Wed·May 29, 2019Wednesday·May 29, 2019

1. 01*

   Polarization of $\Lambda$ ($\bar{\Lambda }$) hyperons along the beam direction in Au+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV

   STAR Collaboration: J. Adam🇺🇸 · L. Adamczyk🇵🇱 · J. R. Adams🇺🇸 · J. K. Adkins🇺🇸 · G. Agakishiev🇷🇺 · M. M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · I. Alekseev🇷🇺 · D. M. Anderson🇺🇸 · R. Aoyama🇯🇵 · A. Aparin🇷🇺 · D. Arkhipkin🇺🇸 and 340 other authors

   The $\Lambda$ ($\bar{\Lambda }$) hyperon polarization along the beam direction has been measured for the first time in Au+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV. The polarization dependence on the hyperons' emission angle relative to the second-order event plane exhibits a sine modulation, indicating a quadrupole pattern of the vorticity component along the beam direction. The polarization is found to increase in more peripheral collisions, and shows no strong transverse momentum ($p_T$) dependence at $p_T>1$ GeV/$c$. The magnitude of the signal is about five times smaller than those predicted by hydrodynamic and multiphase transport models; the observed phase of the emission angle dependence is also opposite to these model predictions. In contrast, blast-wave model calculations reproduce the modulation phase measured in the data and capture the centrality and transverse momentum dependence of the signal once the model is required to reproduce the azimuthal dependence of the Gaussian source radii measured via the Hanbury-Brown and Twiss intensity interferometry technique.

   nucl-exPRL(2019)·339 citations
2. 02*

   Improving the resolving power of Isochronous Mass Spectrometry by employing an in-ring mechanical slit

   J. H. Liu🇨🇳 · X. Xu🇨🇳 · P. Zhang🇨🇳 · P. Shuai🇨🇳 · X. L. Yan🇨🇳 · Y. H. Zhang🇨🇳 · M. Wang🇨🇳 · Yu. A. Litvinov🇩🇪 · H. S. Xu🇨🇳 · K. Blaum🇩🇪 · T. Bao🇨🇳 · H. Chen🇺🇸 and 22 other authors

   Isochronous Mass Spectrometry (IMS) in heavy-ion storage rings is an excellent experimental method for precision mass measurements of exotic nuclei. In the IMS, the storage ring is tuned in a special isochronous ion-optical mode. Thus, the mass-over-charge ratios of the stored ions are directly reflected by their respective revolution times in first order. However, the inevitable momentum spread of secondary ions increases the peak widths in the measured spectra and consequently limits the achieved mass precision. In order to achieve a higher mass resolving power, the ring aperture was reduced to 60 mm by applying a mechanical slit system at the dispersive straight section. The momentum acceptance was reduced as well as better isochronous conditions were achieved. The results showed a significant improvement of the mass resolving power reaching $5.2\times 10^5$, though at the cost of about 40\% ion loss.

   nucl-exNucl.Instrum.Meth.B(2020)·8 citations
3. 03*

   Quadrupole dominance in light Cd and Sn isotopes

   A.P. Zuker🇫🇷

   Shell model calculations with the neutron effective charge as single free parameter describe well the \bet and \bef rates for $N\le 64$ in the Cd and Sn isotopes. The former exhibit weak permanent deformation corroborating the prediction of a pseudo SU3 symmetry, which remains of heuristic value in the latter, though the pairing force erodes the quadrupole dominance. Calculations in $10^7$ and $10^{10}$-dimensional spaces exhibit almost identical patterns: A vindication of the shell model. For $N\ge 64$ quadrupole dominance is accentuated in the Cd isotopes and gives way to seniority dominance for the Sn isotopes.

   ↳ nucl-thnucl-ex2 citations
4. 04*

   Improved STEREO simulation with a new gamma ray spectrum of excited gadolinium isotopes using FIFRELIN

   H. Almazán🇩🇪 · L. Bernard🇫🇷 · A. Blanchet🇫🇷 · A. Bonhomme🇩🇪 · C. Buck🇩🇪 · A. Chebboubi🇫🇷 · P. del Amo Sanchez🇫🇷 · I. El Atmani🇫🇷 · J. Haser🇩🇪 · F. Kandzia🇫🇷 · S. Kox🇫🇷 · L. Labit🇫🇷 and 18 other authors

   The STEREO experiment measures the electron antineutrino spectrum emitted in a research reactor using the inverse beta decay reaction on H nuclei in a gadolinium loaded liquid scintillator. The detection is based on a signal coincidence of a prompt positron and a delayed neutron capture event. The simulated response of the neutron capture on gadolinium is crucial for the comparison with data, in particular in the case of the detection efficiency. Among all stable isotopes, ${}^{155}$Gd and ${}^{157}$Gd have the highest cross sections for thermal neutron capture. The excited nuclei after the neutron capture emit gamma rays with a total energy of about 8 MeV. The complex level schemes of ${}^{156}$Gd and ${}^{158}$Gd are a challenge for the modeling and prediction of the deexcitation spectrum, especially for compact detectors where gamma rays can escape the active volume. With a new description of the Gd(n,$\gamma$) cascades obtained using the FIFRELIN code, the agreement between simulation and measurements with a neutron calibration source was significantly improved in the STEREO experiment. A database of ten millions of deexcitation cascades for each isotope has been generated and is now available for the user.

   ↳ physics.ins-dethep-exnucl-exEPJA(2019)·30 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.