Thu·Nov 5, 2015Thursday·November 5, 2015

1. 01*

   Electroweak bosons in Pb+Pb and p+Pb collisions from ATLAS

   Thomas Balestri (for the ATLAS Collaboration)🇺🇸

   Electroweak boson ($W$, $Z$, $\gamma$) measurements in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV and in $p$+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV are presented with the ATLAS detector at the LHC. In Pb+Pb, electroweak boson yields are shown to be independent of centrality. Differential measurements in absolute pseudorapidity are used to investigate nuclear effects to the free-proton parton distribution function (PDF). The distributions lack the experimental precision to unambiguously identify the presence of nuclear modifications. In $p$+Pb, the $Z$ boson cross section is measured as a function of center-of-mass rapidity $y_Z^{\ast }$ and the momentum fraction of the lead-going parton (Bjorken $x_{Pb}$). The distributions are asymmetric and model predictions underestimate the data at large $x_{Pb}$. The overall shape is best described by including nuclear effects. The differential cross section is also measured in different centrality classes and shows evidence of spatially-dependent nuclear PDFs. The $Z$ boson production yields are measured as a function of the mean number of participants using Glauber and Glauber-Gribov color fluctuation models. Binary scaling of the yields is observed utilizing the standard Glauber model after applying a centrality-bias correction.

   nucl-ex0 citations
2. 02*

   First measurement of several $\beta$-delayed neutron emitting isotopes beyond N=126

   R. Caballero-Folch🇪🇸 · C. Domingo-Pardo🇪🇸 · J. Agramunt🇪🇸 · A. Algora🇪🇸 · F. Ameil🇩🇪 · A. Arcones🇩🇪 · Y. Ayyad🇯🇵 · J. Benlliure🇪🇸 · I.N. Borzov · M. Bowry🇺🇸 · F. Calvino🇪🇸 · D. Cano-Ott🇪🇸 and 53 other authors

   The $\beta$-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with $\beta$-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb and Bi in the mass region N$\gtrsim$126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the $\beta$-decay strength distribution. In doing so, it provides important constraints to global theoretical models currently used in $r$-process nucleosynthesis.

   nucl-exnucl-thPRL(2016)·61 citations
3. 03*

   Compositeness of baryonic resonances: Applications to the Delta(1232), N(1535), and N(1650) resonances

   Takayasu Sekihara (Osaka U., Res. Ctr. Nucl. Phys.)🇯🇵 · Takashi Arai (KEK, Tsukuba)🇯🇵 · Junko Yamagata-Sekihara (Nat. Inst. Tech., Oshima Coll.)🇯🇵 · Shigehiro Yasui (Tokyo Inst. Tech.)🇯🇵

   We present a formulation of the compositeness for baryonic resonances in order to discuss the meson-baryon molecular structure inside the resonances. For this purpose, we derive a relation between the residue of the scattering amplitude at the resonance pole position and the two-body wave function of the resonance in a sophisticated way, and we define the compositeness as the norm of the two-body wave functions. As applications, we investigate the compositeness of the $\Delta (1232)$, $N(1535)$, and $N(1650)$ resonances from precise $\pi N$ scattering amplitudes in a unitarized chiral framework with the interaction up to the next-to-leading order in chiral perturbation theory. The $\pi N$ compositeness for the $\Delta (1232)$ resonance is evaluated in the $\pi N$ single-channel scattering, and we find that the $\pi N$ component inside $\Delta (1232)$ in the present framework is nonnegligible, which supports the previous work. On the other hand, the compositeness for the $N(1535)$ and $N(1650)$ resonances is evaluated in a coupled-channels approach, resulting that the $\pi N$, $\eta N$, $K\Lambda$ and $K\Sigma$ components are negligible for these resonances.

   ↳ hep-phhep-exnucl-exnucl-thPRC(2016)·46 citations
4. 04*

   Design and performance of an ionisation chamber for the measurement of low alpha-activities

   Andreas Hartmann🇩🇪 · Jochen Hutsch · Felix Krüger · Manfred Sobiella · Heinrich Wilsenach · Kai Zuber🇩🇪

   A new ionisation chamber for alpha-spectroscopy has been built from radio-pure materials for the purpose of investigating long lived alpha-decays. The measurement makes use of pulse shape analysis to discriminate between signal and background events. The design and performance of the chamber is described in this paper. A background rate of ($10.9\pm 0.6$) counts per day in the energy region of 1 MeV to 9 MeV was achieved with a run period of 30.8 days. The background is dominantly produced by radon daughters.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2016)·12 citations
5. 05*

   Target Studies for Surface Muon Production

   F. Berg🇨🇭 · L. Desorgher🇨🇭 · A. Fuchs🇨🇭 · W. Hajdas🇨🇭 · Z. Hodge🇨🇭 · P.-R. Kettle🇨🇭 · A. Knecht🇨🇭 · R. Lüscher🇨🇭 · A. Papa🇨🇭 · G. Rutar🇨🇭 · M. Wohlmuther🇨🇭

   Meson factories are powerful drivers of diverse physics programmes. With beam powers already in the MW-regime attention has to be turned to target and beam line design to further significantly increase surface muon rates available for experiments. For this reason we have explored the possibility of using a neutron spallation target as a source of surface muons by performing detailed Geant4 simulations with pion production cross sections based on a parametrization of existing data. While the spallation target outperforms standard targets in the backward direction by more than a factor 7 it is not more efficient than standard targets viewed under 90{\deg}. Not surprisingly, the geometry of the target plays a large role in the generation of surface muons. Through careful optimization, a gain in surface muon rate of between 30 - 60% over the standard "box-like" target used at the Paul Scherrer Institute could be achieved by employing a rotated slab target. An additional 10% gain could also be possible by utilizing novel target materials such as, e.g., boron carbide.

   ↳ physics.ins-dethep-exnucl-exphysics.acc-phPhys.Rev.Accel.Beams(2016)·55 citations
6. 06*

   On microscopic theory of radiative nuclear reaction characteristics

   Sergei Kamerdzhiev · Oleg Achakovskiy · Alexander Avdeenkov · Stephane Goriely🇧🇪

   A survey of some results in the modern microscopic theory of properties of nuclear reactions with gamma-rays is given. First of all, we discuss the impact of phonon coupling (PC) on the photon strength function (PSF) because it represents the most natural physical source of additional strength found for Sn isotopes in recent experiments that could not be explained within the stan- dard HFB+QRPA approach. The self-consistent version of the Extended Theory of Finite Fermi Systems in the Quasiparticle Time Blocking Approximation, or simply QTBA, is applied. It uses the HFB mean field and includes both the QRPA and PC effects on the basis of the SLy4 Skyrme force. With our microscopic E1 PSFs, the following properties have been calculated for many stable and unstable even-even semi-magic Sn and Ni isotopes as well as for double-magic 132Sn and 208Pb using the reaction codes EMPIRE and TALYS with several nuclear level density (NLD) models: 1) the neutron capture cross sections, 2) the corresponding neutron capture gamma spectra, 3) the av- erage radiative widths of neutron resonances. In all the properties considered, the PC contribution turned out to be significant, as compared with the standard QRPA one, and necessary to explain the available experimental data. The results with the phenomenological so-called generalized super- fluid NLD model turned out to be worse, on the whole, than those obtained with the microscopic HFB+combinatorial NLD model. Finally, we also discuss the modern microscopic NLD models based on the self-consistent HFB method and show their relevance to explain experimental data as compared with the phenomeno- logical models. The use of these self-consistent microscopic approaches is of particular relevance for nuclear astrophysics, but also for the study of double-magic nuclei.

   ↳ nucl-thnucl-exPhys.Atom.Nucl.(2016)·2 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.