Mon·Apr 1, 2019Monday·April 1, 2019

1. 01*

   Shell evolution approaching the N=20 island of inversion: Structure of 29Mg

   A. Matta🇬🇧 · W.N. Catford🇬🇧 · N.A. Orr🇫🇷 · J. Henderson🇨🇦 · P. Ruotsalainen🇨🇦 · G. Hackman🇨🇦 · A.B. Garnsworthy🇨🇦 · F. Delaunay🇫🇷 · R. Wilkinson🇬🇧 · G. Lotay🇬🇧 · Naofumi Tsunoda🇯🇵 · Takaharu Otsuka🇯🇵 and 27 other authors

   The "Island of Inversion" for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modelling of shell evolution with isospin. In this context, the structure of the transitional nucleus 29Mg is critical. The first quantitative measurements of the single particle structure of 29Mg are reported, using data from the d(28Mg,p gamma)29Mg reaction. Two key states carrying significant ell=3 (f-wave) strength were identified at 2.40 +/- 0.10 (Jpi = 5/2-) and 4.28 +/- 0.04 MeV (7/2-). New state-of-the-art shell model calculations have been performed and the predictions are compared in detail with the experimental results. Whilst the two lowest 7/2- levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2- and 5/2- levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell model calculations.

   nucl-exPRC(2019)·11 citations
2. 02*

   $\beta$ and $\beta$-delayed neutron decay of the $N=82$ nucleus ${}_{49}^{131}$In${}_{82}$

   R. Dunlop🇨🇦 · C. E. Svensson🇨🇦 · C. Andreoiu🇨🇦 · G. C. Ball🇨🇦 · N. Bernier🇨🇦 · H. Bidaman🇨🇦 · V. Bildstein🇨🇦 · M. Bowry🇨🇦 · D. S. Cross🇨🇦 · I. Dillmann🇨🇦 · M. R. Dunlop🇨🇦 · F. H. Garcia🇨🇦 and 17 other authors

   The half-lives of three $\beta$ decaying states of ${}_{49}^{131}$In${}_{82}$ have been measured with the GRIFFIN $\gamma$-ray spectrometer at the TRIUMF-ISAC facility to be $T_{1/2}(1/2^{-})=328(15)$~ms, $T_{1/2}(9/2^{+})=265(8)$~ms, and $T_{1/2}(21/2^{+})=323(55)$~ms, respectively. The first observation of $\gamma$-rays following the $\beta n$ decay of ${}^{131}$In into ${}^{130}$Sn is reported. The $\beta$-delayed neutron emission probability is determined to be $P_{1n}=12(7)\%$ for the $21/2^{+}$ state and $2.3(3)\%$ from the combined $1/2^{-}$ and $9/2^{+}$ states of ${}_{49}^{131}$In${}_{82}$ observed in this experiment. A significant expansion of the decay scheme of ${}^{131}$In, including 17 new excited states and 34 new $\gamma$-ray transitions in ${}_{50}^{131}$Sn${}_{81}$ is also reported. This leads to large changes in the deduced $\beta$ branching ratios to some of the low-lying states of ${}^{131}$Sn compared to previous work with implications for the strength of the first-forbidden $\beta$ transitions in the vicinity of doubly-magic ${}_{50}^{132}$Sn${}_{82}$.

   nucl-exPRC(2019)·11 citations
3. 03*

   One-dimensional charged kaon femtoscopy in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The correlations of identical charged kaons were measured in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV by the ALICE experiment at the LHC. The femtoscopic invariant radii and correlation strengths were extracted from one-dimensional kaon correlation functions and were compared with those obtained in pp and Pb-Pb collisions at $\sqrt{s}=7$ TeV and $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV, respectively. The presented results also complement the identical-pion femtoscopic data published by the ALICE collaboration. The extracted radii increase with increasing charged-particle multiplicity and decrease with increasing pair transverse momentum. At comparable multiplicities, the radii measured in p-Pb collisions are found to be close to those observed in pp collisions. The obtained femtoscopic parameters are reproduced by the EPOS 3 hadronic interaction model and disfavor models with large initial size or strong collective expansion at low multiplicities.

   nucl-exhep-exPRC(2019)·18 citations
4. 04*

   Searching for flavor dependence in nuclear quark behavior

   J. Arrington🇺🇸 · N. Fomin🇺🇸

   The observed correlation between the EMC effect and the contribution of short-range correlations (SRCs) in nuclei suggests that the modification of the quark distributions of bound protons and neutrons might occur within SRCs. This raises the possibility that the EMC effect may have an isospin dependence arising from the np dominance of SRCs. We discuss previous attempts to test this possibility and perform a new analysis of existing data. We find no experimental support for the observation of an isospin dependence of the EMC effect.

   nucl-exnucl-thPRL(2019)·27 citations
5. 05*

   High Density with Elliptic Flows

   W. Trautmann🇩🇪

   The elliptic flow of emitted particles and fragments observed in heavy-ion reactions at high energy has become an important observable reflecting the pressure generated in the dense collision zone. More recently, the strength of the nuclear symmetry energy has been investigated by measuring the ratios or differences of the elliptic flows exhibited by neutrons and charged particles in 197Au+197Au collisions at 400 MeV/nucleon incident energy at the GSI laboratory. A moderately soft to linear dependence on density was deduced for a range of densities shown to reach beyond twice the saturation value in these experiments. The known sources of uncertainties and possible model dependencies were thoroughly studied with transport models of the UrQMD and Tuebingen QMD type. A new source of information on the nuclear equation of state at high density has opened up with the observation of the first LIGO and Virgo GW170817 gravitational wave signal from a neutron star merger. The quantitative comparison of terrestrial and celestial results on the basis of measured or inferred neutron star radii or core pressures, including those obtained from X-ray observations, reveals a rather satisfactory agreement. Depending on the precision that can be achieved with future measurements and observations, it will thus become possible to assess the validity of the applied models and methods. The perspectives for improved experiments at FAIR using the NeuLAND and KRAB detection systems are outlined.

   nucl-exastro-ph.HEnucl-thAIP Conf.Proc.(2019)·11 citations
6. 06*

   Geometry of ultraperipheral nuclear collisions

   I.M. Dremin🇷🇺

   It is advocated that geometry of the interaction region of two heavy nuclei colliding at large impact parameters is important for the relative role of light-by-light scattering and QCD-initiated processes. Exclusive production of resonances is possible by dense electromagnetic fields in the interior space between the nuclei. The cross section of these processes is evaluated and some examples are considered. It is speculated that the exclusive production of ${\rho }^0$-mesons by two-photon processes forbidden by the Landau-Yang rule may become allowed within strong magnetic fields.

   ↳ nucl-thhep-exhep-phnucl-exInt.J.Mod.Phys.A(2019)·9 citations
7. 07*

   Ab initio short-range-correlation scaling factors from light to medium-mass nuclei

   J. E. Lynn🇩🇪 · D. Lonardoni🇺🇸 · J. Carlson🇺🇸 · J.-W. Chen🇹🇼 · W. Detmold🇺🇸 · S. Gandolfi🇺🇸 · A. Schwenk🇩🇪

   High-energy scattering processes, such as deep inelastic scattering (DIS) and quasielastic (QE) scattering provide a wealth of information about the structure of atomic nuclei. The remarkable discovery of the empirical linear relationship between the slope of the European Muon Collaboration (EMC) effect in DIS and the short-range-correlation (SRC) scaling factors $a_2$ in QE kinematics is naturally explained in terms of scale separation in effective field theory. This explanation has powerful consequences, allowing us to calculate and predict SRC scaling factors from ab initio low-energy nuclear theory. We present ab initio calculations of SRC scaling factors for a nucleus $A$ relative to the deuteron $a_2(A/d)$ and relative to ${}^3\mathrm{He}$ $a_2(A{/}^3\mathrm{He})$ in light and medium-mass nuclei. Our framework further predicts that the EMC effect and SRC scaling factors have minimal or negligible isovector corrections.

   ↳ nucl-thnucl-exJ.Phys.G(2020)·36 citations
8. 08*

   Nuclear Parton Distributions from Lepton-Nucleus Scattering and the Impact of an Electron-Ion Collider

   Rabah Abdul Khalek🇳🇱 · Jacob J. Ethier🇳🇱 · Juan Rojo🇳🇱

   We present a first determination of the nuclear parton distribution functions (nPDF) based on the NNPDF methodology: nNNPDF1.0. This analysis is based on neutral-current deep-inelastic structure function data and is performed up to NNLO in QCD calculations with heavy quark mass effects. For the first time in the NNPDF fits, the ${\chi }^2$ minimization is achieved using stochastic gradient descent with reverse-mode automatic differentiation (backpropagation). We validate the robustness of the fitting methodology through closure tests, assess the perturbative stability of the resulting nPDFs, and compare them with other recent analyses. The nNNPDF1.0 distributions satisfy the boundary condition whereby the NNPDF3.1 proton PDF central values and uncertainties are reproduced at $A=1$, which introduces important constraints particularly for low-$A$ nuclei. We also investigate the information that would be provided by an Electron-Ion Collider (EIC), finding that EIC measurements would significantly constrain the nPDFs down to $x\simeq 5\times 10^{-4}$. Our results represent the first-ever nPDF determination obtained using a Monte Carlo methodology consistent with that of state-of-the-art proton PDF fits, and provide the foundation for a subsequent global nPDF analyses including also proton-nucleus data.

   ↳ hep-phhep-exnucl-exnucl-thEPJC(2019)·147 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.