Tue·May 29, 2018Tuesday·May 29, 2018

1. 01*

   Photoproduction of {\boldmath{${\pi }^0$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region

   M.Dieterle🇨🇭 · D.Werthmüller🇨🇭 · S.Abt🇨🇭 · F.Afzal🇩🇪 · P.Aguar Bartolome🇩🇪 · Z.Ahmed🇨🇦 · J.Ahrens🇩🇪 · J.R.M.Annand🇬🇧 · H.J.Arends🇩🇪 · M.Bashkanov🇬🇧 · R.Beck🇩🇪 · M.Biroth🇩🇪 and 72 other authors

   Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single ${\pi }^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an almost $4\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Reaction model predictions and PWA for $\gamma n\to n{\pi }^0$, based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. The results demonstrate clearly the importance of a measurement of the fully neutral final state for the isospin decomposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood.

   nucl-exPRC(2018)·10 citations
2. 02*

   Important role of projectile excitation in ${}^{16}$O+${}^{60}$Ni and ${}^{16}$O+${}^{27}$Al scattering at intermediate energies

   V.A.B. Zagatto🇧🇷 · F. Cappuzzello🇮🇹 · J. Lubian🇧🇷 · M. Cavallaro🇮🇹 · R. Linares · D. Carbone🇮🇹 · C. Agodi🇮🇹 · A. Foti🇮🇹 · S. Tudisco🇮🇹 · J.S. Wang🇨🇳 · J.R.B. Oliveira🇧🇷 · M. S. Hussein🇧🇷

   The elastic scattering angular distribution of the ${}^{16}$O${+}^{60}$Ni system at $260$ MeV was measured in the range of the Rutherford cross section down to $7$ orders of magnitude below. The cross sections of the lowest $2^{+}$ and $3^{-}$ inelastic states of the target were also measured over a several orders of magnitude range. Coupled channel (CC) calculations were performed and are shown to be compatible with the whole set of data only when including the excitation of the projectile and when the deformations of the imaginary part of the nuclear optical potential are taken into account. Similar results were obtained when the procedure is applied to the existing data on ${}^{16}$O${+}^{27}$Al elastic and inelastic scattering at $100$ and $280$ MeV. An analysis in terms of Dynamical Polarization Potentials (DPP) indicate the major role of coupled channel effects in the overlapping surface region of the colliding nuclei.

   nucl-exnucl-thPRC(2018)·26 citations
3. 03*

   The Nuclear Symmetry Energy at Sub-saturation Densities

   W.G. Lynch🇺🇸 · M.B. Tsang🇺🇸

   The density dependence of the nuclear symmetry energy governs important aspects of very neutron rich systems such as heavy nuclei and their collisions, neutron stars and their mergers. Many analyses of experimental data have generated constraints on the symmetry energy and its first derivative at saturation density, rho_0 ~ 2.7xE14 g/cm3. We show that each analysis does not accurately constrain the symmetry energy at rho_0, but rather at a lower density, rho_s, that is most sensitively probed by that analysis. Using published constraints on the symmetry energy and its first derivative at rho_0, we constrain the symmetry energy within a density range of 0.25rho_0 to 0.75rho_0 that is relevant to the inner crusts of neutron stars and to the neutrino-sphere of core-collapse supernovae. With appropriate data, the symmetry energy can be similarly constrained over a wider density range.

   nucl-exnucl-th15 citations
4. 04*

   The partial widths of the 16.1 MeV 2+ resonance in 12C

   Michael Munch · Hans Otto Uldall Fynbo🇩🇰

   The 16.1MeV 2+ resonance in 12C situated slightly above the proton threshold can decay by proton-, $\alpha$-, and $\gamma$ emission. The partial width for proton emission cannot be directly measured due to the low proton energy and the small branching ratio. Instead it must be indirectly derived from other observables. However, due to several inconsistent data the derived partial width varies by almost a factor 2 dependent on the data used. Here we trace the majority of this inconsistency to different measurements of the $(p,\alpha )$ cross sections. We have remeasured this cross section using modern large area silicon strip detectors allowing to measure all final state particles, which circumvents a normalization issue affecting some of the previous measurements. Based on this we determine ${\Gamma }_p$ = 21.0(13)eV. We discuss the implications for other observables related to the 16.1 MeV $2^{+}$ resonance and for isospin symmetry in the $A=12$ system. In addition, we conclude that the dataset currently used for the NACRE and NACRE II evaluation of the ${}^{11}\mathrm{B}(p,3\alpha )$ reaction should be scaled by a factor of 2/3. This impacts the reaction rate accordingly.

   nucl-exEPJA(2018)·7 citations
5. 05*

   Dispersion Theory in Electromagnetic Interactions

   B. Pasquini (Pavia U. & INFN, Pavia)🇮🇹 · M. Vanderhaeghen (Mainz U., Inst. Kernphysik & U. Mainz, PRISMA)🇩🇪

   We review various applications of dispersion relations (DRs) to the electromagnetic structure of hadrons. We discuss the way DRs allow one to extract information on hadron structure constants by connecting information from complementary scattering processes. We consider the real and virtual Compton scattering processes off the proton, and summarize recent advances in the DR analysis of experimental data to extract the proton polarizabilities, in comparison with alternative studies based on chiral effective field theories. We discuss a multipole analysis of real Compton scattering data, along with a DR fit of the energy-dependent dynamical polarizabilities. Furthermore, we review new sum rules for the double-virtual Compton scattering process off the proton, which allow for model independent relations between polarizabilities in real and virtual Compton scattering, and moments of nucleon structure functions. The information on the double-virtual Compton scattering is used to predict and constrain the polarizability corrections to muonic hydrogen spectroscopy.

   ↳ hep-phhep-exnucl-exnucl-thAnn.Rev.Nucl.Part.Sci.(2018)·40 citations
6. 06*

   New spectrum of negative-parity doubly charmed baryons: Possibility of two quasistable states

   Mao-Jun Yan🇨🇳 · Xiao-Hai Liu🇩🇪 · Sergi Gonzàlez-Solís🇨🇳 · Feng-Kun Guo🇨🇳 · Christoph Hanhart🇩🇪 · Ulf-G. Meißner🇩🇪 · Bing-Song Zou🇨🇳

   The discovery of ${\Xi }_{cc}^{++}$ by the LHCb Collaboration triggers predictions of more doubly charmed baryons. By taking into account both the $P$-wave excitations between the two charm quarks and the scattering of light pseudoscalar mesons off the ground state doubly charmed baryons, a set of negative-parity spin-1/2 doubly charmed baryons are predicted already from a unitarized version of leading order chiral perturbation theory. Moreover, employing heavy antiquark-diquark symmetry the relevant low-energy constants in the next-to-leading order are connected with those describing light pseudoscalar mesons scattering off charmed mesons, which have been well determined from lattice calculations and experimental data. Our calculations result in a spectrum richer than that of heavy mesons. We find two very narrow $J^P=1/2^{-}$ ${\Omega }_{cc}^P$, which very likely decay into ${\Omega }_{cc}{\pi }^0$ breaking isospin symmetry. In the isospin-1/2 ${\Xi }_{cc}^P$ sector, three states are predicted to exist below 4.2~GeV with the lowest one being narrow and the other two rather broad. We suggest to search for the ${\Xi }_{cc}^P$ states in the ${\Xi }_{cc}^{++}{\pi }^{-}$ mode. Searching for them and their analogues are helpful to establish the hadron spectrum.

   ↳ hep-phhep-exhep-latnucl-ex+1PRD(2018)·41 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.