Mon·Mar 16, 2015Monday·March 16, 2015

1. 01*

   Study of the quasi-free $np\to np{\pi }^{+}{\pi }^{-}$ reaction with a deuterium beam at 1.25 GeV/nucleon

   G. Agakishiev🇷🇺 · A. Balanda🇵🇱 · D. Belver🇪🇸 · A.V. Belyaev🇷🇺 · A. Blanco🇵🇹 · M. Böhmer🇩🇪 · J.L. Boyard🇫🇷 · P. Braun-Munzinger🇩🇪 · P. Cabanelas🇪🇸 · E. Castro🇪🇸 · S. Chernenko🇷🇺 · T. Christ🇩🇪 and 93 other authors

   The tagged quasi-free $np\to np{\pi }^{+}{\pi }^{-}$ reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 GeV/nucleon ($\sqrt{s}\sim$ 2.42 GeV/c for the quasi-free collision). For the first time, differential distributions for ${\pi }^{+}{\pi }^{-}$ production in $np$ collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the $np\to np{\pi }^{+}{\pi }^{-}$ reaction are compared with different models. This comparison confirms the dominance of the $t$-channel with $\Delta \Delta$ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the ${\pi }^{+}{\pi }^{-}$ invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M$\sim$ 2.38 GeV and with width $\Gamma \sim$ 70 MeV.

   nucl-exPLB(2015)·36 citations
2. 02*

   Uncertainties of optical-model parameters for the study of the threshold anomaly

   Daniel Abriola · A. Arazi · J. Testoni · F. Gollan · G.V. Martí

   In the analysis of elastic-scattering experimental data, optical-model parameters (usually, depths of real and imaginary potentials) are fitted and conclusions are drawn analyzing their variations at bombardment energies close to the Coulomb barrier (threshold anomaly). The judgement about the shape of this variation (related to the physical processes producing this anomaly) depends on these fitted values but the robustness of the conclusions strongly depends on the uncertainties with which these parameters are derived. We will show that previous published studies have not used a common criterium for the evaluation of the parameter uncertainties. In this work, a study of these uncertainties is presented, using conventional statistic tools as well as bootstrapping techniques. As case studies, these procedures are applied to re-analyze detailed elastic-scattering data for the ${}^{12}$C + ${}^{208}$Pb and the ${}^6$Li + ${}^{80}$Se systems.

   nucl-exJ.Phys.Conf.Ser.(2015)·8 citations
3. 03*

   Test of the Atiyah-Singer Index Theorem for Fullerene with a Superconducting Microwave Resonator

   B. Dietz🇩🇪 · T. Klaus · M. Miski-Oglu🇩🇪 · A. Richter🇩🇪 · M. Bischoff🇩🇪 · L. von Smekal🇩🇪 · J. Wambach🇩🇪

   Experiments have been performed using a spherical superconducting microwave resonator that simulates the geometric structure of the C60 fullerene molecule. The objective was to study with very high resolution the exceptional spectral properties emerging from the symmetries of the icosahedral structure of the carbon lattice. In particular, the number of zero modes has been determined to test the predictions of the Atiyah-Singer index theorem, which relates it to the topology of the curved carbon lattice. This is, to the best of our knowledge, the first experimental verification of the index theorem.

   ↳ cond-mat.mes-hallnucl-exnucl-thquant-phPRL(2015)·10 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.