1. SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
2. University of Alberta, Edmonton, Alberta T6G 1H9, Canada
3. Institute of Physics, University of Rostock, D-18051 Rostock, Germany
4. Aeronautics and Astronautics Department, Stanford University, Stanford, California 94305, USA
5. Northwestern University, Evanston, Illinois 60208, USA
6. European XFEL, 22869 Schenefeld, Germany
7. Friedrich Schiller University Jena, 07743 Jena, Germany
8. Technical University Darmstadt, 64289 Darmstadt, Germany
9. Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany