Thu·Jun 30, 2016Thursday·June 30, 2016

1. 01*

   First Measurement of Collectivity of Coexisting Shapes based on Type II Shell Evolution: The Case of ${}^{96}$Zr

   C. Kremer🇩🇪 · S. Aslanidou · S. Bassauer · M. Hilcker · A. Krugmann🇩🇪 · P. von Neumann-Cosel🇩🇪 · T. Otsuka🇯🇵 · N. Pietralla🇩🇪 · V. Yu. Ponomarev🇩🇪 · N. Shimizu🇯🇵 · M. Singer · G. Steinhilber and 4 other authors

   Background: Type II shell evolution has recently been identified as a microscopic cause for nuclear shape coexistence. Purpose: Establish a low-lying rotational band in 96-Zr. Methods: High-resolution inelastic electron scattering and a relative analysis of transition strengths are used. Results: The B(E2; 0_1^+ -> 2_2^+) value is measured and electromagnetic decay strengths of the secdond 2^+ state are deduced. Conclusions: Shape coexistence is established for 96-Zr. Type II shell evolution provides a systematic and quantitative mechanism to understand deformation at low excitation energies.

   nucl-exnucl-thPRL(2016)·112 citations
2. 02*

   Spectroscopy of the neutron-rich hypernucleus ${}_{\Lambda }^7$He from electron scattering

   T. Gogami🇯🇵 · C. Chen🇺🇸 · D. Kawama🇯🇵 · P. Achenbach🇩🇪 · A. Ahmidouch🇺🇸 · I. Albayrak🇺🇸 · D. Androic🇭🇷 · A. Asaturyan🇦🇲 · R. Asaturyan🇦🇲 · O. Ates🇺🇸 · P. Baturin🇺🇸 · R. Badui🇺🇸 and 74 other authors

   The missing mass spectroscopy of the ${}_{\Lambda }^7$He hypernucleus was performed, using the ${}^7$Li$(e,e^{\prime }{K}^{+}{)}_{\Lambda }^7$He reaction at the Thomas Jefferson National Accelerator Facility Hall C. The $\Lambda$ binding energy of the ground state (1/2${}^{+}$) was determined with a smaller error than that of the previous measurement, being $B_{\Lambda }$ = 5.55 $\pm$ 0.10(stat.) $\pm$ 0.11(sys.) MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at $B_{\Lambda }$ = 3.65 $\pm$ 0.20(stat.) $\pm$ 0.11(sys.) MeV was observed and assigned as a mixture of 3/2${}^{+}$ and 5/2${}^{+}$ states, confirming the "gluelike" behavior of $\Lambda$, which makes an unstable state in ${}^6$He stable against neutron emission.

   nucl-exnucl-thPRC(2016)·44 citations
3. 03*

   Production of highly-polarized positrons using polarized electrons at MeV energies

   (PEPPo Collaboration) D. Abbott🇺🇸 · P. Adderley🇺🇸 · A. Adeyemi🇺🇸 · P. Aguilera🇺🇸 · M. Ali🇺🇸 · H. Areti🇺🇸 · M. Baylac🇫🇷 · J. Benesch🇺🇸 · G. Bosson🇫🇷 · B. Cade🇺🇸 · A. Camsonne🇺🇸 · L.S. Cardman🇺🇸 and 53 other authors

   The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-$Z$ target. Positron polarization up to 82\% have been measured for an initial electron beam momentum of 8.19~MeV/$c$, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

   ↳ physics.acc-phhep-exnucl-exPRL(2016)·116 citations
4. 04*

   Multiplicity and Pseudorapidity distributions of charged particles in asymmetric and deformed nuclear collisions in a Wounded Quark Model

   O. S. K. Chaturvedi🇮🇳 · P. K. Srivastava🇮🇳 · Ashwini Kumar🇮🇳 · B. K. Singh🇮🇳

   The charged particle multiplicity ($n_{ch}$) and pseudorapidity density $(d{n}_{ch}/d\eta )$ are key observables to characterize the properties of matter created in heavy ion collisions. The dependence of these observables on collision energy and the collision geometry are a key tool to understand the underlying particle production mechanism. Recently a lot of focus has been made on asymmetric and deformed nuclei collisions since these collisions can provide a deeper understanding about the nature of quantum chromodynamics (QCD). On phenomenological perspective a unified model which describes the experimental data coming from various kind of collision experiments, is much needed to provide the physical insights about the production mechanism. In this paper, we have calculated the charged hadron multiplicities for nucleon-nucleus (such as proton-lead $(p-Pb)$ and asymmetric nuclei collisions like deutron-gold $(d-Au)$, and copper-gold $(Cu-Au)$ within a new version of wounded quark model (WQM) and shown their variation with respect to centrality. Further we have used a suitable density function within our WQM to calculate pseudorapidity density of charged hadrons at mid-rapidity in the collisions of deformed uranium nuclei. We found that our model with suitable density functions describes the experimental data for symmetric, asymmetric and deformed nuclei collisions simultaneously over a wide range of collision energy.

   ↳ hep-phnucl-exEur.Phys.J.Plus(2016)·16 citations
5. 05*

   Tetrahedral shapes of neutron-rich Zr isotopes from multidimensionally-constrained relativistic Hartree-Bogoliubov model

   Jie Zhao🇨🇳 · Bing-Nan Lu🇩🇪 · En-Guang Zhao🇨🇳 · Shan-Gui Zhou🇨🇳

   We develop a multidimensionally constrained relativistic Hartree-Bogoliubov (MDC-RHB) model in which the pairing correlations are taken into account by making the Bogoliubov transformation. In this model, the nuclear shape is assumed to be invariant under the reversion of $x$ and $y$ axes; i.e., the intrinsic symmetry group is $V_4$ and all shape degrees of freedom ${\beta }_{\lambda \mu }$ with even $\mu$ are included self-consistently. The RHB equation is solved in an axially deformed harmonic oscillator basis. A separable pairing force of finite range is adopted in the MDC-RHB model. The potential energy curves of neutron-rich even-even Zr isotopes are calculated with relativistic functionals DD-PC1 and PC-PK1 and possible tetrahedral shapes in the ground and isomeric states are investigated. The ground state shape of ${}^{110}$Zr is predicted to be tetrahedral with both functionals and so is that of ${}^{112}$Zr with the functional DD-PC1. The tetrahedral ground states are caused by large energy gaps around $Z=40$ and $N=70$ when ${\beta }_{32}$ deformation is included. Although the inclusion of the ${\beta }_{30}$ deformation can also reduce the energy around ${\beta }_{20}=0$ and lead to minima with pear-like shapes for nuclei around ${}^{110}$Zr, these minima are unstable due to their shallowness.

   ↳ nucl-thnucl-exPRC(2017)·61 citations
6. 06*

   Neutron-skin effect and centrality dependence of high-$p_{\mathrm{T}}$ observables in nuclear collisions

   Ilkka Helenius🇸🇪 · Hannu Paukkunen🇫🇮 · Kari J. Eskola🇫🇮

   We report on our studies of the neutron-skin effects in high-$p_{\mathrm{T}}$ observables at the LHC. We study the impact of the neutron-skin effect on the centrality dependence of inclusive direct photon, high-$p_{\mathrm{T}}$ hadron and $W^{\pm }$ production in nuclear collisions at the LHC. The neutron-skin effect refers to the observation that in spherical heavy nuclei, the tail of the neutron distribution extends farther than the distribution of protons, which can affect observables sensitive to electroweak phenomena in very peripheral collisions. We quantify this effect for direct photons, charged hadrons and W bosons as a function of the collision centrality. In the case of direct photons we find that it will be difficult to resolve the neutron-skin effect, given the uncertainties in the nuclear PDFs and their spatial dependence. With charged hadrons and W's, however, up to 20~\% unambiguous effects are expected for most peripheral collisions.

   ↳ hep-phnucl-exPoS(2016)·0 citations
7. 07*

   Quantum Phase Transition in the Shape of Zr isotopes

   Tomoaki Togashi🇯🇵 · Yusuke Tsunoda🇯🇵 · Takaharu Otsuka🇯🇵 · Noritaka Shimizu🇯🇵

   The rapid shape change in Zr isotopes near neutron number $N$=60 is identified to be caused by type II shell evolution associated with massive proton excitations to its $0g_{9/2}$ orbit, and is shown to be a quantum phase transition. Monte Carlo shell-model calculations are carried out for Zr isotopes of $N$=50-70 with many configurations spanned by eight proton orbits and eight neutron orbits. Energy levels and B(E2) values are obtained within a single framework in a good agreement with experiments, depicting various shapes in going from $N$=50 to 70. Novel coexistence of prolate and triaxial shapes is suggested.

   ↳ nucl-thnucl-exPRL(2016)·230 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.