Nuclear Theory·nucl-th

Tuesday·May 3, 2022

15 papers—9 primary·6 cross-listed

01
Perturbative approaches in relativistic kinetic theory and the emergence of first-order hydrodynamics
Gabriel S. Rocha🇧🇷 · Gabriel S. Denicol🇧🇷 · Jorge Noronha🇺🇸
Hydrodynamics can be formulated in terms of a perturbative series in derivatives of the temperature, chemical potential, and flow velocity around an equilibrium state. Different formulations for this series have been proposed over the years, which consequently led to the development of various hydrodynamic theories. In this work, we discuss the relativistic generalizations of the perturbative expansions put forward by Chapman and Enskog, and Hilbert, using general matching conditions in kinetic theory. This allows us to describe, in a comprehensive way, how different out-of-equilibrium definitions for the hydrodynamic fields affect the development of the hydrodynamic perturbative series. We provide a perturbative method for systematically deriving the hydrodynamic formulation recently proposed by Bemfica, Disconzi, Noronha, and Kovtun (BDNK) from relativistic kinetic theory. The various transport coefficients that appear in BDNK (at first-order) are explicitly computed using a new formulation of the relaxation time approximation for the Boltzmann equation. Assuming Bjorken flow, we also determine the hydrodynamic attractors of BDNK theory and compare the overall hydrodynamic evolution obtained using this formulation with that generated by the Israel-Stewart equations of motion and also kinetic theory.
nucl-thhep-phhep-thPRD(2022)·46 citations
02
Implications of the isobar run results for chiral magnetic effect in heavy ion collisions
Dmitri E. Kharzeev🇺🇸 · Jinfeng Liao🇺🇸 · Shuzhe Shi🇺🇸
Chiral magnetic effect (CME) is a macroscopic transport phenomenon induced by quantum anomaly in the presence of chiral imbalance and an external magnetic field. Relativistic heavy ion collisions provide the unique opportunity to look for CME in a non-Abelian plasma, where the chiral imbalance is created by topological transitions similar to those occurring in the Early Universe. The isobar run at Relativistic Heavy Ion Collider was proposed as a way to separate the possible CME signal driven by magnetic field from the background. The first blind analysis results from this important experiment have been recently released by the STAR Collaboration. Under the pre-defined assumption of identical background in RuRu and ZrZr, the results are inconsistent with the presence of CME, as well as with all existing theoretical models (whether including CME or not). However the observed difference of backgrounds must be taken into account before any physical conclusion is drawn. In this paper, we show that once the observed difference in hadron multiplicity and collective flow are quantitatively taken into account, the STAR results could be consistent with a finite CME signal contribution of about $(6.8 \pm 2.6) %$ .
nucl-thhep-phnucl-exPRC(2022)·46 citations
03
Rate and ellipticity of dilepton production in a magnetized quark-gluon plasma
Xinyang Wang🇨🇳 · Igor A. Shovkovy🇺🇸
Using the Landau-level representation for the imaginary part of the photon polarization tensor, we derive an explicit expression for the dilepton production rate from a hot quark-gluon plasma in a quantizing background magnetic field. We study in detail the dependence of the production rate on the dilepton invariant mass and the transverse momentum at mid-rapidity. We also investigate the angular dependence and ellipticity of dilepton emission. By comparing the result with the zero-field Born approximation, we find that the magnetic field leads to a strong enhancement of the dilepton rate at small values of the invariant mass ( $M ≲ ∣ e B ∣$ ). In the same kinematic region, the dilepton production is characterized by a sizable ellipticity. At large values of the dilepton invariant mass ( $M ≳ ∣ e B ∣$ ), the role of the magnetic field decreases and the result approaches the isotropic zero-field Born rate. By investigating the dependence of ellipticity on the transverse momentum, we argue that the future measurements of dilepton rate in the region of small invariant masses can constrain the magnetic field produced in heavy-ion collisions.
nucl-thhep-phPRD(2022)·34 citations
04
Isotopic Production Cross Sections in Proton- $^{12}$ C Interactions for Energies from 10 MeV/N to 100 GeV/N
Francis A. Cucinotta🇺🇸 · Sungmin Pak🇺🇸
Proton interactions with $^{12}$ C nuclei are a frequent nuclear interaction leading to secondary radiation in tissues for space radiation and cancer therapy with protons or $^{12}$ C beams. The fragmentation of $^{12}$ C by protons produces a large number of heavy ion (A>4) target or projectile fragments often with high ionization density. Here we develop an analytical model of energy dependent proton- $^{12}$ C cross sections for isotopic nuclei production. Using experimental data and a 2nd order optical model an accurate formula for the p- $^{12}$ C absorption cross section from <10 MeV/n to >10 GeV/N is obtained. The energy dependence of the elemental and isotopic cross sections is modeled as multiplicities scaled to absorption cross section with average isotopic fractions estimated from experimental data. We show that this approach results in an accurate analytic formula model over the full energy range in Hadron therapy and space radiation protection studies.
nucl-thNucl.Instrum.Meth.B(2023)·1 citation
05
Rotating Hybrid Stars with Color-Flavor-Locked Quark Matter
Debashree Sen🇮🇳 · Gargi Chaudhuri🇮🇳
In the present work we have achieved phase transition from $β$ stable hadronic matter to color-flavor locked (CFL) quark matter with Maxwell construction. The hybrid equation of state (EoS), obtained for different values of bag pressure $B$ and gap parameter $Δ$ , have been used to compute the speed of sound in hybrid star (HS) matter. The structural properties of the HSs in both static and rotating conditions have been calculated in the light of various constraints from different astrophysical and empirical perspectives. The effects of $B$ and $Δ$ on the EoS and structural properties have been investigated. At a certain density, shortly after phase transition, the HSs become unstable. In static conditions, the mass-radius solutions satisfy the constraints from GW190425, NICER experiment for PSR J0030+0451 and PSR J0740+6620 and from massive pulsars like PSR J0348+0432 and PSR J0740+6620. In rapidly rotating conditions at Kepler frequency, the constraints on maximum mass from the secondary component of GW190814 and that on rotational frequency from fast pulsars like PSR B1937+21 and PSR J1748-2446ad are all satisfied. In slowly rotating conditions, the universality relations in terms of normalized moment of inertia also hold quite well for most of our HS configurations.
nucl-thJ.Phys.G(2022)·9 citations
06
Investigating Possible Existence of Hyper-Heavy Nuclei in Neutron Star Environment
M. Veselsky · V. Petousis · Ch. C. Moustakidis · G. A. Souliotis · A. Bonasera
The synthesis of hyper-heavy elements is investigated under conditions simulating neutron star environment. The Constrained Molecular Dynamics (CoMD) approach is used to simulate low energy collisions of extremely n-rich nuclei. A new type of the fusion barrier due to a "neutron wind" is observed when the effect of neutron star environment (screening of Coulomb interaction) is introduced implicitly. When introducing also a background of surrounding nuclei, the nuclear fusion becomes possible down to temperatures of 10 $^{8}$ K and synthesis of extremely heavy and n-rich nuclei appears feasible. A possible existence of hyper-heavy nuclei in a neutron star environment could provide a mechanism of extra coherent neutrino scattering or an additional mechanism, resulting in X-ray burst or a gravitational wave signal and, thus, becoming another crucial process adding new information to the suggested models on neutron star evolution.
nucl-thastro-ph.HEnucl-exPRC(2022)·3 citations
07
Quantum computing of the $^{6}$ Li nucleus via ordered unitary coupled clusters
Oriel Kiss🇨🇭 · Michele Grossi🇨🇭 · Pavel Lougovski🇺🇸 · Federico Sanchez🇨🇭 · Sofia Vallecorsa🇨🇭 · Thomas Papenbrock🇺🇸
The variational quantum eigensolver (VQE) is an algorithm to compute ground and excited state energy of quantum many-body systems. A key component of the algorithm and an active research area is the construction of a parametrized trial wavefunction -- a so called variational ansatz. The wavefunction parametrization should be expressive enough, i.e. represent the true eigenstate of a quantum system for some choice of parameter values. On the other hand, it should be trainable, i.e. the number of parameters should not grow exponentially with the size of the system. Here, we apply VQE to the problem of finding ground and excited state energies of the odd-odd nucleus $^{6}$ Li. We study the effects of ordering fermionic excitation operators in the unitary coupled clusters ansatz on the VQE algorithm convergence by using only operators preserving the $J_{z}$ quantum number. The accuracy is improved by two order of magnitude in the case of descending order. We first compute optimal ansatz parameter values using a classical state-vector simulator with arbitrary measurement accuracy and then use those values to evaluate energy eigenstates of $^{6}$ Li on a superconducting quantum chip from IBM. We post-process the results by using error mitigation techniques and are able to reproduce the exact energy with an error of 3.8% and 0.1% for the ground state and for the first excited state of $^{6}$ Li, respectively.
nucl-thPRC(2022)·92 citations
08
Theoretical study of the $γ d \to π^{0} η d$ reaction
A. Martinez Torres🇧🇷 · K. P. Khemchandani🇧🇷 · E. Oset🇪🇸
We have done a theoretical study of the $γ d \to π^{0} η d$ reaction starting with a realistic model for the $γ N \to π^{0} η N$ reaction that reproduces cross sections and polarization observables at low energies and involves the $γ N \to Δ (1700) \to η Δ (1232) \to η π^{0} N$ process. For the coherent reaction in the deuteron we considered the impulse approximation together with the rescattering of the pions and the $η$ on a different nucleon than the one where they are produced. We found this second mechanism very important since it helps share between two nucleons the otherwise large momentum transfer of the reaction. Other contributions to the $γ d \to π^{0} η d$ reaction, involving the $γ N \to π^{\pm} π^{0} N^{'}$ process, followed by the rescattering of the $π^{\pm}$ with another nucleon to give $η$ and a nucleon, have also been included. We find a natural explanation, tied to the dynamics of our model, for the shift of the $η - d$ mass distribution to lower invariant masses, and of the $π^{0} - d$ mass distribution to larger invariant masses, compared to a phase space calculation. We also study theoretical uncertainties related to the large momenta of the deuteron wave function involved in the process as well as to the couplings present in the model. Striking differences are found with the experimental angular distribution and further theoretical investigations might be necessary.
nucl-thhep-phnucl-exPRC(2023)·10 citations
09
Pre-hydrodynamic evolution and its impact on quark-gluon plasma signatures
Dananjaya Liyanage🇺🇸 · Derek Everett🇺🇸 · Chandrodoy Chattopadhyay🇺🇸 · Ulrich Heinz🇺🇸
State-of-the-art hydrodynamic models of heavy-ion collisions have considerable theoretical model uncertainties in the description of the very early pre-hydrodynamic stage. We add a new computational module, K $_{T}$ Iso, that describes the pre-hydrodynamic evolution kinetically, based on the relativistic Boltzmann equation with collisions treated in the Isotropization Time Approximation. As a novelty, K $_{T}$ Iso allows for the inclusion and evolution of initial-state momentum anisotropies. To maintain computational efficiency K $_{T}$ Iso assumes strict longitudinal boost invariance and allows collisions to isotropize only the transverse momenta. We use it to explore the sensitivity of hadronic observables measured in relativistic heavy-ion collisions to initial-state momentum anisotropies and microscopic scattering during the pre-hydrodynamic stage.
nucl-thphysics.comp-phPRC(2022)·14 citations
10
Hybrid model of proton structure functions
S. A. Kulagin🇷🇺 · V. V. Barinov🇷🇺
We develop a "hybrid" model of the proton inelastic structure functions applicable in a wide region of invariant mass of produced states $W$ and invariant momentum transfer $Q$ including deep inelastic scattering (DIS), nucleon resonance production as well as the region close to inelastic threshold. DIS is described in terms of the parton distributions together with higher-twist corrections from an available global QCD fit. The resonant part is addressed in terms of the Breit-Wiegner contributions from five states including the $Δ (1232)$ resonance, the $N (1440)$ Roper resonance, and three effective resonances describing the second and third resonance regions. The couplings of the nucleon resonances to photon are described in terms of helicity amplitudes. The nonresonant background is addressed in terms of DIS structure functions smoothly extrapolated to low- $W$ and low- $Q$ values with the proper behavior at the real photon limit $Q^{2} = 0$ as well as near the inelastic threshold. We independently treat the transverse $F_{T}$ and the longitudinal $F_{L}$ structure function and fix the model parameters from a global analysis of the world hydrogen electroproduction and photoproduction cross-section data. We demonstrate a very good performance of the model by comparing our predictions with data on differential cross sections and the structure functions $F_{2}$ and $R = F_{L} / F_{T}$ .
↳ hep-phhep-exnucl-exnucl-thPRC(2022)·4 citations
11
QCD at finite temperature and density within the fRG approach: An overview
Wei-jie Fu🇨🇳
In this paper we present an overview on recent progress in studies of QCD at finite temperature and densities within the functional renormalization group (fRG) approach. The fRG is a nonperturbative continuum field approach, in which quantum, thermal and density fluctuations are integrated in successively with the evolution of the renormalization group (RG) scale. The fRG results for the QCD phase structure and the location of the critical end point (CEP), the QCD equation of state (EoS), the magnetic EoS, baryon number fluctuations confronted with recent experimental measurements, various critical exponents, spectral functions in the critical region, the dynamical critical exponent, etc., are presented. Recent estimates of the location of the CEP from first-principle QCD calculations within fRG and Dyson-Schwinger Equations, which passes through lattice benchmark tests at small baryon chemical potentials, converge in a rather small region at baryon chemical potentials of about 600 MeV. A region of inhomogeneous instability indicated by a negative wave function renormalization is found with $μ_{B} ≳ 420$ MeV. It is found that the non-monotonic dependence of the kurtosis of the net-proton number distributions on the beam collision energy observed in experiments, could arise from the increasingly sharp crossover in the regime of low collision energy.
↳ hep-phnucl-exnucl-thCommun.Theor.Phys.(2022)·126 citations
12
Hybrid Equations of State for Neutron Stars with Hyperons and Deltas
A. Clevinger🇺🇸 · J. Corkish🇺🇸 · K. Aryal🇺🇸 · V. Dexheimer🇺🇸
In this contribution, we describe new chemically-equilibrated charge-neutral hybrid equations of state for neutron stars. They present a first-order phase transition to quark matter and differentiate by the particle population considered and how these particles interact. While some equations of state contain just nucleons and up, down-quarks, others also contain hyperons, Delta baryons, and strange quarks. The hybrid equations of state, together with corresponding hadronic ones, are available on the CompOSE repository and can be used for different astrophysical applications.
↳ astro-ph.HEastro-ph.SRnucl-thEPJA(2022)·22 citations
13
Regarding the possibility to observe the LHCb hidden-charm strange pentaquark $P_{cs} (4459)^{0}$ in antikaon-induced $J / ψ$ meson production on protons and nuclei near the $J / ψ$ $Λ$ production threshold
E. Ya. Paryev🇷🇺
We study the near-threshold $J / ψ$ meson production on protons and nuclei by considering incoherent direct non-resonant $K^{-} p \to J / ψ Λ$ and two-step resonant $K^{-} p \to P_{cs} (4459)^{0} \to J / ψ Λ$ charmonium production processes. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of $J / ψ$ mesons off protons as well as off carbon and tungsten target nuclei at near-threshold incident antikaon energies by considering these elementary production channels as well as by assuming the spin-parity assignment of the hidden-charm resonance $P_{cs} (4459)^{0}$ with strangeness as $J^{P} = (3/2)^{-}$ within six different scenarios for the branching ratio $B r [P_{cs} (4459)^{0} \to J / ψ Λ]$ of the decay $P_{cs} (4459)^{0} \to J / ψ Λ$ . We show that the combined observables considered reveal definite sensitivity to these scenarios, which means that they may be an important tool to provide further evidence for the existence of the pentaquark $P_{cs} (4459)^{0}$ resonance and to get valuable information on its decay rate to the $J / ψ Λ$ final state. Their measurements could be performed in the future at the J-PARC Hadron Experimental Facility.
↳ hep-phnucl-exnucl-thNPA(2022)·6 citations
14
The electromagnetic Sigma-to-Lambda transition form factors with coupled-channel effects in the space-like region
Yong-Hui Lin🇩🇪 · Hans-Werner Hammer🇩🇪 · Ulf-G. Meißner🇩🇪
Using dispersion theory, the electromagnetic Sigma-to-Lambda transition form factors are expressed as the product of the pion electromagnetic form factor and the $Σ Λ ˉ \to π π$ scattering amplitudes with the latter estimated from SU(3) chiral perturbation theory including the baryon decuplet as explicit degrees of freedom. The contribution of the $K K ˉ$ channel is also taken into account and the $π π$ - $K K ˉ$ coupled-channel effect is included by means of a two-channel Muskhelishvili-Omnès representation. It is found that the electric transition form factor shows a significant shift after the inclusion of the $K K ˉ$ channel, while the magnetic transition form factor is only weakly affected. However, the $K K ˉ$ effect on the electric form factor is obscured by the undetermined coupling $h_{A}$ in the three-flavor chiral Lagrangian. The error bands of the Sigma-to-Lambda transition form factors from the uncertainties of the couplings and low-energy constant in three-flavor chiral perturbation theory are estimated by a bootstrap sampling method.
↳ hep-phhep-exnucl-exnucl-thEPJA(2023)·11 citations
15
Updated QCD global analysis of single transverse-spin asymmetries I: Extracting $H ~$ , and the role of the Soffer bound and lattice QCD
Leonard Gamberg🇺🇸 · Michel Malda🇺🇸 · Joshua A. Miller🇺🇸 · Daniel Pitonyak🇺🇸 · Alexei Prokudin🇺🇸 · Nobuo Sato🇺🇸
We present an update to the QCD global analysis of single transverse-spin asymmetries presented in Cammarota, et al., PRD 102, 054002 (2020) (JAM3D-20). JAM3D-20 simultaneously included transverse momentum dependent and collinear twist-3 observables, both of which are sensitive to quark-gluon-quark correlations in hadrons. In this study we extract for the first time the twist-3 chiral odd fragmentation function $H ~$ by incorporating the $sin ϕ_{s}$ modulation data from SIDIS along with its contribution to the single transverse-spin asymmetry in pion production from proton-proton collisions. We also explore the impact of lattice QCD tensor charge calculations and the Soffer bound on our global analysis. We find that both constraints can be accommodated within our results, with $H ~$ playing a key role in maintaining agreement with the data from proton-proton collisions.
↳ hep-phhep-exnucl-exnucl-thPRD(2022)·80 citations

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