Thu·Aug 14, 2014Thursday·August 14, 2014

1. 01*

   Influence of angular momentum and Coulomb interaction of colliding nuclei on their multifragmentation

   A. Ergun · H. Imal · N. Buyukcizmeci🇩🇪 · R. Ogul🇹🇷 · A.S. Botvina🇩🇪

   Theoretical calculations are performed to investigate the angular momentum and Coulomb effects on fragmentation and multifragmentation in peripheral heavy-ion collisions at Fermi energies. Inhomogeneous distributions of hot fragments in the freeze-out volume are taken into account by microcanonical Markov chain calculations within the Statistical Multifragmentation Model (SMM). Including an angular momentum and a long-range Coulomb interaction between projectile and target residues leads to new features in the statistical fragmentation picture. In this case, one can obtain specific correlations of sizes of emitted fragments with their velocities and an emission in the reaction plane. In addition, one may see a significant influence of these effects on the isotope production both in the midrapidity and in the kinematic regions of the projectile/target. The relation of this approach to the simulations of such collisions with dynamical models is also discussed.

   ↳ nucl-thnucl-exPRC(2015)·10 citations
2. 02*

   Nucleon and $\Delta$ elastic and transition form factors

   Jorge Segovia🇺🇸 · Ian C. Cloet🇺🇸 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪

   We compute nucleon and Delta elastic and transition form factors, and compare predictions made using a framework built upon a Faddeev equation kernel and interaction vertices that possess QCD-like momentum dependence with results obtained using a vector-vector contact-interaction. The comparison emphasises that experiment is sensitive to the momentum dependence of the running couplings and masses in the strong interaction sector of the Standard Model and highlights that the key to describing hadron properties is a veracious expression of dynamical chiral symmetry breaking in the bound-state problem. Amongst the results we describe, the following are of particular interest: $G_E^p(Q^2)/G_M^p(Q^2)$ possesses a zero at $Q^2=9.5Ge{V}^2$; any change in the interaction which shifts a zero in the proton ratio to larger $Q^2$ relocates a zero in $G_E^n(Q^2)/G_M^n(Q^2)$ to smaller $Q^2$; and there is likely a value of momentum transfer above which $G_E^n>G_E^p$. Regarding the $\Delta (1232)$-baryon, we find that, inter alia: the electric monopole form factor exhibits a zero; the electric quadrupole form factor is negative, large in magnitude, and sensitive to the nature and strength of correlations in the $\Delta (1232)$ Faddeev amplitude; and the magnetic octupole form factor is negative so long as rest-frame P- and D-wave correlations are included. In connection with the N-to-Delta transition, the momentum-dependence of the magnetic transition form factor, $G_M^{\ast }$, matches that of $G_M^n$ once the momentum transfer is high enough to pierce the meson-cloud; and the electric quadrupole ratio is a keen measure of diquark and orbital angular momentum correlations.

   ↳ nucl-thhep-lathep-phnucl-exFew Body Syst.(2014)·135 citations
3. 03*

   Old neutron stars as probes of isospin-violating dark matter

   Hao Zheng🇨🇳 · Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳

   Isospin-violating dark matter (IVDM), which couples differently with protons and neutrons, provides a promising mechanism to ameliorate the tension among recent direct detection experiments. Assuming DM is non-interacting bosonic asymmetric IVDM, we investigate how the existence of old neutron stars limits the DM-proton scattering cross-section ${\sigma }_{\mathrm{p}}$, especially the effects of the isospin violating DM-nucleon interactions and the symmetry energy in the equation of state of isospin asymmetric nuclear matter. Our calculations are completely based on general relativity and especially the structure of neutron stars is obtained by solving the Tolman-Oppenheimer-Volkoff equations with nuclear matter equation of state constrained by terrestrial experiments. We find that, by considering the more realistic neutron star model rather than a simple uniform neutron sphere as usual, the ${\sigma }_{\mathrm{p}}$ bounds from old neutron stars can be varied by more than an order of magnitude depending on the specific values of the DM neutron-to-proton coupling ratio $f_{\mathrm{n}}/f_{\mathrm{p}}$, and they can be further varied by more than a factor of two depending on the density dependence of the symmetry energy. In particular, we demonstrate that the observed nearby isolated old neutron star PSR B1257+12 can set a very strong limit on ${\sigma }_{\mathrm{p}}$ for low-mass DM particles ($\le 20\mathrm{GeV}$) that reaches a sensitivity beyond the current best limits from direct detection experiments and disfavors the DM interpretation of previously-reported positive experimental results, including the IVDM.

   ↳ nucl-thastro-ph.COastro-ph.SRhep-ph+1ApJ(2015)·23 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.