• Revisiting the thermodynamics of the BTZ black hole with a variable gravitational constant
    The thermodynamics of BTZ black holes are revisited with a variable gravitational constant. A new pair of conjugated thermodynamic variables are introduced, including the central charge C and chemical potential μ. The first law of thermodynamics and the Euler relationship, instead of the Smarr relationship in the extended phase space formalism, are matched perfectly in the proposed formalism. Compatible with the standard extensive thermodynamics of an ordinary system, the black hole mass is verified to be a first order homogeneous function of the related extensive variables, and restores the role of internal energy. In addition, the heat capacity has also resulted in a first order homogeneous function using this formalism, and asymptotic behavior is demonstrated at the high temperature limit. The non-negativity of the heat capacity indicates that the rotating and charged BTZ black holes are thermodynamically stable.
  • Study of neutron density fluctuation and neutron-proton correlation in Au+Au collisions using PYTHIA8/Angantyr
    Utilizing the PYTHIA8 Angantyr model, which incorporates the multiple-parton interaction (MPI) based color reconnection (CR) mechanism, we study the relative neutron density fluctuation and neutron-proton correlation in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV. In this study, we not only delve into the dependence of these two remarkable observations on rapidity, centrality, and energy, but also analyze their interplay with the MPI and CR. Our results show that the light nuclei yield ratio of protons, deuterons, and tritons, expressed by the elegant expression $N_tN_p/N_d^2$, remains unchanged even as the rapidity coverage and collision centrality increase. Interestingly, we also reveal that the effect of CR is entirely dependent on the presence of the MPI; CR has no impact on the yield ratio if the MPI is off. Our findings further demonstrate that the light nuclei yield ratio experiences a slight increase with increasing collision energy, as predicted by the PYTHIA8 Angantyr model; however, it cannot describe the non-monotonic trend observed by the STAR experiment. Based on the Angantyr model simulation results, it is essential not to overlook the correlation between neutron and proton fluctuations. The Angantyr model is a good baseline for studying collisions in the absence of a quark-gluon plasma system, given its lack of flow and jet quenching.
  • Possible molecular states from interactions of charmed strange baryons
    In this study, we investigate possible molecular states composed of two charmed strange baryons from the$ \Xi_c^{(',*)}{\Xi}_c^{(',*)} $ interaction and their hidden-charm hidden-strange partners from the $ \Xi_c^{(',*)}\bar{\Xi}_c^{(',*)} $ interaction. With the aid of heavy quark chiral effective Lagrangians, the interactions of charmed strange baryons are described with light meson exchanges. The potential kernels are constructed and inserted into the quasipotential Bethe–Salpeter equation. The bound states are produced from most interactions considered, which suggests that strong attractions exist widely between the charmed strange baryons. Experimental search for these types of molecular states is suggested in future high-precision measurements.
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  • Uncertainties of critical temperatures based on higher-order fluctuations of the largest fragment charge
    2024, 48(1): 014104-014104-15. doi: 10.1088/1674-1137/ad021d
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    The new signature of liquid-gas phase transition has been well indicated by the higher-order fluctuations of the largest fragment charge, but the uncertainties of critical temperatures based on this signature have not been revealed. This study extracts the critical temperatures of liquid-gas phase transition in nuclear reactions and investigates their uncertainties. Utilizing the isospin-dependent quantum molecular dynamics model in conjunction with the statistical model GEMINI enables us to describe the dynamical path from the initial to the final state. An isotope thermometer and a quantum fluctuation thermometer are employed to extract the nuclear temperature. The higher-order fluctuations of the largest fragment charge and critical temperatures are studied in 124Sn + 120Sn collisions ranging from 400 to 1000 MeV/nucleon and 124Sn + AZ collisions at 600 MeV/nucleon. Observations revealed that the pseudo-critical point is robustly indicated by the higher-order fluctuations of the largest fragment charge. The critical temperatures extracted by the isotope thermometer are relatively consistent, with an uncertainty of 15%, while those obtained by the quantum fluctuation thermometer are heavily influenced by the incident energy and mass number of target nuclei. The excitation energy $ E^{*} $ and bound charge $Z_{\rm bound}$ are used for event-sorting. These two ensembles represent the statistical properties of the initial and final states of the system, respectively. The initial-final correlations of statistical properties might lead to two phenomena. First, the size distribution of the largest fragment at the pseudo-critical point based on the $Z_{\rm bound}$ ensemble is wide, while that based on $ E^{*} $ ensemble exhibits bimodality, which is a typical characteristic in the liquid-gas coexistence of a finite system. Second, the temperature at the pseudo-critical point based on the $Z_{\rm bound}$ ensemble is higher than that based on the $ E^{*} $ ensemble. Furthermore, the projectile-like system exhibits a significant dynamical effect in its evolution path from the initial to final state, closely associated with the fluctuation of critical temperature.
  • Theoretical predictions on cluster radioactivity of superheavy nuclei with Z = 119, 120
    2024, 48(1): 014105-014105-13. doi: 10.1088/1674-1137/ad0827
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    In this study, we investigate the cluster radioactivity (CR) of new superheavy elements with $ Z=119 $ and 120 based on two successful theoretical methods with modified parameters: the density-dependent cluster model (DDCM) and unified decay formula (UDF). First, we employ the DDCM and UDF to accurately reproduce the experimental half-lives of cluster emissions, which demonstrates the high reliability of our theoretical methods. Then, we systematically predict the probable cluster modes of 293-311119 and 293-302120 as well as their corresponding decay energies and half-lives. The half-lives of cluster decay derived from the DDCM are consistent with those from the UDF. Therefore, our results reveal that the cluster emission of 8Be, emitted from the $ Z= $119 and 120 isotopic chains, exhibits the minimum half-life for cluster emission, and hence, 8Be emission is considered the most probable cluster decay mode. Moreover, we explore the competition between α decay and CR and find that α decay may be the dominant decay mode against CR. Furthermore, the good linear relationship between the decay energy and the number of α particles within the emitted cluster is extended to the range of superheavy nuclei (SHN). We anticipate that our theoretical predictions for CR will provide valuable references for the experimental synthesis of new SHN.
  • Bethe-Heitler lepton pair production in the deuteron breakup reaction
    2024, 48(1): 014103-014103-16. doi: 10.1088/1674-1137/ad0375
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    We study the lepton pair production via the Bethe-Heitler mechanism in the deuteron breakup reaction. The complete seven-fold differential cross section is calculated with final state interactions taken into account. The deuteron bound state is described by a relativistic covariant deuteron-nucleon vertex. The numerical results indicate that the differential cross section is highly dependent on the lepton's azimuthal angle in regions of small polar angles and exhibits sharp peaks in the distribution over the invariant mass of the generated lepton pair or the two nucleons in the final state. We demonstrate that such a nearly singular feature originates from the collinearity between the produced lepton or antilepton and the incident photon, and it is physically regularized by the lepton mass in our calculation. The final state interaction between the knocked-out nucleon and recoil nucleon redistributes the differential cross section over the missing momentum, with a significant enhancement at a large missing momentum and a suppression in the intermediate region. With a further decomposition of the final state interaction contribution, It is found that the on-shell term dominates the near quasi-elastic region, while the off-shell term dominates the other end. Additionally, we examine the contribution from the interference between the proton amplitude and neutron amplitude, which, as expected, is found negligible even if the proton-neutron rescattering is included. The results of this study can serve as inputs for the analysis and background estimation of multiple exclusive measurements at Jefferson Lab and future electron-ion colliders.
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