Tue·Jul 14, 2020Tuesday·July 14, 2020

1. 01*

   Electric and magnetic dipole strength in 112,114,116,118,120,124Sn

   S. Bassauer (1) · P. von Neumann-Cosel (1)🇩🇪 · P.-G. Reinhard (2)🇩🇪 · A. Tamii (3)🇯🇵 · S. Adachi (3) · C.A. Bertulani (4)🇺🇸 · P.Y. Chan (3) · A. D'Alessio (1) · H. Fujioka (5)🇯🇵 · H. Fujita (3) · Y. Fujita (3)🇯🇵 · G. Gey (3)🇯🇵 and 24 other authors

   Inelastic proton scattering experiments were performed at the Research Center for Nuclear Physics, Osaka, with a 295 MeV beam covering laboratory angles 0{\deg}-6{\deg} and excitation energies 6-22 MeV. Cross sections due to E1 and M1 excitations were extracted with a multipole decomposition analysis and then converted to reduced transition probabilities with the "virtual photon method" for E1 and the "unit cross section method" for M1 excitations, respectively. Including a theory-aided correction for the high excitation energy region not covered experimentally, the electric dipole polarizability was determined from the E1 strength distributions. Total photoabsorption cross sections derived from the E1 and M1 strength distributions show significant differences compared to those from previous ($\gamma$,xn) experiments in the energy region of the isocvector giant dipole resonance (IVGDR). The widths of the IVGDR deduced from the present data with a Lorentz parameterization show an approximately constant value of about 4.5 MeV in contrast to the large variations between isotopes observed in previous work. The IVGDR centroid energies are in good correspondence to expectations from systematics of their mass dependence. Furthermore, a study of the dependence of the IVGDR energies on bulk matter properties is presented. The E1 strengths below neutron threshold show fair agreement with results from ($\gamma$,$\gamma$') experiments on 112,116,120,124Sn in the energy region between 6 and 7 MeV. At higher excitation energies large differences are observed pointing to a different nature of the excited states with small ground state branching ratios. The isovector spin-M1 strengths exhibit a broad distribution between 6 and 12 MeV in all studied nuclei.

   nucl-exnucl-thPRC(2020)·48 citations
2. 02*

   Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons

   M. Dieterle · L. Witthauer · A. Fix · S. Abt · P. Achenbach · P. Adlarson · F. Afzal · P. Aguar Bartolome · Z. Ahmed · J.R.M. Annand · H.J. Arends · M. Bashkanov and 79 other authors

   The double-polarization observable $E$ and helicity-dependent cross sections ${\sigma }_{1/2}$, ${\sigma }_{3/2}$ have been measured for the photoproduction of ${\pi }^0$ pairs off quasi-free protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost $4\pi$ covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the $\gamma N\to N{\pi }^0{\pi }^0$ reaction. They are compared to predictions from reaction models in view of nucleon resonance contributions and also to a refit of one model that predicted results for the proton and for the neutron target. The comparison of the prediction and the refit demonstrate the large impact of the new data.

   nucl-exPRL(2020)·8 citations
3. 03*

   Total and differential cross sections of the $\mathbf{dp}\to {}^3\text{He}\mathbf{\eta }$ reaction at excess energies between 1 and 15 MeV

   C. Fritzsch🇩🇪 · S. Barsov🇷🇺 · I. Burmeister🇩🇪 · S. Dymov🇩🇪 · R. Gebel🇩🇪 · M. Hartmann🇩🇪 · A. Kacharava🇩🇪 · A. Khoukaz🇩🇪 · V. Komarov🇷🇺 · P. Kulessa🇵🇱 · A. Kulikov🇷🇺 · A. Lehrach🇩🇪 and 14 other authors

   New high precision total and differential cross sections are reported for the $dp\to {}^3\text{He}\eta$ reaction close to threshold. The measurements were performed using the magnetic spectrometer ANKE, which is an internal fixed target facility at the COSY cooler synchrotron. The data were taken for deuteron beam momenta between $3.14641\text{GeV}/c$ and $3.20416\text{GeV}/c$, which corresponds to the range in excess energy $Q$ for this reaction between $1.14\text{MeV}$ and $15.01\text{MeV}$. The normalization was established through the measurement in parallel of deuteron-proton elastic scattering and this was checked through the study of the $dp\to {}^3\text{He}{\pi }^0$ reaction. The previously indicated possible change of sign of the slope of the differential cross sections near the production threshold, which could be explained by a rapid variation of the $s$- and $p$-wave interference term, is not confirmed by the new data. The energy dependence of the total cross section and the $90^{\circ }$ slope parameter are well explained by describing the final state interaction in terms of a complex Jost function and the results are significant in the discussion of $\eta$-mesic nuclei. In combination with recently published WASA-at-COSY data [P. Adlarson $etal.$, Phys. Lett. B 782, 297 (2018)], a smooth variation of the slope parameter is achieved up to an excess energy of $80.9\text{MeV}$.

   nucl-exnucl-thPRC(2020)·0 citations
4. 04*

   The SPOT-IL Positron Beam Construction and Its Use for Doppler Broadening Measurement of Titanium Thin Films

   P. Or · G. Erlichman · D. Cohen · I. Sabo-Napadesky · E. Gordon · S. Cohen · O. Presler · E. O. Cohen · E. Piasetzky · H. Steinberg · S. May-Tal Beck · Guy Ron

   The construction and first operation of the slow positron beam built at the Hebrew University is reported here. The beam follows a traditional design, using a 22Na source, a Tungsten moderator, and a target cell equipped with a load-lock system for easy sample insertion. The beam energy varies between 0.03 keV and 30 keV. The detection system consists of two high purity Germanium detectors, facing each other, allowing low-background Doppler-Broadening (DB) measurements. Event readout is done using a state-of-the-art compact desktop system. The target cell is designed to allow a combined measurement of DB and sample conductivity, with the flexibility to add more detection options in the future. The beam has been successfully tested by using it to charecterize Titanium (Ti) films. Two 1.2 {\mu}m Ti films -- as produced, and after annealing, were measured at various energies (2 keV - 25 keV), and the results show consistent behavior with previous measurements.

   ↳ physics.ins-detcond-mat.mtrl-scinucl-exphysics.app-phNucl.Instrum.Meth.B(2024)·0 citations
5. 05*

   Probing chemical freeze-out criteria in relativistic nuclear collisions with coarse grained transport simulations

   Tom Reichert🇩🇪 · Gabriele Inghirami🇫🇮 · Marcus Bleicher🇩🇪

   We introduce a novel approach based on elastic and inelastic scattering rates to extract the hyper-surface of the chemical freeze-out from a hadronic transport model in the energy range from E${}_{\mathrm{lab}}=1.23$ AGeV to $\sqrt{s_{\mathrm{NN}}}=62.4$ GeV. For this study, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model combined with a coarse-graining method is employed. The chemical freeze-out distribution is reconstructed from the pions through several decay and re-formation chains involving resonances and taking into account inelastic, pseudo-elastic and string excitation reactions. The extracted average temperature and baryon chemical potential are then compared to statistical model analysis. Finally we investigate various freeze-out criteria suggested in the literature. We confirm within this microscopic dynamical simulation, that the chemical freeze-out at all energies coincides with $⟨E⟩/⟨N⟩\approx 1$ GeV, while other criteria, like $s/T^3=7$ and $n_{\mathrm{B}}+n_{\bar{\mathrm{B}}}\approx 0.12$ fm${}^{-3}$ are limited to higher collision energies.

   ↳ nucl-thhep-phnucl-exEPJA(2020)·20 citations
6. 06*

   Valence parton distribution of pion from lattice QCD: Approaching continuum

   Xiang Gao🇺🇸 · Luchang Jin🇺🇸 · Christos Kallidonis🇺🇸 · Nikhil Karthik🇺🇸 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸 · Charles Shugert🇺🇸 · Sergey Syritsyn🇺🇸 · Yong Zhao🇺🇸

   We present a high-statistics lattice QCD determination of the valence parton distribution function (PDF) of the pion, with a mass of 300 MeV, using two very fine lattice spacings of $a=0.06$ fm and 0.04 fm. We reconstruct the $x$-dependent PDF, as well as infer the first few even moments of the PDF using leading-twist 1-loop perturbative matching framework. Our analyses use both RI-MOM and ratio-based schemes to renormalize the equal-time bi-local quark-bilinear matrix elements of pions boosted up to 2.4 GeV momenta. We use various model-independent and model-dependent analyses to infer the large-$x$ behavior of the valence PDF. We also present technical studies on lattice spacing and higher-twist corrections present in the boosted pion matrix elements.

   ↳ hep-lathep-exhep-phnucl-ex+1PRD(2020)·125 citations
7. 07*

   On Multifractal Spectra and Renyi Dimensions in 14.5A GeV/c ${}^{28}$Si-nucleus Collisions

   N. Ahmad🇮🇳 · A. Kamal🇸🇦 · M. M. Khan🇮🇳 · Hushnud🇮🇳 · A. Tufail🇮🇳

   A systematic analysis of the data on 14.5A GeV/c ${}^{28}$Si-nucleus collisions is carried out to investigate the behaviours of Renyi dimensions, Dq and Multifractal Spectral Function, $f({\alpha }_q)$. The Renyi dimensions, $D_q$, are observed to decrease with increasing order of the moments, $q$. However, the Multifractal Spectra are concave downwards with their maxima occurring around ${\alpha }_q=1.21\pm 0.01$. A continuous curve representing Multifractal Spectral Function, $f({\alpha }_q)$, characterizes manifestation of fluctuations in the rapidity space.

   ↳ hep-exnucl-exnucl-thJ.Mod.Phys.(2014)·4 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.