Wed·Aug 28, 2019Wednesday·August 28, 2019

1. 01*

   Vector analyzing powers in the $d(p,pp)n$ and $d(p,{}^2\mathrm{He})n$ channels at 135 MeV

   H. Tavakoli-Zaniani · M. Eslami-Kalantari · M. T. Bayat · N. Kalantar-Nayestanaki · St. Kistryn · A. Kozela · J.G. Messchendorp · M. Mohammadi-Dadkan · R. Ramazani-Sharifabadi · E. Stephan

   Vector analyzing powers, $A_x$ and $A_y$, of the proton-deuteron break-up reaction have been measured by using a polarized-proton beam at 135 MeV impinging on a liquid-deuterium target. For the experiment, the Big Instrument for Nuclear-polarization Analysis (BINA) was used at KVI, Groningen, the Netherlands. The data are compared to the predictions of Faddeev calculations using state-of-the-art two- and three-nucleon potentials. Our data are reasonably well described by calculations for the kinematical configurations at which the three-nucleon force (3NF) effect is predicted to be small. However, striking discrepancies are observed at specific configurations, in particular in the cases of symmetric configurations, where the relative azimuthal angle between the two protons is small which corresponds to the $d(p,{}^2\mathrm{He})n$ channel. The vector analyzing powers of these configurations are compared to the proton deuteron elastic scattering to study the spin-isospin sensitivity of the 3NF models. The results are compared to the earlier results of the proton-deuteron break-up reaction at 190 MeV proton-beam energy \cite{Mardanpour2010}. A disagreement is observed for both proton-beam energies between data and calculations which points to a deficiency in the treatment of spin-isospin part of the 3NF.

   nucl-exnucl-thEPJA(2020)·12 citations
2. 02*

   A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment

   M. W. Ahmed🇺🇸 · R. Alarcon🇺🇸 · A. Aleksandrova🇺🇸 · S. Baessler🇺🇸 · L. Barron-Palos🇲🇽 · L. M. Bartoszek🇺🇸 · D. H. Beck🇺🇸 · M. Behzadipour🇺🇸 · I. Berkutov🇺🇸 · J. Bessuille🇺🇸 · M. Blatnik🇺🇸 · M. Broering🇺🇸 and 82 other authors

   A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid ${}^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized ${}^3$He from an Atomic Beam Source injected into the superfluid ${}^4$He and transported to the measurement cells as a co-magnetometer. The superfluid ${}^4$He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of $2-3\times 10^{-28}$ e-cm, with anticipated systematic uncertainties below this level.

   ↳ physics.ins-detnucl-exJINST(2019)·80 citations
3. 03*

   The Exposure-Background Duality in the Searches of Neutrinoless Double Beta Decay

   M.K. Singh🇹🇼 · H.T. Wong🇹🇼 · L. Singh🇹🇼 · V. Sharma🇹🇼 · V. Singh🇮🇳 · Q. Yue🇨🇳

   Tremendous efforts are required to scale the summit of observing neutrinoless double beta decay ($0\nu \beta \beta$). This article quantitatively explores the interplay between exposure (target mass X data taking time) and background levels in $0\nu \beta \beta$ experiments. In particular, background reduction can substantially alleviate the necessity of unrealistic large exposure as the normal mass hierarchy (NH) is probed. The non-degenerate (ND)-NH can be covered with an exposure of O(100) ton-year, which is only an order of magnitude larger than those planned for next generation projects - provided that the background could be reduced by 0($10^{-6}$) relative to the current best levels. It follows that background suppression will be playing increasingly important and investment-effective, if not determining, roles in future $0\nu \beta \beta$ experiments with sensitivity goals of approaching and covering ND-NH.

   ↳ hep-exhep-phnucl-exPRD(2020)·17 citations
4. 04*

   Back-to-back relative-excess observable in search for the chiral magnetic effect

   Yicheng Feng🇺🇸 · Jie Zhao🇺🇸 · Fuqiang Wang🇺🇸

   $\text{Background:}$ The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at RHIC and LHC. In the commonly used reaction plane (RP) dependent, charge dependent azimuthal correlator ($\Delta \gamma$), both the close and back-to-back pairs are included. Many backgrounds contribute to the close pairs (e.g. resonance decays, jet correlations), whereas the back-to-back pairs are relatively free of those backgrounds. $\text{Purpose:}$ In order to reduce those backgrounds, we propose a new observable which only focuses on the back-to-back pairs, namely, the relative back-to-back opposite-sign (OS) over same-sign (SS) pair excess ($r_{\text{BB}}$) as a function of the pair azimuthal orientation with respect to the RP (${\phi }_{\text{BB}}$). $\text{Methods:}$ We use analytical calculations and toy model simulations to demonstrate the sensitivity of $r_{\text{BB}}({\phi }_{\text{BB}})$ to the CME and its insensitivity to backgrounds. $\text{Results:}$ With finite CME, the ${\phi }_{\text{BB}}$ distribution of $r_{\text{BB}}$ shows a clear characteristic modulation. Its sensitivity to background is significantly reduced compared to the previous $\Delta \gamma$ observable. The simulation results are consistent with our analytical calculations. $\text{Conclusions:}$ Our studies demonstrate that the $r_{\text{BB}}({\phi }_{\text{BB}})$ observable is sensitive to the CME signal and rather insensitive to the resonance backgrounds.

   ↳ nucl-thnucl-exPRC(2020)·3 citations
5. 05*

   Influence of the neutron-skin effect on nuclear isobar collisions at RHIC

   Jan Hammelmann🇩🇪 · Alba Soto-Ontoso🇺🇸 · Massimiliano Alvioli🇮🇹 · Hannah Elfner🇩🇪 · Mark Strikman🇺🇸

   The unambiguous observation of a Chiral Magnetic Effect (CME)-driven charge separation is the core aim of the isobar program at RHIC consisting of ${}_{40}^{96}$Zr+${}_{40}^{96}$Zr and ${}_{44}^{96}$Ru+${}_{44}^{96}$Ru collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. We quantify the role of the spatial distributions of the nucleons in the isobars on both eccentricity and magnetic field strength within a relativistic hadronic transport approach (SMASH, Simulating Many Accelerated Strongly-interacting Hadrons). In particular, we introduce isospin-dependent nucleon-nucleon spatial correlations in the geometric description of both nuclei, deformation for ${}_{44}^{96}$Ru and the so-called neutron skin effect for the neutron-rich isobar i.e. ${}_{40}^{96}$Zr. The main result of this study is a reduction of the magnetic field strength difference between ${}_{44}^{96}$Ru+${}_{44}^{96}$Ru and ${}_{40}^{96}$Zr+${}_{40}^{96}$Zr by a factor of 2, from $10\%$ to $5\%$ in peripheral collisions when the neutron-skin effect is included. Further, we find an increase of eccentricity by up to 10$\%$ when deformation is taken into account while neither the neutron skin effect nor the nucleon-nucleon correlations result into a significant modification of this observable with respect to the traditional Woods-Saxon modeling. Our results suggest a significantly smaller CME signal to background ratio for the experimental charge separation measurement in peripheral collisions with the isobar systems than previously expected.

   ↳ nucl-thhep-phnucl-exPRC(2020)·44 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.