Fri·Jul 8, 2022Friday·July 8, 2022

1. 01*

   gamma-UPC: Automated generation of exclusive photon-photon processes in ultraperipheral proton and nuclear collisions with varying form factors

   Hua-Sheng Shao🇫🇷 · David d'Enterria🇨🇭

   The automated generation of arbitrary exclusive final states produced via photon fusion in ultraperipheral high-energy collisions of protons and/or nuclei is implemented in the MadGraph5_aMC@NLO and HelacOnia Monte Carlo codes. Cross sections are calculated in the equivalent photon approximation using $\gamma$ fluxes derived from electric dipole and charge form factors, and incorporating hadronic survival probabilities. Multiple examples of $\gamma \gamma$ cross sections computed with this setup, named gamma-UPC, are presented for proton-proton, proton-nucleus, and nucleus-nucleus ultraperipheral collisions (UPCs) at the Large Hadron Collider and Future Circular Collider. Total photon-fusion cross sections for the exclusive production of spin-0,2 resonances (quarkonia, ditauonium, and Higgs boson; as well as axions and gravitons), and for pairs of particles ($J/\psi J/\psi$, WW, ZZ, Z$\gamma$, $t\bar{t}$, HH) are presented. Differential cross sections for exclusive dileptons and light-by-light scattering are compared to LHC data. This development paves the way for the upcoming automatic event generation of any UPC final state with electroweak corrections at next-to-leading-order accuracy and beyond.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2022)·100 citations
2. 02*

   Bayesian Inference of the Symmetry Energy and the Neutron Skin in ${}^{48}$Ca and ${}^{208}$Pb from CREX and PREX-2

   Zhen Zhang🇨🇳 · Lie-Wen Chen🇨🇳

   Using the recent model-independent determination of the charge-weak form factor difference $\Delta F_{\mathrm{CW}}$ in ${}^{48}$Ca and ${}^{208}$Pb by the CREX and PREX-2 collaborations together with some well-determined properties of doubly magic nuclei, we perform Bayesian inference of the symmetry energy $E_{\mathrm{sym}}(\rho )$ and the neutron skin thickness $\Delta r_{\mathrm{np}}$ of ${}^{48}$Ca and ${}^{208}$Pb within the Skyrme energy density functional (EDF). We find the inferred $E_{\mathrm{sym}}(\rho )$ and $\Delta r_{\mathrm{np}}$ separately from CREX and PREX-2 are compatible with each other at $90\%$ C.L., although they are inconsistent at $68.3\%$ C.L. with CREX (PREX-2) favoring a very soft (stiff) $E_{\mathrm{sym}}(\rho )$ and rather small (large) $\Delta r_{\mathrm{np}}$. By combining the CREX and PREX-2 data, we obtain a soft symmetry energy around saturation density ${\rho }_0$ and thinner $\Delta r_{\mathrm{np}}$ of ${}^{48}$Ca and ${}^{208}$Pb, which are found to be closer to the corresponding results from CREX alone, implying the PREX-2 is less effective to constrain the $E_{\mathrm{sym}}(\rho )$ and $\Delta r_{\mathrm{np}}$ due to its lower precision of $\Delta F_{\mathrm{CW}}$. Furthermore, we find the Skyrme EDF results inferred by combining the CREX and PREX-2 data nicely agree with the measured dipole polarizabilities ${\alpha }_D$ in ${}^{48}$Ca and ${}^{208}$Pb as well as the neutron matter equation of state from microscopic calculations. The implications of the inferred soft $E_{\mathrm{sym}}(\rho )$ around ${\rho }_0$ are discussed.

   ↳ nucl-thastro-ph.HEhep-phnucl-exPRC(2023)·91 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.