The multinucleon transfer reaction 238U + 248Cm is studied at incident energies <math altimg='si1.svg'><msub><mrow><mi>E</mi></mrow><mrow><mi mathvariant='normal'>c</mi><mo>.</mo><mi mathvariant='normal'>m</mi><mo>.</mo></mrow></msub></math> = 898 and 800 MeV using the Isospin-dependent Quantum Molecular Dynamics model. In this work, we investigate the angular distribution of products and their correlations with incident energy, charge distribution fluctuations, and kinetic energy. At 898 MeV, the angular distribution of heavy actinide products peaks near the grazing angle, whereas at 800 MeV, it shifts near <math altimg='si2.svg'><msup><mrow><mn>0</mn></mrow><mrow><mo>&#8728;</mo></mrow></msup></math>. Moreover, at 800 MeV, the proportion of isotopes emitted at forward angles increases with atomic number. These results suggest that current gas-filled recoil separators and velocity filters, which are highly effective for small-angle fusion-evaporation products, could be adapted for low-energy multinucleon transfer reactions. Given the challenges in the separation and identification of transfer products, the results of this study provide valuable guidance for future experimental investigations.

China

Yu Yang

Long Zhu

Zehong Liao

Zepeng Gao

Yueping Fang

Jun Su

Zhong Liu

Hong Kong

Dongsheng Hou

Hao Huang

Cheng Li

Fengshou Zhang

Production of actinide isotopes near <italic>&#952;</italic> <inf><italic>lab</italic></inf>&#8239;=&#8239;0 &#8728; in multinucleon transfer reaction 238U + 248Cm

The Gao-Wald theorem says that the Penrose diagram of de Sitter spacetime reacts to a positive energy perturbation by getting “taller”. How does this change in the presence of timelike boundaries? We study this question in two-dimensional de Sitter JT gravity coupled to conformal matter. The effect of the boundaries has its roots in quantum corrections to the vacuum energy of the CFT due to Casimir-like effects. We consider two different kinds of timelike boundaries, and for each kind we compute the vacuum expectation value of the matter CFT stress tensor. The stress tensor violates the null energy condition in the first case and saturates it in the second case, with each case exhibiting a negative energy density in the vacuum state. We then compute the semiclassical backreaction of this energy density and show how it can make the spacetime “fatter” or “taller” or a combination of both, depending on the regime. The spacetime getting fatter corresponds to an increase in the value of the dilaton at the horizon and hence also in the static patch horizon area in the higher-dimensional solution. We comment on the implications of our results for the quantum theories living on the timelike boundaries.

United States

Gauri Batra

Timelike boundaries in de Sitter JT gravity and the Gao-Wald theorem

To improve the theoretical prediction power for synthesizing superheavy elements beyond Og, a Bayesian uncertainty quantification method is employed to evaluate the uncertainty of the calculated evaporation residue cross sections (ERCS) for the first time. The key parameters of the dinuclear system model (DNS-sysu), such as the diffusion parameter a, the damping factor <math><msub><mrow><mi>E</mi></mrow><mrow><mi>d</mi></mrow></msub></math>, and the level-density parameter ratio <math><msub><mrow><mi>a</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>/</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>n</mi></mrow></msub></math> are systematically constrained by the Bayesian analysis of recent ERCS data. One intriguing behaviour is shown that the optimal incident energies (OIE) corresponding to the largest ERCS weakly depend on the fission process. We also find that these parameters are strongly correlated and the uncertainty propagation considering the parameters independently is not reasonable. The 2σ confidence level of posterior distributions for <math><mi>a</mi><mo>=</mo><msubsup><mrow><mn>0.586</mn></mrow><mrow><mo>−</mo><mn>0.002</mn></mrow><mrow><mo>+</mo><mn>0.002</mn></mrow></msubsup></math> fm, <math><msub><mrow><mi>E</mi></mrow><mrow><mi>d</mi></mrow></msub><mo>=</mo><msubsup><mrow><mn>25.65</mn></mrow><mrow><mo>−</mo><mn>3.41</mn></mrow><mrow><mo>+</mo><mn>3.43</mn></mrow></msubsup></math> MeV, and <math><msub><mrow><mi>a</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>/</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>=</mo><msubsup><mrow><mn>1.081</mn></mrow><mrow><mo>−</mo><mn>0.021</mn></mrow><mrow><mo>+</mo><mn>0.021</mn></mrow></msubsup></math> are obtained. Furthermore, the confidence levels of the ERCS and OIE for synthesizing Z = 119 via the reactions <math><mmultiscripts><mrow><mi>Cr</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>54</mn></mrow></mmultiscripts><mo>+</mo><msup><mrow></mrow><mrow><mn>243</mn></mrow></msup><mrow><mi>Am</mi></mrow></math>, <math><mmultiscripts><mrow><mi>Ti</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>50</mn></mrow></mmultiscripts><mo>+</mo><msup><mrow></mrow><mrow><mn>249</mn></mrow></msup><mrow><mi>Bk</mi></mrow></math>, and <math><mmultiscripts><mrow><mi>V</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>51</mn></mrow></mmultiscripts><mo>+</mo><msup><mrow></mrow><mrow><mn>248</mn></mrow></msup><mrow><mi>Cm</mi></mrow></math> are predicted. This work sets the stage for future analyses to explore the OIE and reaction systems for the synthesis of superheavy elements.

Yinu Zhang

Bayesian uncertainty quantification for synthesizing superheavy elements

Within the ultrarelativistic quantum molecular dynamics (UrQMD) model, by reversely tracing nucleons that are finally emitted at mid-rapidity (|<math><msub><mrow><mi>y</mi></mrow><mrow><mn>0</mn></mrow></msub></math>| &lt; 0.1) in the entire reaction process, the time evolution of elliptic flow (<math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math>) of these traced nucleons is studied in Au+Au collisions at beam energy of 0.4 GeV/nucleon with different impact parameters. The initial value of <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> is positive and increases with impact parameter, it then decreases as time passes and tends to saturate at a negative value. It is found that nucleon-nucleon collisions always suppress the value of <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> (enhance the out-of-plane emission), while the nuclear mean field potential effect is more complex, which depends on both impact parameter and reaction time. The most relevant density probed by <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> of nucleons at mid-rapidity is found to be ∼ 60% of the maximum density reached during the collisions.

Bo Gao

Yongjia Wang

Qingfeng Li

Elliptic flow in heavy-ion collisions at intermediate energy: The role of impact parameter, mean field potential, and collision term

Inferences of the nuclear symmetry energy from heavy-ion collisions are currently based on the comparison of measured observables and transport model simulations. Only the expectation values of observables over all considered events are used in these approaches, however, observables can be obtained event-by-event both in experiments and transport model simulations. By using the light gradient boosting machine (LightGBM), a modern machine-learning algorithm, we present a framework for inferring the density-dependent nuclear symmetry energy from observables in heavy-ion collisions on the event-by-event analysis. The ultrarelativistic quantum molecular dynamics (UrQMD) model simulations are used as training data. The symmetry energy slope parameter extracted with LightGBM event-by-event from test data also by UrQMD has an average spread of approximately 30 MeV from the truth, and is found to be robust against variations in model parameters. In addition, LightGBM can identify features that have the greatest effect on the physics of interest, thereby offering valuable insights. Our study suggests that the present framework can be a powerful tool and may offer a new paradigm to study the underlying physics in heavy-ion collisions.

Hongliang Lü

Decoding the nuclear symmetry energy event-by-event in heavy-ion collisions with machine learning

None Supervisory Editors of Nuclear Physics B

Editorial note on “Lepton-flavor violation and (g−2)μ in the μν SSM” by Hai-Bin Zhang, Tai-Fu Feng, Shu-Min Zhao and Tie-Jun Gao [Nucl. Phys. B 873 (2) (2013) 300–324]