Mon·Oct 16, 2017Monday·October 16, 2017

1. 01*

   Search for excited states in ${}^{25}$O

   M.D. Jones🇺🇸 · K. Fossez🇺🇸 · T. Baumann🇺🇸 · P.A. DeYoung🇺🇸 · J.E. Finck🇺🇸 · N. Frank🇺🇸 · A.N. Kuchera🇺🇸 · N. Michel🇺🇸 · W. Nazarewicz🇺🇸 · J. Rotureau🇺🇸 · J.K. Smith🇺🇸 · S.L. Stephenson🇺🇸 and 3 other authors

   Theoretical calculations suggest the presence of low-lying excited states in ${}^{25}$O. Previous experimental searches by means of proton knockout on ${}^{26}$F produced no evidence for such excitations. We search for excited states in ${}^{25}$O using the ${}^{24}\text{O}(d,p){}^{25}\text{O}$ reaction. The theoretical analysis of excited states in unbound ${}^{25,27}$O is based on the configuration interaction approach that accounts for couplings to the scattering continuum. We use invariant-mass spectroscopy to measure neutron-unbound states in ${}^{25}$O. For the theoretical approach, we use the complex-energy Gamow Shell Model and Density Matrix Renormalization Group method with a finite-range two-body interaction optimized to the bound states and resonances of ${}^{23-26}$O, assuming a core of ${}^{22}$O. We predict energies, decay widths, and asymptotic normalization coefficients. Our calculations in a large $spdf$ space predict several low-lying excited states in ${}^{25}$O of positive and negative parity, and we obtain an experimental limit on the relative cross section of a possible $J^{\pi }={1/2}^{+}$ state with respect to the ground-state of ${}^{25}$O at ${\sigma }_{1/2+}/{\sigma }_{g.s.}=0.25_{-0.25}^{+1.0}$. We also discuss how the observation of negative parity states in ${}^{25}$O could guide the search for the low-lying negative parity states in ${}^{27}$O. Previous experiments based on the proton knockout of ${}^{26}$F suffered from the low cross sections for the population of excited states in ${}^{25}$O because of low spectroscopic factors. In this respect, neutron transfer reactions carry more promise.

   nucl-exPRC(2017)·22 citations
2. 02*

   New results on collectivity with ALICE

   Omar Vázquez🇲🇽

   An overview of recent ALICE results aimed to understand collective phenomena in Pb-Pb collisions at the LHC is presented. These include the centrality dependence of the transverse momentum ($p_{\mathrm{T}}$) distributions of charged pions, kaons, and protons as well as results on anisotropic flow using data from Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. In addition, comparisons between data and model predictions are presented.

   ↳ hep-exnucl-ex2 citations
3. 03*

   Universality of the underlying event in pp collisions

   Antonio Ortiz🇲🇽 · Lizardo Valencia Palomo🇲🇽

   In this paper we study ATLAS results on underlying event in pp collisions at $\sqrt{s}$=0.9, 7 and 13 TeV. We show that the center-of-mass energy dependences of the charged-particle production sensitive to the underlying event ("transverse" region) and to the hardest partonic interaction ("towards" and "away" regions) in pp collisions can be both understood in terms of the change of the inclusive average multiplicity. Within uncertainties, the corresponding particle production as a function of the leading charged particle shows no significant $\sqrt{s}$-dependence for the three regions once they are scaled according to the relative change in multiplicity. The scaling properties reported here are well reproduced by PYTHIA 8.212 tune Monash 2013 and suggest an universality of the underlying event in hadronic interactions at high $\sqrt{s}$. Based on the simulations, we observed that the same scaling properties are also present in the average number of multi-partonic interactions as a function of the leading charged particle. Moreover, the multiplicity distributions associated to the underlying event exhibit a KNO scaling.

   ↳ hep-exnucl-exPRD(2017)·37 citations
4. 04*

   Light Neutron-Rich Hypernuclei from the Importance-Truncated No-Core Shell Model

   Roland Wirth🇩🇪 · Robert Roth🇩🇪

   We explore the systematics of ground-state and excitation energies in singly-strange hypernuclei throughout the helium and lithium isotopic chains --- from ${}_{\Lambda }^5$He to ${}_{\Lambda }^{11}$He and from ${}_{\Lambda }^7$Li to ${}_{\Lambda }^{12}$Li --- in the ab initio no-core shell model with importance truncation. All calculations are based on two- and three-baryon interaction from chiral effective field theory and we employ a similarity renormalization group transformation consistently up to the three-baryon level to improve the model-space convergence. While the absolute energies of hypernuclear states show a systematic variation with the regulator cutoff of the hyperon-nucleon interaction, the resulting neutron separation energies are very stable and in good agreement with available data for both nucleonic parents and their daughter hypernuclei. We provide predictions for the neutron separation energies and the spectra of neutron-rich hypernuclei that have not yet been observed experimentally. Furthermore, we find that the neutron drip lines in the helium and lithium isotopic chains are not changed by the addition of a hyperon.

   ↳ nucl-thhep-phnucl-exPLB(2018)·57 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.