Proton-rich nuclei beyond the proton drip line are of great interest in nuclear structure physics, due to exotic phenomena such as proton emissions and the Thomas-Ehrman shift (TES). In this work, we employ the Gamow shell model (GSM) to investigate the structure and decay of 20Si, a candidate for six-proton (6 <italic>p</italic>) emission, which can be produced via two-neutron knockout from the drip line nucleus 22Si. We predict that its ground state decays via 6 <italic>p</italic> emission to the ground state of 14O, with a decay energy <math altimg='si21.svg'><mrow><msub><mi>E</mi><mrow><mn>6</mn><mi>p</mi></mrow></msub><mo linebreak='goodbreak'>=</mo><mn>10.125</mn></mrow></math> MeV and a width of 371 keV. A <math altimg='si22.svg'><msup><mn>2</mn><mo>+</mo></msup></math> state is predicted at 1.7 MeV, comparable with that in 18Mg, indicating the disappearance of the <math altimg='si23.svg'><mrow><mi>Z</mi><mo linebreak='goodbreak'>=</mo><mn>14</mn></mrow></math> magic number in 20Si. Instead, analyses of the many-body configurations and the average occupancies of the mirror states suggest the presence of <italic>dynamic</italic> TES in low-lying states of 19Al/ 19C and 20Si/ 20C. Further evidence is provided by analyzing the contributions of different components of the GSM Hamiltonian. Moreover, this study offers the first theoretical description of 20Si and guidance for future experiments.

China

J.L. Wang

M.R. Xie

K.H. Li

P.Y. Wang

N. Michel

Q. Yuan

J.G. Li

Gamow shell model predictions for six-proton unbound nucleus 20Si

The proton-rich nucleus <math altimg='si1.svg'><msup><mrow /><mn>22</mn></msup></math>Si is studied using Nuclear Lattice Effective Field Theory with high-fidelity chiral forces. Our results indicate that <math altimg='si1.svg'><msup><mrow /><mn>22</mn></msup></math>Si is more tightly bound than <math altimg='si2.svg'><msup><mrow /><mn>20</mn></msup></math>Mg, thereby excluding the possibility of two-proton emission. The <math altimg='si18.svg'><mrow><mi>Z</mi><mo linebreak='goodbreak'>=</mo><mn>14</mn></mrow></math> shell closure in <math altimg='si1.svg'><msup><mrow /><mn>22</mn></msup></math>Si is investigated through the evolution of the <math altimg='si8.svg'><msup><mn>2</mn><mo>+</mo></msup></math> state in the neighboring nuclei. We then focus on the charge radius and spatial distribution information of <math altimg='si1.svg'><msup><mrow /><mn>22</mn></msup></math>Si, considering the novel phenomena that may emerge due to the small two-proton separation energy and the shell closure. We present the distribution of the 14 protons and 8 neutrons obtained from our lattice simulation, revealing insights into the spatial arrangement of the nucleons. Moreover, the spatial localization of the outermost proton and neutron suggests that <math altimg='si1.svg'><msup><mrow /><mn>22</mn></msup></math>Si is a doubly magic nucleus. Furthermore, we develop the pinhole method based on the harmonic oscillator basis, which gives insight into the nuclear structure in terms of the shell model picture from lattice simulations. Our calculated occupation numbers support that <math altimg='si18.svg'><mrow><mi>Z</mi><mo linebreak='goodbreak'>=</mo><mn>14</mn></mrow></math> and <math altimg='si6.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>8</mn></mrow></math> are the shell closures and show that the <math altimg='si19.svg'><mrow><mi>&#960;</mi><mn>1</mn><msub><mi>s</mi><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub></mrow></math> orbital component is minor in <math altimg='si1.svg'><msup><mrow /><mn>22</mn></msup></math>Si.

Germany

Shuang Zhang

Saudi Arabia

Türkiye

Serdar Elhatisari

Ulf-G. Meißner

Shihang Shen

Lattice simulation of nucleon distribution and shell closure in the proton-rich nucleus <math altimg='si1.svg'><msup><mrow /><mn>22</mn></msup></math>Si

We report on the first measurement of the elemental fragmentation cross sections (EFCSs) of <math><mmultiscripts><mrow><mi>Si</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>29</mn><mo>−</mo><mn>33</mn></mrow></mmultiscripts></math> on a carbon target at ∼230 MeV/nucleon. The experimental data covering charge changes of ΔZ = 1-4 are reproduced well by the isospin-dependent quantum molecular dynamics (IQMD) coupled with the evaporation GEMINI (IQMD+GEMINI) model. We further explore the mechanisms underlying the single-proton removal reaction in this model framework. We conclude that the cross sections from direct proton knockout exhibit an overall weak dependence on the mass number of Si projectiles. The proton evaporation induced after the projectile excitation significantly affects the cross sections for neutron-deficient Si isotopes, while neutron evaporation plays a crucial role in the reactions of neutron-rich Si isotopes. It is presented that the relative magnitude of one-proton and one-neutron separation energies is an essential factor that influences evaporation processes. Therefore, proton evaporation should be incorporated into the reaction model in addition to the direct proton knockout in analyses of Gade-Tostevin systematic for single-proton removal reactions.

Guang-Shuai Li

Bao-Hua Sun

Jun Su

Japan

Isao Tanihata

Satoru Terashima

Jian-Wei Zhao

Er-Xi Xiao

Ji-Chao Zhang

Liu-Chun He

Ge Guo

Wei-Ping Lin

Wen-Jian Lin

Chuan-Ye Liu

Chen-Gui Lu

Bo Mei

Dan-Yang Pang

Ye-Lei Sun

Zhi-Yu Sun

Meng Wang

Feng Wang

Jing Wang

Shi-Tao Wang

Xiu-Lin Wei

Xiao-Dong Xu

Jun-Yao Xu

Li-Hua Zhu

Yong Zheng

Mei-Xue Zhang

Xue-Heng Zhang

Single-proton removal reaction in the IQMD+GEMINI model benchmarked by elemental fragmentation cross sections of Si on carbon at ∼230 MeV/nucleon

Recent study in [1] discovered that introducing a massive charged scalar field and requiring the Weak Gravity Conjecture (WGC) to hold can eliminate a class of Weak Cosmic Censorship Conjecture (WCCC) counterexamples in anti-de Sitter spacetime, indicating a potential connection between WCCC and WGC. In this paper, we extend the study to the case of excited-state scalar fields, and numerically construct the static solutions of excited massive charged scalar fields coupled to the Einstein-Maxwell field in four dimensional spacetime with asymptotically anti-de Sitter boundary conditions. In the absence of scalar field, there is a class of counterexamples to cosmic censorship. However, after adding the scalar field with sufficiently large charge, the original counterexamples can be removed and cosmic censorship is preserved. We find this conclusion also applies to the excited-state of scalar field. There is a minimum value $$ {q}_c^{\textrm{bound}} $$ . When the charge of the excited scalar field is larger than this minimum value, for sufficiently large boundary electric amplitude $\textit{a}$, there will not appear a region with arbitrarily large curvature. That means there exists lower bound on the charge for excited state fields which protects cosmic censorship from being violated.

Si-Yuan Cui

Tie-Feng Fang

Yong-Qiang Wang

Weak cosmic censorship with excited scalar fields and bound on charge-to-mass ratio

In this paper, we construct a Dirac star model composed of $$|\kappa |$$ <math> <mrow> <mo>|</mo> <mi>κ</mi> <mo>|</mo> </mrow> </math> pairs of spinor fields. The azimuthal harmonic indices m of these spinor fields are half-integers, and they satisfy $$-(|\kappa |-\frac{1}{2})\le m \le |\kappa |-\frac{1}{2}$$ <math> <mrow> <mo>-</mo> <mrow> <mo>(</mo> <mo>|</mo> <mi>κ</mi> <mo>|</mo> </mrow> <mo>-</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <mrow> <mo>)</mo> <mo>≤</mo> <mi>m</mi> <mo>≤</mo> <mo>|</mo> <mi>κ</mi> <mo>|</mo> <mo>-</mo> </mrow> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </math> . When $$\kappa =1$$ <math> <mrow> <mi>κ</mi> <mo>=</mo> <mn>1</mn> </mrow> </math> , it corresponds to the conventional Dirac star model, formed by two spinor fields with $$m=\frac{1}{2}$$ <math> <mrow> <mi>m</mi> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </math> and $$m=-\frac{1}{2}$$ <math> <mrow> <mi>m</mi> <mo>=</mo> <mo>-</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </math> . When $$|\kappa |&gt;1$$ <math> <mrow> <mo>|</mo> <mi>κ</mi> <mo>|</mo> <mo>&gt;</mo> <mn>1</mn> </mrow> </math> , among these $$|\kappa |$$ <math> <mrow> <mo>|</mo> <mi>κ</mi> <mo>|</mo> </mrow> </math> pairs of spinor fields, there exist spinor fields with azimuthal harmonic indices $$m&gt;\frac{1}{2}$$ <math> <mrow> <mi>m</mi> <mo>&gt;</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </math> , and all spinor fields still conform to the same Dirac field equation. Different families of solutions are distinguished by the value of $$\kappa $$ <math> <mi>κ</mi> </math> , so we named these solutions $$\kappa $$ <math> <mi>κ</mi> </math> -Dirac stars. We obtain solutions for $$\kappa =\pm 1,\pm 2,\pm 3,\pm 4,\pm 5,\pm 6$$ <math> <mrow> <mi>κ</mi> <mo>=</mo> <mo>±</mo> <mn>1</mn> <mo>,</mo> <mo>±</mo> <mn>2</mn> <mo>,</mo> <mo>±</mo> <mn>3</mn> <mo>,</mo> <mo>±</mo> <mn>4</mn> <mo>,</mo> <mo>±</mo> <mn>5</mn> <mo>,</mo> <mo>±</mo> <mn>6</mn> </mrow> </math> by using numerical methods. Additionally, we compute their ADM mass M, Noether charge Q, and binding energy E, and illustrate how these quantities change with the spinor field’s frequency $$\omega $$ <math> <mi>ω</mi> </math> for different $$\kappa $$ <math> <mi>κ</mi> </math> . We observe significant differences between solutions for $$|\kappa |&gt;1$$ <math> <mrow> <mo>|</mo> <mi>κ</mi> <mo>|</mo> <mo>&gt;</mo> <mn>1</mn> </mrow> </math> and the $$|\kappa |=1$$ <math> <mrow> <mo>|</mo> <mi>κ</mi> <mo>|</mo> <mo>=</mo> <mn>1</mn> </mrow> </math> case. Furthermore, we provide the energy density distribution of the Dirac stars, wherein for $$|\kappa |&gt;1$$ <math> <mrow> <mo>|</mo> <mi>κ</mi> <mo>|</mo> <mo>&gt;</mo> <mn>1</mn> </mrow> </math> scenarios, the Dirac stars exhibit a spherical shell-like structure. Moreover, we employ three-dimensional diagrams to intuitively depict how $$\kappa $$ <math> <mi>κ</mi> </math> influences the combination of spinor fields to form a spherically symmetric configuration.

Shi-Xian Sun

Long-Xing Huang

$$\kappa $$ <math> <mi>κ</mi> </math> -Dirac stars

The spin-orbit splitting between neutron 1p orbitals at $^{33}$Si has been deduced using the single-neutron-adding (d,p) reaction in inverse kinematics with a beam of $^{32}$Si, a long-lived radioisotope. Reaction products were analyzed by the newly implemented SOLARIS spectrometer at the reaccelerated-beam facility at the National Superconducting Cyclotron Laboratory. The measurements show reasonable agreement with shell-model calculations that incorporate modern cross-shell interactions, but they contradict the prediction of proton density depletion based on relativistic mean-field theory. The evolution of the neutron 1p-shell orbitals is systematically studied using the present and existing data in the isotonic chains of <math><mi>N</mi><mo>=</mo><mn>17</mn></math>, 19, and 21. In each case, a smooth decrease in the separation of the <math><mn>1</mn><msub><mrow><mi>p</mi></mrow><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msub></math>-<math><mn>1</mn><msub><mrow><mi>p</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub></math> orbitals is seen as the respective p-orbitals approach zero binding, suggesting that the finite nuclear potential strongly influences the evolution of nuclear structure in this region.

United States

J. Chen

B.P. Kay

C.R. Hoffman

T.L. Tang

I.A. Tolstukhin

D. Bazin

R.S. Lubna

Spain

Y. Ayyad

S. Beceiro-Novo

Australia

B.J. Coombes

United Kingdom

CERN

S.J. Freeman

L.P. Gaffney

R. Garg

H. Jayatissa

A.N. Kuchera

P. MacGregor

A.J. Mitchell

W. Mittig

B. Monteagudo

A. Munoz-Ramos

C. Müller-Gatermann

Italy

F. Recchia

N. Rijal

C. Santamaria

M.Z. Serikow

D.K. Sharp

J. Smith

J.K. Stecenko

G.L. Wilson

A.H. Wuosmaa

C.X. Yuan

J.C. Zamora

Y.N. Zhang

Evolution of the nuclear spin-orbit splitting explored via the Si( , ) Si reaction using SOLARIS

We construct rotating hybrid axion-miniboson stars (RHABSs), which are asymptotically flat, stationary, axially symmetric solutions of (3+1)-dimensional Einstein–Klein–Gordon theory. RHABSs consist of an axion field (ground state) and a free complex scalar field (first excited state). The solutions of RHABSs have two types of nodes, including $$^1S^2S$$ <math> <mrow> <msup> <mrow></mrow> <mn>1</mn> </msup> <msup> <mi>S</mi> <mn>2</mn> </msup> <mi>S</mi> </mrow> </math> state and $$^1S^2P$$ <math> <mrow> <msup> <mrow></mrow> <mn>1</mn> </msup> <msup> <mi>S</mi> <mn>2</mn> </msup> <mi>P</mi> </mrow> </math> state. For different axion decay constants $$f_a$$ <math> <msub> <mi>f</mi> <mi>a</mi> </msub> </math> , we present the mass M of RHABSs as a function of the synchronized frequency, as well as the nonsynchronized frequency, and explore the mass M versus the angular momentum J for the synchronized frequency and the nonsynchronized frequency, respectively. Furthermore, we study the effect of axion decay constant $$f_a$$ <math> <msub> <mi>f</mi> <mi>a</mi> </msub> </math> and free scalar field mass $$\mu _f$$ <math> <msub> <mi>μ</mi> <mi>f</mi> </msub> </math> on the existence domain of the synchronized frequency $$\omega $$ <math> <mi>ω</mi> </math> .

Yan-Bo Zeng

Hong-Bo Li

Yu-Peng Zhang

Rotating hybrid axion-miniboson stars

We numerically construct the stationary solutions of SU(2) Einstein-Yang-Mills theory in four dimensional anti-de Sitter spacetime. When the t component of the SU(2) gauge field is taken to the only nonzero component, we construct a class of counterexamples to the weak cosmic censorship conjecture in Einstein-Maxwell theory. However, including a nonzero ϕ component of SU(2) gauge field, we can argue that there is a minimum value q  W , when the charge carried by the ϕ component is larger than this minimum value, for sufficiently large boundary electric amplitude a, the original counterexamples can be removed and cosmic censorship is preserved.

Yan Song

Weak cosmic censorship with SU(2) gauge field and bound on charge-to-mass ratio

We performed ab initio valence-space in-medium similarity renormalization group calculations based on chiral nucleon-nucleon and three-nucleon interactions to study the neutron-rich nuclei around <math><mi>N</mi><mo>=</mo><mn>28</mn></math>, where the experimental and theoretical evidence point to a rapid transition from spherical to rotational regimes. First, the rotational spectra of $^{40}$Mg, $^{42}$Si, and $^{44}$S are established theoretically, anchored by the calculated E2 transition strength. The results suggest that $^{40}$Mg and $^{42}$Si exhibit large deformations. After that, the erosion of the <math><mi>N</mi><mo>=</mo><mn>28</mn></math> shell closure, especially the evolutions of shape deformation and the emergence of shape coexistence, are discussed in <math><mi>N</mi><mo>=</mo><mn>28</mn></math> even-even isotones ranging from $^{40}$Mg to $^{48}$Ca. Finally, the shell evolution of <math><mi>N</mi><mo>=</mo><mn>28</mn></math> in Mg and Si chains is discussed based on the experimental and predicted excitation energies of low-lying states. The results from our ab initio calculations align well with available experimental data, furnishing essential insights into the structure of neutron-rich nuclei, particularly deformations in the vicinity of $^{40}$Mg and $^{42}$Si.

H.H. Li

Calculations for Well Deformed Nuclei: Mg and Si

Quasi-elastic (QEL) scattering measurements have been performed using a $^{28}$Si projectile off a $^{90}$Zr target at energies around the Coulomb barrier. A Bayesian analysis within the framework of coupled channels (CC) calculations is performed in a large parameter space of quadrupole and hexadecapole deformations (<math><msub><mrow><mi>β</mi></mrow><mrow><mn>2</mn></mrow></msub></math> and <math><msub><mrow><mi>β</mi></mrow><mrow><mn>4</mn></mrow></msub></math>) of $^{28}$Si. Our results unambiguously show that $^{28}$Si is an oblate shaped nucleus with <math><msub><mrow><mi>β</mi></mrow><mrow><mn>2</mn></mrow></msub></math>=-<math><mn>0.38</mn><mo>±</mo><mn>0.01</mn></math> which is in excellent agreement with results from electromagnetic probes. The sign and magnitude of quadrupole deformation along with a precise value of hexadecapole deformation (<math><msub><mrow><mi>β</mi></mrow><mrow><mn>4</mn></mrow></msub></math>=+<math><mn>0.03</mn><mo>±</mo><mn>0.01</mn></math>) of $^{28}$Si have been determined for the first time using QEL scattering. A remarkable agreement is obtained between the experimental and calculated <math><msub><mrow><mi>β</mi></mrow><mrow><mn>4</mn></mrow></msub></math> values of $^{28}$Si based on Skyrme-Hartree-Fock method. The present results demonstrate the strong sensitivity of the quasi-elastic scattering to the sign and magnitude to the ground state deformation parameters, thus affirming its suitability to be used for rare exotic nuclei using low intensity RIBs.

India

Y.K. Gupta

V.B. Katariya

G.K. Prajapati

K. Hagino

D. Patel

V. Ranga

U. Garg

L.S. Danu

A. Pal

B.N. Joshi

S. Dubey

V.V. Desai

S. Panwar

N. Kumar

S. Mukhopadhyay

Pawan Singh

N. Sirswal

R. Sariyal

I. Mazumdar

B.V. John

Precise determination of quadrupole and hexadecapole deformation parameters of the -shell Nucleus, Si