Fri·Jan 11, 2019Friday·January 11, 2019

1. 01*

   Novel data and a new parametrization of the electric dipole strength in nuclei with 88 < A < 116

   Eckart Grosse🇩🇪 · Arnd R. Junghans🇩🇪 · Krasimir Kosev · Gencho Rusev🇺🇸 · Klaus D. Schilling · Ronald Schwengner🇩🇪 · Andreas Wagner🇩🇪

   A hitherto unexplored method for the experimental determination of the photon strength function up to the neutron separation energy was developed at the Radiation Source ELBE in Dresden. It was applied to various heavy nuclei, preferentially to nuclides with increasing distance to the N=50 neutron shell, and it covers the high level density excitation energy range above 4 MeV. The observed quasi-continuous spectra of scattered photons can be -- after a proper correction for multi-step processes -- directly combined to nuclear photo effect data from literature. A remarkably good match of the photon strengths as measured below and above the neutron emission threshold is observed. The wide energy coverage of the combined data forms an excellent basis to derive a parameterization for the dipole strength function fully covering the range across the nucleon separation energies. In addition to the parameters defining the deformation of the nuclear ground states only one additional constant is needed to describe the dipole strength in the nuclei with 88<A<116. The new parameterization differs significantly from the prescriptions generally used in network calculations, e.g. those of interest for the cosmic nucleo-synthesis.

   nucl-exProceedings of Science(PSF)004 (2007)·0 citations
2. 02*

   Performance studies of anisotropic flow with MPD at NICA

   Petr Parfenov🇷🇺 · Arkadiy Taranenko🇷🇺 · Ilya Selyuzhenkov🇷🇺 · Peter Senger🇷🇺

   The Multi-Purpose Detector (MPD) at NICA collider has a substantial discovery potential concerning the exploration of the QCD phase diagram in the region of high net-baryon densities and moderate temperatures. The anisotropic transverse flow is one of the key observables to study the properties of dense matter created in heavy-ion collisions. The MPD performance for anisotropic flow measurements is studied with Monte-Carlo simulations of gold ions at NICA energies $\sqrt{s_{NN}}=4-11$ GeV using different heavy-ion event generators. Different combinations of the MPD detector subsystems are used to investigate the possible systematic biases in flow measurements, and to study effects of detector azimuthal non-uniformity. The resulting performance of the MPD for flow measurements is demonstrated for directed and elliptic flow of identified charged hadrons as a function of rapidity and transverse momentum in different centrality classes.

   ↳ hep-exnucl-exnucl-thEPJ Web Conf.(2019)·10 citations
3. 03*

   The pion-nucleon $\sigma$ term from pionic atoms

   E. Friedman🇮🇱 · A. Gal🇮🇱

   Earlier work suggested that the in-medium $\pi N$ threshold isovector amplitude $b_1(\rho )$ gets renormalized in pionic atoms by about 30% away from its $\rho =0$ free-space value, relating such renormalization to the leading low-density decrease of the in-medium quark condensate $<\bar{q}q>$ and the pion decay constant $f_{\pi }$ in terms of the pion-nucleon $\sigma$ term ${\sigma }_{\pi N}$. Accepting the validity of this approach, we extracted ${\sigma }_{\pi N}$ from a large-scale fit of pionic-atom level shift and width data across the periodic table. Our fitted value ${\sigma }_{\pi N}=57\pm 7$ MeV is robust with respect to variation of $\pi N$ interaction terms other than the isovector $s$-wave term with which ${\sigma }_{\pi N}$ was associated. Higher order corrections to the leading order in density involve some cancellations, suggesting thereby only a few percent overall systematic uncertainty. The value of ${\sigma }_{\pi N}$ derived here agrees with values obtained in several recent studies based on near-threshold $\pi N$ phenomenology, but sharply disagrees with values obtained in recent direct lattice QCD calculations.

   ↳ nucl-thhep-phnucl-exPLB(2019)·47 citations
4. 04*

   Event activity measurements and mid-rapidity correlations in 200 GeV p+Au collisions at STAR

   David Stewart🇺🇸

   These proceedings report preliminary measurements of correlations between mid-rapidity charged tracks and high-rapidity event activity (EA) at STAR for $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ p+Au collisions taken in 2015. These correlations are intriguing because they inform the current debate over use of the Glauber model in `small' systems (here meaning p+A or d+A and denoted as `s+A') and have implications for calculating nuclear modification and quenching observables in these systems. The results support concerns about centrality binning in p+Au collisions, and as such motivate using ratios of semi-inclusive, as opposed to fully inclusive, jet spectra to look for jet enhancement or suppression.

   ↳ hep-exnucl-exMDPI Proc.(2019)·0 citations
5. 05*

   Spectrum and structure of octet and decuplet baryons and their positive-parity excitations

   Chen Chen🇧🇷 · Gastao Krein🇧🇷 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪 · Jorge Segovia🇪🇸

   A continuum approach to the three valence-quark bound-state problem in quantum field theory, employing parametrisations of the necessary kernel elements, is used to compute the spectrum and Poincaré-covariant wave functions for all flavour-$SU(3)$ octet and decuplet baryons and their first positive-parity excitations. Such analyses predict the existence of nonpointlike, dynamical quark-quark (diquark) correlations within all baryons; and a uniformly sound description of the systems studied is obtained by retaining flavour-antitriplet--scalar and flavour-sextet--pseudovector diquarks. Thus constituted, the rest-frame wave function of every system studied is primarily $S$-wave in character; and the first positive-parity excitation of each octet or decuplet baryon exhibits the characteristics of a radial excitation. Importantly, every ground-state octet and decuplet baryon possesses a radial excitation. Hence, the analysis predicts the existence of positive-parity excitations of the $\Xi$, ${\Xi }^{\ast }$, $\Omega$ baryons, with masses, respectively (in GeV): 1.84(08), 1.89(04), 2.05(02). These states have not yet been empirically identified. This body of analysis suggests that the expression of emergent mass generation is the same in all $u$, $d$, $s$ baryons and, notably, that dynamical quark-quark correlations play an essential role in the structure of each one. It also provides the basis for developing an array of predictions that can be tested in new generation experiments.

   ↳ nucl-thhep-exhep-lathep-ph+1PRD(2019)·48 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.