Tue·Nov 29, 2016Tuesday·November 29, 2016

1. 01*

   Precise measurement of the thermal and stellar ${}^{54}$Fe($n,\gamma$)${}^{55}$Fe cross sections via AMS

   Anton Wallner🇦🇺 · Tamas Belgya🇭🇺 · Kathrin Buczak🇦🇹 · Laurent Coquard🇩🇪 · Max Bichler🇦🇹 · Iris Dillmann🇩🇪 · Robin Golser🇦🇹 · Franz Käppeler🇩🇪 · Amanda Karakas🇦🇺 · Walter Kutschera🇦🇹 · Claudia Lederer🇦🇹 · Alberto Mengoni🇮🇹 and 5 other authors

   The detection of long-lived radionuclides through ultra-sensitive single atom counting via accelerator mass spectrometry (AMS) offers opportunities for precise measurements of neutron capture cross sections, e.g. for nuclear astrophysics. The technique represents a truly complementary approach, completely independent of previous experimental methods. The potential of this technique is highlighted at the example of the ${}^{54}$Fe($n,\gamma$)${}^{55}$Fe reaction. Following a series of irradiations with neutrons from cold and thermal to keV energies, the produced long-lived ${}^{55}$Fe nuclei ($t_{1/2}=2.744(9)$ yr) were analyzed at the Vienna Environmental Research Accelerator (VERA). A reproducibility of about 1% could be achieved for the detection of ${}^{55}$Fe, yielding cross section uncertainties of less than 3%. Thus, the new data can serve as anchor points to time-of-flight experiments. We report significantly improved neutron capture cross sections at thermal energy (${\sigma }_{th}=2.30\pm 0.07$ b) as well as for a quasi-Maxwellian spectrum of $kT=25$ keV ($\sigma =30.3\pm 1.2$ mb) and for $E_n=481\pm 53$ keV ($\sigma =6.01\pm 0.23$ mb). The new experimental cross sections have been used to deduce improved Maxwellian average cross sections in the temperature regime of the common $s$-process scenarios. The astrophysical impact is discussed using stellar models for low-mass AGB stars.

   nucl-exastro-ph.SRPRC(2017)·12 citations
2. 02*

   A test of local Lorentz invariance with Compton scattering asymmetry

   P. Mohanmurthy🇺🇸 · A. Narayan🇺🇸 · D. Dutta🇺🇸

   We report on a measurement of the constancy and anisotropy of the speed of light relative to the electrons in photon-electron scattering. We used the Compton scattering asymmetry measured by the new Compton polarimeter in Hall~C at Jefferson Lab to test for deviations from unity of the vacuum refractive index ($n$). For photon energies in the range of 9 - 46 MeV, we obtain a new limit of $1-n<1.4\times 10^{-8}$. In addition, the absence of sidereal variation over the six month period of the measurement constrains any anisotropies in the speed of light. These constitute the first study of Lorentz invariance using Compton asymmetry. Within the minimal standard model extension framework, our result yield limits on the photon and electron coefficients ${\tilde{\kappa }}_{0^{+}}^{YZ},c_{TX},{\tilde{\kappa }}_{0^{+}}^{ZX}$, and $c_{TY}$. Although, these limits are several orders of magnitude larger than the current best limits, they demonstrate the feasibility of using Compton asymmetry for tests of Lorentz invariance. Future parity violating electron scattering experiments at Jefferson Lab will use higher energy electrons enabling better constraints.

   nucl-exgr-qchep-exMod.Phys.Lett.A(2016)·8 citations
3. 03*

   Ab initio calculation of the potential bubble nucleus ${}^{34}$Si

   T. Duguet🇫🇷 · V. Somà🇫🇷 · S. Lecluse🇧🇪 · C. Barbieri🇬🇧 · P. Navrátil🇨🇦

   The possibility that an unconventional depletion in the center of the charge density distribution of certain nuclei occurs due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. We report on ab initio self-consistent Green's function calculations of one of such candidates, ${}^{34}$Si, together with its Z+2 neighbour ${}^{36}$S. Binding energies, rms radii and density distributions of the two nuclei as well as low-lying spectroscopy of ${}^{35}$Si, ${}^{37}$S, ${}^{33}$Al and ${}^{35}$P are discussed. The interpretation of one-nucleon removal and addition spectra in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input inter-nucleon interactions. The prediction regarding the (non-)existence of the bubble structure in ${}^{34}$Si varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root mean square radius of ${}^{36}$S are well reproduced, along with ${}^{34}$Si and ${}^{36}$S binding energies, only leaves the NNLO${}_{\text{sat}}$ Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of ${}^{34}$Si, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1/2${}^{-}$-3/2${}^{-}$ splitting in the spectrum of ${}^{35}$Si as compared to ${}^{37}$S.

   ↳ nucl-thnucl-exPRC(2017)·74 citations
4. 04*

   Event Shape Sorting: selecting events with similar evolution

   Boris Tomasik🇸🇰 · Renata Kopecna🇩🇪

   We present novel method for the organisation of events. The method is based on comparing event-by-event histograms of a chosen quantity Q that is measured for each particle in every event. The events are organised in such a way that those with similar shape of the Q-histograms end-up placed close to each other. We apply the method on histograms of azimuthal angle of the produced hadrons in ultrarelativsitic nuclear collisions. By selecting events with similar azimuthal shape of their hadron distribution one chooses events which are likely that they underwent similar evolution from the initial state to the freeze-out. Such events can more easily be compared to theoretical simulations where all conditions can be controlled. We illustrate the method on data simulated by the AMPT model.

   ↳ physics.data-anhep-exhep-phnucl-ex+1EPJ Web Conf.(2017)·0 citations
5. 05*

   Performance of the ALICE secondary vertex b-tagging algorithm in p-Pb collisions

   Lukáš Kramárik (for the ALICE Collaboration)🇨🇿

   The hot and dense nuclear matter, that is produced in heavy-ion collisions, could be studied by jets originating from beauty quarks. In-medium energy loss of these quarks provides information on several properties of the quark-gluon plasma, produced in ultra-relativistic heavy-ion collisions. Reconstructed jets are powerful tools, since they offer access to kinematics of these hard-scattered partons. Beauty hadrons are specific for their long lifetime, large mass and large-multiplicity decays. Due to the long lifetime beauty hadrons decay at displaced secondary vertices. In the ALICE experiment, secondary vertex properties are used to tag b-jets. The study of Monte Carlo based performance of the b-tagging algorithm for charged jets in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is discussed in proceedings.

   ↳ hep-exnucl-exPoS(2016)·0 citations
6. 06*

   Non-equilibrium dilepton production in hadronic transport approaches

   Jan Staudenmaier🇩🇪 · Janus Weil🇩🇪 · Hannah Petersen🇩🇪

   In this work the non-equilibrium dilepton production from a hadronic transport approach (SMASH) is presented. The dilepton emission from the hadronic stage is of interest for current HADES results measured at GSI in the beam energy range from 1.25 - 3.5 GeV. Also at high collision energies (RHIC/LHC) the later dilute stages of the reaction are dominated by hadronic dynamics. The newly developed hadronic transport approach called SMASH (=Simulating Many Accelerated Strongly-interacting Hadrons) is introduced first. After explaining the basic interaction mechanisms, a comparison of elementary cross sections for pion production to experimental data is shown. The dilepton production within SMASH is explained in detail. The main contribution to the dilepton spectra in the low energy regime of GSI/FAIR/RHIC-BES originates from resonance decays. Results of the dilepton production with SMASH such as invariant mass spectra are shown.

   ↳ nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2017)·6 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.