Chinese Physics C

Initial years’ neutron-induced cross-section measurements at the CSNS Back-n white neutron source

Jingyu Tang, Rong Liu, Guohui Zhang, Xichao Ruan, Xiaoguang Wu, Qi An, Jiangbo Bai, Jie Bao, Yu Bao, Ping Cao, Haolei Chen, Qiping Chen, Yonghao Chen, Zhen Chen, Zengqi Cui, Ruirui Fan, Changqing Feng, Lin Gan, Keqing Gao, Xiaolong Gao, Minhao Gu, Changcai Han, Zijie Han, Guozhu He, Yongcheng He, Yang Hong, Yiwei Hu, Hanxiong Huang, Xiru Huang, Haoyu Jiang, Wei Jiang, Zhijie Jiang, Hantao Jing, Ling Kang, Bo Li, Chao Li, Jiawen Li, Qiang Li, Xiao Li, Yang Li, Jie Liu, Minliang Liu, Shubin Liu, Xingyan Liu, Ze Long, Guangyuan Luan, Changjun Ning, Mengchen Niu, Binbin Qi, Jie Ren, Zhizhou Ren, Zhaohui Song, Kang Sun, Zhijia Sun, Zhixin Tan, Xinyi Tang, Binbin Tian, Lijiao Wang, Pengcheng Wang, Zhaohui Wang, Jie Wen, Zhongwei Wen, Xuan Wu, Likun Xie, Xiaoyun Yang, Yiwei Yang, Han Yi, Li Yu, Tao Yu, Yongji Yu, Linhao Zhang, Qiwei Zhang, Xianpeng Zhang, Yuliang Zhang, Zhiyong Zhang, Luping Zhou, Zhihao Zhou, Kejun Zhu, (The Back-n Collaboration)

2021, 45(6): 062001. doi: 10.1088/1674-1137/abf138

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Abstract:
The Back-n white neutron source (known as Back-n) is based on back-streaming neutrons from the spallation target at the China Spallation Neutron Source (CSNS). With its excellent beam properties, e.g., a neutron flux of approximately 1.8×10⁷ n/cm²/s at 55 m from the spallation target, energy range spanning from 0.5 eV to 200 MeV, and time-of-flight resolution of a few per thousand, along with the equipped physical spectrometers, Back-n is considered to be among the best facilities in the world for carrying out nuclear data measurements. Since its completion and commencement of operation in May 2018, five types of cross-section measurements concerning neutron capture cross-sections, fission cross-sections, total cross-sections, light charged particle emissions, in-beam gamma spectra, and more than forty nuclides have been measured. This article presents an overview of the experimental setup and result analysis on the neutron-induced cross-section measurements and gamma spectroscopy at Back-n in the initial years.

Interpretation of the Galactic gamma-ray excess with the dark matter indicated by ⁸Be and ⁴He anomalous transitions

Lian-Bao Jia, Tong Li

2021, 45(6): 063101. doi: 10.1088/1674-1137/abeda6

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The long-standing Galactic center gamma-ray excess could be explained by GeV dark matter (DM) annihilation, but the DM interpretation seems to conflict with recent joint limits from different astronomical scale observations such as dwarf spheroidal galaxies, the Milky Way halo, and galaxy groups/clusters. Motivated by ⁸Be and ⁴He anomalous transitions with possible new interactions mediated by a vector boson X, we consider a small fraction of DM mainly annihilating into a pair of on-shell vector bosons

\begin{document}$X X$\end{document}

followed by

\begin{document}$X \to e^+ e^-$\end{document}

in this paper. The Galactic center gamma-ray excess is explained by this DM cascade annihilation. The gamma rays are mainly from inverse Compton scattering emission, and the DM cascade annihilation could be compatible with joint astrophysical limits and meanwhile be allowed by AMS-02 positron observation. The direct detection of this model is also discussed.

Molecular picture for X₀(2900) and X₁(2900)

Jun He, Dian-Yong Chen

2021, 45(6): 063102. doi: 10.1088/1674-1137/abeda8

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Inspired by the newly observed

\begin{document}$X_{0}(2900)$\end{document}

and

\begin{document}$X_1(2900)$\end{document}

states at LHCb, the

\begin{document}$K^*\bar{D}^*$\end{document}

and

\begin{document}$K\bar{D}_1$\end{document}

interactions are studied in the quasipotential Bethe-Salpeter equation approach combined with the one-boson-exchange model. The bound and virtual states from the interactions are searched for as poles in the complex energy plane of scattering amplitude. A bound state with

\begin{document}$I(J^P)=0(0^+)$\end{document}

and a virtual state with

\begin{document}$0(1^-)$\end{document}

are produced from the

\begin{document}$K^*\bar{D}^*$\end{document}

interaction and

\begin{document}$K\bar{D}_1$\end{document}

interaction, and can be related to the

\begin{document}$X_{0}(2900)$\end{document}

and

\begin{document}$X_1(2900)$\end{document}

observed at LHCb, respectively. A bound state with

\begin{document}$I(J^P)=0(1^+)$\end{document}

and a virtual state with

\begin{document}$I(J^P)=0(2^+)$\end{document}

are also predicted from the

\begin{document}$K^*\bar{D}^*$\end{document}

interaction, with the same

\begin{document}$\alpha$\end{document}

value, to reproduce the

\begin{document}$X_{0,1}(2900)$\end{document}

, which can be searched for in future experiments.

A novel method to test particle ordering and final state alignment in helicity formalism

Mengzhen Wang, Yi Jiang, Yinrui Liu, Wenbin Qian, Xiao-Rui Lyu, Liming Zhang

2021, 45(6): 063103. doi: 10.1088/1674-1137/abf139

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Abstract:
In this study, the non-trival effect of the selection of reference particles for decay angle definitions is demonstrated when constructing the partial-wave amplitude of multi-body decays using helicity formalism. This issue is often ignored in the standard use case of helicity formalism. A new technique is proposed to test the selection of the particle ordering, and it can also be used as a generalized method to calculate the rotation operators that are used for the final-state alignment between different decay chains. Moreover, numerical validations are performed to support the arguments and to verify the effectiveness of the proposed technique.

Hadronic coupling constants of the lowest hidden-charm pentaquark state, using QCD sum rules with rigorous quark-hadron duality

Zhigang Wang, Huijuan Wang, Qi Xin

2021, 45(6): 063104. doi: 10.1088/1674-1137/abf13b

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Abstract:
In this article, we illustrate how to calculate the hadronic coupling constants of the pentaquark states with QCD sum rules based on rigorous quark-hadron quality. We then study the hadronic coupling constants of the lowest diquark-diquark-antiquark type hidden-charm pentaquark state with spin-parity

\begin{document}$ J^P = {\dfrac{1}{2}}^- $\end{document}

in detail, and calculate the partial decay widths. The total width

\begin{document}$ \Gamma(P_c) = 14.32\pm3.31\;\rm{MeV} $\end{document}

is compatible with the experimental value

\begin{document}$ \Gamma_{P_c(4312)} = 9.8\pm2.7^{+ 3.7}_{- 4.5} \; \rm{ MeV} $\end{document}

from the LHCb collaboration, and favors assigning the

\begin{document}$ P_c(4312) $\end{document}

to be the

\begin{document}$ [ud][uc]\bar{c} $\end{document}

pentaquark state with

\begin{document}$ J^P = {\dfrac{1}{2}}^- $\end{document}

. The hadronic coupling constants have the relation

\begin{document}$ |G_{PD^-\Sigma_c^{++}}| = \sqrt{2}|G_{P\bar{D}^0\Sigma_c^+}|\gg $\end{document}

\begin{document}$ |G_{P\bar{D}^0\Lambda_c^+}| $\end{document}

, and favor the hadronic dressing mechanism. The

\begin{document}$ P_c(4312) $\end{document}

may have a diquark-diquark-antiquark type pentaquark core with the typical size of the

\begin{document}$ qqq $\end{document}

-type baryon states. The strong couplings to the meson-baryon pairs

\begin{document}$ \bar{D}\Sigma_c $\end{document}

lead to some pentaquark molecule components, and the

\begin{document}$ P_c(4312) $\end{document}

may spend a rather large time as the

\begin{document}$ \bar{D}\Sigma_c $\end{document}

molecular state.

Importance of heavy quark longitudinal structure function measurements at future circular collider energies

G. R. Boroun

2021, 45(6): 063105. doi: 10.1088/1674-1137/abf1de

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In this article, we consider the ratio of structure functions for heavy quark pair production at low values of

\begin{document}$ x $\end{document}

. The importance of this ratio for charm and beauty pair production is examined according to the Hadron Electron Ring Accelerator (HERA) data. The behavior of these ratios is considered due to the hard pomeron behavior of the gluon distribution function. The results are in good agreement with the HERA data. Expanding this data to the range of new energies underscores the importance of these measurements for heavy quarks. The ratio of charm and beauty structure functions at the proposed Large Hadron electron Collider (LHeC) is considered as a function of invariant center-of-mass energy. For top pair production this ratio is extracted with known kinematics of the LHeC and Future Circular Collider electron-hadron (FCC-eh) colliders. Comparison of the results obtained for the ratio of top structure functions in LHeC and FCC-eh are proportional to the specified inelasticity

\begin{document}$ y $\end{document}

range.

NNLO QCD predictions of electron charge asymmetry for inclusive pp → W + X production in forward region at 13 and 14 TeV

Kadir Ocalan

2021, 45(6): 063106. doi: 10.1088/1674-1137/abf488

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This paper presents perturbative QCD predictions of the electron charge asymmetry for inclusive

\begin{document}$ W^{\pm}+X \rightarrow e^{\pm} \nu +X $\end{document}

production in proton-proton (pp) collisions. Perturbative QCD calculations are performed at next-to-next-to-leading order (NNLO) accuracy using different parton distribution function (PDF) models at 8, 13, and 14 TeV center-of-mass energies of CERN LHC pp collisions. NNLO calculations are performed for electrons with transverse momenta above 20 GeV in the forward electron pseudorapidity region

\begin{document}$ 2.0 \leqslant \eta_{e} \leqslant 4.25 $\end{document}

. NNLO predictions are first compared at 8 TeV with the measurements of the LHCb experiment at the LHC for the

\begin{document}$ W^{+} $\end{document}

/

\begin{document}$ W^{-} $\end{document}

cross section ratio and charge asymmetry distributions. The 8 TeV predictions using NNPDF3.1, CT14, and MMHT2014 PDF sets are reported to be in good agreement with the LHCb data for the entire

\begin{document}$ \eta_{e} $\end{document}

region, justifying the extension of the calculations to 13 and 14 TeV energies. The charge asymmetry predictions at NNLO accuracy are reported in the forward

\begin{document}$ \eta_{e} $\end{document}

bins at 13 and 14 TeV and compared among NNPDF3.1, CT14, and MMHT2014 PDF sets. Overall, the predicted

\begin{document}$ W^{\pm} $\end{document}

differential cross-section and charge asymmetry distributions based on different PDF sets are found to be consistent with each other for the entire

\begin{document}$ \eta_{e} $\end{document}

region. The charge asymmetry distributions are shown to be more sensitive to discriminate among different PDF models in terms of the 14 TeV predictions.

Investigation on effects of new physics in ${ { c}\to{{ (s,d)}}\ell^+\nu_\ell} $ transitions

Xue Leng, Xiao-Long Mu, Zhi-Tian Zou, Ying Li

2021, 45(6): 063107. doi: 10.1088/1674-1137/abf489

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Anomalies in decays induced by

\begin{document}$b\to c \ell^- \bar\nu_\ell$\end{document}

(

\begin{document}$\ell = e, \mu, \tau$\end{document}

) transitions may imply lepton flavor universality violations, which raises questions on such phenomena in the D decays induced by

\begin{document}$ c\to (s,d)\ell^+\nu_\ell $\end{document}

transitions. Current measurements of the pure leptonic and semi-leptonic D decays agree with the standard model (SM) predictions, and such agreements can be used to constrain the new physics (NP) contributions. In this work, we extend SM by assuming general effective Hamiltonians describing the

\begin{document}$ c\to (s,d)\ell^+\nu_\ell $\end{document}

transitions including the full set of the four-fermion operators. With the latest experimental data, we perform a least

\begin{document}$ \chi^2 $\end{document}

fit of the Wilson coefficient corresponding to each operator. The results indicate that the Wilson coefficients of tensor and scalar operators in the muon sector are in the order of

\begin{document}$ {\cal O}(10^{-2}) $\end{document}

while others are in the order of

\begin{document}$ {\cal O}(10^{-3}) $\end{document}

. The lepton flavor universality could be violated by interactions with the scalar operators. We also determine that the pure leptonic decays are significantly sensitive to scalar operators. The effects of NP on the semi-leptonic decays with electron final state are negligible; however, for the decays with the muon final state, the effects of scalar and tensor operators will appear in the forward-backward asymmetries and the muon helicity asymmetries of

\begin{document}$ D \to P\mu^+ \nu_\mu $\end{document}

decays. The future measurements of these decays in the BESIII and Belle II experiments will facilitate the evaluation of NP effects.

Spectroscopic investigation of light strange S = −1 Λ and Σ and S = −2 Ξ baryons

Chandni Menapara, Ajay Kumar Rai

2021, 45(6): 063108. doi: 10.1088/1674-1137/abf4f4

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The present study is dedicated to light-strange

\begin{document}$\Lambda$\end{document}

with strangeness S = −1 and isospin I = 0,

\begin{document}$\Sigma$\end{document}

with S = −1 and I = 1, and

\begin{document}$\Xi$\end{document}

baryon with S = −2 and

\begin{document}$I=\dfrac{1}{2}$\end{document}

. In this study, the hypercentral constituent quark model with linear confining potential has been employed along with a first order correction term to obtain the resonance masses up to approximately 4 GeV. The calculated states include 1S-5S, 1P-4P, 1D-3D, 1F-2F, and 1G (in a few cases) along with all possible spin-parity assignments. Regge trajectories have been explored for the linearity of the calculated masses for

\begin{document}$(n,M^{2})$\end{document}

and

\begin{document}$(J,M^{2})$\end{document}

. Magnetic moments have been intensively studied for ground state spin

\begin{document}$\dfrac{1}{2}$\end{document}

and

\begin{document}$\dfrac{3}{2}$\end{document}

, in addition to the configuration mixing of the first negative parity state for

\begin{document}$\Xi$\end{document}

. Lastly, the transition magnetic moments and radiative decay widths have been presented.

Measurement of differential cross sections of neutron-induced deuteron production reactions on carbon from 25 to 52 MeV

Zengqi Cui, Haoyu Jiang, Kang Sun, Guohui Zhang, Ruirui Fan, Wei Jiang, Huaiyong Bai, Yiwei Hu, Jie Liu, Han Yi, Changjun Ning, Zhijia Sun, Jingyu Tang, Qi An, Jie Bao, Yu Bao, Ping Cao, Haolei Chen, Qiping Chen, Yonghao Chen, Yukai Chen, Zhen Chen, Changqing Feng, Keqing Gao, Minhao Gu, Changcai Han, Zijie Han, Guozhu He, Yongcheng He, Yang Hong, Hanxiong Huang, Weiling Huang, Xiru Huang, Xiaolu Ji, Xuyang Ji, Zhijie Jiang, Hantao Jing, Ling Kang, Mingtao Kang, Bo Li, Chao Li, Jiawen Li, Lun Li, Qiang Li, Xiao Li, Yang Li, Rong Liu, Shubin Liu, Xingyan Liu, Guangyuan Luan, Qili Mu, Binbin Qi, Jie Ren, Zhizhou Ren, Xichao Ruan, Zhaohui Song, Yingpeng Song, Hong Sun, Xiaoyang Sun, Zhixin Tan, Hongqing Tang, Xinyi Tang, Binbin Tian, Lijiao Wang, Pengcheng Wang, Qi Wang, Taofeng Wang, Zhaohui Wang, Jie Wen, Zhongwei Wen, Qingbiao Wu, Xiaoguang Wu, Xuan Wu, Likun Xie, Yiwei Yang, Li Yu, Tao Yu, Yongji Yu, Linhao Zhang, Qiwei Zhang, Xianpeng Zhang, Yuliang Zhang, Zhiyong Zhang, Yubin Zhao, Luping Zhou, Zuying Zhou

2021, 45(6): 064001. doi: 10.1088/1674-1137/abf136

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Abstract:
The angle-differential cross sections of neutron-induced deuteron production from carbon were measured at six neutron energies from 25 to 52 MeV relative to those of n-p elastic scattering at the China Spallation Neutron Source (CSNS) Back-n white neutron source. By employing the ΔE-E telescopes of the Light-charged Particle Detector Array (LPDA) system at 15.1° to 55.0° in the laboratory system, ratios of the angle-differential cross sections of the ¹²C(n, xd) reactions to those of the n-p scattering were measured, and then, the angle-differential cross sections of the ¹²C(n, xd) reactions were obtained using the angle-differential cross sections of the n-p elastic scattering from the JENDL-4.0/HE-2015 library as the standard. The obtained results are compared with data from previous measurements, all of which are based on mono-energic neutrons, the evaluated data from the JENDL-4.0/ HE-2015 library and the ENDF-B/VIII.0 library, and those from theoretical calculations based on INCA code and Talys-1.9 code. Being the first white-neutron-source-based systematic measurement of the angle-differential cross sections of neutron-induced deuteron production reactions on carbon in several tens of MeV, the present work can provide a reference to the data library considering the lack of experimental data.

Strongly enhanced quadrupole deformation in a class of N ≈ Z nuclei driven by large-scale clustering?

P. Petkov, C. Müller-Gatermann

2021, 45(6): 064002. doi: 10.1088/1674-1137/abf137

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The formation of large size clusters, and/or their relative motion as a possible excitation mode, are suggested to be closely related to the origin of deformation in specific cases, namely the case of two doubly-magic clusters or two clusters with nearby characterization. New lifetime data in N = Z ⁷⁶Sr and ⁸⁰Zr leading to large B(E2) values are reproduced consistently and well within this approach, along with data for a few neighboring N

\begin{document}$\approx $\end{document}

Z nuclei. These results are compared to previous studies of ³²S and ²⁰Ne and all of them support the ideas of the large-scale cluster approach.

Effects of centrality fluctuation and deuteron formation on the proton number cumulant in Au+Au collisions at ${ \sqrt {{{ s}_{{{NN}}}}}\; } $ = 3 GeV from the JAM model

Arghya Chatterjee, Yu Zhang, Hui Liu, Ruiqin Wang, Shu He, Xiaofeng Luo

2021, 45(6): 064003. doi: 10.1088/1674-1137/abf427

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We studied the effects of centrality fluctuation and deuteron formation on the cumulant (

\begin{document}$C_n$\end{document}

) and correlation functions (

\begin{document}$\kappa_n$\end{document}

) of protons up to the sixth order in the most central (

\begin{document}$b$\end{document}

< 3 fm) Au+Au collisions at

\begin{document}$ \sqrt {{s_{{{NN}}}}}\; $\end{document}

= 3 GeV in a microscopic transport model (JAM). The results are presented as a function of rapidity acceptance within the transverse momentum 0.4 < p_T < 2 GeV/c. We compared the results obtained by the centrality bin width correction (CBWC) using charged reference particle multiplicities with the CBWC using impact parameter bins. It was found that, at low energies, the centrality resolution for determining the collision centrality using charged particle multiplicities is not sufficient to reduce the initial volume fluctuation effect for higher-order cumulant analysis. New methods need to be developed to classify events with high centrality resolution for heavy-ion collisions at low energies. Finally, we observed that the formation of deuterons suppresses the higher-order cumulants and correlation functions of protons and found it to be similar to the efficiency effect. This work can serve as a noncritical baseline for the QCD critical point search in the high baryon density region.

Change in ⁷Be half-life in host media

Farshid Gholamian, Mohammad Mehdi Firoozabadi, Reza Sarhaddi

2021, 45(6): 064101. doi: 10.1088/1674-1137/abeda7

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First-principle calculations within the density functional theory framework are used to study the probability of electron capture for the ⁷Be nucleus. For this purpose, electron density at the ⁷Be nucleus is computed in Al, Au, Pd, Pt, and Pb environments. Our results show that the half-life of ⁷Be is changed by implanting ⁷Be in host environments. Electron affinity of the media and confinement effects are responsible for the change in the half-life of ⁷Be nucleus. Moreover, electric potential at the ⁷Be nucleus is calculated. Results show that variations in electric potential are usually consistent with those in electron density at the ⁷Be nucleus.

QCD phase diagram at finite isospin and baryon chemical potentials with the self-consistent mean field approximation

Zu-Qing Wu, Jia-Lun Ping, Hong-Shi Zong

2021, 45(6): 064102. doi: 10.1088/1674-1137/abefc3

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The self-consistent mean field approximation of the two-flavor NJL model, with a free parameter

\begin{document}$\alpha$\end{document}

to reflect the competition between the "direct" channel and the "exchange" channel, is employed to study the QCD phase structure at finite isospin chemical potential

\begin{document}$\mu_I$\end{document}

, finite baryon chemical potential

\begin{document}$\mu_B$\end{document}

and finite temperature T, and especially to study the location of the QCD critical point. Our results show that in order to match the corresponding lattice results of isospin density and energy density, the contributions of the "exchange" channel need to be considered in the framework of the NJL model, and a weighting factor

\begin{document}$\alpha=0.5$\end{document}

should be taken. It is also found that for fixed isospin chemical potentials, the lower temperature of the phase transition is obtained with increasing

\begin{document}$\alpha$\end{document}

in the

\begin{document}$T-\mu_I$\end{document}

plane, and the largest difference of the phase transition temperature with different

\begin{document}$\alpha$\end{document}

's appears at

\begin{document}$\mu_I \sim 1.5m_{\pi}$\end{document}

. At

\begin{document}$\mu_I=0$\end{document}

the temperature of the QCD critical end point (CEP) decreases with increasing

\begin{document}$\alpha$\end{document}

, while the critical baryon chemical potential increases. At high isospin chemical potential (

\begin{document}$\mu_I=500$\end{document}

MeV), the temperature of the QCD tricritical point (TCP) increases with increasing

\begin{document}$\alpha$\end{document}

, and in the low temperature regions the system will transition from the pion superfluidity phase to the normal phase as

\begin{document}$\mu_B$\end{document}

increases. At low density, the critical temperature of the QCD phase transition with different

\begin{document}$\alpha$\end{document}

's rapidly increases with

\begin{document}$\mu_I$\end{document}

at the beginning, and then increases smoothly around

\begin{document}$\mu_I>300$\end{document}

MeV. In the high baryon density region, the increase of the isospin chemical potential will raise the critical baryon chemical potential of the phase transition.

Exploring effects of tensor force and its strength via neutron drops

Zhiheng Wang, Tomoya Naito, Haozhao Liang, Wen Hui Long

2021, 45(6): 064103. doi: 10.1088/1674-1137/abf036

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The tensor-force effects on the evolution of spin-orbit splittings in neutron drops are investigated within the framework of the relativistic Hartree-Fock theory. For a fair comparison on the pure mean-field level, the results of the relativistic Brueckner-Hartree-Fock calculation with the Bonn A interaction are adopted as meta-data. Through a quantitative analysis, we certify that the

\begin{document}$ \pi $\end{document}

-pseudovector (

\begin{document}$ \pi $\end{document}

-PV) coupling affects the evolutionary trend through the embedded tensor force. The strength of the tensor force is explored by enlarging the strength

\begin{document}$ f_{\pi} $\end{document}

of the

\begin{document}$ \pi $\end{document}

-PV coupling. It is found that weakening the density dependence of

\begin{document}$ f_{\pi} $\end{document}

is slightly better than enlarging it with a factor. We thus provide a semiquantitative support for the renormalization persistency of the tensor force within the framework of density functional theory. This will serve as important guidance for further development of relativistic effective interactions with particular focus on the tensor force.

Bayesian inference on isospin splitting of nucleon effective mass from giant resonances in ²⁰⁸Pb

Zhen Zhang, Xue-Bin Feng, Lie-Wen Chen

2021, 45(6): 064104. doi: 10.1088/1674-1137/abf428

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From a Bayesian analysis of the electric dipole polarizability, the constrained energy of isovector giant dipole resonance, the peak energy of isocalar giant quadrupole resonance, and the constrained energy of isocalar giant monopole resonance in ²⁰⁸Pb, we extract the isoscalar and isovector effective masses in nuclear matter at saturation density

\begin{document}$ \rho_0 $\end{document}

as

\begin{document}$ m_{s,0}^{\ast}/m = 0.87_{-0.04}^{+0.04} $\end{document}

and

\begin{document}$ m_{v,0}^{\ast}/m = 0.78_{-0.05}^{+0.06} $\end{document}

, respectively, at 90% confidence level. The constraints obtained on

\begin{document}$ m_{s,0}^{\ast} $\end{document}

and

\begin{document}$ m_{v,0}^{\ast} $\end{document}

lead to a positive isospin splitting of nucleon effective mass in asymmetric nuclear matter of isospin asymmetry

\begin{document}$ \delta $\end{document}

at

\begin{document}$ \rho_0 $\end{document}

as

\begin{document}$ m_{n-p}^* / m = (0.20^{+0.15}_{-0.14})\delta $\end{document}

. In addition, the symmetry energy at the subsaturation density

\begin{document}$ \rho^{\ast} = 0.05\; \mathrm{fm}^{-3} $\end{document}

is determined to be

\begin{document}$ E_{\mathrm{sym}}(\rho^{\ast}) = 16.7\pm1.3 $\end{document}

MeV at 90% confidence level.

Radial profile of bottom quarks in jets in high-energy nuclear collisions

Sa Wang, Wei Dai, Ben-Wei Zhang, Enke Wang

2021, 45(6): 064105. doi: 10.1088/1674-1137/abf4f5

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Angular correlations between a heavy quark (HQ) and its tagged jet are potentially new tools to gain insight into the in-medium partonic interactions in relativistic heavy-ion collisions. In this work, we present the first theoretical study on the radial profiles of B mesons in jets in Pb+Pb collisions at the Large Hadron Collider (LHC). The initial production of a bottom quark tagged jet in p+p is computed by SHERPA, which matches the next-to-leading order matrix elements with contributions of parton showers, whereas the massive quark traversing the quark-gluon plasma is described by a Monte Carlo model, SHELL, which can simultaneously simulate light and heavy flavor in-medium energy loss within the framework of Langevin evolution. In p+p collisions, we find that at lower

\begin{document}$p_T^Q$\end{document}

the radial profiles of heavy flavors in jets are sensitive to the heavy quark mass. In 0-10% Pb+Pb collisions at

\begin{document}$\sqrt{s_{NN}} = 5.02$\end{document}

TeV, we observe an inverse modification pattern of the B meson radial profiles in jets at

\begin{document}$ 4<p_T^Q<20 $\end{document}

GeV compared to those of D mesons: the jet quenching effects narrow the jet radial profiles of B mesons in jets while broadening those of D mesons in jets. We find that in A+A collisions, the contribution dissipated from the higher

\begin{document}$p_T^Q > 20$\end{document}

GeV region naturally has a narrower initial distribution and consequently leads to a narrower modification pattern of the radial profile; however the diffusion nature of the heavy flavor in-medium interactions will give rise to a broader modification pattern of the radial profile. These two effects consequently compete and offset with each other, and the b quarks in jets benefit more from the former and suffer less diffusion effect compared to that of c quarks in jets. These findings can be tested in the future experimental measurements at the LHC to gain better understanding of the mass effect of jet quenching.

Informational properties of holographic Lifshitz field theory

Huajie Gong, Peng Liu, Guoyang Fu, Xiao-Mei Kuang, Jian-Pin Wu

2021, 45(6): 065101. doi: 10.1088/1674-1137/abefca

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In this paper, we explore the properties of holographic entanglement entropy (HEE), mutual information (MI) and entanglement of purification (EoP) in holographic Lifshitz theory. These informational quantities exhibit some universal properties of holographic dual field theory. For most configuration parameters and temperatures, these informational quantities change monotonically with the Lifshitz dynamical critical exponent z. However, we also observe some non-monotonic behaviors for these informational quantities in some specific spaces of configuration parameters and temperatures. A particularly interesting phenomenon is that a dome-shaped diagram emerges in the behavior of MI vs z, and correspondingly a trapezoid-shaped profile appears in that of EoP vs z. This means that for some specific configuration parameters and temperatures, the system measured in terms of MI and EoP is entangled only in a certain intermediate range of z.

High energy window for probing dark matter with cosmic-ray antideuterium and antihelium

Yu-Chen Ding, Nan Li, Chun-Cheng Wei, Yu-Feng Zhou

2021, 45(6): 065102. doi: 10.1088/1674-1137/abf13a

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Abstract:
Cosmic-ray (CR) anti-nuclei are often considered important observables for indirect dark matter (DM) detection at low kinetic energies, below GeV per nucleon. Since the primary CR fluxes drop quickly towards high energies, the secondary anti-nuclei in CR are expected to be significantly suppressed in high energy regions (

\begin{document}$\gtrsim 100$\end{document}

GeV per nucleon). If DM particles are heavy, the annihilation productions of DM can be highly boosted, and thus the fluxes of anti-nuclei produced by DM annihilation may exceed the secondary background at high energies, which opens a high energy window for indirect DM detection. We investigate the possibility of detecting heavy DM particles which annihilate into high energy anti-nuclei. We use the Monte Carlo generators PYTHIA, EPOS-LHC and DPMJET and the coalescence model to simulate the production of anti-nuclei, and constrain the DM annihilation cross-sections by using the AMS-02 and HAWC antiproton data and the HESS galactic center

\begin{document}$ \gamma $\end{document}

-ray data. We find that the conclusion depends on the choice of DM density profiles. For the “Cored” type profile with a DM particle mass

\begin{document}$\gtrsim 10$\end{document}

TeV, the contributions from DM annihilation can exceed the secondary background in high energy regions, which opens the high energy window, while for the “Cuspy” type profile, the excess disappears.

Thermodynamic instability of 3D Einstein-Born-Infeld AdS black holes

Hongmei Jing, Benrong Mu, Jun Tao, Peng Wang

2021, 45(6): 065103. doi: 10.1088/1674-1137/abf1dc

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Abstract:
Super-entropic black holes possess finite-area but noncompact event horizons and violate the reverse isoperimetric inequality. It has been conjectured that such black holes always have negative specific heat at constant volume

\begin{document}$ C_{V} $\end{document}

or negative specific heat at constant pressure

\begin{document}$ C_{P} $\end{document}

whenever

\begin{document}$ C_{V}>0 $\end{document}

, making them unstable in extended thermodynamics. In this paper, we describe a test of this instability conjecture with a family of nonlinear electrodynamic black holes, namely 3D Einstein-Born-Infeld (EBI) AdS black holes. Our results show that when nonlinear electrodynamics effects are weak, the instability conjecture is valid. However, the conjecture can be violated in some parameter region when nonlinear electrodynamics effects are strong enough. This observation thus provides a counter example to the instability conjecture, which suggests that super-entropic black holes may be thermodynamically stable.

Exploring the potentiality of future standard candles and standard sirens to detect cosmic opacity

Xiangyun Fu, Lu Zhou, Jianfei Yang, Zhen-Yan Lu, Ying Yang, Guo Tang

2021, 45(6): 065104. doi: 10.1088/1674-1137/abf48a

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Abstract:
In this work, we explore the potentiality of future gravitational wave (GW) and Type Ia supernovae (SNe Ia) measurements to detect cosmic opacity by comparing the opacity-free luminosity distance (LD) of GW events with the opacity-dependent LD of SNe Ia observations. The GW data are simulated from the future measurements of the ground-based Einstein Telescope (ET) and the space-borne Deci-Herz Interferometer Gravitational wave Observatory (DECIGO). The SNe Ia data are simulated from the observations of the Wide Field Infrared Survey Telescope (WFIRST) that will be collected over the next few decades. A binning method is adopted to match the GW data with the SNe Ia data at the same redshift z with a selection criterion

\begin{document}$ |\Delta z|<0.005$\end{document}

, and most of the available data from the GW measurements is employed to detect cosmic opacity due to improvements in the distribution of the future SNe Ia observations. Results show that the uncertainties of the constraints on cosmic opacity can be reduced to

\begin{document}$ \sigma_{\epsilon}\sim 0.0041$\end{document}

and 0.0014 at the

\begin{document}$ 1\sigma$\end{document}

confidence level (CL) for 1000 data points from the ET and DECIGO measurements, respectively. Compared with the allowable limits of intergalactic opacity obtained from quasar continuum observations, these future astronomical observations can be used to verify the cosmic opacity. In this way, GW and SNe Ia measurements can be used as important and effective tools to detect cosmic opacity in the future.

Pair production in Reissner-Nordström-Anti de Sitter black holes

Jun Zhang, Yi-Yu Lin, Hao-Chun Liang, Ke-Jia Chi, Chiang-Mei Chen, Sang Pyo Kim, Jia-Rui Sun

2021, 45(6): 065105. doi: 10.1088/1674-1137/abf4f6

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Abstract:
We studied the pair production of charged scalar particles of a five-dimensional near extremal Reissner-Nordström-Anti de Sitter (RN-AdS₅) black hole. The pair production rate and the absorption cross section ratio in full spacetime are obtained and are shown to have a concise relation with their counterparts in the near horizon region. In addition, the holographic descriptions of the pair production, both in the IR CFT in the near horizon region and the UV CFT at the asymptotic spatial boundary of the RN-AdS₅ black hole, are analyzed in the AdS₂/CFT₁ and AdS₅/CFT₄ correspondences, respectively. This work gives a complete description of scalar pair production in a near extremal RN-AdS₅ black hole.

2021 Vol. 45, No. 6