations of a BC-422 detector demonstrate a 7.2% reduction in detected photon counts when using our measured $n(\lambda)$ compared to the constant manufacturer value, highlighting the practical importance of accurate optical property data for detector design and calibration. We successfully measure absorption lengths for BC-430 across most of the visible spectrum (2.2-12.4 mm) and for all materials at 372 nm (21-38 mm), while establishing lower bounds exceeding 750 mm for weakly absorbing formulations at longer wavelengths.
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Nuclear Experiment · Cross-listed from hep-ph

Non-perturbative quark production and transport in the evolving glasma: the WAGASHI event generator

Nicholas J. Benoit, Chiho Nonaka and Hidetoshi Taya

We study non-perturbative quark-antiquark pair production and the subsequent quark dynamics in the earliest glasma stage of relativistic heavy-ion collisions. For that, we develop a new model, WAGASHI (Wong-precessing Anisotropic Glasma And ScHwinger-produced Initial-conditions), which combines classical Yang-Mills glasma evolution, Wong-equation transport, and Schwinger pair production on an event-by-event basis. We find that a sizeable number of quarks, comparable to the final hadron yields, are produced already during the glasma stage and subsequently undergo substantial momentum broadening and spin randomization, suggesting a significant contribution toward the early equilibration of the quark-gluon plasma. We also determine the event-by-event distributions of baryon number, electric charge, strangeness, and spin polarization in Pb-Pb and O-O collisions at LHC energies, finding particularly large fluctuations in the smaller O-O system. These results provide dynamical initial conditions for the subsequent hydrodynamic evolution of the quark-gluon plasma.
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Nuclear Experiment · Cross-listed from nucl-th

Relativistic dynamical effects in proton emission: the Wentzel-Kramers-Brillouin method for 1+1 dimensional Dirac equation

Guangping Chen, Wenmin Deng, Ganlong Ding et al. (+3 more)

Starting from the $1+1$ dimensional (one spatial and one temporal dimension) Dirac equation, we employ the Wentzel-Kramers-Brillouin (WKB) approximation to derive the corresponding relativistic penetration probability. The derivation shows that the semiclassical momentum is determined by the Schrödinger-equivalent potential $ U_{\text{eff}}(r) = S(r) + \frac{E}{m}V(r) + \frac{S^{2}(r)-V^{2}(r)}{2m}$, instead of the simple sum of scalar and vector potentials $S(r)+V(r)$, which has been adopted widely in the studies of relativistic quantum tunneling. We then quantify the relativistic dynamical effects in proton emission by comparing the results obtained with $U_{\text{eff}}(r)$ and those obtained with $S(r)+V(r)$. Incorporating $U_{\text{eff}}(r)$ systematically reduces the penetration probability and the assault frequency, and consequently increases the predicted half-life. The relativistic dynamical effect becomes more pronounced with higher orbital angular momentum and can reach about $84\%$ in the half-life of $^{144}\mathrm{Tm}$.
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All authors Guangping Chen, Wenmin Deng, Ganlong Ding, Sibo Wang, Jing Peng, Haozhao Liang

Wednesday 12 August

Nuclear Experiment · Cross-listed from physics.ins-det

Ultracold Neutron Sources: An Essentially Enhanced Optimal Operation Temperature for Ortho-Deuterium-Based Superthermal Converters

Erik Walz and Christoph Morkel

There is a longstanding dogma in the physics of ultracold neutrons (UCN): The optimal temperature of ortho-deuterium based UCN-sources must not exceed $5\,\mathrm{K}$. This value has been established by the pioneering work of Golub et al. decades ago, utilizing previously established cross sections for solid ortho-deuterium. But recently, an improved calculation of the crucial 1-phonon up-scattering cross section - using the so-called corrected Incoherent Approximation - leads to a new upper limit for the optimal operation temperature of ortho-deuterium based UCN sources. After a discussion of the relevant cross sections of the \(\mathrm{D}_2\)-molecule we conclude that the optimal temperature lies between $10\,\mathrm{K}$ and $12\,\mathrm{K}$, a factor 2 higher than estimated earlier. This offers significantly relaxed cryogenic conditions for UCN experiments with solid ortho-deuterium and especially for the operation of ortho-deuterium based ultracold neutron sources.
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