Fri·Apr 28, 2017Friday·April 28, 2017

1. 01*

   Extension of the Bjorken energy density formula of the initial state for relativistic heavy ion collisions

   Zi-Wei Lin🇺🇸

   For relativistic heavy ion collisions, the Bjorken formula is very useful for estimating the initial energy density once an initial time ${\tau }_0$ is specified. However, it cannot be trusted at low energies, e.g. well below $\sqrt{s_{{}_{\mathrm{NN}}}}\approx 50$ GeV for central Au+Au collisions, when ${\tau }_0$ is smaller than the finite time it takes for the two nuclei to cross each other. Here I extend the Bjorken formula by including the finite time duration of the initial energy production. Analytical solutions for the formed energy density in the central spacetime-rapidity region are derived for several time profiles. Compared to the Bjorken formula at low energies, the maximum energy density reached is much lower, increases much faster with the collision energy, and is much less sensitive to the uncertainty of the formation time, while the energy density time evolution is much longer. Comparisons with results from a multi-phase transport confirm the key features of these solutions. The effect of the finite longitudinal width of the initial energy production, which is neglected in the analytical results, is investigated with the transport model and shown to be small. This work thus provides a general model for the initial energy production of relativistic heavy ion collisions that is also valid at low energies.

   ↳ nucl-thnucl-exPRC(2018)·22 citations
2. 02*

   From bare interactions, low--energy constants and unitary gas to nuclear density functionals without free parameters: application to neutron matter

   Denis Lacroix🇫🇷 · Antoine Boulet🇫🇷 · Marcella Grasso🇫🇷 · C.-J. Yang🇫🇷

   We further progress along the line of Ref. [Phys. Rev. {\bf A 94}, 043614 (2016)] where a functional for Fermi systems with anomalously large $s$-wave scattering length $a_s$ was proposed that has no free parameters. The functional is designed to correctly reproduce the unitary limit in Fermi gases together with the leading-order contributions in the s- and p-wave channels at low density. The functional is shown to be predictive up to densities $\sim 0.01$ fm${}^{-3}$ that is much higher densities compared to the Lee-Yang functional, valid for $\rho <10^{-6}$ fm${}^{-3}$. The form of the functional retained in this work is further motivated. It is shown that the new functional corresponds to an expansion of the energy in $(a_s{k}_F)$ and $(r_e{k}_F)$ to all orders, where $r_e$ is the effective range and $k_F$ is the Fermi momentum. One conclusion from the present work is that, except in the extremely low--density regime, nuclear systems can be treated perturbatively in $-(a_s{k}_F{)}^{-1}$ with respect to the unitary limit. Starting from the functional, we introduce density--dependent scales and show that scales associated to the bare interaction are strongly renormalized by medium effects. As a consequence, some of the scales at play around saturation are dominated by the unitary gas properties and not directly to low-energy constants. For instance, we show that the scale in the s-wave channel around saturation is proportional to the so-called Bertsch parameter ${\xi }_0$ and becomes independent of $a_s$. We also point out that these scales are of the same order of magnitude than those empirically obtained in the Skyrme energy density functional. We finally propose a slight modification of the functional such that it becomes accurate up to the saturation density $\rho \simeq 0.16$ fm${}^{-3}$.

   ↳ nucl-thcond-mat.quant-gascond-mat.str-elnucl-exPRC(2017)·20 citations
3. 03*

   Six-quark structure of $d^{\ast }(2380)$ in chiral constituent quark model

   Qi-Fang Lü🇨🇳 · Fei Huang🇨🇳 · Yu-Bing Dong🇨🇳 · Peng-Nian Shen🇨🇳 · Zong-Ye Zhang🇨🇳

   The structure of $d^{\ast }(2380)$ is re-studied with the single cluster structure in the chiral SU(3) quark model which has successfully been employed to explain the $N-N$ scattering data and the binding energy of deuteron. The binding behavior of such a six quark system is solved by using a variational method. The trial wave function is chosen to be a combination of a basic spherical symmetric component of $[(0s{)}^6{]}_{orb}$ in the orbital space with $0\hslash \omega$ excitation and an inner structural deformation component of $[(0s{)}^5(1s){]}_{orb}$ and $[(0s{)}^4(0p{)}^2{]}_{orb}$ in the orbital space with $2\hslash \omega$ excitation, both of which are in the spatial [6] symmetry. It is shown that the mass of the system is about $2356$ MeV, which is qualitative consistent with the result both from the two-cluster configuration calculation and from the data measured by the WASA Collaborations. This result tells us that as long as the medium-range interaction due to the chiral symmetry consideration is properly introduced, the mass of system will be reduced in a rather large extent. It also implies that the observed $d^{\ast }$ is a six-quark bound state with respect to the $\Delta \Delta$ threshold, which again supports the conclusion that $d^{\ast }$ is a hexaquark dominant state.

   ↳ nucl-thhep-phnucl-exPRD(2017)·26 citations
4. 04*

   A spallation-based neutron target for direct studies of neutron-induced reactions in inverse kinematics

   René Reifarth🇩🇪 · Kathrin Göbel🇩🇪 · Tanja Heftrich🇩🇪 · Mario Weigand🇩🇪 · Beatriz Jurado🇫🇷 · Franz Käppeler🇩🇪 · Yuri A. Litvinov🇩🇪

   We discuss the possibility to build a neutron target for nuclear reaction studies in inverse kinematics utilizing a storage ring and radioactive ion beams. The proposed neutron target is a specially designed spallation target surrounded by a large moderator of heavy water (D${}_2$O). We present the resulting neutron spectra and their properties as a target. We discuss possible realizations at different experimental facilities.

   ↳ physics.ins-detnucl-exphysics.acc-phPhys.Rev.Accel.Beams(2017)·39 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.