Fri·Jan 5, 2018Friday·January 5, 2018

1. 01*

   Components of polarization-transfer to a bound proton in a deuteron measured by quasi-elastic electron scattering

   A1 Collaboration: D. Izraeli (1)🇮🇱 · I. Yaron (1)🇮🇱 · B.S. Schlimme (2)🇩🇪 · P. Achenbach (2)🇩🇪 · H. Arenhövel (2)🇩🇪 · A. Ashkenazi (1)🇮🇱 · J. Beričič (3)🇸🇮 · R. Böhm (2)🇩🇪 · D. Bosnar (4)🇭🇷 · E.O. Cohen (1)🇮🇱 · M.O. Distler (2)🇩🇪 · A. Esser (2)🇩🇪 and 22 other authors

   We report the first measurements of the transverse ($P_x$ and $P_y$) and longitudinal ($P_z$) components of the polarization transfer to a bound proton in the deuteron via the ${}^2\mathrm{H}(\vec{e},e^{\prime }\vec{p})$ reaction, over a wide range of missing momentum. A precise determination of the electron beam polarization reduces the systematic uncertainties on the individual components, to a level that enables a detailed comparison to a state-of-the-art calculation of the deuteron that uses free-proton electromagnetic form factors. We observe very good agreement between the measured and the calculated $P_x/P_z$ ratios, but deviations of the individual components. Our results cannot be explained by medium modified electromagnetic form factors. They point to an incomplete description of the nuclear reaction mechanism in the calculation.

   nucl-exPLB(2018)·11 citations
2. 02*

   Chronology of the three-body dissociation of ${}^8$He

   B. Laurent🇫🇷 · F.M. Marqués🇫🇷 · C. Angulo🇧🇪 · N.I. Ashwood🇬🇧 · M.J.G. Borge🇪🇸 · V. Bouchat🇧🇪 · W.N. Catford🇬🇧 · N.M. Clarke🇬🇧 · N. Curtis🇬🇧 · M. Freer🇬🇧 · F. Hanappe🇧🇪 · V. Kinnard🇧🇪 and 11 other authors

   The space and time configurations of the dissociation of ${}^8$He into ${}^6$He+$n$+$n$, on C and Pb targets, have been explored simultaneously for the first time. The final-state interactions in the $n$-$n$ and ${}^6$He-$n$ channels are successfully described within a model that considers independent emission of neutrons from a Gaussian volume with a given lifetime. The dissociation on C target exhibits a dominant sequential decay through the ground state of ${}^7$He, consistent with neutrons being emitted from a Gaussian volume of $r_{nn}^{\mathrm{rms}}=7.3\pm 0.6$~fm with a $n$-$n$ delay in the sequential channel of $1400\pm 400$~fm/$c$, in agreement with the lifetime of ${}^7$He. The lower-statistics data on Pb target correspond mainly to direct breakup, and are well described using the $n$-$n$ volume measured, without any $n$-$n$ delay. The validity of the phenomenological model used is discussed.

   nucl-exnucl-thJ.Phys.G(2019)·9 citations
3. 03*

   The formation of the heaviest elements

   Anna Frebel (MIT)🇺🇸 · Timothy C. Beers (Notre Dame)🇺🇸

   The rapid neutron-capture process needed to build up many of the elements heavier than iron seems to take place primarily in neutron-star mergers, not supernova explosions.

   ↳ astro-ph.SRastro-ph.COastro-ph.GAnucl-ex+1Phys.Today·9 citations
4. 04*

   Nucleon Effective Masses in Neutron-Rich Matter

   Bao-An Li🇺🇸 · Bao-Jun Cai🇨🇳 · Lie-Wen Chen🇨🇳 · Jun Xu🇨🇳

   Various kinds of isovector nucleon effective masses are used in the literature to characterize the momentum/energy dependence of the nucleon symmetry potential or self-energy due to the space/time non-locality of the underlying isovector strong interaction in neutron-rich nucleonic matter. The multifaceted studies on nucleon isovector effective masses are multi-disciplinary in nature. Besides structures, masses and low-lying excited states of nuclei as well as nuclear reactions, studies of the isospin dependence of short-range correlations in nuclei from scatterings of high-energy electrons and protons on heavy nuclei also help understand nucleon effective masses especially the so-called E-mass in neutron-rich matter. A thorough understanding of all kinds of nucleon effective masses has multiple impacts on many interesting issues in both nuclear physics and astrophysics. We review some of the significant progresses made in recent years by the nuclear physics community in resolving some of the hotly debated and longstanding issues regarding nucleon effective masses especially in dense neutron-rich matter.

   ↳ nucl-thastro-ph.HEhep-exhep-ph+1PPNP(2018)·220 citations
5. 05*

   Examining empirical evidence of the effect of superfluidity on the fusion barrier

   Guillaume Scamps🇯🇵

   Background: Several Time-Dependent Hartree-Fock-Bogoliubov (TDHFB) calculations predict that the super- fluidity enhances the fluctuations of the fusion barrier. This effect is not fully understood and not yet revealed experimentally. Purpose: The goal of this study is to investigate empirically the effect of the superfluidity on the fusion barrier width. Method: First, the local regression method is introduce and used to determine the barrier distribution more precisely. A second method that requires only the calculation of an integral of the cross section is developed to determine accurately the fluctuations of the barrier. A benchmark is done between this two methods and with the fitting method usually used. This integral method showing a better agreement in a test case, it is applied systematically in a selection of 115 fusion reactions. Results: The fluctuations of the barrier for superfluid systems are on average larger than for magic or semi-magic nuclei. This is due to the deformation effects and the effect of the superfluidity. To disentangle those two effects, we compare the experimental width to the width estimated from a model that takes into account the tunneling, the deformation and the vibration effect. The deviation of the experimental width from this theory for reaction between superfluid nuclei shows that the superfluidity enhance the fusion barrier width. Conclusions: This analysis shows that the predicted effect of the superfluidity on the width of the barrier is real and is of the order of 1 MeV.

   ↳ nucl-thnucl-exPRC(2018)·20 citations
6. 06*

   A remark on the sign change of the four-particle azimuthal cumulant in small systems

   Adam Bzdak🇵🇱 · Guo-Liang Ma🇨🇳

   The azimuthal cumulants, $c_2\{2\}$ and $c_2\{4\}$, originating from the global conservation of transverse momentum in the presence of hydro-like elliptic flow are calculated. We observe the sign change of $c_2\{4\}$ for small number of produced particles. This is in a qualitative agreement with the recent ATLAS measurement of multi-particle azimuthal correlations with the subevent cumulant method.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2018)·10 citations
7. 07*

   $N^{\ast }$ Form Factors based on a Covariant Quark Model

   G. Ramalho🇧🇷

   We discuss the results of the covariant spectator quark model for the several ${\gamma }^{\ast }N\to N^{\ast }$ transitions, where $N$ is the nucleon and $N^{\ast }$ a nucleon excitation. More specifically, we present predictions for the form factors and transition amplitudes associated with the resonances $N(1440)1/2^{+}$, $N(1535)1/2^{-}$, $N(1520)3/2^{-}$, $\Delta (1620)1/2^{-}$ and $N(1650)1/2^{-}$. The estimates based on valence quark degrees of freedom are compared with the available data, particularly with the recent Jefferson Lab data at low and large momentum transfer ($Q^2$). In general, the estimates are in good agreement with the empirical data for $Q^2>2$ GeV${}^2$, with a few exceptions. The results are discussed in terms of the role of the valence quarks and the meson cloud excitations for the different resonances $N^{\ast }$. We also review our results for the resonance $\Delta (1232)3/2^{+}$ and discuss the relevance of the pion cloud component for the magnetic dipole form factor and the electric and Coulomb quadrupole form factors.

   ↳ hep-phhep-exhep-latnucl-ex+1Few Body Syst.(2018)·25 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.