## 2022 Vol. 46, No. 7

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2022, 46(7): 071001. doi: 10.1088/1674-1137/ac5fa2
Abstract:
By analyzing existing data on pseudoscalar charmonium decays, we obtain the ratio of the branching fractions of \begin{document}$\eta_c(2S)$\end{document} and \begin{document}$\eta_c$\end{document} decays into ten different final states with light hadrons. For the first time, we test the two existing theoretical predictions of these decays and find that the experimental data are significantly different from both of them. The lack of observation of any decay mode with higher rate in \begin{document}$\eta_c(2S)$\end{document} than in \begin{document}$\eta_c$\end{document} decays suggests very unusual decay dynamics in pseudoscalar charmonium decays to be identified. We also report the first model-independent evaluation of the partial width of \begin{document}$\eta_c(2S)\to \gamma\gamma$\end{document} (\begin{document}$2.21_{-0.64}^{+0.88}$\end{document} keV) and improve determination of that of \begin{document}$\eta_c\to \gamma\gamma$\end{document} (\begin{document}$5.43_{-0.38}^{+0.41}$\end{document} keV). The latter shows a tension with the most recent lattice QCD calculation.
2022, 46(7): 073101. doi: 10.1088/1674-1137/ac5c2d
Abstract:
According to gauge/gravity duality, we use an Einstein-Maxwell-dilaton (EMD) model to study the running coupling constant at finite chemical potential and magnetic field. First, we calculate the effect of temperature on the running coupling constant and find the results are qualitatively consistent with lattice guage theory. Subsequently, we calculate the effect of chemical potential and magnetic field on running coupling. It is found that the chemical potential and magnetic field both suppress the running coupling constant. However, the effect of the magnetic field is slightly larger than that of chemical potential for a fixed temperature. Compared with the confinement phase, the magnetic field has a large influence on the running coupling in the deconfinement phase.
2022, 46(7): 073102. doi: 10.1088/1674-1137/ac5db9
Abstract:
Using gauge/gravity duality, we investigate the string breaking and dissolution of two heavy quarks coupled to a light quark at finite temperature. It is found that three configurations of QQq exist with the increase in separation distance for heavy quarks in the confined phase. Furthermore, string breaking occurs at the distance \begin{document}$L_{QQq} = 1.27\; {\rm{fm}}$\end{document} (\begin{document}$T = 0.1\; {\rm{GeV}}$\end{document}) for the decay mode \begin{document}${Q Q q} \rightarrow {Q q q+Q \bar{q}}$\end{document}. In the deconfined phase, QQq melts at a certain distance and then becomes free quarks. Finally, we compare the potential of QQq with that of \begin{document}${Q\bar{Q}}$\end{document}, and it is found that \begin{document}${Q\bar{Q}}$\end{document} is more stable than QQq at high temperatures.
2022, 46(7): 073104. doi: 10.1088/1674-1137/ac5f9c
Abstract:
Based on the recent precise measurements by the BESIII collaboration for electron–positron annihilation into a neutron and antineutron pair, the effective form factors of the neutron were determined in the time-like region, and it was found that the effective form factors of the neutron are smaller than those of the proton. The effective form factors of the neutron show a periodic behaviour, similar to those of the proton. Here, a comparative analysis for Λ, \begin{document}$\Sigma^0$\end{document} and \begin{document}$\Xi^0$\end{document} hyperons is performed. Fits of the available data on the effective form factors of Λ, \begin{document}$\Sigma^0$\end{document} and \begin{document}$\Xi^0$\end{document} with zero charge show an interesting phenomenon in the oscillating behavior of their effective form factors. However, this will need to be confirmed by future precise experiments. Both theoretical and experimental investigations of this phenomenon can shed light on the reaction mechanisms of the electron–positron annihilation processes.
2022, 46(7): 073105. doi: 10.1088/1674-1137/ac600b
Abstract:
The two-body weak decays \begin{document}$\bar B \to \pi D$\end{document}/\begin{document}$\bar B \to \rho D$\end{document} and \begin{document}$\bar B \to \pi {D^*}$\end{document} are examined using isospin analysis to study nonfactorizable contributions. After determining strong interaction phases and obtaining factorizable contributions from spectator-quark diagrams for Nc=3, we determine nonfactorizable isospin amplitudes from the experimental data for these modes. Our results support the universality of the ratio of nonfactorizable isospin reduced amplitudes for these decays within experimental errors. To demonstrate that these systematics are not coincidental, we also plot our results w. r. t. this ratio.
2022, 46(7): 073106. doi: 10.1088/1674-1137/ac600c
Abstract:
In this study, we perform systematic estimations of the radiative decays of the charmed mesons in a modified relativistic quark model. Our estimations indicate that the branching ratios of the processes of \begin{document}$D_2^0(1^3P_2) \to D^{\ast 0}(1^3S_1) \gamma$\end{document}, \begin{document}$D_3^0(1D_3) \to D_2^0(1^3P_2) \gamma$\end{document}, \begin{document}$D_2^0(2D_2^\prime) \to D_1^{0}(2P_1) \gamma$\end{document}, \begin{document}$D_3^0(2^3D_3) \to D_2^0(2^3P_2) \gamma$\end{document}, and \begin{document}$D^{\ast 0}(1^3S_1) \to$\end{document}\begin{document}$D^0(1^1S_0) \gamma$\end{document} are of the order of \begin{document}$10^{-2}$\end{document}, which are sizable to be detected experimentally. Moreover, the branching ratios of some channels, for example, \begin{document}$D_1^0(1P_1) \to D(1^1S_0)^0 \gamma$\end{document}, \begin{document}$D^0(3^1S_0) \to D_1^{\prime 0}(2P^\prime_{1}) \gamma$\end{document}, and \begin{document}$D^0(3^3S_1) \to D_2^0(2^3P_2) \gamma$\end{document}, are estimated to be of the order of \begin{document}$10^{-3}$\end{document}, which may be accessible with the accumulation of data in future experiments.
2022, 46(7): 073107. doi: 10.1088/1674-1137/ac62ca
Abstract:
The stellar energy loss rates due to the production of neutrino pairs \begin{document}$e^+e^- \rightarrow (W, Z, \gamma) \rightarrow \nu_e \overline{\nu_e}$\end{document} are calculated using the minimal extension of the Standard Model with the electromagnetic properties of the Dirac neutrinos, which takes the contributions of the neutrino charge radius, anapole moment, and dipole moments into account. We show that the contribution of the electron neutrino's dipole moment is small compared with that of the charge radius. The obtained results are also compared with the results obtained using the Standard Model.
2022, 46(7): 074001. doi: 10.1088/1674-1137/ac5c2e
Abstract:
Using inclusive decays of \begin{document}$J/\psi$\end{document}, a precise determination of the number of \begin{document}$J/\psi$\end{document} events collected with the BESIII detector was performed. For the two data sets taken in 2009 and 2012, the numbers of \begin{document}$J/\psi$\end{document} events were recalculated to be \begin{document}$(224.0 \pm 1.3)\times10^6$\end{document} and \begin{document}$(1088.5 \pm 4.4)\times10^6$\end{document}, respectively; these numbers are in good agreement with the previous measurements. For the \begin{document}$J/\psi$\end{document} sample taken in 2017–2019, the number of events was determined to be \begin{document}$(8774.0 \pm 39.4)\times10^{6}$\end{document}. The total number of \begin{document}$J/\psi$\end{document} events collected with the BESIII detector was determined to be \begin{document}$(10087 \pm 44)\times10^{6}$\end{document}, where the uncertainty is dominated by systematic effects, and the statistical uncertainty is negligible.
2022, 46(7): 073103. doi: 10.1088/1674-1137/ac5f9d
Abstract:
The entropy per rapidity \begin{document}${\rm d} S/{\rm d} y$\end{document} produced in central Pb-Pb ultra-relativistic nuclear collisions at LHC energies is calculated using experimentally identified particle spectra and source radii estimated from Hanbury Brown-Twiss (HBT) correlations for particles π, k, p, Λ, Ω, and \begin{document}$\bar{\Sigma}$\end{document} and π, k, p, Λ, and \begin{document}$K_s^0$\end{document} at \begin{document}$\sqrt{s} =2.76$\end{document} and \begin{document}$5.02$\end{document} TeV, respectively. An artificial neural network (ANN) simulation model is used to estimate the entropy per rapidity \begin{document}${\rm d} S/{\rm d} y$\end{document} at the considered energies. The simulation results are compared with equivalent experimental data, and a good agreement is achieved. A mathematical equation describing the experimental data is obtained. Extrapolation of the transverse momentum spectra at \begin{document}$p_{\rm T} =0$\end{document} is required to calculate \begin{document}${\rm d} S/{\rm d} y$\end{document}; thus, we use two different fitting functions, the Tsallis distribution and hadron resonance gas (HRG) model. The success of the ANN model in describing the experimental measurements leads to the prediction of several spectra values for the mentioned particles, which may lead to further predictions in the absence of experiments.
2022, 46(7): 074002. doi: 10.1088/1674-1137/ac5e93
Abstract:
Polarization transfer measurement plays an important role in the search for new physics processes in charmed baryon decays. The measurement of the \begin{document}${\Lambda_c^+}\to {pK^-\pi^+}$\end{document} decay is suggested as a spin polarimeter. A general description of the decay is developed using Euler angles, and the polarization parameters are derived. Its relationship with parity violation is found using the phenomenological amplitude model. A Monte-Carlo simulation is performed, and the results show that charmed baryon polarization is well determined using a set of Monte-Carlo events with selected asymmetry parameters. The experimental measurement of these asymmetry parameters is suggested.
2022, 46(7): 074101. doi: 10.1088/1674-1137/ac5cb0
Abstract:
The interacting boson model with \begin{document}$S U(3)$\end{document} higher-order interactions offers a new route to enhance our understanding on γ-soft rotation. In this paper, \begin{document}$U(5)$\end{document}-like and \begin{document}$O(6)$\end{document}-like new γ-softness are observed, in which the corresponding energy levels in the ground and quasi-γ bands can be exactly degenerate and have a partial \begin{document}$O(5)$\end{document} dynamical symmetry. The spherical-like γ-softness is not related to the classical \begin{document}$O(6)$\end{document} dynamical symmetry. The transitional behaviors of \begin{document}$B(E2)$\end{document} values of the low-lying levels and quadrupole moment of the \begin{document}$2^{+}_{1}$\end{document} state are also discussed. Spherical-like γ-softness can be used to explain the low-lying spectra and \begin{document}$B(E2)$\end{document} values in 110Cd normal states.
2022, 46(7): 074102. doi: 10.1088/1674-1137/ac5d29
Abstract:
Excited states in low-energy spectra of \begin{document}$^{70-76}$\end{document}Ni are considered. Accordingly, pairing forces in the form of surface delta interaction are employed to account for the formation of the ground state multiplet with seniority \begin{document}$\nu = 2$\end{document} states. The multiplet splitting is described with mass relationships of masses of neighboring nuclei. Subsequently, the seniority model is adopted to reproduce or predict the states \begin{document}$\nu = 3$\end{document} in odd-even isotopes and \begin{document}$\nu = 4$\end{document} in even-even isotopes. The correct account of the \begin{document}$2_1^+$\end{document} state should allow for the description of the reversed order of \begin{document}$J = 4$\end{document} states with \begin{document}$\nu = 2$\end{document} and \begin{document}$\nu = 4$\end{document} observed in experiments. The results obtained are compared with the structure of similar multiplets in \begin{document}$N=50$\end{document} isotones.
2022, 46(7): 074103. doi: 10.1088/1674-1137/ac5db8
Abstract:
Understanding the gluonic structure in nuclei is one of the most important goals in modern nuclear physics, for which J/ψ photoproduction is suggested as a powerful tool to probe the gluon density distribution. The experimental investigation of the photoproduction process is conventionally studied in ultra-peripheral heavy-ion collisions, and has recently been extended to hadronic collisions. However, theoretical efforts in hadronic heavy-ion collisions are still lacking in the literature. In this paper, we build up a phenomenological framework to calculate the differential momentum transfer spectra for J/ψ photoproduction in hadronic heavy-ion collisions based on a vector meson dominance model. For the first time, we include the effect of internal photon radiation in the calculations, and we find that the results with internal photon radiation could describe the experimental measurements from STAR very well.
2022, 46(7): 074104. doi: 10.1088/1674-1137/ac5efb
Abstract:
Machine learning models are constructed to predict fragment production cross sections in projectile fragmentation (PF) reactions using Bayesian neural network (BNN) techniques. The massive learning for BNN models is based on 6393 fragments from 53 measured projectile fragmentation reactions. A direct BNN model and physical guiding BNN via FRACS parametrization (BNN + FRACS) model have been constructed to predict the fragment cross section in projectile fragmentation reactions. It is verified that the BNN and BNN + FRACS models can reproduce a wide range of fragment productions in PF reactions with incident energies from 40 MeV/u to 1 GeV/u, reaction systems with projectile nuclei from 40Ar to 208Pb, and various target nuclei. The high precision of the BNN and BNN + FRACS models makes them applicable for the low production rate of extremely rare isotopes in future PF reactions with large projectile nucleus asymmetry in the new generation of radioactive nuclear beam factories.
2022, 46(7): 074105. doi: 10.1088/1674-1137/ac6154
Abstract:
The kernel ridge regression (KRR) method with a Gaussian kernel is used to improve the description of the nuclear charge radius by several phenomenological formulae. The widely used \begin{document}$A^{1/3}$\end{document}, \begin{document}$N^{1/3}$\end{document} and \begin{document}$Z^{1/3}$\end{document} formulae, and their improved versions including isospin dependence, are adopted as examples. The parameters in these six formulae are refitted using the Levenberg–Marquardt method, which give better results than the previous versions. The radius for each nucleus is predicted with the KRR network, which is trained with the deviations between experimental and calculated nuclear charge radii. For each formula, the resultant root-mean-square deviations of 884 nuclei with proton number \begin{document}$Z \geq 8$\end{document} and neutron number \begin{document}$N \geq 8$\end{document} can be reduced to about 0.017 fm after considering the modification by the KRR method. The extrapolation ability of the KRR method for the neutron-rich region is examined carefully and compared with the radial basis function method. It is found that the improved nuclear charge radius formulae using the KRR method can avoid the risk of overfitting, and have a good extrapolation ability. The influence of the ridge penalty term on the extrapolation ability of the KRR method is also discussed. Finally, the nuclear charge radii of several recently observed K and Ca isotopes are analyzed.
2022, 46(7): 074106. doi: 10.1088/1674-1137/ac6153
Abstract:
In this study, shape evolution and possible shape coexistence are explored in odd-A Ne isotopes in the framework of the multidimensionally constrained relativistic-mean-field (MDC-RMF) model. By introducing \begin{document}$s_\Lambda$\end{document} and \begin{document}$p_{\Lambda}$\end{document} hyperons, the impurity effects on the nuclear shape, energy, size, and density distribution are investigated. For the \begin{document}$NN$\end{document} interaction, the PK1 parameter set is adopted, and for the \begin{document}$\Lambda N$\end{document} interaction, the PK1-Y1 parameter set is used. The nuclear ground state and low-lying excited states are determined by blocking the unpaired odd neutron in different orbitals around the Fermi surface. Moreover, the potential energy curves (PECs), quadrupole deformations, nuclear r.m.s. radii, binding energies, and density distributions for the core nuclei as well as the corresponding hypernuclei are analyzed. By examining the PECs, possibilities for shape coexistence in \begin{document}$^{27,29}$\end{document}Ne and a triple shape coexistence in 31Ne are found. In terms of the impurity effects of Λ hyperons, as noted for even-even Ne hypernuclear isotopes, the \begin{document}$s_{\Lambda}$\end{document} hyperon exhibits a clear shrinkage effect, which reduces the nuclear size and results in a more spherical nuclear shape. The \begin{document}$p_{\Lambda}$\end{document} hyperon occupying the \begin{document}$1/2^-[110]$\end{document} orbital is prolate, which causes the nuclear shape to be more prolate, and the \begin{document}$p_{\Lambda}$\end{document} hyperon occupying the \begin{document}$3/2^-[101]$\end{document} orbital displays an oblate shape, which drives the nuclei to be more oblate.
2022, 46(7): 074107. doi: 10.1088/1674-1137/ac6248
Abstract:
The chirality in thallium isotopes is investigated using the adiabatic and configuration-fixed constrained triaxial relativistic mean field theory. Several minima with prominent triaxial deformation and proper configuration, where the chiral doublet bands may appear, are obtained in odd-odd nuclei \begin{document}$^{192,194,196,198}$\end{document}Tl and odd-mass nuclei \begin{document}$^{193,195,197}$\end{document}Tl. Furthermore, the possible existence of multiple chiral doublet bands (MχD) is demonstrated in \begin{document}$^{192,193,194,195,196,197,198}$\end{document}Tl. As the chiral doublet bands in \begin{document}$^{193,194,198}$\end{document}Tl and MχD in 195Tl have been observed experimentally, further experimental exploration for the chirality in \begin{document}$^{192,196,197}$\end{document}Tl and MχD in thallium isotopes is expected to verify the predictions.
2022, 46(7): 074108. doi: 10.1088/1674-1137/ac6249
Abstract:
The spallation of 238U is an important way to produce rare isotopes. This work aims at studying the cross sections of isotopes produced in 238U + p, d and 9Be reactions at 1 A GeV and their target dependence. (1) A physical model dependent (Bayesian neural network) BNN, which includes the details of IQMD-GEMINI++ model and BNN, was developed for a more accurate evaluation of production cross sections. The isospin-dependent quantum molecular dynamics (IQMD) model is used to study the non-equilibrium thermalization of the 238U nuclei and fragmentation of the hot system. The subsequent decay of the pre-fragments is simulated by the GEMINI++ model. The BNN algorithm is used to improve the prediction accuracy after learning the residual error between experimental data and calculations by the IQMD-GEMINI++ model. It is shown that the IQMD-GEMINI++ model can reproduce the available experimental data (3282 points) within 1.5 orders of magnitude. After being fine tuned by the BNN algorithm, the deviation between calculations and experimental data were reduced to within 0.4 order of magnitude. (2) Based on the predictions by the IQMD-GEMINI++-BNN framework, the target dependence of isotopic cross sections was studied. The cross sections to produce the rare isotopes by the 238U + p, d and 9Be reactions at 1 A GeV are compared. For the generation of neutron-rich fission products, the cross sections for the 238U + 9Be are the largest. For the generation of neutron-deficient nuclei in the region of A = 200–220, the cross sections for 238U + p reaction are the largest. Considering the largest cross sections and the atomic density, the beryllium target is recommended to produce the neutron-rich fission products by the 238U beam at 1 A GeV, while the liquid-hydrogen target is suggested to produce the neutron-deficient nuclei in the region of A = 200–220.
2022, 46(7): 074109. doi: 10.1088/1674-1137/ac6357
Abstract:
We present the hypernuclear states of \begin{document}$^{37}_{\; {\Lambda}}$\end{document}Ar obtained using the Skyrme-Hartree-Fock (SHF) model and a beyond-mean-field approach, including angular momentum projection (AMP) and the generator coordinate method (GCM). A comprehensive energy spectrum is given, which includes normally deformed (ND) and super deformed (SD) hypernuclear states with positive or negative parities. Energy levels corresponding to the configurations in which a \begin{document}${\Lambda}$\end{document} hyperon occupies the s-, p-, or sd-shell orbitals are discussed. For the s-shell \begin{document}${\Lambda}$\end{document}, we pay special attention to the ND and SD states corresponding to the configurations \begin{document}$^{36}$\end{document}Ar\begin{document}$^{{\rm{N}}} \otimes$\end{document} s\begin{document}$_{\Lambda}$\end{document} and \begin{document}$^{36}$\end{document}Ar\begin{document}$^{{\rm{S}}} \otimes$\end{document} s\begin{document}$_{\Lambda}$\end{document}, where \begin{document}$^{36}$\end{document}Ar\begin{document}$^{{\rm{N}}}$\end{document} and \begin{document}$^{36}$\end{document}Ar\begin{document}$^{{\rm{S}}}$\end{document} denote the ND and SD nuclear cores, respectively. The disagreements between different models over the \begin{document}${\Lambda}$\end{document} separation energy of the SD state in previous studies are revisited. For the p-shell \begin{document}${\Lambda}$\end{document}, four rotational bands are predicted, and the impurity effects are shown. Furthermore, two energy levels corresponding to the configurations \begin{document}$^{36}$\end{document}Ar\begin{document}$^{{\rm{S}}} \otimes {\Lambda}$\end{document}[101]\begin{document}$\frac{3}{2}^{-}$\end{document} and \begin{document}$^{36}$\end{document}Ar\begin{document}$^{{\rm{S}}} \otimes {\Lambda}$\end{document}[101]\begin{document}$\frac{1}{2}^{-}$\end{document} are obtained below the separation threshold of \begin{document}$^{36}$\end{document}Ar+\begin{document}${\Lambda}$\end{document} within 0.5 MeV. For the sd-shell \begin{document}${\Lambda}$\end{document}, three bound states are found near the separation threshold, and the mechanism behind these states are discussed.
2022, 46(7): 074110. doi: 10.1088/1674-1137/ac6490
Abstract:
In this study, Au+Au collisions with an impact parameter of \begin{document}$0 \leq b \leq 12.5$\end{document} fm at \begin{document}$\sqrt{s_{NN}} = 200$\end{document} GeV are simulated using the AMPT model to provide preliminary final-state information. After transforming this information into appropriate input data (the energy spectra of final-state charged hadrons), we construct a multi-layer perceptron (MLP) and convolutional neural network (CNN) to connect final-state observables with the impact parameters. The results show that both the MLP and CNN can reconstruct the impact parameters with a mean absolute error approximately \begin{document}$0.4$\end{document} fm, although the CNN behaves slightly better. Subsequently, we test the neural networks at different beam energies and pseudorapidity ranges in this task. These two models work well at both low and high energies. However, when conducting a test for a larger pseudorapidity window, the CNN exhibits a higher prediction accuracy than the MLP. Using the Grad-CAM method, we shed light on the 'attention' mechanism of the CNN model.
2022, 46(7): 075101. doi: 10.1088/1674-1137/ac5d2a
Abstract:
We investigate the gravitational wave spectrum originating from the cosmological first-order phase transition. We compare two models: one is a scalar field model without gravitation, while the other is a scalar field model with gravitation. Based on the sensitivity curves of the LISA space-based interferometer on the stochastic gravitational-wave background, we compare the difference between the gravitational wave spectra of the former and the latter cases obtained from the bubble collision process. In particular, we numerically calculate the speed of the bubble wall before collision for the two models. We demonstrate that the difference between the amplitudes of these spectra can clearly distinguish between the two models. We expect that the LISA with Signal to Noise Ratio = 10 could observe the spectrum as the fast first-order phase transition.
2022, 46(7): 075102. doi: 10.1088/1674-1137/ac5e92
Abstract:
The application of fast radio bursts (FRBs) as probes for investigating astrophysics and cosmology requires proper modelling of the dispersion measures of the Milky Way (\begin{document}$DM_{\rm MW}$\end{document}) and host galaxy (\begin{document}$DM_{\rm host}$\end{document}). \begin{document}$DM_{\rm MW}$\end{document} can be estimated using the Milky Way electron models, such as the NE2001 model and YMW16 model. However, \begin{document}$DM_{\rm host}$\end{document} is hard to model due to limited information on the local environment of the FRBs. In this study, using 17 well-localized FRBs, we search for possible correlations between \begin{document}$DM_{\rm host}$\end{document} and the properties of the host galaxies, such as the redshift, stellar mass, star-formation rate, age of galaxy, offset of the FRB site from the galactic center, and half-light radius. We find no strong correlation between \begin{document}$DM_{\rm host}$\end{document} and any of the host properties. Assuming that \begin{document}$DM_{\rm host}$\end{document} is a constant for all host galaxies, we constrain the fraction of the baryon mass in the intergalactic medium today to be \begin{document}$f_{\rm IGM,0}=0.78_{-0.19}^{+0.15}$\end{document}. If we model \begin{document}$DM_{\rm host}$\end{document} as a log-normal distribution, however, we obtain a larger value, \begin{document}$f_{\rm IGM,0}= 0.83_{-0.17}^{+0.12}$\end{document}. Based on the limited number of FRBs, no strong evidence for a redshift evolution of \begin{document}$f_{\rm IGM}$\end{document} is found.
2022, 46(7): 075103. doi: 10.1088/1674-1137/ac624a
Abstract:
The shadow and observation intensity of a black hole surrounded by a thin spherical accretion in the Randall–Sundrum brane world model are investigated. The bulk metric depends on the tidal charge parameter, q, and deformation parameter, C. It reduces to the metric that possesses similar form with the Reissner–Nordström metric if \begin{document}$C=0$\end{document}. It is shown that the radius of the photon sphere of this black hole depends only on the tidal charge parameter. The radius of the photon sphere decreases with higher q. The observation intensity is mainly influenced by the tidal charge parameter, q, and the deformation parameter, C, is of secondary importance. In the optical observation, the black holes appear brighter with higher q or lower C.
2022, 46(7): 079001. doi: 10.1088/1674-1137/ac5e26
Abstract:
Experimentally measured neutron activation cross sections are presented for the \begin{document}$^{65}$\end{document}Cu(n, α)\begin{document}$^{62m}$\end{document}Cu, \begin{document}$^{41}$\end{document}K(n, α)\begin{document}$^{38}$\end{document}Cl, and \begin{document}$^{65}$\end{document}Cu(n,2n)\begin{document}$^{64}$\end{document}Cu reactions with detailed uncertainty propagation. The neutron cross sections were measured at an incident energy of 14.92 \begin{document}$\pm$\end{document} 0.02 MeV, and the neutrons were based on the t(d, n)α fusion reaction. The \begin{document}$^{27}$\end{document}Al(n, α)\begin{document}$^{24}$\end{document}Na reaction was used as a reference reaction for the normalization of the neutron flux. The pre-calibrated lead-shielded HPGe detector was used to detect the residues' γ-ray spectra. The data from the measured cross sections are compared to the previously measured cross sections from the EXFOR database, theoretically calculated cross sections using the TALYS and EMPIRE codes, and evaluated nuclear data.