Helicity-dependent cross sections for the photoproduction of π0\pi^0 pairs from nucleons

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 $\gamma N\rightarrow N\pi^0\pi^0$ 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.Comment: Submitted to Phys. Rev. Let

Generation of recombinant lymphocytic choriomeningitis viruses with trisegmented genomes stably expressing two additional genes of interest

Several arenaviruses cause hemorrhagic fever disease in humans for which no licensed vaccines are available and current therapeutic intervention is limited to the off-label use of the wide-spectrum antiviral ribavirin. However, the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) has proven to be a Rosetta stone for the investigation of virus–host interactions. Arenaviruses have a bisegmented negative-strand RNA genome. The S segment encodes for the virus nucleoprotein and glycoprotein, whereas the L segment encodes for the virus polymerase (L) and Z protein. The ability to generate recombinant LCMV (rLCMV) expressing additional foreign genes of interest would open novel avenues for the study of virus–host interactions and the development of novel vaccine strategies and high-throughput screens to identify antiarenaviral molecules. To this end, we have developed a trisegmented (1L + 2S) rLCMV-based approach (r3LCMV). Each of the two S segments in r3LCMV was altered to replace one of the viral genes by a gene of interest. All r3LCMVs examined expressing different reported genes were stable both genetically and phenotypically and exhibited wild-type growth properties in cultured cells. Reporter gene expression in r3LCMV-infected cells provided an accurate surrogate of levels of virus multiplication. Notably, some r3LCMVs displayed highly attenuated virulence in mice but induced protective immunity against a subsequent lethal challenge with wild-type LCMV, supporting the potential development of r3LCMV-based vaccines