Mon·Jan 28, 2019Monday·January 28, 2019

1. 01*

   Virtual Compton Scattering measurements in the nucleon resonance region

   A. Blomberg🇺🇸 · H. Atac🇺🇸 · N. Sparveris🇺🇸 · M. Paolone🇺🇸 · P. Achenbach🇩🇪 · M. Benali🇫🇷 · J. Beričič🇸🇮 · R. Böhm🇩🇪 · L. Correa🇩🇪 · M.O. Distler🇩🇪 · A. Esser🇩🇪 · D. Flay🇺🇸 and 16 other authors

   We report on new measurements of the electric Generalized Polarizability (GP) of the proton ${\alpha }_E$ in a kinematic region where a puzzling dependence on momentum transfer has been observed, and we have found that ${\alpha }_E=(5.3\pm 0.6_{stat}\pm 1.3_{sys})10^{-4}f{m}^3$ at $Q^2=0.20(GeV/c{)}^2$. The new measurements, when considered along with the rest of the world data, suggest that ${\alpha }_E$ can be described by either a local plateau or by an enhancement in the region $Q^2=0.20(GeV/c{)}^2$ to $0.33(GeV/c{)}^2$. The experiment also provides the first measurement of the Coulomb quadrupole amplitude in the $N\to \Delta$ transition through the exploration of the $p(e,e^{\prime }p)\gamma$ reaction. The new measurement gives $CMR=(-4.4\pm 0.8_{stat}\pm 0.6_{sys})\%$ at $Q^2=0.20(GeV/c{)}^2$ and is consistent with the results from the pion electroproduction world data. It has been obtained using a completely different extraction method, and therefore represents a strong validation test of the world data model uncertainties.

   nucl-exEPJA(2019)·15 citations
2. 02*

   The nucleon resonance structure from exclusive ${\pi }^{+}{\pi }^{-}p$ photo-/electroproduction off protons

   V.D. Burkert🇺🇸 · V.I. Mokeev🇺🇸 · B.S. Ishkhanov🇷🇺

   The results on the photo- and electroexcitation amplitudes of most nucleon resonances in the mass range up to 2.0 GeV determined from the CLAS experimental data on exclusive ${\pi }^{+}{\pi }^{-}p$ photo-/electroproduction off protons in collaboration between the Jefferson Lab and Moscow State University are presented. The first and only available results on electroexcitation amplitudes from CLAS in a wide range of photon virtualities $Q^2$ $<$ 5.0 GeV${}^2$ revealed the nucleon resonance structure as a complex interplay between the inner core of three dressed quarks and external meson-baryon cloud. These results shed light on the strong QCD dynamics which underlines the generation of excited nucleon states of different structural features from confined quarks and gluons. The future prospects of these studies in the new era of experiments with the CLAS12 detector, which started successfully in Spring of 2018, are outlined.

   nucl-exhep-phMoscow Univ.Phys.Bull.(2019)·16 citations
3. 03*

   Longitudinal Double-Spin Asymmetries for Dijet Production at Intermediate Pseudorapidity in Polarized $pp$ Collisions at $\sqrt{s}$ = 200 GeV

   Ting Lin (for the STAR Collaboration)🇺🇸

   One of the primary goals of the RHIC spin program is to determine the spin-dependent gluon distribution, $\Delta g(x)$, of the proton. The measurements of the 2009 longitudinal double-helicity asymmetry, $A_{LL}$, for mid-rapidity inclusive jet and ${\pi }^0$ production place strong constraints on $\Delta g(x)$ and, for the first time, find evidence for non-zero gluon polarization values for partonic momentum fraction $x$ greater than 0.05. In contrast to inclusive jets, dijet correlation measurements provide access to partonic kinematics at leading order, and thus give better constraints on the behavior of $\Delta g(x)$ as a function of gluon momentum fraction. Furthermore, dijet measurements at higher rapidity probe the lower $x$ values where $\Delta G$ is poorly constrained.\\ In these proceedings, we present the first measurement of $A_{LL}$ for dijets with at least one jet reconstructed within the pseudorapidity range 0.8 $<\eta <$ 1.8 at STAR. The dijets were measured in polarized proton+proton collisions at a center-of-mass energy $\sqrt{s}$ = 200 GeV. Values of $A_{LL}$ are determined for several distinct event topologies, defined by the jet pseudorapidities, and span a range of parton momentum fraction $x$ down to $x\sim 0.01$. The measured asymmetries are found to be consistent with the predictions of global analyses that incorporate the results of previous RHIC measurements. They will provide new constraints on $\Delta g(x)$ in this poorly constrained region when included in future global analyses.

   ↳ hep-exnucl-exPoS(2018)·1 citation
4. 04*

   NCrystal : a library for thermal neutron transport

   Xiao-Xiao Cai🇨🇳 · Thomas Kittelmann🇸🇪

   An open source software package for modelling thermal neutron transport is presented. The code facilitates Monte Carlo-based transport simulations and focuses in the initial release on interactions in both mosaic single crystals as well as polycrystalline materials and powders. Both coherent elastic (Bragg diffraction) and incoherent or inelastic (phonon) scattering are modelled, using basic parameters of the crystal unit cell as input. Included is a data library of validated crystal definitions, standalone tools and interfaces for C++, C and Python programming languages. Interfaces for two popular simulation packages, Geant4 and McStas, are provided, enabling highly realistic simulations of typical components at neutron scattering instruments, including beam filters, monochromators, analysers, samples and detectors. All interfaces are presented in detail, along with the end-user configuration procedure which is deliberately kept user-friendly and consistent across all interfaces. An overview of the relevant neutron scattering theory is provided, and the physics modelling capabilities of the software are discussed. Particular attention is given here to the ability to load crystal structures and form factors from various sources of input, and the results are benchmarked and validated against experimental data and existing crystallographic software. Good agreements are observed.

   ↳ physics.comp-phcond-mat.mtrl-scinucl-exnucl-thComput.Phys.Commun.(2020)·30 citations
5. 05*

   Critical view of nonlocal nuclear potentials in alpha decay

   J. E. Perez Velasquez · N. G. Kelkar🇨🇴 · N. J. Upadhyay

   Different models for the nonlocal description of the nuclear interaction are compared through a study of their effects on the half-lives of radioactive nuclei decaying by the emission of alpha particles. The half-lives are evaluated by considering a pre-formed alpha particle (${}^4$He nucleus) which tunnels through the Coulomb barrier generated by its interaction with the daughter nucleus. An effective potential obtained from a density dependent double folding strong potential between the alpha and the daughter nucleus within the nonlocal framework is found to decrease the half-lives as compared to those in the absence of nonlocalities. Whereas the percentage decrease within the older Perey-Buck and São Paulo models ranges between 20 to 40\% for medium to heavy nuclei, a recently proposed effective potential leads to a decrease of only 2 - 4 \%. In view of these results, we provide a closer examination of the approximations used in deriving the local equivalent potentials and propose that apart from the scattering data, the alpha decay half-lives could be used as a complementary tool for constraining the nonlocality models.

   ↳ nucl-thnucl-exPRC(2019)·16 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.