Nuclear Theory·nucl-th

Tuesday·June 14, 2022

12 papers—6 primary·6 cross-listed

01
Impact of nuclear deformation on collective flow observables in relativistic U+U collisions
Niseem Magdy🇺🇸
A Multi-Phase Transport (AMPT) model is used to investigate the efficacy of several flow observables to constrain the initial-state deformation of the Uranium nuclei in U $+$ U collisions at nucleon-nucleon center-of-mass energy $s_{N N}$ = 193 GeV. The multiparticle azimuthal cumulant method is used to investigate the sensitivity of (I) a set of quantities that are sensitive to both initial- and final-state effects as well as (II) a set of dimensionless quantities that are more sensitive to initial-state effects to the Uranium nuclei quadrupole shape deformation. We find that the combined use of the flow harmonics, flow fluctuations and correlations, linear and non-linear flow correlations to the quadrangular flow harmonic, and the correlations between elliptic flow and the mean-transverse momentum could serve to constrain the nuclear deformation of the Uranium nuclei. Therefore, a comprehensive set of measurements of such observables can provide a quantifying tool for the quadrupole shape deformation via data-model comparisons.
nucl-thhep-phnucl-exEPJA(2023)·29 citations
02
Nuclear Josephson-like $γ$ -emission
R. A. Broglia · F. Barranco · L. Corradi · G. Potel · S. Szilner · E. Vigezzi
Josephson-like junctions, transiently established in heavy ion collisions between superfluid nuclei, few MeV below the Coulomb barrier, allow for the back and forth transfer of a nuclear Cooper pair of effectively charged nucleons and thus the emission of $γ$ -rays. The second order DWBA $T$ -matrix formulation of single Cooper pair alternating current is shown to contain the gauge phases and gauge rotational frequencies as required by the Josephson (ac) effect, in keeping with the derivation of the transfer (tunneling) Hamiltonian in a gauge invariant representation. We describe the emergence of two strongly convergent parameters (conserved quantities) within the time the abnormal densities of the two superfluid nuclei overlap: a) the correlation length (dc); b) the number of emitted $γ$ -rays per cycle (ac), and thus the dipole moment of the successively transferred nucleons. Result which leads to a nuclear parallel with the direct current (dc) and alternating current (ac) Josephson effects, and which testifies to the validity of BCS theory of superconductivity down to few Cooper pair condensates, and single Cooper pair alternating currents. The physics at the basis of a quantitative description of Cooper pair tunneling between weakly coupled superconductors or superfluid nuclei at energies below the Coulomb barrier, is that the process is dominated by the successive transfer of the two partner fermions entangled over distances of the order of the coherence length, $\approx 1 0^{4}$ Å in the case of lead, and 13.5 fm in the case of the reaction $^{116} Sn +^{60} Ni \to^{114} Sn(gs) +^{62} Ni(gs)$ at few MeV below the Coulomb barrier.
nucl-th1 citation
03
The European Muon Collaboration effect in Light-Front Hamiltonian Dynamics
Emanuele Pace (Rome Univ. "Tor Vergata")🇮🇹 · Matteo Rinaldi (Perugia Univ.)🇮🇹 · Giovanni Salme` (INFN - Rome)🇮🇹 · Sergio Scopetta (Perugia Univ.)🇮🇹
A rigorous light-front formalism for electron deep inelastic scattering on unpolarized nuclei, in Bjorken limit, is reported. It preserves Poincaré covariance, macroscopic locality, both number of particles and momentum sum rules. The scheme is applied to the A=3 iso-doublet, very relevant in view of the planned operation with unpolarized and polarized beams at the Electron-Ion Collider. At variance with previous light-front estimates, our procedure, including a realistic nuclear description and free-nucleon structure functions, predicts a sizeable European Muon Collaboration effect for $^{3}$ He. This will allow to analyze deviations from the proposed baseline in terms of genuine QCD effects. The extension to heavier nuclei is straightforward, although numerically challenging.
nucl-thhep-phPLB(2023)·10 citations
04
Ab initio estimation of $E 2$ strengths in $^{8}$ Li and its neighbors by normalization to the measured quadrupole moment
Mark A. Caprio · Patrick J. Fasano
For electric quadrupole ( $E 2$ ) observables, which depend on the large-distance tails of the nuclear wave function, ab initio no-core configuration interaction (NCCI) calculations converge slowly, making meaningful predictions challenging to obtain. Nonetheless, the calculated values for different $E 2$ matrix elements, particularly those involving levels with closely-related structure (e.g., within the same rotational band) are found to be robustly proportional. This observation suggests that a known value for one observable may be used to determine the overall scale of $E 2$ strengths, and thereby provide predictions for others. In particular, we demonstrate that meaningful predictions for $E 2$ transitions may be obtained by calibration to the ground-state quadrupole moment. We test this approach for well-measured low-lying $E 2$ transitions in $^{7}$ Li and $^{9}$ Be, then provide predictions for transitions in $^{8}$ Li and $^{9}$ Li. In particular, we address the $2^{+} \to 1^{+}$ transition in $^{8}$ Li, for which the reported measured strength exceeds ab initio Green's function Monte Carlo (GFMC) predictions by over an order of magnitude.
nucl-thPRC(2022)·12 citations
05
Laurent+Pietarinen Partial Wave Analysis
A. Svarc🇭🇷 · R. L. Workman🇺🇸
A new energy-dependent fit strategy, independent of any specific microscopic theory, is applied to kaon photoproduction data with center-of-mass energies ranging from 1625 MeV to 2296 MeV. Experimental data are fitted in terms of a modified Laurent expansion (Laurent+Pietarinen expansion) which previously has been successfully applied to multipoles. The present aim is to extract resonance pole parameters directly from the data, rather than from sets of multipoles. A constrained single-energy fit is then used to search for missing structures. In this proof-of-principle study, the data are well-described by the initial L+P fit, and it is shown that only a moderate amount of structure, mostly in higher multipoles, is missing from the original fit. Problems due to an unmeasurable overall phase, plaguing single-channel multipole analyses, are mitigated by implementing a form of phase limitation, fixing the initial values of fit parameters using a multi-channel analysis.
nucl-thnucl-exPRC(2023)·4 citations
06
Speed of sound in dense strong-interaction matter
Jens Braun🇩🇪 · Andreas Geißel🇩🇪 · Benedikt Schallmo🇩🇪
We study the speed of sound in strong-interaction matter at zero temperature and in density regimes which are expected to be governed by the presence of a color-superconducting gap. At (very) high densities, our analysis indicates that the speed of sound approaches its asymptotic value associated with the non-interacting quark gas from below, in agreement with first-principles studies which do not take the presence of a color-superconducting gap into account. Towards lower densities, however, the presence of a gap induces an increase of the speed of sound above its asymptotic value. Importantly, even if gap-induced corrections to the pressure may appear small, we find that derivatives of the gap with respect to the chemical potential can still be sizeable and lead to a qualitative change of the density dependence of the speed of sound. Taking into account constraints on the density dependence of the speed of sound at low densities, our general considerations suggest the existence of a maximum in the speed of sound. Interestingly, we also observe that specific properties of the gap can be related to characteristic properties of the speed of sound which are indirectly constrained by observations.
nucl-thhep-phSciPost Phys.Core(2024)·35 citations
07
Open Bottom Mesons and Upsilon States in Hot Magnetized Strange Hadronic Matter
Amal Jahan C.S.🇮🇳 · Amruta Mishra🇮🇳
The masses of open bottom mesons ( $B$ ( $B^{+}$ , $B^{0}$ ), $B ˉ$ ( $B^{-}$ , $B^{0} ˉ$ ), $B_{s}$ ( $B_{s}^{0}$ , $B_{s}^{0} ˉ$ )) and upsilon states ( $Υ (1 S)$ , $Υ (2 S)$ , $Υ (3 S)$ , $Υ (4 S)$ , and $Υ (1 D)$ ) are investigated in the isospin asymmetric strange hadronic medium at finite temperature in the presence of strong magnetic fields using a chiral effective Lagrangian approach. For charged baryons, the magnetic field introduces contribution from Landau energy levels. The masses of the open bottom mesons get modified through their interactions with the baryons and the scalar mesons, which undergo modifications in a magnetized medium. The charged open bottom mesons have additional positive mass shifts due to Landau quantization in the presence of the magnetic field. The medium mass shift of the upsilon states originates from the modification of the gluon condensates simulated by the variation of dilaton field ( $χ$ ) and a quark mass term in the magnetized medium. The open bottom mesons and upsilon states experience a mass drop in the magnetized medium. The masses of these mesons initially increase with a rise in temperature, and beyond a high value of temperature, their masses are observed to drop. When the temperature is below 90 MeV, the in-medium masses of the mesons increase with an increase in the magnetic field. However, at high temperatures (T $>$ 90 MeV), the masses are observed to drop with an increase in the magnetic field. The dominant in-medium effects are the density effects, which can have observable effects in asymmetric heavy-ion collisions planned at compressed baryonic matter experiments at FAIR at the future facility of GSI.
↳ hep-phnucl-thIJMPE(2022)·5 citations
08
Scaling Properties of the $Δ γ$ Correlator: Constraints on Background and CME-Sensitive Charge Separation in Heavy-Ion Collisions
Roy A. Lacey (1) · Niseem Magdy (2) ((1) Depts. of Chemistry and Physics, Stony Brook University, Stony Brook, New York 11794, USA (2) Dept. of Physics, Texas Southern University, Houston, TX 77004, USA)
The scaling properties of the $Δ γ$ correlator are used to investigate charge separation associated with the chiral magnetic effect (CME) in $p$ +Au, $d$ +Au, Ru+Ru, Zr+Zr, and Au+Au collisions at $s_{NN} = 200$ ~GeV, and in $p$ +Pb and Pb+Pb collisions at $s_{NN} = 5.02$ and $2.76$ ~TeV. Anomalous Viscous Fluid Dynamics (AVFD) calculations provide complementary benchmarks for background and signal+background behavior. Scaling $Δ γ$ by the elliptic-flow coefficient $v_{2}$ reduces the leading flow-coupled background dependence, while the resulting $Δ γ / v_{2}$ exhibits a common approximate $1/ N_{ch}$ scaling behavior for $p$ +Au, $d$ +Au, $p$ +Pb, and Pb+Pb collisions, consistent with multiplicity dilution of background-driven charge correlations across markedly different collision systems and environments. In contrast, Ru+Ru, Zr+Zr, and Au+Au collisions exhibit systematic positive deviations from their respective $1/ N_{ch}$ background-scaling trends. These scaling violations are qualitatively similar to those generated by AVFD calculations with an input CME signal and, relative to the experimentally constrained background scaling, provide evidence for a CME contribution to the measured charge separation. The inferred CME fraction is approximately $27%$ for mid-central Au+Au collisions and roughly a factor of two smaller for Ru+Ru and Zr+Zr, whose values are consistent within uncertainties. The inferred CME fractions reduce the expected Ru+Ru--Zr+Zr difference to only $\sim 1.3%$ in the total charge-separation signal, explaining its limited experimental sensitivity. These results demonstrate that scaling violations relative to an experimentally constrained background provide a quantitative strategy for isolating a CME contribution to charge separation in heavy-ion collisions.
↳ nucl-exhep-exnucl-th7 citations
09
Leading order, next-to-leading order, and non-perturbative parton collision kernels: effects in static and evolving media
Rouzbeh Modarresi Yazdi🇨🇦 · Shuzhe Shi🇨🇦 · Charles Gale🇨🇦 · Sangyong Jeon🇨🇦
Energetic partons traveling in a strongly interacting medium lose energy by emitting radiation and through collisions with medium constituents. Non-perturbative, next-to-leading order and leading order collision kernels are implemented within AMY-McGill formalism. The resulting gluon emission rates are then evaluated and compared by considering scattering occurring in a brick of quark-gluon plasma, as well as in a realistic simulation of Pb-Pb, collisions at $s = 2.76$ ATeV using MARTINI. We find that the variations in quenching of hard partons resulting from using different kernels can be important, depending on the overall value of the strong coupling constant $α_{s}$ .
↳ hep-phnucl-thPRC(2022)·16 citations
10
Relativistic spin dynamics for vector mesons
Xin-Li Sheng🇨🇳 · Lucia Oliva🇮🇹 · Zuo-Tang Liang🇨🇳 · Qun Wang🇨🇳 · Xin-Nian Wang🇺🇸
We propose a relativistic theory for spin density matrices of vector mesons based on Kadanoff-Baym equations in the closed-time-path formalism. The theory puts the calculation of spin observables such as the spin density matrix element $ρ_{00}$ for vector mesons on a solid ground. Within the theory we formulate $ρ_{00}$ for $ϕ$ mesons into a factorization form in separation of momentum and space-time variables. We argue that the main contribution to $ρ_{00}$ at lower energies should be from the $ϕ$ fields that can polarize the strange quark and antiquark in the same way as electromagnetic fields. The key observation is that there is correlation inside the $ϕ$ meson wave function between the $ϕ$ field that polarizes the strange quark and that polarizes the strange antiquark. This is reflected by the fact that the contributions to $ρ_{00}$ are all in squares of fields which are nonvanishing even if the fields may strongly fluctuate in space-time. The fluctuation of strong force fields can be extracted from $ρ_{00}$ of quarkonium vector mesons as links to fundamental properties of quantum chromodynamics.
↳ hep-phnucl-thPRD(2024)·71 citations
11
Constraints on key $^{17}$ O( $α, γ$ ) $^{21}$ Ne resonances and impact on the weak s-process
M. Williams · A.M. Laird · A. Choplin · P. Adsley · B. Davids · U. Greife · K. Hudson · D. Hutcheon · A. Lennarz · C. Ruiz
The efficiency of the slow neutron-capture process in massive stars is strongly influenced by neutron-capture reactions on light elements. At low metallicity, $^{16}$ O is an important neutron absorber, but the effectiveness of $^{16}$ O as a light-element neutron poison is modified by competition between subsequent $^{17}$ O $(α, n)^{20}$ Ne and $^{17}$ O $(α, γ)^{21}$ Ne reactions. The strengths of key $^{17}$ O $(α, γ)^{21}$ Ne resonances within the Gamow window for core helium burning in massive stars are not well constrained by experiment. This work presents more precise measurements of resonances in the energy range $E_{c . m .} = 612 - 1319$ keV. We extract resonance strengths of $ω γ_{638} = 4.85 \pm 0.79$ $μ$ eV, $ω γ_{721} = 13. 0_{- 2.4}^{+ 3.3}$ $μ$ eV, $ω γ_{814} = 7.72 \pm 0.55$ meV and $ω γ_{1318} = 136 \pm 13$ meV, for resonances at $E_{c . m .} =$ 638, 721, 814 and 1318 keV, respectively. We also report an upper limit for the 612 keV resonance of $ω γ < 140$ neV ( $95%$ c.l.), which effectively rules out any significant contribution from this resonance to the reaction rate. From this work, a new $^{17}$ O $(α, γ)^{21}$ Ne thermonuclear reaction rate is calculated and compared to the literature. The effect of present uncertainties in the $^{17}$ O $(α, γ)^{21}$ Ne reaction rate on weak s-process yields are then explored using post-processing calculations based on a rotating $20 M_{⊙}$ low-metallicity massive star. The resulting $^{17}$ O $(α, γ)^{21}$ Ne reaction rate is lower with respect to the pre-existing literature and found to enhance weak s-process yields in rotating massive star models.
↳ nucl-exastro-ph.SRnucl-thPRC(2022)·5 citations
12
Subleading contributions to $N$ -boson systems inside the universal window
Paolo Recchia🇫🇷 · Alejandro Kievsky🇮🇹 · Luca Girlanda🇮🇹 · Mario Gattobigio🇫🇷
We study bosonic systems in the regime in which the two-body system has a shallow bound state or, equivalently, a large value of the two-body scattering length. Using the effective field theory framework as a guide, we construct a series of potential terms which have decreasing importance in the description of the binding energy of the systems. The leading order potential terms consist of a two-body term, usually attractive, plus a three-body term, usually repulsive; this last term is required to prevent the collapse of systems with more than two particles. At this order, the parametrization of the two-body potential is done to obtain a correct description of the scattering length, which governs the dynamics in this regime, whereas the three-body term fixes a three-body datum. We investigate the role of the cut-off in the leading order description and we extend the exploration beyond the leading order by including the next-to-leading order terms in both, the two- and three-body potentials. We use the requirement of the stability of the N-body system, whose energy is variationally estimated, to introduce the three-body forces. The potential parametrization, as a function of the cut-off, is fixed to describe the energy of 4 He clusters up to seven particles within the expected accuracy. Finally, we also explore the possibility to describe at the same time the atom-dimer scattering length.
↳ physics.atom-phnucl-thPRA(2022)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE