Fri·Oct 19, 2018Friday·October 19, 2018

1. 01*

   New measurement of pion directed flow relative to the spectator plane by the NA49 experiment at CERN

   Evgeny Kashirin🇷🇺 · Oleg Golosov🇷🇺 · Viktor Klochkov🇩🇪 · Ilya Selyuzhenkov (for the NA49 Collaboration)🇷🇺

   We report a new measurement of negatively charged pion directed flow $v_1$ relative to the spectator plane for Pb+Pb collisions at the beam energy 40A GeV recorded by the NA49 experiment at CERN. $v_1$ is reported as a function of rapidity and transverse momentum in different classes of collision centrality. The projectile spectator plane is estimated using transverse segmentation of the NA49 forward hadron calorimeter. The new results extend the NA49 data for $v_1$, which was previously measured only relative to the participant plane, and complement recent preliminary data by the NA61/SHINE collaboration and published results from the STAR at RHIC beam energy scan program.

   nucl-exhep-ex3 citations
2. 02*

   Interplay between nuclear shell evolution and shape deformation revealed by magnetic moment of 75Cu

   Y. Ichikawa · H. Nishibata · Y. Tsunoda · A. Takamine · K. Imamura · T. Fujita · T. Sato · S. Momiyama · Y. Shimizu · D. S. Ahn · K. Asahi · H. Baba and 32 other authors

   Exotic nuclei are characterized by a number of neutrons (or protons) in excess relative to stable nuclei. Their shell structure, which represents single-particle motion in a nucleus, may vary due to nuclear force and excess neutrons, in a phenomenon called shell evolution. This effect could be counterbalanced by collective modes causing deformations of the nuclear surface. Here, we study the interplay between shell evolution and shape deformation by focusing on the magnetic moment of an isomeric state of the neutron-rich nucleus 75Cu. We measure the magnetic moment using highly spin-controlled rare-isotope beams and achieving large spin alignment via a two-step reaction scheme that incorporates an angular-momentum-selecting nucleon removal. By combining our experiments with numerical simulations of many-fermion correlations, we find that the low-lying states in 75Cu are, to a large extent, of single-particle nature on top of a correlated 74Ni core. We elucidate the crucial role of shell evolution even in the presence of the collective mode, and within the same framework, we consider whether and how the double magicity of the 78Ni nucleus is restored, which is also of keen interest from the perspective of nucleosynthesis in explosive stellar processes.

   nucl-exNat.Phys.(2019)·29 citations
3. 03*

   Nucleon spin structure measurements at Jefferson Lab

   Alexandre Deur🇺🇸

   We summarize the measurements investigating the nucleon spin structure done at Jefferson Lab, a multi-GeV continuous electron beam facility located in Newport News, Virgina, USA. After motivating spin structure studies, we explain how Jefferson Lab uniquely contributes to them and describe the experimental program that was achieved with energies up to 6 GeV. We then discuss the continuation of this program at the higher energies now available thanks to the recent 12 GeV upgrade of Jefferson Lab's accelerator.

   nucl-exnucl-th1 citation
4. 04*

   Large violation of the flavour SU(3) symmetry in $\eta$MAID2018 isobar model

   V. A. Kuznetsov🇷🇺 · M.V. Polyakov🇷🇺

   We demonstrate that the explanation of the neutron anomaly around $W\sim 1685$MeV in $\gamma N\to \eta N$ reactions provided by the $\eta$MAID2018 isobar model is based on large violation of the flavour SU(3) symmetry in hadron interactions. This is yet another example of how conventional explanation (without invoking exotic narrow nucleon resonance) of the neutron anomaly metamorphoses into unconventional physics picture of hadron interactions. A possibility to mend the flavour SU(3) symmetry for some of resonances in $\eta$MAID model is discussed.

   ↳ nucl-thhep-phnucl-ex1 citation
5. 05*

   Recent developments in radioactive charged-particle emissions and related phenomena

   Chong Qi🇸🇪 · Roberto Liotta🇸🇪 · Ramon Wyss🇸🇪

   The advent and intensive use of new detector technologies as well as radioactive ion beam facilities have opened up possibilities to investigate alpha, proton and cluster decays of highly unstable nuclei. This article provides a review of the current status of our understanding of clustering and the corresponding radioactive particle decay process in atomic nuclei. We put alpha decay in the context of charged-particle emissions which also include one- and two-proton emissions as well as heavy cluster decay. The experimental as well as the theoretical advances achieved recently in these fields are presented. Emphasis is given to the recent discoveries of charged-particle decays from proton-rich nuclei around the proton drip line. Those decay measurements have shown to provide an important probe for studying the structure of the nuclei involved. Developments on the theoretical side in nuclear many-body theories and supercomputing facilities have also made substantial progress, enabling one to study the nuclear clusterization and decays within a microscopic and consistent framework. We report on properties induced by the nuclear interaction acting in the nuclear medium, like the pairing interaction, which have been uncovered by studying the microscopic structure of clusters. The competition between cluster formations as compared to the corresponding alpha-particle formation are included. In the review we also describe the search for super-heavy nuclei connected by chains of alpha and other radioactive particle decays.

   ↳ nucl-thnucl-exPPNP(2019)·119 citations
6. 06*

   Partial conservation of seniority and its unexpected influence on E2 transitions in $g_{9/2}$ nuclei

   Chong Qi🇸🇪

   There exist two uniquely defined $v=4$ states in systems within a $j=9/2$ subshell, which automatically conserve seniority and do not mix with other states. Here I show that the partial conservation of seniority plays an essential role in our understanding of the electric quadrupole transitions of the semimagic nuclei involving $j=9/2$ subshells, including the long-lived $8^{+}$ isomer in ${}^{94}$Ru. The effects of configuration mixing from neighboring subshells on the structure of those unique states are analysed. It is shown that a sharp transition from pure seniority coupling to a significant mixture between the $v=2$ and $v=4$ states may be induced by the cross-orbital non-diagonal interaction matrix elements. Such strong mixture is essential to explain the observed E2 transition properties of $N=50$ isotones ${}^{96}$Pd and ${}^{94}$Ru.

   ↳ nucl-thnucl-exPLB(2017)·25 citations
7. 07*

   Effect of energy conservation on in-medium $\text{mbox}NN\to \text{mbox}N\Delta$ cross section in isospin-asymmetric nuclear matter

   Ying Cui🇨🇳 · Yingxun Zhang🇨🇳 · Zhuxia Li🇨🇳

   In this paper, the in-medium $NN\to N\Delta$ cross section is calculated in the framework of the one-boson exchange model by including the isovector mesons, i.e. $\delta$ and $\rho$ mesons. Due to the isospin exchange in the $NN\to N\Delta$ process, the vector self-energies of the outgoing particles are modified relative to the incoming particles in isospin asymmetric nuclear matter, and it leads to the effective energies of the incoming $NN$ pair being different from the outgoing $N\Delta$ pair. This effect is investigated in the calculation of the in-medium $NN\to N\Delta$ cross section. With the corrected energy conservation, the cross sections of the ${\Delta }^{++}$ and ${\Delta }^{+}$ channels are suppressed, and the cross sections of the ${\Delta }^0$ and ${\Delta }^{-}$ channels are enhanced relative to the results obtained without properly considering the potential energy changes. Our results further confirm the dependence of medium correction factor, $R={\sigma }_{NN\to N\Delta }^{\ast }/{\sigma }_{NN\to N\Delta }^{\text{free}}$, on the charge state of $NN\to N\Delta$ especially around the threshold energy, but the isospin splitting of medium correction factor $R$ becomes weak at high beam energies.

   ↳ nucl-thnucl-exPRC(2018)·14 citations
8. 08*

   Elliptic flow of transported and non-transported proton in Au+Au collisions within the UrQMD model

   Biao Tu🇨🇳 · Shusu Shi🇨🇳 · Feng Liu🇨🇳

   With the framework of UrQMD model, by tracing the number of initial quarks in protons, we study the elliptic flow of transported protons, poduced protons and anti-protons in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 39, 200 GeV. The difference of elliptic flow between transported protons and anti-protons is observed. The results of UrQMD model show a good agreement with the STAR results at low energies, but are deviate at high energies. It partly explains the $v_2$ difference between proton and anti-proton observed in the Beam Energy Scan program in Relativistic Heavy Ion Collider~(RHIC).

   ↳ nucl-thnucl-exCPC(2019)·9 citations
9. 09*

   Low-energy Bremsstrahlung photon in relativistic nucleon+nucleon collisions

   Taesoo Song🇩🇪 · Pierre Moreau🇩🇪

   We study the production of Bremsstrahlung photon in relativistic nucleon+nucleon collisions by introducing a deceleration time of electromagnetic currents. It is found that Bremsstrahlung photon spectrum at low energy does not depend on the deceleration time but solely on the amount of reduced electromagnetic current in collision. On the other hand, the photon spectrum becomes soft with increasing deceleration time. We also find that Bremsstrahlung photon spectrum in p+n collisions is considerably different from that in p+p collisions at low energy.

   ↳ nucl-thnucl-exPRD(2018)·4 citations
10. 10*

    Recovery of Saturated $\gamma$ Signal Waveforms by Artificial Neural Networks

    Yu Liu🇨🇳 · Jing-Jun Zhu🇨🇳 · Neil Roberts🇬🇧 · Ke-Ming Chen🇨🇳 · Yu-Lu Yan🇨🇳 · Shuang-Rong Mo🇨🇳 · Peng Gu🇨🇳 · Hao-Yang Xing🇨🇳

    Particle may sometimes have energy outside the range of radiation detection hardware so that the signal is saturated and useful information is lost. We have therefore investigated the possibility of using an Artificial Neural Network (ANN) to restore the saturated waveforms of $\gamma$ signals. Several ANNs were tested, namely the Back Propagation (BP), Simple Recurrent (Elman), Radical Basis Function (RBF) and Generalized Radial Basis Function (GRBF) neural networks (NNs) and compared with the fitting method based on the Marrone model. The GBRFNN was found to perform best.

    ↳ physics.data-anhep-exnucl-ex3 citations
11. 11*

    The new Felsenkeller 5 MV underground accelerator

    Daniel Bemmerer🇩🇪 · Thomas E. Cowan🇩🇪 · Alexander Domula🇩🇪 · Toralf Döring🇩🇪 · Marcel Grieger🇩🇪 · Sebastian Hammer🇩🇪 · Thomas Hensel🇩🇪 · Lisa Hübinger🇩🇪 · Arnd R. Junghans🇩🇪 · Felix Ludwig🇩🇪 · Stefan E. Müller🇩🇪 · Stefan Reinicke🇩🇪 and 9 other authors

    The field of nuclear astrophysics is devoted to the study of the creation of the chemical elements. By nature, it is deeply intertwined with the physics of the Sun. The nuclear reactions of the proton-proton cycle of hydrogen burning, including the 3He({\alpha},{\gamma})7Be reaction, provide the necessary nuclear energy to prevent the gravitational collapse of the Sun and give rise to the by now well-studied pp, 7Be, and 8B solar neutrinos. The not yet measured flux of 13N, 15O, and 17F neutrinos from the carbon-nitrogen-oxygen cycle is affected in rate by the 14N(p,{\gamma})15O reaction and in emission profile by the 12C(p,{\gamma})13N reaction. The nucleosynthetic output of the subsequent phase in stellar evolution, helium burning, is controlled by the 12C({\alpha},{\gamma})16O reaction. In order to properly interpret the existing and upcoming solar neutrino data, precise nuclear physics information is needed. For nuclear reactions between light, stable nuclei, the best available technique are experiments with small ion accelerators in underground, low-background settings. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso/Italy, using a 0.4 MV accelerator. The present contribution reports on a higher-energy, 5.0 MV, underground accelerator in the Felsenkeller underground site in Dresden/Germany. Results from {\gamma}-ray, neutron, and muon background measurements in the Felsenkeller underground site in Dresden, Germany, show that the background conditions are satisfactory for nuclear astrophysics purposes. The accelerator is in the commissioning phase and will provide intense, up to 50{\mu}A, beams of 1H+, 4He+ , and 12C+ ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity.

    ↳ physics.acc-phnucl-exphysics.ins-det8 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.