Thu·Dec 9, 2021Thursday·December 9, 2021

1. 01*

   Light Nuclei Collectivity from $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV Au+Au Collisions at RHIC

   STAR Collaboration: M. S. Abdallah · B. E. Aboona · J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · A. Aitbaev · I. Alekseev and 385 other authors

   In high-energy heavy-ion collisions, partonic collectivity is evidenced by the constituent quark number scaling of elliptic flow anisotropy for identified hadrons. A breaking of this scaling and dominance of baryonic interactions is found for identified hadron collective flow measurements in $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV Au+Au collisions. In this paper, we report measurements of the first- and second-order azimuthal anisotropic parameters, $v_1$ and $v_2$, of light nuclei ($d$, $t$, ${}^3$He, ${}^4$He) produced in $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV Au+Au collisions at the STAR experiment. An atomic mass number scaling is found in the measured $v_1$ slopes of light nuclei at mid-rapidity. For the measured $v_2$ magnitude, a strong rapidity dependence is observed. Unlike $v_2$ at higher collision energies, the $v_2$ values at mid-rapidity for all light nuclei are negative and no scaling is observed with the atomic mass number. Calculations by the Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, are in good agreement with our observations, implying baryonic interactions dominate the collective dynamics in 3 GeV Au+Au collisions at RHIC.

   nucl-exPLB(2022)·66 citations
2. 02*

   Testing CPT symmetry in ortho-positronium decays with positronium annihilation tomography

   Paweł Moskal🇵🇱 · Aleksander Gajos🇵🇱 · Muhsin Mohammed🇵🇱 · Jyoti Chhokar🇵🇱 · Neha Chug🇵🇱 · Catalina Curceanu🇮🇹 · Eryk Czerwiński🇵🇱 · Meysam Dadgar🇵🇱 · Kamil Dulski🇵🇱 · Marek Gorgol🇵🇱 · Jacek Goworek🇵🇱 · Beatrix Hiesmayr🇦🇹 and 26 other authors

   Charged lepton system symmetry under combined charge, parity, and time-reversal transformation (CPT) remains scarcely tested. Despite stringent quantum-electrodynamic limits, discrepancies in predictions for the electron-positron bound state (positronium atom) motivate further investigation, including fundamental symmetry tests. While CPT noninvariance effects could be manifested in non-vanishing angular correlations between final-state photons and spin of annihilating positronium, measurements were previously limited by knowledge of the latter. Here, we demonstrate tomographic reconstruction techniques applied to three-photon annihilations of ortho-positronium atoms to estimate their spin polarisation without magnetic field or polarised positronium source. We use a plastic-scintillator-based positron-emission-tomography scanner to record ortho-positronium (o-Ps) annihilations with single-event estimation of o-Ps spin and determine the complete spectrum of an angular correlation operator sensitive to CPT-violating effects. We find no violation at the precision level of 10^{-4}, with an over threefold improvement on the previous measurement.

   nucl-exhep-exNature Commun.(2021)·75 citations
3. 03*

   Translating neutron star observations to nuclear symmetry energy via artificial neural networks

   Plamen G. Krastev (Harvard University)🇺🇸

   One of the most significant challenges involved in efforts to understand the equation of state of dense neutron-rich matter is the uncertain density dependence of the nuclear symmetry energy. Because of its broad impact, pinning down the density dependence of the nuclear symmetry energy has been a longstanding goal of both nuclear physics and astrophysics. Recent observations of neutron stars, in both electromagnetic and gravitational-wave spectra, have already constrained significantly the nuclear symmetry energy at high densities. Training deep neural networks to learn a computationally efficient representation of the mapping between astrophysical observables of neutron stars, such as masses, radii, and tidal deformabilities, and the nuclear symmetry energy allows its density dependence to be determined reliably and accurately. In this work we use a deep learning approach to determine the nuclear symmetry energy as a function of density directly from observational neutron star data. We show for the first time that artificial neural networks can precisely reconstruct the nuclear symmetry energy from a set of available neutron star observables, such as, masses and radii as those measured by, e.g., the NICER mission, or masses and tidal deformabilities as measured by the LIGO/VIRGO/KAGRA gravitational-wave detectors. These results demonstrate the potential of artificial neural networks to reconstruct the symmetry energy, and the equation of state, directly from neutron star observational data, and emphasize the importance of the deep learning approach in the era of Multi-Messenger Astrophysics.

   ↳ nucl-thastro-ph.HEnucl-exGalaxies(2022)·35 citations
4. 04*

   Thermal properties of hot and dense medium in interacting hadron resonance gas model

   S. Sahoo🇮🇳 · D. K. Mishra🇮🇳 · P. K. Sahu🇮🇳

   The meson exchange interaction based on relativistic mean-field (RMF) theory has been introduced in the hadron resonance gas (HRG) model, called interacting HRG (iHRG) model. This model can be used to explain the experimental data both at finite temperature ($T$) with finite chemical potential (${\mu }_B$) and finite temperature at vanishing chemical potential. The nuclear matter equation of state also can be explained at zero temperature with finite baryon density (finite chemical potential) due to the presence of attractive and repulsive interactions between the hadrons in the iHRG model. Similarly, the lattice equation of state is well described at ${\mu }_B$ = 0 and finite temperature by the iHRG model. In the present study, we have calculated the thermodynamical quantities as a function of temperature and chemical potential using both HRG and iHRG models. Also, we have presented the isothermal compressibility ($k_T$), specific heat ($C_V$), and speed of sound ($c_s^2$) as a function of ${\mu }_B$, $T$, and center of mass energies. The effect of kinematic acceptance on these quantities are also presented as a function of $\mu$ and $T$. Results from this study on $k_T$ are compared with results from other heavy-ion transport models and experimental data up to LHC energies.

   ↳ nucl-thhep-phnucl-exNPA(2022)·4 citations
5. 05*

   Lepton-Flavor-Violating ALPs at the Electron-Ion Collider: A Golden Opportunity

   Hooman Davoudiasl🇺🇸 · Roman Marcarelli🇺🇸 · Ethan T. Neil🇺🇸

   Axion-like particles (ALPs) arise in a variety of theoretical contexts and can, in general, mediate flavor violating interactions and parity non-conservation. We consider lepton flavor violating ALPs with GeV scale or larger masses which may, for example, arise in composite dark sector models. We show that a future Electron-Ion Collider (EIC) can uncover or constrain such ALPs via processes of the type $e{A}_Z\to \tau A_{Z}a$, where $A_Z$ is a nucleus of charge $Z$ and $a$ is an ALP in the range $m_{\tau }\le m_a\lesssim 20$ GeV. The production of the ALP can have a large $Z^2$ enhancement from low $Q^2$ electromagnetic scattering of the electron from a heavy ion. Using the gold nucleus ($Z=79$) as an example, we show that the EIC can explore $e-\tau$ flavor violation, mediated by GeV-scale ALPs, well beyond current limits. Importantly, the EIC reach for this interaction is not sensitive to the lepton-flavor conserving ALP couplings, whose possible smallness can render searches using $\tau$ decays ineffective. We also discuss how the EIC electron beam polarization can provide a powerful tool for investigating parity violating ALPs.

   ↳ hep-phhep-exnucl-exJHEP(2023)·46 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.