Nuclear Theory·nucl-th

Thursday·April 23, 2026

11 papers—5 primary·6 cross-listed

06
A First Account of the Impact of Ion Electromagnetic Dissociation on Event Exclusivity in Ultraperipheral LHC Collisions
M. Dyndal🇵🇱 · L. A. Harland-Lang🇬🇧
In this Letter we explore the modelling of hadron production in electromagnetic ion dissociation (EMD) processes in high-energy ultraperipheral collisions at LHC energies. Since EMD can accompany exclusive particle production in these interactions, we demonstrate that the resulting hadrons can break the exclusivity vetos typically imposed by experiments. As two representative examples, we calculate the impact on existing LHC measurements of exclusive muon pair production ( $γ γ \to μμ$ ) and exclusive coherent $J / ψ$ production. We demonstrate that accounting for this effect resolves long-standing tensions between theoretical predictions and experimental measurements.
↳ hep-phhep-exnucl-exnucl-th5 citations
07
Impact of nuclear deformation on particle production in $N e + N e$ collisions at \texorpdfstring{\five}{sqrt(sNN)=5.36 TeV} from AMPT-SM
M. U. Ashraf🇺🇸 · A. M. Khan🇺🇸 · M. Shahid🇺🇸 · Faraz Mohd Mehdi🇺🇸
We present a systematic study of particle production in $N e + N e$ collisions at $s_{NN} = 5.36$ TeV using the A Multi-Phase Transport (AMPT) model with string melting (SM) configuration. The analysis compares spherical and deformed configurations of $^{20} Ne$ to investigate the influence of initial-state nuclear deformation on bulk observables. Charged-particle pseudorapidity ( $⟨ d N_{ch} / d η ⟩$ ) densities, identified particle yields ( $d N / d y$ ), transverse momentum ( $p_{T}$ ) spectra, mean transverse momentum ( $⟨ p_{T} ⟩$ ), and $p_{T}$ -differential particle ratios ( $K / π$ and $p / π$ ) are studied as functions of multiplicity and centrality. The results show that all observables exhibit the expected dependence on event activity, including smooth multiplicity scaling, mass ordering in $⟨ p_{T} ⟩$ , and characteristic features associated with radial flow and quark coalescence. Differences between the two configurations on bulk observables remain small across all observables, typically at the level of a 2\%--6\% percent, with slightly enhanced sensitivity observed in peripheral collisions. These findings suggest that, within the AMPT-SM framework, the collective dynamics and hadrochemical composition are primarily governed by the overall system density and interaction dynamics, while the influence of initial-state deformation is subleading. This study provides a baseline for understanding deformation effects in light-ion collision systems and highlights the limited sensitivity of bulk observables to initial nuclear geometry in transport-based approaches.
↳ hep-phnucl-th0 citations
08
Chiral first order phase transition at finite baryon density and zero temperature from self-consistent pole masses in the linear sigma model with quarks
Alejandro Ayala🇲🇽 · Bruno El-Bennich🇧🇷 · Ricardo L. S. Farias🇺🇸 · Luis A. Hernández🇲🇽 · Bruno S. Lopes🇺🇸 · Luis C. Parra L.🇲🇽 · Renato Zamora🇨🇱
We use the two-flavor Linear Sigma Model with quarks as an effective description of QCD to investigate the nature of the chiral phase transition at finite baryon chemical potential and zero temperature. We work at one-loop order to set up and solve the system of self-consistent coupled equations for the particle pole masses. The chemical potential-dependent value of the chiral order parameter is obtained by minimizing the one-loop effective potential. This treatment goes beyond the conventional ring-diagram approximation and provides a description valid for arbitrary values of the chemical potential. We find that the phase transition is of first order, and occurs when the quark chemical potential reaches the value of the vacuum quark mass for the chosen set of parameters. The first order nature of the transition is signaled by the discontinuous behavior of the chiral condensate, the masses and the couplings. The thermodynamics of the system is readily implemented and in particular, we find that the square of the speed of sound exhibits a discontinuity at the phase transition and then smoothly approaches the conformal limit from below.
↳ hep-phhep-thnucl-thPRD(2026)·0 citations
09
No planar degeneracy for the Landau gauge quark-gluon vertex
Georg Wieland🇦🇹 · Reinhard Alkofer🇦🇹
Based on a suitable basis system for the quark-gluon vertex' transverse tensor structures and on carefully chosen kinematical variables, the transverse part of the quark-gluon vertex in quenched QCD in the Landau gauge is obtained from a system of Dyson-Schwinger equations. We demonstrate by analysing this solution that the angular dependence of these transverse quark-gluon vertex form factors is seemingly weak. We nevertheless argue that this does not imply a planar degeneracy for this vertex because even this mild dependence cannot be neglected when aiming for reasonably precise results for derived quantities. Last but not least, for a self-consistently coupled systems of 3PI Dyson-Schwinger equations for the quark propagator and the quark-gluon vertex we confirm that the core ingredient to dynamical chiral symmetry breaking is the dynamically generated tensor coupling of glue to quarks which itself is only possible because of chiral symmetry breaking. Furthermore, we find (i) a relation in between the calculated chirality violating vertex form factors; (ii) that the quark propagator is identical within numerical errors when obtained either from a decoupling solution or the scaling solution for the Yang-Mills propagators and vertex functions; and (iii) that the resulting quark propagator is consistent with possessing poles only on the real time-like half-axis. Furthermore, we provide high-precision fits for the form factors based on sometimes astonishingly simple model functions.
↳ hep-phhep-thnucl-th2 citations
10
Rank-2 Electromagnetic Backgrounds and Angular Momentum Barriers in Gravitomagnetic Spin-Quadrupole Searches
Leonardo A. Pachon🇨🇴
We present a complete analysis of the angular momentum selection rules and electromagnetic backgrounds that constrain any spectroscopic search for the gravitomagnetic spin-quadrupole coupling in highly charged ions. A sequence of four barriers is identified: (i)~the Wigner-Eckart theorem mandates $j \geq 3/2$ electronic states for sensitivity to the rank-2 gravitomagnetic operator, excluding the deformation-immune $j = 1/2$ states; (ii)~the nuclear electric quadrupole hyperfine interaction (HFS-E2) generates an $\sim 18$ -orders-of-magnitude electromagnetic background in the required $j = 3/2$ channel; (iii)~second-order HFS mixing between fine-structure levels leaves a residual $\sim 1 0^{- 6}$ eV even after centroid extraction; (iv)~tensor nuclear polarizability (TNP), scaling with $B (E 2)$ rather than $Q_{s}$ , introduces an independent rank-2 background of $\sim 1 0^{- 12}$ eV. We derive the algebraic conditions under which a multi-isotope, multi-transition Generalized King Plot can separate these backgrounds from the gravitational signal, and show that the minimum experimental topology requires three transitions and $N_{odd} \geq N_{bkg} + 1$ odd-spin isotopes with linearly independent nuclear parameters. For the molybdenum chain, this yields a first laboratory-derivable bound $∣ χ - 1∣ ≲ 1 0^{8} - 1 0^{9}$ on the gyrogravitational ratio, limited by current precision on nuclear quadrupole moments and transition rates. We quantify the experimental milestones needed to improve this bound by each order of magnitude, providing a roadmap for future searches.
↳ quant-phgr-qcnucl-th0 citations
11
Probing QCD instantons using jet correlation observables in proton-proton collisions at the LHC
Sayak Guin🇮🇳 · Swagatam Tah🇮🇳 · Nihar Ranjan Sahoo🇮🇳 · Sayantan Sharma🇮🇳
Discovery of instantons in colliders will provide experimental evidence for the topological properties of the QCD vacuum. In this work, we propose jet correlation observables that can unambiguously discriminate between instanton-induced processes and perturbative hard scattering events in pp collisions at LHC energies. By calculating the instanton sizes and their separations in 2+1 flavor QCD with physical quark masses, we provide constraints on the center-of-mass energies of the produced hadrons in an instanton-induced process. Our proposal is directly applicable for future ep measurements at the Electron-Ion Collider, offering a cleaner environment to probe instanton-induced processes.
↳ hep-phhep-exhep-latnucl-ex+11 citation

Affiliations

first authorsco-authorsvia INSPIRE

A First Account of the Impact of Ion Electromagnetic Dissociation on Event Exclusivity in Ultraperipheral LHC Collisions

Impact of nuclear deformation on particle production in Ne+Ne collisions at \texorpdfstring{\five}{sqrt(sNN)=5.36 TeV} from AMPT-SM

Chiral first order phase transition at finite baryon density and zero temperature from self-consistent pole masses in the linear sigma model with quarks

No planar degeneracy for the Landau gauge quark-gluon vertex

Rank-2 Electromagnetic Backgrounds and Angular Momentum Barriers in Gravitomagnetic Spin-Quadrupole Searches

Probing QCD instantons using jet correlation observables in proton-proton collisions at the LHC

Affiliations

Impact of nuclear deformation on particle production in $N e + N e$ collisions at \texorpdfstring{\five}{sqrt(sNN)=5.36 TeV} from AMPT-SM