Nuclear Theory·nucl-th

Friday·September 17, 2021

12 papers—4 primary·8 cross-listed

01
Mean-field update in the JAM microscopic model: Mean-field effects on collective flow in high-energy heavy-ion collisions at $s_{N N} = 2 - 20$ GeV energies
Yasushi Nara🇯🇵 · Akira Ohnishi🇯🇵
The beam energy dependence of the directed flow is a sensitive probe for the properties of strongly interacting matter. We consider different implementations of momentum-dependent hadronic mean fields in the relativistic quantum molecular dynamics (RQMD) framework. First, Lorentz scalar implementation of a Skyrme type potential is examined. Then, full implementation of the Skyrme type potential as a Lorentz vector in the RQMD approach is proposed. We find that scalar implementation of the Skyrme force is too weak to generate repulsion explaining observed data of sideward flows at $s_{N N} < 10$ GeV, while vector implementation gives collective flows compatible with the data for a wide range of beam energies $2.7 < s_{N N} < 20$ GeV. We show that our approach reproduces the negative proton directed flow at $s_{N N} > 10$ GeV discovered by experiments. We discuss the dynamical generation mechanisms of the directed flow within a conventional hadronic mean field. A positive slope of proton directed flow is generated predominantly during compression stages of heavy-ion collisions by the strong repulsive interaction due to high baryon densities. In contrast, in the expansion stages of the collision, the negative directed flow is generated more strongly than the positive one by the tilted expansion and shadowing by the spectator matter. At lower collision energies $s_{N N} < 10$ GeV, the positive flow wins against the negative flow because of a long compression time. On the other hand, at higher energies $s_{N N} > 10$ GeV, negative flow wins because of shorter compression time and longer expansion time. A transition beam energy from positive to negative flow is highly sensitive to the strength of the interaction.
nucl-thhep-phnucl-exPRC(2022)·64 citations
02
Effects of $ϕ$ -meson on properties of hyperon stars in density dependent relativistic mean field model
Zhong-Hao Tu🇨🇳 · Shan-Gui Zhou🇨🇳
The effects of $ϕ$ -meson on properties of hyperon stars are studied systematically in the framework of the density dependent relativistic mean field (DDRMF) model. The $ϕ$ -meson shifts hyperon threshold to a higher density and reduces the hyperon fractions in neutron star cores. It also strongly stiffens the equation of state (EoS) calculated with various DDRMF effective interactions and increases the maximum mass of hyperon stars, but only a few effective interactions survive under the constraints from recent astrophysical observations. In the DDRMF model, the conformal limit of sound velocity is still in a strong tension with the fact that the maximum mass of neutron stars obtained in theoretical calculations reaches about two solar masses. Based on different interior composition assumptions, we discuss the possibility of the secondary object of GW190814 as a neutron star. When $ϕ$ -meson is considered, DD-ME2 and DD-MEX support that the secondary object of GW190814 is a hyperon star rapidly rotating with Kepler frequency.
nucl-thApJ(2022)·32 citations
03
Factorization breaking for higher moments of harmonic flow
Piotr Bozek🇵🇱 · Rupam Samanta🇵🇱
We study correlations between harmonic flow vectors squared measured at different transverse momenta. One of the flow harmonics squared is taken at a fixed transverse momentum and correlated to the momentum averaged harmonic flow squared of the same order. Such four particle correlators, dependent on transverse momentum, have been recently measured experimentally. Factorization coefficients based on the ratio of such four-particle correlators allow the independent measurement of the flow vector and flow magnitude factorization breaking coefficient. Moreover, the correlation of the angles of flow harmonics as a function of transverse momentum can be extracted. Results are compared to preliminary data of the ALICE Collaboration. We also present predictions for the momentum dependent factorization breaking coefficient between mixed flow harmonics. The correlators with squares of mixed harmonics can serve as a way to independently measure the flow vector, flow magnitude, and flow angle correlations, and could be used to gain additional information on the fluctuating initial state and the dynamics in heavy-ion collisions.
nucl-thnucl-exPRC(2022)·18 citations
04
Density Functional Equation of State and Its Application to the Phenomenology of Heavy-Ion Collisions
Agnieszka Sorensen🇺🇸
We present a mean-field model of the dense nuclear matter equation of state designed for use in computationally demanding hadronic transport simulations. Our approach, based on the relativistic Landau Fermi-liquid theory, allows us to construct a family of equations of state spanning a wide range of possible bulk properties of dense QCD matter. We implement the developed model in the hadronic transport code SMASH, and show that the resulting dynamic behavior reproduces theoretical expectations for the thermodynamic properties of the system based on the underlying equation of state. In particular, we show that pair distribution functions calculated from hadronic transport simulation data are consistent with theoretical expectations based on the second-order cumulant ratio, and can be used as a signature of crossing the phase diagram in the vicinity of a critical point. We additionally present a novel method that may enable a measurement of the speed of sound and its derivative with respect to the baryon number density in heavy-ion collisions. Application of our approach to available experimental data implies that the derivative of the speed of sound is non-monotonic in systems created in collisions at intermediate to low energies, which in turn may be connected to non-trivial features in the underlying equation of state.
nucl-th4 citations
05
Universality of a truncated sigma-model
Andrei Alexandru🇺🇸 · Paulo F. Bedaque🇺🇸 · Andrea Carosso🇺🇸 · Andy Sheng🇺🇸
Bosonic quantum field theories, even when regularized using a finite lattice, possess an infinite dimensional Hilbert space and, therefore, cannot be simulated in quantum computers with a finite number of qubits. A truncation of the Hilbert space is then needed and the physical results are obtained after a double limit: one to remove the truncation and another to remove the regulator (the continuum limit). A simpler alternative is to find a model with a finite dimensional Hilbert space belonging to the same universality class as the continuum model (a "qubitization"), so only the space continuum limit is required. A qubitization of the $1 + 1$ dimensional asymptotically free $O (3)$ nonlinear $σ$ -model based on ideas of non-commutative geometry was previously proposed arXiv:1903.06577 and, in this paper, we provide evidence that it reproduces the physics of the $σ$ -model both in the infrared and the ultraviolet regimes.
↳ hep-lathep-thnucl-thquant-phPLB(2022)·11 citations
06
Light Cone Distribution Amplitudes of Heavy-Light Mesons and Quarkonia
Fernando E. Serna🇧🇷 · Bruno El-Bennich🇧🇷
In this work we use the framework of the Dyson-Schwinger and Bethe-Salpeter equations to compute Light-Cone Distribution Amplitudes of heavy-light mesons and quarkonia. In studying the meson properties, we introduce a flavor dependence in the heavy-quark sector of the Bethe-Salpeter ladder kernel which yields improved numerical results for masses and leptonic decay constants of the pseudoscalar $D$ , $D_{s}$ , $B$ and $B_{s}$ mesons. Finally, the corresponding heavy-light Bethe-Salpeter amplitudes are projected onto the light front and we reconstruct the distribution amplitudes of the mesons in the full theory.
↳ hep-phnucl-thPoS(2021)·6 citations
07
Probing the gluonic structure of the deuteron with $J / ψ$ photoproduction in d+Au ultra-peripheral collisions
STAR Collaboration: M. S. Abdallah · B. E. Aboona · J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · I. Alekseev · D. M. Anderson and 390 other authors
Understanding gluon density distributions and how they are modified in nuclei are among the most important goals in nuclear physics. In recent years, diffractive vector meson production measured in ultra-peripheral collisions (UPCs) at heavy-ion colliders has provided a new tool for probing the gluon density. In this Letter, we report the first measurement of $J / ψ$ photoproduction off the deuteron in UPCs at the center-of-mass energy $s_{_{NN}} = 200 GeV$ in d $+$ Au collisions. The differential cross section as a function of momentum transfer $- t$ is measured. In addition, data with a neutron tagged in the deuteron-going Zero-Degree Calorimeter is investigated for the first time, which is found to be consistent with the expectation of incoherent diffractive scattering at low momentum transfer. Theoretical predictions based on the Color Glass Condensate saturation model and the gluon shadowing model are compared with the data quantitatively. A better agreement with the saturation model has been observed. With the current measurement, the results are found to be directly sensitive to the gluon density distribution of the deuteron and the deuteron breakup, which provides insights into the nuclear gluonic structure.
↳ nucl-exhep-exnucl-thPRL(2022)·30 citations
08
The production of doubly charmed exotic hadrons in heavy ion collisions
Yuanyuan Hu🇨🇳 · Jinfeng Liao🇺🇸 · Enke Wang🇨🇳 · Qian Wang🇨🇳 · Hongxi Xing🇨🇳 · Hui Zhang🇨🇳
Hadron spectroscopy provides direct physical measurements that shed light on the non-perturbative behavior of quantum chromodynamics (QCD). In particular, various exotic hadrons such as the newly observed $T_{cc}^{+}$ by the LHCb collaboration, offer unique insights on the QCD dynamics in hadron structures. In this letter, we demonstrate how heavy ion collisions can serve as a powerful venue for hadron spectroscopy study of doubly charmed exotic hadrons by virtue of the extremely charm-rich environment created in such collisions. The yields of $T_{cc}^{+}$ as well as its potential isospin partners are computed within the molecular picture for Pb-Pb collisions at center-of-mass energy $2.76 TeV$ . We find about three-order-of-magnitude enhancement in the production of $T_{cc}^{+}$ in Pb-Pb collisions as compared with the yield in proton-proton collisions, with a moderately smaller enhancement in the yields of the isospin partners $T_{cc}^{0}$ and $T_{cc}^{++}$ . The $T_{cc}^{+}$ yield is comparable to that of the $X (3872)$ in the most central collisions while shows a considerably stronger decrease toward peripheral collisions, due to a "threshold" effect of the required double charm quarks for $T_{cc}^{+}$ . Final results for their rapidity and transverse momentum $p_{T}$ dependence as well as the elliptic flow coefficient are reported and can be tested by future experimental measurements.
↳ hep-phhep-exnucl-exnucl-thPRD(2021)·56 citations
09
Weak transition form factors of heavy-light pseudoscalar mesons for space- and timelike momentum transfers
Oliver Heger🇦🇹 · María Gómez-Rocha🇪🇸 · Wolfgang Schweiger🇦🇹
Weak $B^{-} \to D^{0}, π^{0}$ and $D^{-} \to K^{0}, π^{0}$ transition form factors are described in both the space- and time-like momentum transfer regions, within a constituent-quark model. Neutrino-meson scattering and semileptonic weak decays are formulated within the point form of relativistic quantum mechanics to end up with relativistic invariant process amplitudes from which meson transition currents and form factors are extracted in an unambiguous way. For space-like momentum transfers, form factors depend on the frame in which the $W M M^{'}$ vertex is considered. Such a frame dependence is expected from a pure valence-quark picture, since a complete, frame independent description of form factors is supposed to include non-valence contributions. The most important of such contributions are the $Z$ -graphs, which are, however, suppressed in the infinite-momentum frame ( $q^{2} < 0$ ). On the other hand, they can play a significant role in the Breit frame ( $q^{2} < 0$ ) and in the direct decay calculation ( $q^{2} > 0$ ), as a comparison with the infinite-momentum-frame form factors (analytically continued to $q^{2} > 0$ ) reveals. Numerical results for the analytically continued infinite-momentum-frame form factors agree very well with lattice data in the time-like momentum transfer region and the experimental value for the slope of the $F_{B \to D}^{+}$ transition form factor at zero recoil is reproduced satisfactorily. These predictions satisfy heavy-quark-symmetry constraints and their $q^{2}$ dependence is well approximated by a pole fit, reminiscent of a vector-meson-dominance-like decay mechanism. We discuss how such a decay mechanism can be accommodated within an extension of our constituent-quark model, by allowing for a non-valence component in the meson wave functions. We also address the question of wrong cluster properties inherent in the Bakamjian-Thomas formulation.
↳ hep-phnucl-thPRD(2021)·7 citations
10
Reconstruction of high-energy part of gamma-ray spectrum in thermal neutron capture by $^{113}$ Cd
V.A. Plujko · O.M. Gorbachenko · K.M. Solodovnyk · V.M. Petrenko
The average gamma-ray spectrum $^{114}$ Cd after thermal neutron capture in $^{113}$ Cd was evaluated in units of mb/MeV. Two approaches are considered for estimation of the average gamma-ray spectrum with normalization of the experimental data: mean spectra for all gamma-energies were found by averaging frequency polygon for experimental data histogram, and mean spectra were estimated as the combination of theoretical values at low gamma-ray energies and averaging experimental data in high-energy range. The experi mental spectra were evaluated from the gamma-intensities presented by Mheemeed et al. [A. Mheemeed et al., Nucl. Phys. A 412 (1984) 113] and Belgya et al [T. Belgya et al., EPJ Web of Conf. 146 (2017) 05009]. They were normalized to the average theoretical spectrum which was calculated using EMPIRE and TALYS codes. The procedure of normalization of the high-energy part of the spectrum was described. Estimated $γ$ - spectra for $^{113}$ Cd(n,{x $γ$ }) reaction induced by thermal neutrons were presented.
↳ nucl-exnucl-thNucl.Phys.Atom.Energy(2021)·0 citations
11
Charmonium suppression in ultra-relativistic proton-proton collisions at LHC energies: A hint for QGP in small systems
Captain R. Singh🇮🇳 · Suman Deb🇮🇳 · Raghunath Sahoo🇮🇳 · Jan-e Alam🇮🇳
Proton-proton ( $pp$ ) collision has been considered as a baseline to study the system produced in relativistic heavy-ion (AA) collisions with the basic assumption that no thermal medium is formed in $pp$ collisions. This warrants a cautious analysis of the system produced in $pp$ collisions at relativistic energies.In this work we investigate the charmonium suppression in $pp$ collisions at $s = 5.02, 7$ and $13$ TeV energies. Further, charmonium suppression has been studied for various event multiplicities and transverse momenta by including the mechanisms of color screening, gluonic dissociation, collisional damping along with regeneration due to correlated $c c ˉ$ pairs. Here we obtain a net suppression of charmonia at high-multiplicity events indicating the possibility of the formation of quark-gluon plasma in $pp$ collisions.
↳ hep-phhep-exnucl-exnucl-thEPJC(2022)·19 citations
12
Heavy-meson chiral Lagrangians, effective flavored couplings, SU(4) flavor breaking and their consequences
Bruno El-Bennich🇧🇷 · Fernando E. Serna🇧🇷
We review heavy quark flavor and spin symmetries, their exploitation in heavy meson effective theories and the flavored couplings of charmed and light mesons in the definition of their effective Lagrangians. We point out how nonperturbative continuum QCD approaches based on Dyson-Schwinger and Bethe-Salpeter equations can be used to calculate strong and leptonic decays of open-charm mesons and heavy quarkonia. The strong decay $D^{*} \to D π$ serves as a benchmark, as it is the only physical open-charm observable that can be related to the effective Lagrangian's couplings. Nonetheless, a quantitative comparison of $D^{*} D π$ , $ρ D D$ , $ρ D^{*} D$ and $ρ D^{*} D^{*}$ couplings for a range of off-shell momenta of the $ρ$ -meson invalidates SU(4) $_{F}$ symmetry relations between these couplings. Thus, besides the breaking of flavor symmetry by mass terms in the Lagrangians, the flavor-symmetry breaching in couplings and their dependence on the $ρ$ -meson virtuality cannot be ignored. We also take the opportunity to present new results for the effective $J / ψ D D$ and $J / ψ D^{*} D$ couplings. We conclude this contribution with a discussion on how the description of pseudoscalar and vector $D$ , $D_{s}$ , $B$ and $B_{s}$ meson properties can be drastically improved with a modest modification of the flavor-dependence in the Bethe-Salpeter equation.
↳ hep-phhep-exhep-latnucl-thPoS(2021)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE