Wed·Aug 24, 2022Wednesday·August 24, 2022

1. 01*

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

   Yongjia Wang🇨🇳 · Zepeng Gao🇨🇳 · Hongliang Lü🇨🇳 · Qingfeng Li🇨🇳

   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.

   ↳ nucl-thnucl-exPLB(2022)·18 citations
2. 02*

   Isospin blocking and its effects in heavy-ion collisions

   Ya-Fei Guo🇨🇳 · Gao-Chan Yong🇨🇳

   A concept of \emph{isospin blocking} in the process of isospin diffusion in heavy-ion collisions is raised. Generally, in the process of isospin diffusion, isospin asymmetry would diffuse from the place with large asymmetry to the place with small asymmetry. However, our study shows that the isospin diffusion could be blocked in case the local value of the symmetry energy is larger. We dub this phenomenon ``isospin blocking''. To check this behavior, in the framework of an Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, isospin diffusions in the isotope Sn+Sn reactions at 270 MeV/nucleon are studied. It is shown that the value of the after-diffusion asymmetry is distinctly blocked if the local symmetry energy is large. The effects of the isospin blocking on the isospin asymmetry of dilute and dense matter and the final ${\pi }^{-}/{\pi }^{+}$ ratio in heavy ion collisions are demonstrated.

   ↳ nucl-thnucl-exPRC(2022)·0 citations
3. 03*

   Probing system size dependence at high baryon density by systematic comparison of Ag+Ag and Au+Au reactions at 1.23$A$ GeV

   Tom Reichert🇩🇪 · Apiwit Kittiratpattana🇩🇪 · Pengcheng Li🇨🇳 · Jan Steinheimer🇩🇪 · Marcus Bleicher🇩🇪

   We present UrQMD predictions for the comparison of the recently measured Ag+Ag and Au+Au runs at a beam energy of $E_{\mathrm{lab}}$ = 1.23~$A$GeV explored by the HADES experiment. To this aim, different centrality definitions are investigated: We suggest that in the case of particle production, both systems should be compared at the same number of participating nucleons, while for a comparison of the (elliptic) flow, a selection on the initial state eccentricity - as in high energy reaction - is better suited. Generally, we find good agreement between both system, if these centrality criteria are used. Specifically, the deuteron yields per participant and the pion to proton ratios are shown to scale with $A_{\mathrm{part}}$ except for very central Ag+Ag reactions due to stronger stopping in such reactions. The elliptic flow in both systems follows inital state eccentricity scaling, albeit with the opposite sign as compared to high energies, suggesting a strong relation between final flows and the initial state also at the low energies explored here. The observation of this scaling might then allow to obtain further information on the expansion properties (and the EoS) of matter at high baryon densities.

   ↳ nucl-thnucl-exJ.Phys.G(2023)·3 citations
4. 04*

   Multiplicity, transverse momentum and pseudorapidity dependence of open-heavy flavored hadron production in proton+proton collisions at $\sqrt{s}$= 13 TeV using PYTHIA8

   Bhagyarathi Sahoo🇮🇳 · Suman Deb🇮🇳 · Raghunath Sahoo🇮🇳

   Recently, with the upgradation of LHC, it is realized that study of heavy-flavored hadrons, namely ${\Lambda }_c^{+}$ and ${\mathrm{D}}^0$ in hadronic collisions, could reveal the possibility of thermalization of charm quarks. With this motivation, we study the production dynamics of these hadrons using a pQCD-inspired Monte Carlo event generator called PYTHIA8 in proton+proton collisions at $\sqrt{s}$ = 13 TeV. The production dynamics of these hadrons are analyzed through charged-particle multiplicity, transverse momentum, and pseudorapidity. With the help of the established PYTHIA8 tunes to mimic the behavior of flow-like features, we investigated the variation of effective temperature and degree of non-extensivity using thermodynamically consistent non-extensive Tsallis statistics. We further attempted to establish a connection between the initial state and final state by estimating the correlation between the number of multi-partonic interactions (${\mathrm{n}}_{\mathrm{MPI}}$) with the Knudsen number.

   ↳ hep-phhep-exhep-thnucl-ex+1IJMPE(2024)·5 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.