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Nuclear Theory·nucl-th

Tuesday·September 12, 2017

12 papers—5 primary·7 cross-listed

All12Primary5Cross-lists7
  1. 06

    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 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 =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 0.1fm.

    ↳ nucl-exnucl-thPRC(2017)·4 citations
  2. 07

    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 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 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 and the proper time when the gluon distribution is measured. For (i) and (with the saturation scale) we obtain the same results as from the Boltzmann equation. For (ii) 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 theory in the second paper of this duplex.

    ↳ hep-phnucl-exnucl-thJHEP(2018)·12 citations
  3. 08

    Time-Dependent Observables in Heavy Ion Collisions II: in Search of Pressure Isotropization in the 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 scattering process involving two classical fields. To make the calculation tractable we employ the scalar 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 and, for the case of the two-point function, is also in the dependence on the space-time rapidity : 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 rescattering.

    ↳ hep-phnucl-exnucl-thJHEP(2018)·8 citations
  4. 09

    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
  5. 10

    Homogeneous isotropization and equilibration of a strongly coupled plasma with a critical point

    Renato Critelli (1) · Romulo Rougemont (2) · Jorge Noronha (1) ((1) Sao Paulo U., (2) IIP, Brazil)

    We use holography to investigate the process of homogeneous isotropization and thermalization in a strongly coupled Super Yang-Mills plasma charged under a subgroup of the global R-symmetry which features a critical point in its phase diagram. Isotropization dynamics at late times is affected by the critical point in agreement with the behavior of the characteristic relaxation time extracted from the analysis of the lowest non-hydrodynamic quasinormal mode in the quintuplet (external scalar) channel of the theory. In particular, the isotropization time may decrease or increase as the chemical potential increases depending on whether one is far or close enough to the critical point, respectively. On the other hand, the thermalization time associated with the equilibration of the scalar condensate, which happens only after the system has relaxed to a (nearly) isotropic state, is found to always increase with chemical potential in agreement with the characteristic relaxation time associated to the lowest non-hydrodynamic quasinormal mode in the singlet (dilaton) channel. These conclusions about the late dynamics of the system are robust in the sense that they hold for different initial conditions seeding the time evolution of the far-from-equilibrium plasma.

    ↳ hep-thhep-phnucl-thJHEP(2017)·38 citations
  6. 11

    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
  7. 12

    Asymptotically Free Theory with Scale Invariant Thermodynamics

    Gabriel N. Ferrari🇧🇷 · Jean-Loic Kneur🇫🇷 · Marcus B. Pinto🇧🇷 · Rudnei O. Ramos🇧🇷

    A recently developed variational resummation technique, incorporating renormalization group properties consistently, has been shown to solve the scale dependence problem that plagues the evaluation of thermodynamical quantities, e.g., within the framework of approximations such as in the hard-thermal-loop resummed perturbation theory. This method is used in the present work to evaluate thermodynamical quantities within the two-dimensional nonlinear sigma model, which, apart from providing a technically simpler testing ground, shares some common features with Yang-Mills theories, like asymptotic freedom, trace anomaly and the nonperturbative generation of a mass gap. The present application confirms that nonperturbative results can be readily generated solely by considering the lowest-order (quasi-particle) contribution to the thermodynamic effective potential, when this quantity is required to be renormalization group invariant. We also show that when the next-to-leading correction from the method is accounted for, the results indicate convergence, apart from optimally preserving, within the approximations here considered, the sought-after scale invariance.

    ↳ hep-phhep-thnucl-thPRD(2017)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE