Tue·Oct 10, 2017Tuesday·October 10, 2017

1. 01*

   Roper resonance -- solution to the fifty year puzzle

   Volker D. Burkert🇺🇸 · Craig D. Roberts🇺🇸

   For half a century, the Roper resonance has defied understanding. Discovered in 1963, it appears to be an exact copy of the proton except that its mass is 50% greater. The mass is the first problem: it is difficult to explain with any theoretical tool that can validly be used to study quantum chromodynamics [QCD]. In the last decade, a new challenge has appeared, viz. precise information on the proton-to-Roper electroproduction transition form factors, reaching $Q^2\approx 4.5$GeV${}^2$. This scale probes the domain within which hard valence-quark degrees-of-freedom could be expected to determine form factor behavior. Hence, with this new data the Roper resonance becomes a problem for strong-QCD [sQCD]. An explanation of how and where the Roper resonance fits into the emerging spectrum of hadrons cannot rest on a description of its mass alone. Instead, it must combine this with a detailed understanding of the Roper's structure and how that is revealed in the transition form factors. Furthermore, it must unify all this with a similarly complete picture of the proton. This is a prodigious task, but a ten-year international effort, drawing together experimentalists and theorists, has presented a solution to the puzzle. Namely, the Roper is at heart the proton's first radial excitation, consisting of a dressed-quark core augmented by a meson cloud that reduces the core mass by approximately 20% and materially alters its electroproduction form factors on $Q^2<2m_N^2$, where $m_N$ is the proton's mass. We describe the experimental motivations and developments which enabled electroproduction data to be procured within a domain that is unambiguously the purview of sQCD, thereby providing a real challenge and opportunity for modern theory; and survey the developments in reaction models and QCD theory that have enabled this conclusion to be drawn about the nature of the Roper resonance.

   nucl-exhep-lathep-phnucl-thRMP(2019)·161 citations
2. 02*

   Angular Distribution of $\gamma$-rays from Neutron-Induced Compound States of ${}^{140}$La

   T. Okudaira🇯🇵 · S. Takada🇯🇵 · K. Hirota🇯🇵 · A. Kimura🇯🇵 · M. Kitaguchi🇯🇵 · J. Koga🇯🇵 · K. Nagamoto · T. Nakao🇯🇵 · A. Okada · K. Sakai · H. M. Shimizu🇯🇵 · T. Yamamoto🇯🇵 · T. Yoshioka🇯🇵

   Angular distribution of individual $\gamma$-rays, emitted from a neutron-induced compound nuclear state via radiative capture reaction of ${}^{139}$La(n,$\gamma$) has been studied as a function of incident neutron energy in the epithermal region by using germanium detectors. An asymmetry $A_{\mathrm{LH}}$ was defined as $(N_{\mathrm{L}}-N_{\mathrm{H}})/(N_{\mathrm{L}}+N_{\mathrm{H}})$, where $N_{\mathrm{L}}$ and $N_{\mathrm{H}}$ are integrals of low and high energy region of a neutron resonance respectively, and we found that $A_{\mathrm{LH}}$ has the angular dependence of $(A\cos {\theta }_{\gamma }+B)$, where ${\theta }_{\gamma }$ is emitted angle of $\gamma$-rays, with $A=-0.3881\pm 0.0236$ and $B=-0.0747\pm 0.0105$ in 0.74 eV p-wave resonance. This angular distribution was analyzed within the framework of interference between s- and p-wave amplitudes in the entrance channel to the compound nuclear state, and it is interpreted as the value of the partial p-wave neutron width corresponding to the total angular momentum of the incident neutron combined with the weak matrix element, in the context of the mechanism of enhanced parity-violating effects. Additionally we used the result to quantify the possible enhancement of the breaking of the time-reversal invariance in the vicinity of the p-wave resonance.

   nucl-exPRC(2018)·41 citations
3. 03*

   Average CsI neutron density distribution from COHERENT data

   M. Cadeddu🇮🇹 · C. Giunti🇮🇹 · Y.F. Li🇨🇳 · Y.Y. Zhang🇨🇳

   Using the coherent elastic neutrino-nucleus scattering data of the COHERENT experiment, we determine for the first time the average neutron rms radius of ${}^{133}\text{Cs}$ and ${}^{127}\text{I}$. We obtain the practically model-independent value $R_n=5.5{}_{-1.1}^{+0.9}\text{fm}$ using the symmetrized Fermi and Helm form factors. We also point out that the COHERENT data show a $2.3\sigma$ evidence of the nuclear structure suppression of the full coherence.

   ↳ hep-phhep-exnucl-exnucl-thPRL(2018)·158 citations
4. 04*

   $\alpha$ decay properties of nucleus ${}^{297}$Og within two-potential approach

   Jun-Gang Deng · Jun-Hao Cheng · Bo Zheng🇨🇳 · Xiao-Hua Li🇨🇳

   The $\alpha$ decay half-life of unknown nucleus ${}^{297}$Og is predicted within two-potential approach, and $\alpha$ preformation probabilities of 64 odd-$A$ nuclei in the region of proton numbers $82<Z<126$ and neutron numbers $152<N<184$ from ${}^{251}$Cf to ${}^{295}$Og are extracted. In addition, based on the latest experimental data, a new set of parameters for $\alpha$ preformation probabilities considering the shell effect and proton-neutron interaction are obtained. The predicted $\alpha$ decay half-life of ${}^{297}$Og is 0.16 ms within a factor of 4.97 as well as the spin and parity of ground states for nuclei ${}^{269}$Sg, ${}^{285}$Fl and ${}^{293}$Lv are $3/2^{+}$, $3/2^{+}$ and $5/2^{+}$, respectively.

   ↳ nucl-thnucl-exCPC(2017)·26 citations
5. 05*

   Effects of initial-state dynamics on collective flow within a coupled transport and viscous hydrodynamic approach

   Chandrodoy Chattopadhyay🇮🇳 · Rajeev S. Bhalerao🇮🇳 · Jean-Yves Ollitrault🇫🇷 · Subrata Pal🇮🇳

   We evaluate the effects of preequilibrium dynamics on observables in ultrarelativistic heavy-ion collisions. We simulate the initial nonequilibrium phase within A MultiPhase Transport (AMPT) model, while the subsequent near-equilibrium evolution is modeled using (2+1)-dimensional relativistic viscous hydrodynamics. We match the two stages of evolution carefully by calculating the full energy-momentum tensor from AMPT and using it as input for the hydrodynamic evolution. We find that when the preequilibrium evolution is taken into account, final-state observables are insensitive to the switching time from AMPT to hydrodynamics. Unlike some earlier treatments of preequilibrium dynamics, we do not find the initial shear viscous tensor to be large. With a shear viscosity to entropy density ratio of $0.12$, our model describes quantitatively a large set of experimental data on Pb+Pb collisions at the Large Hadron Collider(LHC) over a wide range of centrality: differential anisotropic flow $v_n(p_T)(n=2-6)$, event-plane correlations, correlation between $v_2$ and $v_3$, and cumulant ratio $v_2\{4\}/v_2\{2\}$.

   ↳ nucl-thhep-phnucl-exPRC(2018)·21 citations
6. 06*

   Importance of isobar density distributions on the chiral magnetic effect search

   Hao-jie Xu🇨🇳 · Xiaobao Wang🇨🇳 · Hanlin Li🇨🇳 · Jie Zhao🇺🇸 · Zi-Wei Lin🇺🇸 · Caiwan Shen🇨🇳 · Fuqiang Wang🇺🇸

   Under the approximate chiral symmetry restoration, quark interactions with topological gluon fields in quantum chromodynamics can induce chirality imbalance and parity violation in local domains. An electric charge separation ({\sc cs}) could be generated along the direction of a strong magnetic field ({\bf B}), a phenomenon called the chiral magnetic effect ({\sc cme}). {\sc cs} measurements by azimuthal correlators are contaminated by a major background from elliptic flow anisotropy ($v_2$). Isobaric ${}_{44}^{96}$Ru+${}_{44}^{96}$Ru and ${}_{40}^{96}$Zr+${}_{40}^{96}$Zr collisions have been proposed to identify the {\sc cme} (expected to differ between the two systems) out of the background (expected to be almost the same). We show, by using the density-functional calculated proton and neutron distributions, that these expectations may not hold as originally anticipated, because the two systems may have sizable differences in eccentricity and $v_2$ and because their difference in {\bf B} may suffer from large uncertainties.

   ↳ nucl-thnucl-exPRL(2018)·110 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.