Nuclear Theory·nucl-th

Thursday·October 23, 2025

11 papers—4 primary·7 cross-listed

05
Practical Considerations for Measuring Global Spin Density Matrix Elements of Vector Mesons in Heavy-Ion Collisions
Gavin Wilks🇺🇸 · Xu Sun🇨🇳 · Zhenyu Ye🇺🇸
The STAR Collaboration has reported a significant $ϕ$ -meson global spin alignment ( $ρ_{00}$ ) signal in Au+Au collisions at $s_{N N} \leq 62$ GeV by measuring the polar angle distribution of $ϕ$ -meson daughters with respect to the orbital angular momentum (OAM) direction of the collision system. In this paper, a new method is explored for studying vector-meson global spin alignment in heavy-ion collisions by examining the two dimensional polar and azimuthal angle distribution. This method allows simultaneous extraction of $ρ_{00}$ and off-diagonal spin density matrix elements (SDMEs), providing unique access to local quark-antiquark spin correlations and spin hydrodynamics in quark-gluon plasma (QGP). The new 2D method also removes potential biases from non-zero off-diagonal SDMEs on $ρ_{00}$ with the 1D method. A detailed procedure to correct for detector acceptance and resolution effects is also presented and validated by simulation studies.
↳ nucl-exnucl-thPRC(2026)·0 citations
06
Unified Resummation of Soft Gluon Radiation in Heavy Meson Pair Photoproduction
Cyrille Marquet🇫🇷 · Yu Shi🇫🇷 · Bo-Wen Xiao🇨🇳
We develop a unified resummation framework for heavy-meson pair photoproduction that treats soft-gluon radiation in a massive scheme for $∣ q ∣ ≲ m_{Q}$ and is consistent with the massless limit $m_{Q} ≪ ∣ q ∣$ , where $q$ denotes the transverse momentum of the pair and $m_{Q}$ the quark mass. This framework describes the full correlation regime $∣ q ∣ ≪ ∣ P ∣$ , with $P$ the pair's relative transverse momentum. Next, within the Color Glass Condensate framework, we quantify the impact of soft gluon radiation on two important phenomenological observables, namely, the azimuthal $Δ ϕ$ correlation and the harmonic asymmetries $⟨ cos (2 n ϕ_{q P})⟩$ . Our results show that the resummation provides an excellent description of the H1 $Δ ϕ$ data. We then find that the angular-asymmetry harmonics are sizable and their ratios in $γ A$ to $γ p$ collisions are highly sensitive to gluon saturation. We further find a clear mass hierarchy in both observables, indicating that heavy-quark masses suppress soft radiation and thereby enhance genuine small- $x$ saturation signals. Our work demonstrates that heavy-quark pair photoproduction provides a quantitative probe of gluon saturation, directly measurable in forthcoming EIC and UPC measurements. Finally, the unified resummation is readily extendable to other processes involving massive particles and jets in both $e A$ and $p A$ collisions.
↳ hep-phhep-exhep-thnucl-th9 citations
07
Probing the QGP through $p_{T}$ -differential radial flow of heavy quarks
Maria Lucia Sambataro (1 and 2)🇮🇹 · Salvatore Plumari (1 and 2)🇮🇹 · Santosh K. Das (3)🇮🇳 · Vincenzo Greco (1 and 2) ((1) Department of Physics and Astronomy, University of Catania, Catania, Italy (2) INFN-Laboratori Nazionali del Sud, Catania, Italy, (3) School of Physical Sciences, Indian Institute of Technology Goa, Goa, India)🇮🇹
We introduce the $p_{T}$ -differential radial flow $v_{0} (p_{T})$ in the heavy-quark sector. Within an event-by-event Langevin framework, we show that this observable exhibits a strong sensitivity to the heavy quark-bulk interaction. It provides a powerful and novel tool to constrain the transport coefficients of heavy quarks in the QGP and, more generally, to assess the strength of the interaction of a Brownian particle in an expanding bulk medium. The results further indicate that heavy quarks exhibit collective behavior driven by the isotropic expansion of the QGP in heavy-ion collisions and, at low $p_{T}$ , it offers a marked signature of the heavy quark hadronization mechanism.
↳ hep-phnucl-thPRL(2026)·7 citations
08
Coherent and incoherent antineutrino scattering on stable even-even isotopes of molybdenum detectors
T.S. Kosmas🇬🇷 · R. Sahu🇮🇳 · V.K.B. Kota🇮🇳
The recent observations of the coherent neutrino- and antineutrino-nucleus scattering have opened up a plethora of opportunities to probe physics within standard and non-standard theories of the electroweak interactions. In the present article, our goal is to explore the possibility of using the molybdenum material as detection medium for coherent and incoherent antineutrino- and neutrino- Mo scattering in the ongoing and future coherent elastic neutrino-nucleus scattering (CE{\nu}NS) experiments by using relevant (anti-)neutrino beams as e.g. stopped pion-decay neutrino beams, reactor antineutrino beams, astrophysical (solar or supernova) (anti)neutrino beams, etc. Our present coherent and incoherent scattering cross sections of Mo isotopes with neutrinos and antineutrinos are based on the deformed shell model (DSM) that has been previously employed for studying similar processes. On the other hand, in the past, CE{\nu}NS events obtained with this model provided us with better fits to COHERENT experimental data compared to phenomenological form factors.
↳ hep-phnucl-thPRD(2025)·0 citations
09
The Regulated GeAs Cycles with the New $^{63}$ Ga(p, $γ$ ) $^{64}$ Ge and $^{64}$ Ge(p, $γ$ ) $^{65}$ As Reaction Rates and Their Impact on the GS 1826 $-$ 24 Clocked Bursts and SAX J1808.4 $-$ 3658 Photospheric Radius Expansion Bursts
Yi Hua Lam🇨🇳 · Ning Lu🇨🇳 · Alexander Heger🇦🇺 · Zi Xin Liu🇨🇳 · Zac Johnston🇺🇸 · Hidetoshi Yamaguchi🇯🇵
The $^{63}$ Ga(p, $γ$ ) $^{64}$ Ge and $^{64}$ Ge(p, $γ$ ) $^{65}$ As thermonuclear reactions connect the ZnGa and GeAs cycles by diverting the flow of the rapid proton capture process from $^{63}$ Ga to $^{65}$ As. Changes in these two reaction rates regulate the ZnGa and GeAs cycles and may affect the modeled properties matching with the observed counterparts of a type I X-ray burster. We implement the latest $^{63}$ Ga(p, $γ$ ) $^{64}$ Ge and $^{64}$ Ge(p, $γ$ ) $^{65}$ As reaction rates to the state-of-the-art self-consistent one-dimensional multi-zone thermo-hydrodynamic code, KEPLER, to study the influence of these new reaction rates on the models of the GS 1826 $-$ 24 clocked burster and SAX J1808.4 $-$ 3658 photospheric radius expansion burster. Both new reaction rates obtained by Lu et al. [Phys. Rev. C 110, 065804 (2024)] are determined from complementing the experimental input with the nuclear spectroscopic information deduced from the full pf-shell space configuration-interaction shell-model calculations. By constraining the models on reproducing the observed burst peak, light-curve profile, fluence, and recurrence time, we find that the impact of the newly measured proton thresholds and respective proton-capture reactions on the burst light-curve profile of the GS 1826 $-$ 24 clocked burster is, in fact, not as significant as claimed by Zhou et al. [Nat. Phys. 19, 1091 (2023)]. With or without the inclusion of the newly determined reaction rate of the highly influential $^{22}$ Mg( $α$ ,p) $^{25}$ Al reaction, the impact of the new $^{63}$ Ga(p, $γ$ ) $^{64}$ Ge and $^{64}$ Ge(p, $γ$ ) $^{65}$ As reaction rates on SAX J1808.4 $-$ 3658 photospheric radius expansion bursts is evident. Our finding indicates that the models reproducing the 2002 October epoch of SAX J1808.4 $-$ 3658 photospheric radius expansion burster is more sensitive to the uncertainties of thermonuclear reaction rates.
↳ astro-ph.HEnucl-exnucl-thApJ(2025)·2 citations
10
Engineering the shapes of quark-gluon plasma droplets by comparing anisotropic flow in small symmetric and asymmetric collision systems
STAR Collaboration
The observation of collective flow phenomena in small collision systems challenges our understanding of quark-gluon plasma (QGP) formation and evolution. This complexity lies in the initial geometries, which are influenced by both nucleon configuration and subnucleonic fluctuations, introducing uncertainties in interpreting flow patterns. We disentangle these contributions through comparative measurements of elliptic ( $v_{2}$ ) and triangular ( $v_{3}$ ) flow in asymmetric $d$ +Au and symmetric $^{16}$ O+ $^{16}$ O collisions at $s_{N N} = 200$ GeV, which produce medium of comparable sizes but with vastly different initial geometries. The larger $v_{2}$ in $d$ +Au reflects its dominant elliptic geometry, while the similar $v_{3}$ in both systems is better explained by considering subnucleonic fluctuations. These contrasting flow patterns are quantitatively described by a state-of-the-art hydrodynamic model tuned to large-system Au+Au data, indicating efficient transformation of initial geometries to final-state anisotropies. These results provide evidence for droplet formation in small systems with transport properties that are similar to those observed in large collision systems, consistent with QGP-like behavior.
↳ nucl-exhep-phnucl-th16 citations
11
Beta-decay Half Lives beyond $^{54}$ Ca: A Systematic Survey of Decay Properties approaching the Neutron Dripline
W.-J. Ong🇺🇸 · Z. Y. Xu🇺🇸 · R. Grzywacz🇺🇸 · A. Ravlić🇺🇸 · I. Cox🇺🇸 · J. M. Allmond🇺🇸 · T. T. King🇺🇸 · B. C. Rasco🇺🇸 · K. P. Rykaczewski🇺🇸 · H. Schatz🇺🇸 · B. M. Sherrill🇺🇸 · B. Tarasov🇺🇸 and 74 other authors
In an experiment performed at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator (FDSi), 15 new half lives of isotopes near $^{54}$ Ca were measured. A new method of extracting lifetimes from experimental data, taking into account the unknown $β$ -delayed neutron emission branches of very neutron-rich nuclei, was developed to enable systematic uncertainty analysis. The experiment observed a dramatic change in the half-life systematics for the isotopes with neutron number N =34. Beyond N =34, the decline of nuclear lifetime is much slower, leading to longer than anticipated lifetimes for near-dripline nuclei. State-of-the-art shell-model calculations can explain the experimental results for Z $>$ 19 nuclei, revealing the imprint of shell effects and the need for modification of single-particle neutron states. The results from a newly developed QRPA model with potential for making global predictions were also tested against the experimental results and good agreement was found.
↳ nucl-exnucl-thPRL(2026)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Practical Considerations for Measuring Global Spin Density Matrix Elements of Vector Mesons in Heavy-Ion Collisions

Unified Resummation of Soft Gluon Radiation in Heavy Meson Pair Photoproduction

Probing the QGP through pT​-differential radial flow of heavy quarks

Coherent and incoherent antineutrino scattering on stable even-even isotopes of molybdenum detectors

The Regulated GeAs Cycles with the New 63Ga(p,γ)64Ge and 64Ge(p,γ)65As Reaction Rates and Their Impact on the GS 1826−24 Clocked Bursts and SAX J1808.4−3658 Photospheric Radius Expansion Bursts

Engineering the shapes of quark-gluon plasma droplets by comparing anisotropic flow in small symmetric and asymmetric collision systems

Beta-decay Half Lives beyond 54Ca: A Systematic Survey of Decay Properties approaching the Neutron Dripline

Affiliations

Probing the QGP through $p_{T}$ -differential radial flow of heavy quarks

The Regulated GeAs Cycles with the New $^{63}$ Ga(p, $γ$ ) $^{64}$ Ge and $^{64}$ Ge(p, $γ$ ) $^{65}$ As Reaction Rates and Their Impact on the GS 1826 $-$ 24 Clocked Bursts and SAX J1808.4 $-$ 3658 Photospheric Radius Expansion Bursts

Beta-decay Half Lives beyond $^{54}$ Ca: A Systematic Survey of Decay Properties approaching the Neutron Dripline