Wed·Dec 9, 2020Wednesday·December 9, 2020

1. 01*

   Spin alignment measurements of vector mesons with ALICE at LHC

   Bedangadas Mohanty (for the ALICE Collaboration)🇮🇳

   We present the measurements related to the spin alignment of ${\mathrm{K}}^{\ast 0}$ and $\varphi$ vector mesons at mid-rapidity for Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV using the ALICE detector at the LHC. The second diagonal spin density matrix element (${\rho }_{00}$) is measured from the angular distribution of the decay daughters of the vector meson in the decay rest frame, with respect to the event plane and the production plane. The ${\rho }_{00}$ values are found to be less than 1/3 at low $p_{\mathrm{T}}$ ($<$ 2 GeV/$c$) for both vector mesons. The observed deviations from 1/3 are maximal for mid-central collisions at a level of 3$\sigma$ for ${\mathrm{K}}^{\ast 0}$ and 2$\sigma$ for $\varphi$ mesons. As a control measurement the \rh~values were found to be consistent with 1/3, i.e., no significant spin alignment, for pp collisions with respect to the production plane. The results are qualitatively consistent with the expectation from a model that attributes the spin alignment to a polarization of quarks in the presence of large initial angular momentum and a subsequent hadronization by the process of recombination.

   nucl-exhep-exPoS(2021)·5 citations
2. 02*

   Estimating non-flow effects in measurements of directed flow of protons with the HADES experiment at GSI

   Mikhail Mamaev🇷🇺 · Oleg Golosov🇷🇺 · Ilya Selyuzhenkov (for the HADES Collaboration)🇷🇺

   Centrality dependence of the directed flow of protons in Au+Au collisions at the beam energy of 1.23A GeV collected by the HADES experiment at GSI is presented. Measurements are performed with respect to the spectators plane estimated using the Forward Wall hodoscope. Biases due to non-flow correlations and correlated detector effects are evaluated. The corresponding systematic uncertainties are quantified using estimates of the spectators plane from various forward rapidity regions constructed from groups of Forward Wall channels and protons reconstructed with the HADES tracking system.

   nucl-exhep-exPhys.Part.Nucl.(2022)·9 citations
3. 03*

   Enhanced search sensitivity to the double beta decay of ${}^{136}$Xe to excited states with topological signatures

   Chen Xie🇨🇳 · Kaixiang Ni🇨🇳 · Ke Han🇨🇳 · Shaobo Wang🇨🇳

   Double beta decay of ${}^{136}$Xe to excited states of ${}^{136}$Ba (DBD-ES) has not yet been discovered experimentally yet. The experimental signature of such decays, one or two gamma rays following the beta signals, can be identified more effectively in a gaseous detector with the help of topological signatures. We have investigated key parameters of particle trajectories of DBD-ES with Monte Carlo simulation data of the proposed PandaX-III detector as an example. The background rates can be reduced by about one order of magnitude while keeping more than half of signals with topological analysis. The estimated half-life sensitivity of DBD-ES can be improved by 1.8 times to 4.1$\times$10${}^{23}$ yr (90\% CL). Similarly, the half-life sensitivity of neutrinoless double beta decay of ${}^{136}$Xe to excited states of ${}^{136}$Ba can be improved by a factor of 4.8 with topological signatures.

   nucl-exhep-exSCPMA(2021)·5 citations
4. 04*

   Electric dipole response of low-lying excitations in the two-neutron halo nucleus ${}^{29}$F

   J. Casal🇮🇹 · Jagjit Singh🇯🇵 · L. Fortunato🇮🇹 · W. Horiuchi🇯🇵 · A. Vitturi🇮🇹

   The neutron-rich ${}^{28,29}$F isotopes have been recently studied via knockout and interaction cross-section measurements. The $2n$ halo in ${}^{29}$F has been linked to the occupancy of $pf$ intruder configurations. We investigate bound and continuum states in ${}^{29}$F, focusing on the $E1$ response of low-lying excitations and the effect of dipole couplings on nuclear reactions. ${}^{29}\text{F}$ (${}^{27}\text{F}+n+n$) wave functions are built within the hyperspherical harmonics formalism, and reaction cross sections are calculated using the Glauber theory. Continuum states and $B(E1)$ transition probabilities are described in a pseudostate approach using the analytical THO basis. The corresponding structure form factors are used in CDCC calculations to describe low-energy scattering. Parity inversion in ${}^{28}$F leads to a ${}^{29}$F ground state characterized by 57.5% of $(p_{3/2}{)}^2$ intruder components, a strong dineutron configuration, and an increase of the matter radius with respect to the core radius of $\Delta R=0.20$ fm. Glauber-model calculations for a carbon target at 240 MeV/nucleon provide a total reaction cross section of 1370 mb, in agreement with recent data. The model produces also a barely bound excited state corresponding to a quadrupole excitation. $B(E1)$ calculations into the continuum yield a total strength of 1.59 e${}^2$fm${}^2$ up to 6 MeV, and the $E1$ distribution exhibits a resonance at $\approx$ 0.85 MeV. Results using a standard shell-model order for ${}^{28}$F lead to a considerable reduction of the $B(E1)$ distribution. The four-body CDCC calculations for ${}^{29}\text{F}{+}^{120}\text{Sn}$ around the Coulomb barrier are dominated by dipole couplings, which totally cancel the Fresnel peak in the elastic cross section. These results are consistent with a two-neutron halo and may guide future experimental campaigns.

   ↳ nucl-thnucl-exPRC(2020)·33 citations
5. 05*

   The Shape of the Correlation Function

   Jakub Cimerman🇨🇿 · Chrisopher Plumberg🇺🇸 · Boris Tomášik🇸🇰

   The correlation function measured in ultrarelativistic nuclear collisions is strongly non-Gaussian. Using two different models we study which effects can influence its shape and how much. In particular, we focus on the parametrizations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as resonance decays, event-by-event fluctuations and functional dependence on $Q_{LI}$ or similar. We also study the corrections including the first-order Lévy expansion.

   ↳ nucl-thhep-phnucl-exPoS(2021)·2 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.