Tue·Aug 25, 2020Tuesday·August 25, 2020

1. 01*

   Medium-induced modification of $Z$-tagged charged particle yields in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

   ATLAS Collaboration

   The yield of charged particles opposite to a $Z$ boson with large transverse momentum ($p_T$) is measured in 260 pb${}^{-1}$ of $pp$ and 1.7 nb${}^{-1}$ of Pb+Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The $Z$ boson tag is used to select hard-scattered partons with specific kinematics, and to observe how their showers are modified as they propagate through the quark-gluon plasma created in Pb+Pb collisions. Compared with $pp$ collisions, charged-particle yields in Pb+Pb collisions show significant modifications as a function of charged-particle $p_T$ in a way that depends on event centrality and $Z$ boson $p_T$. The data are compared with a variety of theoretical calculations and provide new information about the medium-induced energy loss of partons in a $p_T$ regime difficult to measure through other channels.

   nucl-exPRL(2021)·46 citations
2. 02*

   Measurement of inclusive jet production in Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 200 GeV by the STAR experiment

   Robert Licenik (for the STAR Collaboration)🇨🇿

   The STAR Collaboration reports the measurement of inclusive jet production in central (0-10%) and peripheral (60-80%) Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 200 GeV, using both charged-particle and fully-reconstructed jets. Jet reconstruction is carried out using the anti-$k_{\text{T}}$ algorithm with resolution parameters $R$ = 0.2, 0.3 and 0.4. Yield suppression of charged-particle jets is observed for central Au+Au collisions relative to both peripheral Au+Au collisions and a vacuum baseline utilizing PYTHIA 6 simulations. The magnitude of the suppression is similar to that measured at the LHC and can be described by theoretical calculations. No evidence of significant medium-induced jet broadening is observed, based on comparison of jet spectra at varying $R$. The yield suppression, when expressed as the jet transverse momentum shift corresponding to energy loss, is consistent in magnitude with coincidence measurements at RHIC based on direct-photon and hadron triggers. There is an indication of larger energy loss observed at the LHC.

   nucl-exhep-exPoS(2021)·2 citations
3. 03*

   Probing the Z = 6 spin-orbit shell gap with (p,2p) quasi-free scattering reactions

   I. Syndikus · M. Petri · A. O. Macchiavelli · S. Paschalis · C. A. Bertulani · T. Aumann · H. Alvarez-Pol · L. Atar · S. Beceiro-Novo · J. Benlliure · J. M. Boillos · K. Boretzky and 67 other authors

   The evolution of the traditional nuclear magic numbers away from the valley of stability is an active field of research. Experimental efforts focus on providing key spectroscopic information that will shed light into the structure of exotic nuclei and understanding the driving mechanism behind the shell evolution. In this work, we investigate the Z = 6 spin-orbit shell gap towards the neutron dripline. To do so, we employed ${}^A$N(p,2p)${}^{A-1}$C quasi-free scattering reactions to measure the proton component of the 2${}_1^{+}$ state of ${}^{16,18,20}$C. The experimental findings support the notion of a moderate reduction of the proton 1p${}_{1/2}$-1p${}_{3/2}$ spin-orbit splitting, at variance to recent claims for a prevalent Z = 6 magic number towards the neutron dripline.

   nucl-exPhys.Lett.(2020)·5 citations
4. 04*

   Beta decay of the very neutron-deficient ${}^{60}$Ge and ${}^{62}$Ge nuclei

   S.E.A. Orrigo🇪🇸 · B. Rubio🇪🇸 · W. Gelletly🇬🇧 · P. Aguilera🇨🇱 · A. Algora🇪🇸 · A.I. Morales🇪🇸 · J. Agramunt🇪🇸 · D.S. Ahn🇯🇵 · P. Ascher🇫🇷 · B. Blank🇫🇷 · C. Borcea🇷🇴 · A. Boso🇮🇹 and 39 other authors

   We report here the results of a study of the $\beta$ decay of the proton-rich Ge isotopes, ${}^{60}$Ge and ${}^{62}$Ge, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of ${}^{62}$Ge (73.5(1) ms), ${}^{60}$Ge (25.0(3) ms) and its daughter nucleus, ${}^{60}$Ga (69.4(2) ms). We measured individual $\beta$-delayed proton and $\gamma$ emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total $\beta$-delayed proton-emission branching ratio of 67(3)% has been obtained for ${}^{60}$Ge. New information has been obtained on the energy levels populated in ${}^{60}$Ga and on the 1/2${}^{-}$ excited state in the $\beta p$ daughter ${}^{59}$Zn. We extracted a ground state to ground state feeding of 85.3(3)% for the decay of ${}^{62}$Ge. Eight new $\gamma$ lines have been added to the de-excitation of levels populated in the ${}^{62}$Ga daughter.

   nucl-exPRC(2021)·22 citations
5. 05*

   Microscopic model for the collective enhancement of nuclear level densities

   Jie Zhao🇺🇸 · Tamara Nikšić🇭🇷 · Dario Vretenar🇭🇷

   A microscopic method for calculating nuclear level densities (NLD) is developed, based on the framework of energy density functionals. Intrinsic level densities are computed from single-quasiparticle spectra obtained in a finite-temperature self-consistent mean-field (SCMF) calculation that takes into account nuclear deformation, and is specified by the choice of the energy density functional (EDF) and pairing interaction. The total level density is calculated by convoluting the intrinsic density with the corresponding collective level density, determined by the eigenstates of a five-dimensional quadrupole or quadrupole plus octupole collective Hamiltonian. The parameters of the Hamiltonian (inertia parameters, collective potential) are consistently determined by deformation-constrained SCMF calculations using the same EDF and pairing interaction. The model is applied in the calculation of NLD of ${}^{94,96,98}$Mo, ${}^{106,108}$Pd, ${}^{106,112}$Cd, ${}^{160,162,164}$Dy, ${}^{166}$Er, and ${}^{170,172}$Yb, in comparison with available data. It is shown that the collective enhancement of the intrinsic level density, consistently computed from the eigenstates of the corresponding collective Hamiltonian, leads to total NLDs that are in excellent agreement with data over the whole energy range of measured values.

   ↳ nucl-thnucl-exPRC(2020)·19 citations
6. 06*

   The total reaction cross section of heavy-ion reactions induced by stable and unstable exotic beams: The low-energy regime

   L. F. Canto · V. Guimaraes🇫🇷 · J. Lubian🇧🇷 · M. S. Hussein🇧🇷

   In this review paper we present a detailed account of the extraction and the calculation of the total reaction cross section of strongly bound and weakly bound, stable and unstable, exotic, nuclei. We discuss the optical model and the more general coupled channels model of direct reactions. The effect of long-range absorption due to the coupling to excited states in the target and to the breakup continuum in the projectile is also discussed. The generalized optical theorem for charged particle scattering and the resulting sum-of differences method is then discussed. The so-called "quarter-point recipe" is discussed next, and the quarter-point angle is introduced as a simple and rapid mean to obtain the total reaction cross section. The last topic discussed is the reduction of the total reaction cross section that would allow a large body of data to sit on a single universal function. Such a universal function exists in the case of the fusion data, and the aim of this last topic of the review is to extend the fusion case to the total reaction, by adding the direct reaction contribution. Also discussed is the inclusive breakup cross section and how it can be used to extract the total reaction cross section of the interacting fragment with the target. This method is also known as the Surrogate method and represents a case of hybrid reactions. The sum of the integrated inclusive breakup cross section with the complete fusion cross section supplies the total fusion cross section. The main experimental methods to determine the total reaction cross section are also discussed, with emphasis in recent techniques developed to deal with reactions induced by unstable beams.

   ↳ nucl-thnucl-exEPJA(2020)·47 citations
7. 07*

   Vertexing detectors and vertexing performance in Run 2 in ALICE

   Mattia Faggin🇮🇹

   The ALICE apparatus includes an Inner Tracking System for high-precision vertexing and tracking at midrapidity. Thanks to this detector, remarkable results were obtained with Run 2 data in all collision systems studied at the LHC. In this contribution, the role of the ITS in the event, track and secondary vertex reconstruction is highlighted, and the comparison of the resolution on the track impact parameter to the collision point in data and Monte Carlo simulations is reported. Finally, some of the main physics results obtained in pp and Pb--Pb collisions relying on the excellent ALICE vertexing and tracking capabilities are presented.

   ↳ physics.ins-detnucl-exPoS(2021)·3 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.