[1] Univ Milan, Dept Phys, Milan, Italy
[2] Ist Nazl Fis Nucl, I-20133 Milan, Italy
[3] Lab Nazl Gran Sasso, Assergi, AQ, Italy
[4] Princeton Univ, Dept Phys, Princeton, NJ 08544 USA
[5] Univ Pavia, Dept Phys, I-27100 Pavia, Italy
[6] Ist Nazl Fis Nucl, Pavia, Italy
[7] MIT, Cambridge, MA 02139 USA
[8] Univ Perugia, Dept Chem, I-06100 Perugia, Italy
[9] Ist Nazl Fis Nucl, I-06100 Perugia, Italy
[10] Tech Univ Munich, D-8046 Garching, Germany
[11] Univ Genoa, Dept Phys, Genoa, Italy
[12] Ist Nazl Fis Nucl, I-16146 Genoa, Italy
[13] Max Planck Inst Kernphys, D-69117 Heidelberg, Germany
[14] Res Inst Part & Nucl Phys, Budapest, Hungary
[15] Bell Labs, Murray Hill, NJ 07974 USA
[16] Joint Nucl Res Inst, Dubna, Russia
[17] Univ Lisbon, Fac Ciencias, Dept Fis, Lisbon, Portugal