Thu·Apr 19, 2018Thursday·April 19, 2018

1. 01*

   Excitation functions for (p,x) reactions of niobium in the energy range of E${}_{\text{p}}$ = 40-90 MeV

   Andrew S. Voyles · Lee A. Bernstein🇺🇸 · Eva R. Birnbaum🇺🇸 · Jonathan W. Engle🇺🇸 · Stephen A. Graves · Toshihiko Kawano🇺🇸 · Amanda M. Lewis · Francois M. Nortier🇺🇸

   A stack of thin Nb foils was irradiated with the 100 MeV proton beam at Los Alamos National Laboratory's Isotope Production Facility, to investigate the ${}^{93}$Nb(p,4n)${}^{90}$Mo nuclear reaction as a monitor for intermediate energy proton experiments and to benchmark state-of-the-art reaction model codes. A set of 38 measured cross sections for ${}^{\text{nat}}$Nb(p,x) and ${}^{\text{nat}}$Cu(p,x) reactions between 40-90 MeV, as well as 5 independent measurements of isomer branching ratios, are reported. These are useful in medical and basic science radionuclide productions at intermediate energies. The ${}^{\text{nat}}$Cu(p,x)${}^{56}$Co, ${}^{\text{nat}}$Cu(p,x)${}^{62}$Zn, and ${}^{\text{nat}}$Cu(p,x)${}^{65}$Zn reactions were used to determine proton fluence, and all activities were quantified using HPGe spectrometry. Variance minimization techniques were employed to reduce systematic uncertainties in proton energy and fluence, improving the reliability of these measurements. The measured cross sections are shown to be in excellent agreement with literature values, and have been measured with improved precision compared with previous measurements. This work also reports the first measurement of the ${}^{\text{nat}}$Nb(p,x)${}^{82\text{m}}$Rb reaction, and of the independent cross sections for ${}^{\text{nat}}$Cu(p,x)${}^{52\text{g}}$Mn and ${}^{\text{nat}}$Nb(p,x)${}^{85\text{g}}$Y in the 40-90 MeV region. The effects of ${}^{\text{nat}}$Si(p,x)${}^{22,24}$Na contamination, arising from silicone adhesive in the Kapton tape used to encapsulate the aluminum monitor foils, is also discussed as a cautionary note to future stacked-target cross section measurements. \emph{A priori} predictions of the reaction modeling codes CoH, EMPIRE, and TALYS are compared with experimentally measured values and used to explore the differences between codes for the ${}^{\text{nat}}$Nb(p,x) and ${}^{\text{nat}}$Cu(p,x) reactions.

   nucl-exNucl.Instrum.Meth.B(2018)·18 citations
2. 02*

   Positron Beams and Two-Photon Exchange: The Key to Precision Form Factors

   Jan C. Bernauer🇺🇸

   The proton elastic form factor ratio can be measured either via Rosenbluth separation in an unpolarized beam and target experiment, or via the use of polarization degrees of freedom. However, data produced by these two approaches show a discrepancy, increasing with $Q^2$. The proposed explanation of this discrepancy---two-photon exchange---has been tested recently by three experiments. The results support the existence of a small two-photon exchange effect but cannot establish that theoretical treatment at the measured momentum transfers are valid. At larger momentum transfers, theory remains untested. This paper investigates the possibilities of measurements at DESY and Jefferson Lab to measure the effect at larger momentum transfers.

   nucl-exAIP Conf.Proc.(2018)·1 citation
3. 03*

   Two-Photon Exchange: Future experimental prospects

   Jan C. Bernauer🇺🇸

   The proton elastic form factor ratio is accessible in unpolarized Rosenbluth-type experiments as well as experiments which make use of polarization degrees of freedom. The extracted values show a distinct discrepancy, growing with $Q^2$. Three recent experiments tested the proposed explanation, two-photon exchange, by measuring the positron-proton to electron-proton cross section ratio. In the results, a small two-photon exchange effect is visible, significantly different from theoretical calculation. Theory at larger momentum transfer remains untested. This paper discusses the possibilities for future measurements at larger momentum transfer.

   nucl-exFew Body Syst.(2018)·1 citation
4. 04*

   Liquid Scintillator Response to Proton Recoils in the 10-100 keV Range

   C. Awe🇺🇸 · P.S. Barbeau🇺🇸 · J.I. Collar🇺🇸 · S. Hedges🇺🇸 · L. Li🇺🇸

   We study the response of EJ-301 liquid scintillator to monochromatic 244.6 $\pm$ 8.4 keV neutrons, targeting the 10-100 keV proton recoil energy interval. Limited experimental information exists for proton light yield in this range, for this or any other organic scintillator. Our results confirm the adequacy of a modified Birks' model, common to all organic scintillator formulations, predicting a marked increase in quenching factor as proton energy approaches the few keV regime. The relevance of this behavior within the context of searches for low-mass particle dark matter is mentioned.

   ↳ physics.ins-detastro-ph.COastro-ph.IMhep-ex+1PRC(2018)·19 citations
5. 05*

   Bayesian parameter estimation for relativistic heavy-ion collisions

   Jonah E. Bernhard🇺🇸

   I develop and apply a Bayesian method for quantitatively estimating properties of the quark-gluon plasma (QGP), an extremely hot and dense state of fluid-like matter created in relativistic heavy-ion collisions. The QGP cannot be directly observed -- it is extraordinarily tiny and ephemeral, about $10^{-14}$ meters in size and living $10^{-23}$ seconds before freezing into discrete particles -- but it can be indirectly characterized by matching the output of a computational collision model to experimental observations. The model, which takes the QGP properties of interest as input parameters, is calibrated to fit the experimental data, thereby extracting a posterior probability distribution for the parameters. In this dissertation, I construct a specific computational model of heavy-ion collisions and formulate the Bayesian parameter estimation method, which is based on general statistical techniques. I then apply these tools to estimate fundamental QGP properties, including its key transport coefficients and characteristics of the initial state of heavy-ion collisions. Perhaps most notably, I report the most precise estimate to date of the temperature-dependent specific shear viscosity $\eta /s$, the measurement of which is a primary goal of heavy-ion physics. The estimated minimum value is $\eta /s=0.085_{-0.025}^{+0.026}$ (posterior median and 90% uncertainty), remarkably close to the conjectured lower bound of $1/4\pi \simeq 0.08$. The analysis also shows that $\eta /s$ likely increases slowly as a function of temperature. Other estimated quantities include the temperature-dependent bulk viscosity $\zeta /s$, the scaling of initial state entropy deposition, and the duration of the pre-equilibrium stage that precedes QGP formation.

   ↳ nucl-thhep-phnucl-exstat.AP108 citations
6. 06*

   Workshop on Pion-Kaon Interactions (PKI2018) Mini-Proceedings. Editors: M. Amaryan, Ulf-G. Meißner, C. Meyer, J. Ritman, and I. Strakovsky

   M. Amaryan · M. Baalouch · G. Colangelo · J. R. de Elvira · D. Epifanov · A. Filippi · B. Grube · V. Ivanov · B. Kubis · P. M. Lo · M. Mai · V. Mathieu and 12 other authors

   This volume is a short summary of talks given at the PKI2018 Workshop organized to discuss current status and future prospects of pi-K interactions. The precise data on pi-K interaction will have a strong impact on strange meson spectroscopy and form factors that are important ingredients in the Dalitz plot analysis of a decays of heavy mesons as well as precision measurement of Vus matrix element and therefore on a test of unitarity in the first raw of the CKM matrix. The workshop has combined the efforts of experimentalists, Lattice QCD, and phenomenology communities. Experimental data relevant to the topic of the workshop were presented from the broad range of different collaborations like CLAS, GlueX, COMPASS, BaBar, BELLE, BESIII, VEPP-2000, and LHCb. One of the main goals of this workshop was to outline a need for a new high intensity and high precision secondary KL beam facility at JLab produced with the 12 GeV electron beam of CEBAF accelerator. This workshop is a successor of the workshops Physics with Neutral Kaon Beam at JLab [1] held at JLab, February, 2016; Excited Hyperons in QCD Thermodynamics at Freeze-Out [2] held at JLab, November, 2016; New Opportunities with High-Intensity Photon Sources [3] held at CUA, February, 2017. Further details about the PKI2018 Workshop can be found on the web page of the conference: http://www.jlab.org/conferences/pki2018/ .

   ↳ hep-phhep-exnucl-exnucl-th2 citations
7. 07*

   Disappearance of nuclear deformation in hypernuclei: a perspective from a beyond-mean-field study

   H. Mei🇺🇸 · K. Hagino · J.M. Yao🇺🇸 · T. Motoba🇯🇵

   The previous mean-field calculation [Myaing Thi Win and K. Hagino, Phys. Rev. C{\bf 78}, 054311 (2008)] has shown that the oblate deformation in ${}^{28,30,32}$Si disappears when a $\Lambda$ particle is added to these nuclei. We here investigate this phenomenon by taking into account the effects beyond the mean-field approximation. To this end, we employ the microscopic particle-rotor model based on the covariant density functional theory. We show that the deformation of ${}^{30}$Si does not completely disappear, even though it is somewhat reduced, after a $\Lambda$ particle is added if the beyond-mean-field effect is taken into account. We also discuss the impurity effect of $\Lambda$ particle on the electric quadrupole transition, and show that an addition of a $\Lambda$ particle leads to a reduction in the $B(E2)$ value, as a consequence of the reduction in the deformation parameter.

   ↳ nucl-thnucl-exPRC(2018)·27 citations
8. 08*

   Pion-kaon femtoscopy in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV modeled in (3+1)D hydrodynamics coupled to Therminator 2 and the effect of delayed kaon emission

   Adam Kisiel🇵🇱

   Non-identical particle femtoscopy measures the size of the system emitting particles ("radius") in heavy-ion collisions as well as the difference between mean emission space-time coordinates of two particle species ("emission asymmetry"). The system created in such collisions at the LHC behaves collectively and its dynamics is well described by hydrodynamic models. A significant emission asymmetry between pions and kaons, coming from collective flow, enhanced by contribution from flowing resonances is predicted. We present calculations within the (3+1)D viscous hydrodynamic model coupled to statistical hadronization code Therminator 2, corresponding to Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. We obtain femtoscopic radii and emission asymmetry for pion-kaon pairs as a function of collision centrality. The radii grow linearly with cube root of particle multiplicity density. The emission asymmetry is negative and comparable to the radius, indicating that pions are emitted closer to the center of the system and/or later than kaons. Recent ALICE Collaboration measurements of identical kaon femtoscopy shows that kaons are emitted, on average, 2.1~fm/$c$ later than pions. We modify our calculation by introducing such delay and find that the system source size is only weakly affected. In contrast the pion-kaon emission asymmetry is directly sensitive to such delays and the modified calculation shows significantly lower values of asymmetry. Therefore we propose the measurement of the pion-kaon femtoscopic correlation function as a sensitive probe of the time delays in particle emission.

   ↳ nucl-thhep-exnucl-exPRC(2018)·18 citations
9. 09*

   Status of the JENSA gas-jet target for experiments with rare isotope beams

   K. Schmidt🇫🇷 · K. A. Chipps🇺🇸 · S. Ahn🇺🇸 · D. W. Bardayan · J. Browne🇺🇸 · U. Greife🇺🇸 · Z. Meisel🇺🇸 · F. Montes🇺🇸 · P. D. O'Malley🇺🇸 · W-J. Ong🇺🇸 · S. D. Pain🇺🇸 · H. Schatz🇺🇸 and 3 other authors

   The JENSA gas-jet target was designed for experiments with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory. The gas jet will be the main target for the Separator for Capture Reactions SECAR at the Facility for Rare Isotope Beams on the campus of Michigan State University, USA. In this work, we describe the advantages of a gas-jet target, detail the current recirculating gas system, and report recent measurements of helium jet thicknesses of up to about $10^{19}$ atoms/cm${}^2$. Finally a comparison with other supersonic gas-jet targets is presented.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2018)·19 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.