Wed·Sep 4, 2019Wednesday·September 4, 2019

1. 01*

   Global polarization of $\Lambda$ and $\overline{\Lambda }$ hyperons in Pb-Pb collisions at the LHC

   ALICE Collaboration

   The global polarization of the $\Lambda$ and $\overline{\Lambda }$ hyperons is measured for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 and 5.02 TeV recorded with the ALICE at the LHC. The results are reported differentially as a function of collision centrality and hyperon's transverse momentum ($p_{\mathrm{T}}$) for the range of centrality 5-50%, $0.5<p_{\mathrm{T}}<5$ GeV/$c$, and rapidity $|y|<0.5$. The hyperon global polarization averaged for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 and 5.02 TeV is found to be consistent with zero, $⟨P_{\mathrm{H}}⟩$ (%) $\approx$ - 0.01 $\pm$ 0.05 (stat.) $\pm$ 0.03 (syst.) in the collision centrality range 15-50%, where the largest signal is expected. The results are compatible with expectations based on an extrapolation from measurements at lower collision energies at RHIC, hydrodynamical model calculations, and empirical estimates based on collision energy dependence of directed flow, all of which predict the global polarization values at LHC energies of the order of 0.01%.

   nucl-exhep-exPRC(2020)·201 citations
2. 02*

   The quest of shape coexistence in Zr isotopes

   J.E. Garcia-Ramos🇪🇸 · K. Heyde🇧🇪

   The mass region with A~100 and Z~40 is known to experience a sudden onset of deformation. The presence of the subshell closure $Z=40$ makes feasible to create particle-hole excitations at a moderate excitation energy and, therefore, likely intruder states could be present in the low-lying spectrum. In other words, shape coexistence is expected to be a key ingredient to understand this mass region. The aim of this work is to describe excitation energies, transition rates, radii, and two-neutron separation energies for the even-even 94-110Zr nuclei and, moreover, to obtain information about wave functions and deformation. The interacting boson model with configuration mixing will be the framework to study the even-even Zr nuclei, considering only two types of configurations: 0particle-0hole and 2p-2h excitations. On one hand, the parameters appearing in the Hamiltonian and in the E2 transition operator are fixed trough a least-squares fit to the whole available experimental information. On the other hand, once the parameters have been fixed, the calculations allow to obtain a complete set of observables for the whole even-even Zr chain of isotopes. Spectra, transition rates, radii, ${\rho }^2(E0)$, and two-neutron separation energies have been calculated and a good agreement with the experimental information has been obtained. Moreover, a detailed study of the wave function has been conducted and mean-field energy surfaces and deformation have been computed too. The importance of shape coexistence has been shown to correctly describe the A~100 mass area for even-even Zr nuclei. This work confirmed the rather spherical nature of the ground state of 94-98Zr and its deformed nature for 100-110Zr isotopes. The sudden onset of deformation in 100Zr is owing to the rapid lowering of a deformed (intruder) configuration which is high-lying in lighter isotopes.

   ↳ nucl-thnucl-exPRC(2019)·58 citations
3. 03*

   The KLOE-2 experiment: overview of recent results

   Wojciech Krzemien🇵🇱 · Elena Perez del Rio🇮🇹

   The KLOE detector at the DA$\Phi$NE $\varphi$-factory has been operating in two periods from 2001 to 2006 and from 2014 to 2018 collecting a large sample of $\varphi$-meson decays. This allowed to perform precision measurements and studies of fundamental symmetries, and searches of New Physics phenomena. In this overview, the results of KLOE and KLOE-2 Collaborations are presented. The most recent results from the KLOE experiment are discussed, covering: the measurement of the running fine-structure constant ${\alpha }_{em}$, the Dalitz plot measurement of $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$, the search of a U boson, tests of discrete symmetries and quantum decoherence.

   ↳ hep-exnucl-exInt.J.Mod.Phys.A(2019)·7 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.