Fri·Oct 25, 2019Friday·October 25, 2019

1. 01*

   First-excited state $g$ factors in the stable, even Ge and Se isotopes

   B. P. McCormick🇦🇺 · A. E. Stuchbery🇦🇺 · B. A. Brown🇺🇸 · G. Georgiev🇫🇷 · B. J. Coombes🇦🇺 · T. J. Gray🇦🇺 · M. S. M. Gerathy🇦🇺 · G. J. Lane🇦🇺 · T. Kibédi🇦🇺 · A. J. Mitchell🇦🇺 · M. W. Reed🇦🇺 · A. Akber🇦🇺 and 6 other authors

   Transient-field $g$-factor measurements in inverse kinematics were performed for the first-excited states of the stable, even isotopes of Ge and Se. The $g$ factors of ${}^{74}$Ge and ${}^{74}$Se were measured simultaneously using a cocktail beam, which eliminates most possible sources of systematic error in a relative $g$-factor measurement. The results are $g{(}^{74}\mathrm{Se})/g{(}^{74}\mathrm{Ge})=1.34(7)$, $g{(}^{70}\mathrm{Ge})/g{(}^{74}\mathrm{Ge})=1.16(15)$, $g{(}^{72}\mathrm{Ge})/g{(}^{74}\mathrm{Ge})=0.92(13)$, $g{(}^{76}\mathrm{Ge})/g{(}^{74}\mathrm{Ge})=0.88(5)$, $g{(}^{76}\mathrm{Se})/g{(}^{74}\mathrm{Se})=0.96(7)$, $g{(}^{78}\mathrm{Se})/g{(}^{74}\mathrm{Se})=0.82(5)$, $g{(}^{80}\mathrm{Se})/g{(}^{74}\mathrm{Se})=0.99(7)$ and $g{(}^{82}\mathrm{Se})/g{(}^{74}\mathrm{Se})=1.19(6)$. The measured $g$-factor ratios are in agreement with ratios from previous measurements, despite considerable variation in previous reported absolute values. The absolute values of the $g$ factors remain uncertain, however the Rutgers parametrization was used to set the transient-field strength and then compare the experimental $g$ factors with shell-model calculations based on the JUN45 and jj44b interactions. Modest agreement was found between experiment and theory for both interactions. The shell model calculations indicate that the $g(2_1^{+})$ values and trends are determined largely by the balance of the spin carried by orbital motion of the protons.

   nucl-exPRC(2019)·6 citations
2. 02*

   Virtual Compton Scattering and Nucleon Generalized Polarizabilities

   H.Fonvieille (1) · B.Pasquini (2)(3) · N.Sparveris (4) · ((1) Université Clermont Auvergne, CNRS/IN2P3, LPC, F-63000 Clermont-Ferrand, France, (2) Dipartimento di Fisica Nucleare e Teorica, Universitá degli Studi di Pavia, (3) Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Italy, (4) Temple University, Philadelphia, PA 19122, USA)

   This review gives an update on virtual Compton scattering (VCS) off the nucleon, ${\gamma }^{\ast }N\to N\gamma$, in the low-energy regime. We recall the theoretical formalism related to the generalized polarizabilities (GPs) and model predictions for these observables. We present the GP extraction methods that are used in the experiments: the approach based on the low-energy theorem for VCS and the formalism of Dispersion Relations. We then review the experimental results, with a focus on the progress brought by recent experimental data on proton generalized polarizabilities, and we conclude by some perspectives in the field of VCS at low energy.

   nucl-exhep-phnucl-thPPNP(2020)·23 citations
3. 03*

   Imaging the nucleus with high-energy photons

   Spencer R. Klein🇺🇸 · Heikki Mantysaari🇫🇮

   In the 1930's, nuclear physicists developed the first realistic atomic models, showing that nuclei were made up of protons and neutrons. In the 1960's, Deep Inelastic Scattering experiments showed that protons and neutrons had internal structure: quarks and gluons (collectively, partons), and later experiments showed that the parton momentum distributions are different in heavy nuclei, compared to those in free nucleons. This difference is not surprising; partons are sensitive to their environment, and two gluons from different nucleons may fuse together, for example. Understanding how quarks and gluons behave in the nuclear environment is a significant focus of modern nuclear physics. Recent measurements have provided us with an improved understanding of how quark and gluon densities are altered in heavy nuclei. We have also begun to make multi-dimensional pictures of the nucleus, exploring how these alterations are distributed within heavy nuclei. We naturally expect these modifications to be largest in the core of a nucleus, and smaller near its periphery; this can change the effective shape of the nucleus. We have also started to explore the transverse momentum distribution of the partons in the nuclei, and, using incoherent photoproduction as a probe, study event-by-event fluctuations in nucleon and nuclei parton densities. This article will explore recent progress in measurements of nuclear structure at high energy, with some emphasis on these multi-dimensional pictures. We will also discuss how a future electron-ion collider (EIC) with high luminosity and center-of-mass energy will make exquisitely detailed images of partons in a nucleus.

   ↳ hep-exhep-phnucl-exNature Rev.Phys.(2019)·159 citations
4. 04*

   Apparatus for in-beam hyperfine interactions and $g$-factor measurements: design and operation

   A.E. Stuchbery🇦🇺 · A.B. Harding · D.C. Weisser · N.R. Lobanov

   The design and operation of apparatus for measurements of in-beam hyperfine interactions and nuclear excited-state $g$ factors is described. This apparatus enables a magnetic field of about 0.1 tesla to be applied to the target and the target temperature to be set between $\sim 4$ K and room temperature. Design concepts are developed mainly in terms of transient-field $g$-factor measurements following Coulomb excitation by the implantation perturbed angular correlation (IMPAC) technique. The formalism for perturbed angular correlations is outlined and a figure of merit for optimizing these measurements is derived to inform design. Particle detection is based on the use of silicon photodiodes of rectangular shape. The particle-$\gamma$ angular correlation formalism for this case is described. The experimental program to date includes temperature-dependent studies of hyperfine fields, transient-field $g$-factor measurements, and time-dependent perturbed angular distribution (TDPAD) studies.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2020)·6 citations
5. 05*

   New front and back-end electronics for the upgraded GABRIELA detection system

   K. Hauschild🇫🇷 · R. Chakma🇫🇷 · A. Lopez-Martens🇫🇷 · K. Rezynkina🇫🇷 · V. Alaphillipe🇫🇷 · L. Gibelin🇫🇷 · N. Karkour🇫🇷 · D. Linget🇫🇷 · A.V. Yeremin🇷🇺 · A.G. Popeko🇷🇺 · O.N. Malyshev🇷🇺 · V.I. Chepigin🇷🇺 and 14 other authors

   The GABRIELA [1] set-up is used at the FLNR to perform detailed nuclear structure studies of transfermium nuclei. Following the modernization of the VASSILISSA separator (SHELS) [2] the GABRIELA detection system has also been upgraded. The characteristics of the upgraded detection system will be presented along with results from some recent electronics tests.

   ↳ physics.ins-detnucl-ex0 citations
6. 06*

   The BGOOD experimental setup at ELSA

   S. Alef · P. Bauer · D. Bayadilov · R. Beck · M. Becker · A. Bella · J. Bieling · S. Boese · A. Braghieri · K.-Th. Brinkmann · P. Cole · R. Di Salvo and 49 other authors

   The BGOOD experiment at the ELSA facility in Bonn has been commissioned within the framework of an international collaboration. The experiment pursues a systematic investigation of non-strange and strange meson photoproduction, in particular $t$-channel processes at low momentum transfer. The setup uniquely combines a central almost $4\pi$ acceptance BGO crystal calorimeter with a large aperture forward magnetic spectrometer providing excellent detection of both neutral and charged particles, complementary to other setups such as Crystal Barrel, Crystal Ball, LEPS and CLAS.

   ↳ physics.ins-detnucl-exEPJA(2020)·34 citations
7. 07*

   Single-layer Compton detectors for measurement of polarization correlations of annihilation quanta

   Mihael Makek🇭🇷 · Damir Bosnar🇭🇷 · Luka Pavelić · Pavla Šenjug · Petar Žugec🇭🇷

   Measurement of gamma-ray polarization can provide valuable insight in different areas of physics. A possible application is in Positron Emission Tomography, where annihilation quanta with orthogonal polarizations are emitted. Since polarization can be measured via Compton scattering, the initial orthogonality of polarizations can be translated to correlation of azimuthal scattering angles, and this correlation may be exploited as an additional handle to identify the true coincidence events. To examine the concept of using the polarization correlations in PET, we have used a system of two compact, position and energy-sensitive Compton detectors in coincidence mode. Each consists of a single matrix of scintillation pixels, read-out by an array of Silicon photomultipliers. The Compton events in each module are clearly identified and the scattering angles are reconstructed from the energy deposition and event topology. We have extracted the polarimetric modulation factors from the distributions of the difference of the azimuthal angles of the two Compton-scattered gammas and studied their dependence on Compton scattering angles $\theta$ and on azimuthal resolution $\Delta \varphi$. For scattering angles around ${\theta }_{1,2}=82^{\circ }$, where the maximum modulation is expected, the modulation factors from $\mu =0.15\pm 0.01$ to $\mu =0.27\pm 0.02$ have been measured, depending on the azimuthal resolution, which is governed by event topology in the detectors. Analogously, for scattering around ${\theta }_{1,2}=70^{\circ }$, modulation factors from $\mu =0.12\pm 0.01$ to $\mu =0.21\pm 0.02$ have been obtained. The results show that the measurement of the polarization correlations of annihilation quanta are feasible with compact single-layer, single-side read-out detectors, which may be used to build cost-efficient systems for various applications where gamma-ray polarization information is of interest.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2020)·15 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.