Wed·Apr 24, 2024Wednesday·April 24, 2024

1. 01*

   Dielectrons at the LHC -- Chances and challenges

   Harald Appelshäuser (for the ALICE Collaboration)🇩🇪

   Dielectrons are unique observables in ultra-relativistic heavy-ion collisions. Thanks to their penetrating nature, they carry information from all stages of the collision and can provide knowledge about pre-equilibirium dynamics, QGP temperature and transport coefficients, and chiral symmetry restoration. On the other hand, experimental challenges are enormous because production cross sections are small and the signal of interest is eclipsed by a huge combinatorial and physics background from light- and heavy-flavour hadron decays. In this talk the status of dielectron measurements with ALICE is shown and the perspectives with the recently installed and planned ALICE detector upgrades are discussed.

   nucl-exNuovo Cim.C(2025)·2 citations
2. 02*

   Shell-model study of ${}^{28}$Si: coexistence of oblate, prolate and superdeformed shapes

   Dorian Frycz🇪🇸 · Javier Menéndez🇪🇸 · Arnau Rios🇪🇸 · Benjamin Bally🇫🇷 · Tomás R. Rodríguez🇪🇸 · Antonio M. Romero🇪🇸

   We study the shape coexistence in the nucleus ${}^{28}$Si with the nuclear shell model using numerical diagonalizations complemented with variational calculations based on the projected generator-coordinate method. The theoretical electric quadrupole moments and transitions as well as the collective wavefunctions indicate that the standard USDB interaction in the $sd$ shell describes well the ground-state oblate rotational band, but misses the experimental prolate band. Guided by the quasi-SU(3) model, we show that the prolate band can be reproduced in the $sd$ shell by reducing the energy of the $0d_{3/2}$ orbital. Alternatively, in the extended $sdpf$ configuration space a modification of the SDPF-NR interaction that accommodates cross-shell excitations also reproduces the oblate and prolate bands. Finally, we address the possibility of superdeformation in ${}^{28}$Si within the $sdpf$ space. Our results indicate that superdeformed structures appear at about $18$-$20$~MeV.

   ↳ nucl-thnucl-exPRC(2024)·9 citations
3. 03*

   Parameter dependence of the $\beta$-decay properties of neutron-rich Zr isotopes within the interacting boson model

   M. Homma · K. Nomura🇯🇵

   We investigate parameter dependence of the calculated $\beta$-decay properties, as well as low-lying states for the neutron-rich Zr isotopes within the neutron-proton interacting boson model (IBM-2) and interacting boson-fermion-fermion model (IBFFM-2). It is shown that the calculated ${\log }_{10}ft$ values for the transitions of the $0_1^{+}$ ground states of the parent even-even nuclei ${}^{96-102}$Zr into the $1_1^{+}$ states of the daughter odd-odd nuclei ${}^{96-102}$Nb consistently exhibit a strong dependence on those parameters associated with the quadrupole-quadrupole boson interaction, and with the residual interaction between an unpaired neutron and an unpaired proton in the IBFFM-2 Hamiltonian for the odd-odd Nb nuclei. By the reduction in magnitude of the quadrupole-quadrupole interaction strength by approximately a factor of 2, the calculated ${\log }_{10}ft$ values for the Zr$(0_1^{+})\to$Nb$(1_1^{+})$ transitions increase and agree with the experimental values. This points to a significant improvement over the previous study performed in the same mass region, that consists of the mapping from a relativistic energy density functional calculation onto the IBM-2 Hamiltonian.

   ↳ nucl-thnucl-exPRC(2024)·5 citations
4. 04*

   Estimating Longitudinal Polarization of $\Lambda$ and $\bar{\Lambda }$ Hyperons at Relativistic Energies using Hydrodynamic and Transport models

   Bhagyarathi Sahoo🇮🇳 · Captain R. Singh🇮🇳 · Raghunath Sahoo🇮🇳

   The global and local spin polarization measurements of $\Lambda$ ($\bar{\Lambda }$) hyperons by STAR and ALICE Collaborations open up an immense interest in investigating the spin polarization dynamics in heavy-ion collisions. Recent studies suggest the transverse component of the vorticity field is responsible for the global spin polarization. In contrast, the longitudinal component of the vorticity field accounts for the local spin polarization. The local (longitudinal) spin polarization of $\Lambda$-hyperons arises due to the anisotropic flows in the transverse plane, indicating a quadrupole pattern of the longitudinal vorticity along the beam direction. In this study, we derive a simple solution relating the longitudinal mean spin vector with the second-order anisotropic flow coefficient due to the thermal shear tensor for an ideal uncharged fluid in a longitudinal boost invariant scenario. The present study focuses on the local spin polarization of $\Lambda$ and $\bar{\Lambda }$ in Au$+$Au and Pb$+$Pb collisions at $\sqrt{s_{NN}}$ = 200 GeV and 5.02 TeV, respectively. Further, we explore the azimuthal angle, centrality, and transverse momentum ($p_{\mathrm{T}}$) dependence study of longitudinal spin polarization using hydrodynamic and transport models. All these models predict a maximum longitudinal spin polarization in mid-central collisions around 30-50 \% centrality at $p_{\mathrm{T}}\approx$ 2.0 - 3.0 GeV/c. These findings on longitudinal spin polarization advocate the existence of a thermal medium in non-central heavy-ion collisions.

   ↳ hep-phhep-exnucl-exnucl-thPhys.Scripta(2025)·11 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.