1. Accelerator Department, iThemba LABS (Laboratory for Accelerator Based Sciences), PO Box 722, Somerset West 7192, South Africa
2. Department of Physics, University of Jyväskylä, 40500 Jyväskylä, Finland
3. Institute of Applied Physics, RAS, 46 Ul'yanova st., 603950 Nizhny Novgorod, Russian Federation
4. Subatomic Physics Department, iThemba LABS (Laboratory for Accelerator Based Sciences), PO Box 722, Somerset West 7192, South Africa