Wed·Jan 10, 2018Wednesday·January 10, 2018

1. 01*

   Probing the single-particle character of rotational states in ${}^{19}$F using a short-lived isomeric beam

   D. Santiago-Gonzalez (1 and 2) · K. Auranen (2)🇫🇮 · M. L. Avila (2) · A. D. Ayangeakaa (2)🇺🇸 · B. B. Back (2)🇺🇸 · S. Bottoni (2)🇺🇸 · M. P. Carpenter (2)🇺🇸 · J. Chen (2)🇨🇳 · C. M. Deibel (1)🇺🇸 · A. A. Hood (1) · C. R. Hoffman (2) · R. V. F. Janssens (2)🇺🇸 and 10 other authors

   A beam containing a substantial component of both the $J^{\pi }=5^{+}$, $T_{1/2}=162$ ns isomeric state of ${}^{18}$F and its $1^{+}$, 109.77-min ground state has been utilized to study members of the ground-state rotational band in ${}^{19}$F through the neutron transfer reaction $(d$,$p)$ in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2${}^{+}$ band-terminating state. The agreement between shell-model calculations, using an interaction constructed within the $sd$ shell, and our experimental results reinforces the idea of a single-particle/collective duality in the descriptions of the structure of atomic nuclei.

   nucl-exPRL(2018)·11 citations
2. 02*

   New mass anchor points for neutron-deficient heavy nuclei from direct mass measurements of radium and actinium isotopes

   M. Rosenbusch🇯🇵 · Y. Ito🇯🇵 · P. Schury🇯🇵 · M. Wada🇯🇵 · D. Kaji🇯🇵 · K. Morimoto🇯🇵 · H. Haba🇯🇵 · S. Kimura🇯🇵 · H. Koura🇯🇵 · M. MacCormick🇫🇷 · H. Miyatake🇯🇵 · J. Y. Moon🇰🇷 and 8 other authors

   The masses of the exotic isotopes ${}^{210-214}$Ac and ${}^{210-214}$Ra have been measured with a multi-reflection time-of-flight mass spectrograph. These isotopes were obtained in flight as fusion-evaporation products behind the gas-filled recoil ion separator GARIS-II at RIKEN. The new direct mass measurements serve as an independent and direct benchmark for existing $\alpha$-$\gamma$ spectroscopy data in this mass region. Further, new mass anchor points are set for U and Np nuclei close to the $N=126$ shell closure for a future benchmark of the $Z=92$ sub-shell for neutron-deficient heavy isotopes. Our mass results are in general in good agreement with the previously indirectly-determined mass values. Together with the measurement data, reasons for possible mass ambiguities from decay-data links between ground states are discussed.

   nucl-exPRC(2018)·23 citations
3. 03*

   Lifetimes of low-lying excited states in ${}_{36}^{86}$Kr${}_{50}$

   J. Henderson🇨🇦 · A. Chester🇨🇦 · G. C. Ball🇨🇦 · R. Caballero-Folch🇪🇸 · T. Domingo🇨🇦 · T. E. Drake · L. J. Evitts🇨🇦 · G. Hackman🇨🇦 · S. Hallam🇨🇦 · A. B. Garnsworthy🇨🇦 · M. Moukaddam🇨🇦 · P. Ruotsalainen🇫🇮 and 5 other authors

   The evolution of nuclear magic numbers at extremes of isospin is a topic at the forefront of contemporary nuclear physics. $N=50$ is a prime example, with increasing experimental data coming to light on potentially doubly-magic ${}^{100}$Sn and ${}^{78}$Ni at the proton-rich and proton-deficient extremes, respectively. Experimental discrepancies exist in the data for less exotic systems. In ${}^{86}$Kr the $B(E2;2_1^{+}\to 0_1^{+})$ value - a key indicator of shell evolution - has been experimentally determined by two different methodologies, with the results deviating by $3\sigma$. Here, we report on a new high-precision measurement of this value, as well as the first measured lifetimes and hence transition strengths for the $2_2^{+}$ and $3_{(2)}^{-}$ states in the nucleus. The Doppler-shift attenuation method was implemented using the TIGRESS gamma-ray spectrometer and TIGRESS integrated plunger (TIP) device. High-statistics Monte-Carlo simulations were utilized to extract lifetimes in accordance with state-of-the-art methodologies. Lifetimes of $\tau (2_1^{+})=336\pm 4\text{(stat.)}\pm 20\text{(sys.)}$ fs, $\tau (2_2^{+})=263\pm 9\text{(stat.)}\pm 19\text{(sys.)}$ fs and $\tau (3_{(2)}^{-})=73\pm 6\text{(stat.)}\pm 32\text{(sys.)}$ fs were extracted. This yields a transition strength for the first-excited state of $B(E2;2_1^{+}\to 0^{+})=259\pm 3\text{(stat.)}\pm 16\text{(sys.)}$ e${}^2$fm${}^4$. The measured lifetime disagrees with the previous Doppler-shift attenuation method measurement by more than $3\sigma$, while agreeing well with a previous value extracted from Coulomb excitation. The newly extracted $B(E2;2_1^{+}\to 0_1^{+})$ value indicates a more sudden reduction in collectivity in the $N=50$ isotones approaching $Z=40$.

   nucl-exPRC(2018)·3 citations
4. 04*

   Doubly charmed baryon production in heavy ion collisions

   Xiaojun Yao🇺🇸 · Berndt Müller🇺🇸

   We give an estimate of ${\Xi }_{cc}^{++}$ production rate and transverse momentum spectra in relativistic heavy ion collisions. We use Boltzmann transport equations to describe the dynamical evolution of charm quarks and diquarks inside quark-gluon plasma. In-medium formation and dissociation rates of charm diquarks are calculated from potential non-relativistic QCD for the diquark sector. We solve the transport equations by Monte Carlo simulations. For $2.76$ TeV Pb-Pb collisions with $0-10\%$ centrality, the number of ${\Xi }_{cc}^{++}$ produced in the transverse momentum range $0-5$ GeV and rapidity from $-1$ to $1$ is roughly $0.02$ per collision. We repeat the calculation with a melting temperature $250$ MeV above which no diquarks can be formed. The number of ${\Xi }_{cc}^{++}$ produced in the same kinematic region is about $0.0125$ per collision. We discuss how to study diquarks at finite temperature on a lattice and construct the anti-triplet free energy in a gauge invariant but path dependent way. We also comment on extensions of the calculation to other doubly heavy baryons and doubly heavy tetraquarks and the feasibility of experimental measurements.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2018)·57 citations
5. 05*

   9Be scattering with microscopic wave functions and the CDCC method

   P. Descouvemont🇧🇪 · N. Itagaki🇯🇵

   We use microscopic 9Be wave functions defined in a alpha+alpha+n multicluster model to compute 9Be+target scattering cross sections. The parameter sets describing 9Be are generated in the spirit of the Stochastic Variational Method (SVM), and the optimal solution is obtained by superposing Slater determinants and by diagonalizing the Hamiltonian. The 9Be three-body continuum is approximated by square-integral wave functions. The 9Be microscopic wave functions are then used in a Continuum Discretized Coupled Channel (CDCC) calculation of 9Be+208Pb and of 9Be+27Al elastic scattering. Without any parameter fitting, we obtain a fair agreement with experiment. For a heavy target, the influence of 9Be breakup is important, while it is weaker for light targets. This result confirms previous non-microscopic CDCC calculations. One of the main advantages of the microscopic CDCC is that it is based on nucleon-target interactions only; there is no adjustable parameter. The present work represents a first step towards more ambitious calculations involving heavier Be isotopes.

   ↳ nucl-thnucl-exPRC(2018)·17 citations
6. 06*

   Three-neutron resonance study using transition operators

   A. Deltuva🇱🇹

   Existing bound-state type calculations of three-neutron resonances yield contradicting results. A direct study of the three-neutron continuum using rigorous scattering equations with realistic potentials and search for possible resonances is aimed. Faddeev-type integral equations for three-neutron transition operators are solved in the momentum-space partial-wave framework. The evolution of resonances is studied by enhancing the strength of the two-neutron interaction in partial waves with nonzero orbital momentum. Calculated three-neutron transition operators exhibit resonant behavior for sufficiently large enhancement factors; pole trajectories in the complex-energy energy plane are extracted from their energy dependence. However, the resonant behavior completely disappears for the physical interaction strength. There are no physically observable three-neutron resonant states consistent with presently accepted interaction models.

   ↳ nucl-thnucl-exPRC(2018)·24 citations
7. 07*

   Precision determination of absolute neutron flux

   A.T. Yue · E.S. Anderson · M.S. Dewey🇺🇸 · D.M. Gilliam · G.L. Greene🇺🇸 · A.B. Laptev🇺🇸 · J.S. Nico🇺🇸 · W.M. Snow🇺🇸

   A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using a method of an alpha-gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024 %. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058 %. We discuss the principle of the alpha-gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.

   ↳ physics.ins-detnucl-exMetrologia(2018)·8 citations
8. 08*

   Construction and Performance of the Barrel Electromagnetic Calorimeter for the GlueX Experiment

   Tegan Beattie🇨🇦 · Ahmed Foda🇨🇦 · Colleen Henschel🇨🇦 · S Katsaganis🇨🇦 · Shaun Krueger🇨🇦 · George Lolos🇨🇦 · Zisis Papandreou🇨🇦 · E.L. Plummer🇨🇦 · Irina Semenova🇨🇦 · Andrei Semenov🇨🇦 · Fernando Barbosa🇨🇦 · Eugene Chudakov🇺🇸 and 27 other authors

   The barrel calorimeter is part of the new spectrometer installed in Hall D at Jefferson Lab for the GlueX experiment. The calorimeter was installed in 2013, commissioned in 2014 and has been operating routinely since early 2015. The detector configuration, associated Monte Carlo simulations, calibration and operational performance are described herein. The calorimeter records the time and energy deposited by charged and neutral particles created by a multi-GeV photon beam. It is constructed as a lead and scintillating-fiber calorimeter and read out with 3840 large-area silicon photomultiplier arrays. Particles impinge on the detector over a wide range of angles, from normal incidence at 90 degrees down to 11.5 degrees, which defines a geometry that is fairly unique among calorimeters. The response of the calorimeter has been measured during a running experiment and performs as expected for electromagnetic showers below 2.5 GeV. We characterize the performance of the BCAL using the energy resolution integrated over typical angular distributions for ${\pi }^0$ and $\eta$ production of ${\sigma }_E/E$=5.2\%/$\sqrt{E(\mathrm{GeV})}\oplus$ 3.6\% and a timing resolution of $\sigma$\,=\,150\,ps at 1\,GeV.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2018)·50 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.