Nuclear Theory·nucl-th

Thursday·February 11, 2021

11 papers—5 primary·6 cross-listed

01
The islands of shape coexistence within the Elliott and the proxy-SU(3) Models
Andriana Martinou🇬🇷 · Dennis Bonatsos🇬🇷 · T. J. Mertzimekis🇬🇷 · K. E. Karakatsanis🇬🇷 · I.E. Assimakis🇬🇷 · S. K. Peroulis🇬🇷 · S. Sarantopoulou🇬🇷 · N. Minkov🇧🇬
A novel dual-shell mechanism for the phenomenon of shape coexistence in nuclei within the Elliott SU(3) and the proxy-SU(3) symmetry is proposed for all mass regions. It is supposed, that shape coexistence is activated by large quadrupole-quadrupole interaction and involves the interchange among the spin-orbit (SO) like shells within nucleon numbers 6-14, 14-28, 28-50, 50-82, 82-126, 126-184, which are being described by the proxy-SU(3) symmetry, and the harmonic oscillator (HO) shells within nucleon numbers 2-8, 8-20, 20-40, 40-70, 70-112, 112-168 of the Elliott SU(3) symmetry. The outcome is, that shape coexistence may occur in certain islands on the nuclear map. The dual-shell mechanism predicts without any free parameters, that nuclei with proton number (Z) or neutron number (N) between 7-8, 17-20, 34-40, 59-70, 96-112, 146-168 are possible candidates for shape coexistence. In the light nuclei the nucleons flip from the HO shell to the neighboring SO-like shell, which means, that particle excitations occur. For this mass region, the predicted islands of shape coexistence, coincide with the islands of inversion. But in medium mass and heavy nuclei, in which the nucleons inhabit the SO-like shells, shape coexistence is accompanied by a merging of the SO-like shell with the open HO shell. The shell merging can be accomplished by the outer product of the SU(3) irreps of the two shells and represents the unification of the HO shell with the SO-like shell.
nucl-thEPJA(2021)·55 citations
02
Non-flow effects in correlation between harmonic flow and transverse momentum in nuclear collisions
Chunjian Zhang🇺🇸 · Arabinda Behera🇺🇸 · Somadutta Bhatta🇺🇸 · Jiangyong Jia🇺🇸
A large anti-correlation signal between elliptic flow $v_{2}$ and average transverse momentum $[p_{T}]$ was recently measured in small collision systems, consistent with a final-state hydrodynamic response to the initial geometry. This negative $v_{2}$ - $[p_{T}]$ correlation was predicted to change to positive correlation for events with very small charged particle multiplicity $N_{ch}$ due to initial-state momentum anisotropies of the gluon saturation effects. However, the role of non-flow correlations is expected to be important in these systems, which is not yet studied. We estimate the non-flow effects in $pp$ , $p$ Pb and peripheral PbPb collisions using {\tt Pythia} and {\tt Hijing} models, and compare them with the experimental data. We show that the non-flow effects are largely suppressed using the rapidity-separated subevent cumulant method (details of the cumulant framework are also provided). The magnitude of the residual non-flow is much less than the experimental observation in the higher $N_{ch}$ region, supporting the final-state response interpretation. In the very low $N_{ch}$ region, however, the sign and magnitude of the residual non-flow depend on the model details. Therefore, it is unclear at this moment whether the sign change of $v_{2}$ - $[p_{T}]$ can serve as evidence for initial state momentum anisotropies predicted by the gluon saturation.
nucl-thhep-phnucl-exPLB(2021)·27 citations
03
Constraints on the Symmetry Energy from PREX-II in the Multimessenger Era
Tong-Gang Yue🇨🇳 · Lie-Wen Chen🇨🇳 · Zhen Zhang🇨🇳 · Ying Zhou🇨🇳
The neutron skin thickness $Δ r_{np}$ of heavy nuclei is essentially determined by the symmetry energy density slope $L (ρ)$ at $ρ_{c} = 0.11 fm^{- 3} \approx 2/3 ρ_{0}$ ( $ρ_{0}$ is nuclear saturation density), roughly corresponding to the average density of finite nuclei. The PREX collaboration recently reported a model-independent extraction of $Δ r_{np}^{208} = 0.283 \pm 0.071$ fm for the $Δ r_{np}$ of $^{208}$ Pb, suggesting a rather stiff symmetry energy $E_{sym} (ρ)$ with $L (ρ_{c}) \geq 52$ MeV. We show that the $E_{sym} (ρ)$ cannot be too stiff and $L (ρ_{c}) \leq 73$ MeV is necessary to be compatible with (1) the ground-state properties and giant monopole resonances of finite nuclei, (2) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (3) the largest neutron star (NS) mass reported so far for PSR J0740+6620, (4) the NS tidal deformability extracted from gravitational wave signal GW170817 and (5) the mass-radius of PSR J0030+045 measured simultaneously by NICER. This allows us to obtain $52 \leq L (ρ_{c}) \leq 73$ MeV and $0.212 \leq Δ r_{np}^{208} \leq 0.271$ fm, and further $E_{sym} (ρ_{0}) = 34.3 \pm 1.7$ MeV, $L (ρ_{0}) = 83.1 \pm 24.7$ MeV, and $E_{sym} (2 ρ_{0}) = 62.8 \pm 15.9$ MeV. A number of critical implications on nuclear physics and astrophysics are discussed.
nucl-thastro-ph.HEhep-phnucl-exPRResearch(2022)·75 citations
04
Baryonic matter and the medium modification of the baryon masses
Nam-Yong Ghim🇰🇷 · Ghil-Seok Yang🇰🇷 · Hyun-Chul Kim🇰🇷 · Ulugbek Yakhshiev🇰🇷
We investigate the properties of baryonic matter within the framework of the in-medium modified chiral soliton model by taking into account the effects of surrounding baryonic environment on the properties of in-medium baryons. The internal parameters of the model are determined based on nuclear phenomenology at nonstrange sector and fitted by reproducing nuclear matter properties near the saturation point. We discuss the equations of state in different nuclear environments such as symmetric nuclear matter, neutron and strange matters. We show that the results for the equations of state are in good agreement with the phenomenology of nuclear matter. We also discuss how the SU(3) baryons masses undergo changes in these various types of nuclear matter.
nucl-thastro-ph.HEhep-phnucl-exPRC(2021)·5 citations
05
Sequential single pion production explaining the dibaryon " $d^{*} (2380)$ " peak
R. Molina · N. Ikeno · E. Oset
We study the two step sequential one pion production mechanism, $n p (I = 0) \to π^{-} pp$ , followed by the fusion reaction $pp \to π^{+} d$ , in order to describe the $n p \to π^{+} π^{-} d$ reaction with $π^{+} π^{-}$ in $I = 0$ , where a narrow peak, so far identified with a " $d (2380)$ " dibaryon, has been observed. We find that the second step $pp \to π^{+} d$ is driven by a triangle singularity that determines the position of the peak of the reaction and the large strength of the cross section. The combined cross section of these two mechanisms produce a narrow peak with the position, width and strength compatible with the experimental observation within the approximations done. This novel interpretation of the peak without invoking a dibaryon explains why the peak is not observed in other reactions where it has been searched for.
nucl-thhep-exhep-phChin.Phys.C 47 (2023) 4, 041001
06
The effect of hadronic scatterings on the measurement of vector meson spin alignments in heavy-ion collisions
Diyu Shen🇨🇳 · Jinhui Chen🇨🇳 · Zi-Wei Lin🇨🇳
Spin alignments of vector mesons and hyperons in relativistic heavy-ion collisions have been proposed as signals of the global polarization. The STAR experiment first observed the $Λ$ polarization. Recently, the ALICE collaboration measured the transverse momentum ( $p_{T}$ ) and the collision centrality dependence of $K^{*}$ and $ϕ$ spin alignments in Pb-Pb collisions at $s_{NN}$ = 2.76 TeV. A large signal is observed in the low $p_{T}$ region of mid-central collisions for $K^{*}$ while the signal is much smaller for $ϕ$ , and these have not been understood yet. Since vector mesons have different lifetimes and their decay products have different scattering cross sections, they suffer from different hadronic effects. In this paper, we study the effect of hadronic interactions on the spin alignment of $K^{*}$ , $ϕ$ and $ρ$ mesons in relativistic heavy-ion collisions with a multi-phase transport model. We find that hadronic scatterings lead to a deviation of the observed spin alignment matrix element $ρ_{00}$ away from the true value for $ρ$ and $K^{*}$ mesons (with a bigger effect on $ρ$ ) while the effect is negligible for the $ϕ$ meson. The effect depends on the kinematic acceptance: the observed $ρ_{00}$ value is lower than the true value when the pseudorapidity ( $η$ ) coverage is small while there is little effect when the $η$ coverage is big. Our study thus provides valuable information to understand the vector meson spin alignment signals observed in the experiments.
↳ nucl-exnucl-thCPC(2021)·15 citations
07
Detecting scale anomaly in chiral phase transition of QCD: new critical endpoint pinned down
Mamiya Kawaguchi🇨🇳 · Shinya Matsuzaki🇨🇳 · Akio Tomiya🇺🇸
Violation of scale symmetry, scale anomaly, being a radical concept in quantum field theory, is of importance to comprehend the vacuum structure of QCD, and should potentially contribute to the chiral phase transition in thermal QCD, as well as the chiral and U(1) axial symmetry. Though it should be essential, direct evidence of scale anomalies has never been observed in the chiral phase transition. We propose a methodology to detect a scale anomaly in the chiral phase transition, which is an electromagnetically induced scale anomaly: apply a weak magnetic field background onto two-flavor massless QCD with an extremely heavy strange quark, first observe the chiral crossover; second, adjusting the strange quark mass to be smaller and smaller, observe the second-order chiral phase transition, and then the first-order one in the massless-three flavor limit. Thus, the second-order chiral phase transition, observed as the evidence of the quantum scale anomaly, is a new critical endpoint. It turns out that this electromagnetic scale anomaly gets most operative in the weak magnetic field regime, rather than a strong field region. We also briefly address accessibility of lattice QCD, a prospected application to dense matter system, and implications to astrophysical observations, such as gravitational wave productions provided from thermomagnetic QCD-like theories.
↳ hep-phhep-lathep-thnucl-thJHEP(2021)·7 citations
08
Can the nature of $a_{0} (980)$ be tested in the $D_{s}^{+} \to π^{+} π^{0} η$ decay?
Xi-Zhe Ling🇨🇳 · Ming-Zhu Liu🇨🇳 · Jun-Xu Lu🇨🇳 · Li-Sheng Geng🇨🇳 · Ju-Jun Xie🇨🇳
From the amplitude analysis of the $D_{s}^{+} \to π^{+} π^{0} η$ decay, the BESIII Collaboration firstly observed the $D_{s}^{+} \to a_{0} (980)^{+} π^{0}$ and $D_{s}^{+} \to a_{0} (980)^{0} π^{+}$ decay modes, which are expected to occur through the pure $W$ -annihilation processes. The measured branching fraction $B [D_{s}^{+} \to a_{0} (980)^{+ (0)} π^{0 (+)}, a_{0} (980)^{+ (0)} \to π^{+ (0)} η]$ is, however, found to be larger than those of known $W$ -annihilation decays by one order of magnitude. This apparent contradiction can be reconciled if the two decays are induced by internal $W$ -conversion or external $W$ -emission mechanisms instead of $W$ -annihilation mechanism. In this work, we propose that the $D_{s}^{+}$ decay proceeds via both the external and internal $W$ -emission instead of $W$ -annihilation mechanisms. In such a scenario, we perform a study of the $D_{s}^{+} \to π^{+} π^{0} η$ decay by taking into account the contributions from the tree diagram $D_{s}^{+} \to ρ^{+} η \to π^{+} π^{0} η$ and the intermediate $ρ^{+} η$ and $K^{*} K ˉ / K K ˉ^{*}$ triangle diagrams. The intermediate $a_{0} (980)$ state can be dynamically generated from the final state interactions of coupled $K K ˉ$ and $π η$ channels, and it is shown that the experimental data can be described fairly well, which supports the interpretation of $a_{0} (980)$ as a molecular state.
↳ hep-phhep-exnucl-exnucl-thPRD(2021)·37 citations
09
Analysis of the kinematic boundaries of the quasi-elastic neutrino-nucleus cross section in the superscaling model with a relativistic effective mass
I. Ruiz Simo🇪🇸 · I.D. Kakorin🇷🇺 · V.A. Naumov🇷🇺 · K.S. Kuzmin🇷🇺 · J.E. Amaro🇪🇸
In this work we obtain the analytical expressions for the boundaries of the charged current quasi-elastic double differential cross section in terms of dimensionless energy and momentum transfers, for the Relativistic Fermi Gas (RFG) and the Super-Scaling approach with relativistic effective mass (SuSAM*) models, within the scaling formalism. In addition, we show that this double differential cross section in the scaling formalism has very good properties to be implemented in the Monte Carlo (MC) neutrino event generators, particularly because its peak is almost flat with the (anti)neutrino energy. This makes it especially well-suited for the event generation by the acceptance-rejection method usually used in the neutrino generators. Finally, we analyze the total charged current quasi-elastic (CCQE) cross section $σ (E_{ν})$ for both models and attribute the enhancement observed in the SuSAM* total cross section to the high-momentum components which are present, in a phenomenological way, in its scaling function, while these are absent in the RFG model.
↳ hep-phnucl-thPRD(2022)·0 citations
10
The relation between instant and light-front formulations of quantum field theory
Wayne Polyzou🇺🇸
The scattering equivalence of quantum field theories formulated with light-front and instant-form kinematic subgroups is established using non-perturbative methods. The difficulty with field theoretic formulations of Dirac's forms of dynamics is that the free and interacting unitary representations of the Poincaré group are defined on inequivalent representations of the Hilbert space, which means that the concept of kinematic transformations must be modified on the Hilbert space of the field theory. This work addresses this problem by assuming the existence of a field theory with the expected properties and constructs equivalent representations with instant and front form kinematic subgroups. In this construction both the light-front and instant-form formulations share the same vacuum and one-particle states. The free field Fock space plays no role. There is no "quantization" of a classical theory. The property that survives from the perturbative approach is the notion of a kinematic subgroup, which means kinematic Poincaré transformations can be trivially implemented by acting on suitable basis vectors. This non-perturbative approach avoids dealing with issues that arise in perturbative treatments where is it necessary to have a consistent treatment of renormalization, rotational covariance, and the structure of the light-front vacuum. While addressing these issues in a computational framework is important for applications, this work may provide some insight into the nature of the expected resolution and identifies the origin of some of differences between the perturbative and non-perturbative approaches.
↳ hep-thmath-phmath.MPnucl-thPRD(2021)·10 citations
11
Transverse $Λ$ Polarization in $e^{+} e^{-}$ collisions
Leonard Gamberg🇺🇸 · Zhong-Bo Kang🇺🇸 · Ding Yu Shao🇺🇸 · John Terry🇺🇸 · Fanyi Zhao🇺🇸
In this paper we study transverse polarization of $Λ$ hyperons in single-inclusive leptonic annihilation. We show that when the transverse momentum of the $Λ$ baryon is measured with respect to the thrust axis, a transverse momentum dependent (TMD) factorization formalism is required and the polarization is generated by the TMD polarizing fragmentation function (TMD PFF), $D_{1 T}^{⊥}$ . However, when the transverse momentum of the $Λ$ baryon is measured with respect to the momentum of the initial leptons, a collinear twist-3 formalism is required and the polarization is generated by the intrinsic collinear twist-3 fragmentation function $D_{T}$ . Thus while these measurements differ from one another only by a change in the measurement axis, they probe different distribution functions. Recently, Belle measured a significant polarization in single-inclusive $Λ$ baryon production as a function of the transverse momentum with respect to the thrust axis. However, this data can in principle be re-analyzed to measure the polarization as a function of the transverse momentum of the $Λ$ baryon with respect to the lepton pair. This observable could be the first significant probe of the function, $D_{T}$ . In this paper, we first develop a TMD formalism for $Λ$ polarization; we then present a recent twist-3 formalism that was established to describe $Λ$ polarization. Using the TMD formalism, we demonstrate that the $Λ$ polarization at OPAL and Belle can be described using the twist-2 TMD factorization formalism. Finally, we make a theoretical prediction for this polarization in the collinear twist-3 formalism at Belle.
↳ hep-phhep-exnucl-exnucl-thPLB(2021)·31 citations

Affiliations

first authorsco-authorsvia INSPIRE