Tue·Sep 12, 2017Tuesday·September 12, 2017

1. 01*

   Kaon transverse charge density from space- and timelike data

   N.A. Mecholsky🇺🇸 · J. Meija-Ott🇺🇸 · M. Carmignotto🇺🇸 · T. Horn🇺🇸 · G.A. Miller🇺🇸 · I.L. Pegg🇺🇸

   We used the world data on the kaon form factor to extract the transverse kaon charge density using a dispersion integral of the imaginary part of the kaon form factor in the timelike region. Our analysis includes recent data from $e^{+}{e}^{-}$ annihiliation measurements extending the kinematic reach of the data into the region of high momentum transfers conjugate to the region of short transverse distances. To calculate the transverse density we created a superset of both timelike and spacelike data and developed an empirical parameterization of the kaon form factor. The spacelike set includes two new data points we extracted from existing cross section data. We estimate the uncertainty on the resulting transverse density to be 5\% at $b$=0.025 fm and significantly better at large distances. New kaon data planned with the 12 GeV Jefferson Lab may have a significant impact on the charge density at distances of $b<$ 0.1fm.

   nucl-exnucl-thPRC(2017)·4 citations
2. 02*

   Measurement of quarkonium production in proton--lead and proton--proton collisions at $5.02$ $\mathrm{TeV}$ with the ATLAS detector

   ATLAS Collaboration

   The modification of the production of $J/\psi$, $\psi (2S)$, and $\text{mit}{\rm Y}(n\mathrm{S})$ ($n=1,2,3$) in $p$+Pb collisions with respect to their production in $pp$ collisions has been studied. The $p$+Pb and $pp$ datasets used in this paper correspond to integrated luminosities of $28$ ${\mathrm{nb}}^{-1}$ and $25$ ${\mathrm{pb}}^{-1}$ respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of $J/\psi$ and $\psi (2S)$ are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, $R_{p\mathrm{Pb}}$ for $J/\psi$ and $\text{mit}{\rm Y}(1S)$. No significant modification of the $J/\psi$ production is observed while $\text{mit}{\rm Y}(1S)$ production is found to be suppressed at low transverse momentum in $p$+Pb collisions relative to $pp$ collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central $p$+Pb collisions.

   nucl-exhep-exEPJC(2018)·165 citations
3. 03*

   The 12C(a,g)16O reaction and its implications for stellar helium burning

   R.J. deBoer🇺🇸 · J. Gorres🇺🇸 · M. Wiescher🇺🇸 · R.E. Azuma🇺🇸 · A. Best🇮🇹 · C.R. Brune🇺🇸 · C.E. Fields🇺🇸 · S. Jones🇩🇪 · M. Pignatari🇭🇺 · D. Sayre🇺🇸 · K. Smith🇺🇸 · F.X. Timmes🇺🇸 · E. Uberseder🇺🇸

   The creation of carbon and oxygen in our universe is one of the forefront questions in nuclear astrophysics. The determination of the abundance of these elements is key to both our understanding of the formation of life on earth and to the life cycles of stars. While nearly all models of different nucleosynthesis environments are affected by the production of carbon and oxygen, a key ingredient, the precise determination of the reaction rate of 12C(a,g)16O, has long remained elusive. This is owed to the reaction's inaccessibility, both experimentally and theoretically. Nuclear theory has struggled to calculate this reaction rate because the cross section is produced through different underlying nuclear mechanisms. Isospin selection rules suppress the E1 component of the ground state cross section, creating a unique situation where the E1 and E2 contributions are of nearly equal amplitudes. Experimentally there have also been great challenges. Measurements have been pushed to the limits of state of the art techniques, often developed for just these measurements. The data have been plagued by uncharacterized uncertainties, often the result of the novel measurement techniques, that have made the different results challenging to reconcile. However, the situation has markedly improved in recent years, and the desired level of uncertainty, about 10%, may be in sight. In this review the current understanding of this critical reaction is summarized. The emphasis is placed primarily on the experimental work and interpretation of the reaction data, but discussions of the theory and astrophysics are also pursued. The main goal is to summarize and clarify the current understanding of the reaction and then point the way forward to an improved determination of the reaction rate.

   nucl-exRMP(2017)·225 citations
4. 04*

   A New Measurement of the 6Li(n,{\alpha})t Cross Section at MeV Energies Using a Fission Chamber and 6Li Scintillators

   Leo E. Kirsch🇺🇸 · M. Devlin🇺🇸 · S.M. Mosby · J.A. Gomez🇺🇸

   A new measurement is presented of the ${}^6$Li(n,$\alpha$)t cross section from 245 keV to 10 MeV using a ${}^{252}$Cf fission chamber with ${}^6$LiI(Eu) and Cs${}_2$LiYCl${}_6$:Ce (CLYC) scintillators which act as both target and detector. Neutron energies are determined from the time of flight (TOF) method using the signals from spontaneous fission and reaction product recoil. Simulations of neutron downscatter in the crystals and fission chamber bring ${}^6$Li(n,$\alpha$)t cross section values measured with the ${}^6$LiI(Eu) into agreement with previous experiments and evaluations, except for two resonances at 4.2 and 6.5 MeV introduced by ENDF/B-VII.1. Suspected neutron transport modeling issues cause the cross section values obtained with CLYC to be discrepant above 2 MeV.

   nucl-exNucl.Instrum.Meth.A(2017)·11 citations
5. 05*

   Evidence for Z=6 `magic number' in neutron-rich carbon isotopes

   D.T. Tran · H.J. Ong🇯🇵 · G. Hagen🇺🇸 · T. D. Morris🇺🇸 · N. Aoi🇯🇵 · T. Suzuki🇯🇵 · Y. Kanada-En'yo🇯🇵 · L.S. Geng🇨🇳 · S. Terashima🇨🇳 · I. Tanihata🇯🇵 · T.T. Nguyen🇩🇪 · Y. Ayyad🇯🇵 and 28 other authors

   The nuclear shell structure, which originates in the nearly independent motion of nucleons in an average potential, provides an important guide for our understanding of nuclear structure and the underlying nuclear forces. Its most remarkable fingerprint is the existence of the so-called `magic numbers' of protons and neutrons associated with extra stability. Although the introduction of a phenomenological spin-orbit (SO) coupling force in 1949 helped explain the nuclear magic numbers, its origins are still open questions. Here, we present experimental evidence for the smallest SO-originated magic number (subshell closure) at the proton number 6 in 13-20C obtained from systematic analysis of point-proton distribution radii, electromagnetic transition rates and atomic masses of light nuclei. Performing ab initio calculations on 14,15C, we show that the observed proton distribution radii and subshell closure can be explained by the state-of-the-art nuclear theory with chiral nucleon-nucleon and three-nucleon forces, which are rooted in the quantum chromodynamics.

   nucl-exnucl-thNature Commun.(2018)·39 citations
6. 06*

   Effect of broken axial symmetry on the electric dipole strength and the collective enhancement of level densities in heavy nuclei

   Eckart Grosse🇩🇪 · Arnd R. Junghans🇩🇪 · Jon N. Wilson🇫🇷

   The basic parameters for calculations of radiative neutron capture , photon strength functions and nuclear level densities near the neutron separation energy are determined based on experimental data without an ad-hoc assumption about axial symmetry - at variance to previous analysis. Surprisingly few global fit parameters are needed in addition to information on nuclear deformation, taken from Hartree Fock Bogolyubov (HFB) calculations with the Gogny force, and the generator coordinator method (GCM) assures properly defined angular momentum. For a large number of nuclei the GDR shapes and the photon strength are described by the sum of three Lorentzians (TLO), extrapolated to low energies and normalized in accordance to the dipole sum rule. Level densities are influenced strongly by the significant collective enhancement based on the breaking of shape symmetry. The replacement of axial symmetry by the less stringent requirement of invariance against rotation by 180 degree leads to a novel prediction for radiative neutron capture. It compares well to recent compilations of average radiative widths and Maxwellian average cross sections for neutron capture by even target nuclei. An extension to higher spin promises a reliable prediction for various compound nuclear reactions also outside the valley of stability. Such predictions are of high importance for future nuclear energy systems and waste transmutation as well as for the understanding of the cosmic synthesis of heavy elements.

   nucl-exastro-ph.SRnucl-thPhys.Scripta(2017)·6 citations
7. 07*

   Emergence of a Brunnian neutron state

   Johannes Kirscher🇺🇸

   We discuss a quantum-statistical feature of non-relativistic identical fermions whose interaction is predominantly attractive at low energies. Specifically, we consider exotic, multi-neutron nuclei. From the enhancement of an arbitrarily small P-wave interaction between two nucleons, we infer the existence of a particle-stable nucleus composed entirely of neutrons. While we cannot specify the number of neutrons in the system, we predict that none of its substructures is bound. The independence of this deduction from the short-distance structure of the nuclear interaction and its consistency with deuteron, triton, and helium-4 properties is established.

   ↳ nucl-thnucl-ex4 citations
8. 08*

   Time-Dependent Observables in Heavy Ion Collisions I: Setting up the Formalism

   Bin Wu🇺🇸 · Yuri V. Kovchegov🇺🇸

   We adapt the Schwinger-Keldysh formalism to study heavy-ion collisions in perturbative QCD. Employing the formalism, we calculate the two-point gluon correlation function $G_{22}^{a\mu ,b\nu }$ due to the lowest-order classical gluon fields in the McLerran-Venugopalan model of heavy ion collisions and observe an interesting transition from the classical fields to the quasi-particle picture at later times. Motivated by this observation, we push the formalism to higher orders in the coupling and calculate the contribution to $G_{22}^{a\mu ,b\nu }$ coming from the diagrams representing a single rescattering between two of the produced gluons. We assume that the two gluons go on mass shell both before and after the rescattering. The result of our calculation depends on the ordering between the proper time of the rescattering ${\tau }_Z$ and the proper time $\tau$ when the gluon distribution is measured. For (i) ${\tau }_Z\gg 1/Q_s$ and $\tau -{\tau }_Z\gg 1/Q_s$ (with $Q_s$ the saturation scale) we obtain the same results as from the Boltzmann equation. For (ii) $\tau -{\tau }_Z\gg {\tau }_Z\gg 1/Q_s$ we end up with a result very different from kinetic theory and consistent with a picture of "free-streaming" particles. Due to the approximations made, our calculation is too coarse to indicate whether the ordering (i) or (ii) is the correct one: to resolve this controversy, we shall present a detailed diagrammatic calculation of the rescattering correction in the ${\phi }^4$ theory in the second paper of this duplex.

   ↳ hep-phnucl-exnucl-thJHEP(2018)·12 citations
9. 09*

   Time-Dependent Observables in Heavy Ion Collisions II: in Search of Pressure Isotropization in the ${\phi }^4$ Theory

   Yuri V. Kovchegov🇺🇸 · Bin Wu🇺🇸

   To understand the dynamics of thermalization in heavy ion collisions in the perturbative framework it is essential to first find corrections to the free-streaming classical gluon fields of the McLerran-Venugopalan model. The corrections that lead to deviations from free streaming (and that dominate at late proper time) would provide evidence for the onset of isotropization (and, possibly, thermalization) of the produced medium. To find such corrections we calculate the late-time two-point Green function and the energy-momentum tensor due to a single $2\to 2$ scattering process involving two classical fields. To make the calculation tractable we employ the scalar ${\phi }^4$ theory instead of QCD. We compare our exact diagrammatic results for these quantities to those in kinetic theory and find disagreement between the two. The disagreement is in the dependence on the proper time $\tau$ and, for the case of the two-point function, is also in the dependence on the space-time rapidity $\eta$: the exact diagrammatic calculation is, in fact, consistent with the free streaming scenario. Kinetic theory predicts a build-up of longitudinal pressure, which, however, is not observed in the exact calculation. We conclude that we find no evidence for the beginning of the transition from the free-streaming classical fields to the kinetic theory description of the produced matter after a single $2\to 2$ rescattering.

   ↳ hep-phnucl-exnucl-thJHEP(2018)·8 citations
10. 10*

    Exploring hadrons' partonic structure using ab initio lattice QCD calculations

    Yan-Qing Ma🇨🇳 · Jian-Wei Qiu🇺🇸

    Following our previous proposal [1], we construct a class of good "lattice cross sections" (LCSs), from which we could study partonic structure of hadrons from ab initio lattice QCD calculations. These good LCSs, on the one hand, can be calculated directly in lattice QCD, and on the other hand, can be factorized into parton distribution functions (PDFs) with calculable coefficients, in the same way as QCD factorization for factorizable hadronic cross sections. PDFs could be extracted from QCD global analysis of the lattice QCD generated data of LCSs. We also show that proposed functions for lattice QCD calculation of PDFs in the literature are special cases of these good LCSs.

    ↳ hep-phhep-latnucl-exnucl-thPRL(2018)·294 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.