The Experimental Discovery of Double-Charm Baryons

Abstract

In 2002, the SELEX [The SELEX (Fermilab E781) Collaboration: Ball State University, Bogazici University, Carnegie-Mellon University, Centro Brasileiro de Pesquisas Fisicas, Fermilab, Institute For High Energy Physics (Protvino), Institute of High Energy Physics (Beijing), Institute of Theoretical and Experimental Physics (Moscow), Max-Planck-Institute for Nuclear Physics, Moscow State University, Petersburg Nuclear Physics Institute, Tel Aviv University, Universidad Autonoma de San Luis Potosi, Universidade Federal da Paraiba, H. H. Wills Physics Laboratory, University of Bristol, University of Iowa, University of Michigan-Flint, University of Rochester, University of Rome La Sapienza and INFN, University of Sao Paulo, University of Trieste and INFN. http://www-selex.fnal.gov ] Experiment (Fermilab E781) reported the first observation of a member of the family of doubly charmed baryons [SELEX Collaboration, M. Mattson et al.: First observation of the doubly charmed baryon Ξ c c + . Phys. Rev. Letters 89 (2002) 112001, [ arXiv:hep-ex/0208014 ]]. During the last two years, additional evidence for more members of that family has been obtained and will be presented. SELEX took data in 1996/7 in the Fermilab PCenter beam line, observing interactions of Σ − , pions and protons with momenta of about 600 GeV/ c on copper and diamond target foils. From about 15 ⋅ 10 9 live interactions the trigger and online filter system selected 10 9 events which were written to tape. SELEX [SELEX Collaboration, J.S. Russ et al.: in Proceedings of the 29th International Conference on High Energy Physics , 1998, edited by A. Astbury et al., (World Scientific, Singapore, 1998), Vol. II, p. 1259, [ arXiv:hep-ex/9812031 ]] features a high resolution Silicon Microstrip Vertex detector, a Photomultiplier RICH detector [J. Engelfried et al.: Nucl. Instrum. Methods A431 (1999) 53, [ arXiv:hep-ex/9811001 ]] for particle identification, and a 3-stage electromagnetic calorimeter.