VOLUME 71, NUMBER 20 PHYSICAL REVIEW LETTERS 15 NOVEMBER 1993 Observation of the Charmed Baryon Z+ and Measurement of the Isospin Mass Splittings of the Z, G. Crawford, 1 C. M. Daubenmier, R. Fulton, D. Fujino, K. K. Gan, K. Honscheid, » H. Kagan, 1 R. Kass, J. Lee, R. Malchow, F. Morrow, Y. Skovpen, * M. Sung, C. White, J. Whitmore, P. Wilson, F. Butler, X. Fu, G. Kalbfleisch, M. Lambrecht, W. R. Ross, P. Skubic, J. Snow, P. L. Wang, 2 M. Wood, D. Bortoletto, D. N. Brown, J. Fast, R. L. McIlwain, T. Miao, D. H. Miller, 3 M. Modesitt, s S. F. Schaff'ner, s E. I. Shibata, s I. P. J. Shipsey, s P. N. Wang, s M. Battle, J. Ernst, 4 H. Kroha, S. Roberts, K. Sparks, E. H. Thorndike, C. H. Wang, J. Dominick, S. Sanghera, T. Skwarnicki, s R. Stroynowski, s M. Artuso, s D. He, s M. Goldberg, s N. Horwitz, s R. Kennett, s G. C. Moneti, 6 F. Muheim, 6 Y. Mukhin, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, G. Zhu, J. Bartelt, S. E. Csorna, 7 Z. Egyed, 7 V. Jain, 7 P. Sheldon, D. S. Akerib, s B. Barish, M. Chadha, s S. Chan, s D. F. Cowen, s G. Eigen, s J. S. Miller, s C. O' Grady, J. Urheim, A. J. Weinstein, D. Acosta, s M. Athanas, G. Masek, s B. Ong, s H. Paar, s M. Sivertz, s A. Bean, o J. Gronberg, K«schke1o S Menary1o R J Morrjson1o S Naka»sh; o H N. Nelson, ' T. K. Nelson, ' J. D. Richman, A. Ryd1o H Tajima1o D Schmidt, D. Sperka, M. S. Witherell zo M Pr S Yang 11 R Balest 12 K Cho M Daoud1 W T Ford D R Johnson K Lingel M Lo ner P. Rankin, J. G. Smith, J. P. Alexander, C. Bebek, K. Berkelman, D. Besson, T. E. Browder, D. G. Cassel H. A. Cho s D. M. Coffman P S. Drell R. Ehrlich R. S. Galik, t M. Garcia- Sciveres, B. Geiser, 3 B. Gittelman, 3 S. W. Gray, D. L. Hartill, B. K. Heltsley, C. D. Jones, S. L. Jones, J. Kandaswamy, N. Katayama, P. C. Kim, D. L. Kreinick, G. S. Ludwig, 3 J. Masui, J. Mevissen, 3 N. B. Mistry, C. R. Ng, 3 E. Nordberg, 3 M. Ogg, t J. R. Patterson, 13 D. Peterson, D. Riley, 1 S. Salman, M. Sapper, H. Worden, F. Wurthwein, 1 P. Avery, A. Freyberger, J. Rodr'iguez, R. Stephens, J. YeltoIl, D. Clnabro, S. Henderson, K. KiIloshlta, T. Llu, M. Saulnier, ts F. Shen, ts R. Wilson, ts H. Yamamoto, ts M. Selen, ts A. J. Sadofl', 7 R. Ammar, ts S. Ball, ts P. Baringer, 8 D. Coppage, 8 N. Copty, 18 R. Davis, 8 N. Hancock, 8 M. Kelly, N. Kwak, 8 H. Lam, 18 Y. KubQta) M. LatteI'y) J K Nelson) S Patton) D PertlcQne) R Poling) V Savlnov) S. Schrenk, R. Wang, M. S. Alam, I. J. Kim, B. Nemati, J. J. O' Neill, H. Severini, C. R. Sun, and M. M. Zoeller (CLEO Collaboration) 'Ohio State University, Columbus, Ohio $M10 University of Oklahoma, Norman, Oklahoma 78019 sPurdue University, West Lafayette, Indiana g'7907 University of Rochester, Rochester, Neuj York 1/697 Southern Methodist University, Dallas, Texas 15275 Syracuse University, Syracuse, New York 1M)g Uanderbilt University, Nashville, Tennessee 87885 California Institute of Technology, Pasadena, California 91125 University of California, San Diego, La Jolla, California M098 University of California, Santa Barbara, California 98106 Carnegie-MeLlon University, Pittsburgh, Pennsylvania 15219 University of Colorado, Boulder, Colorado 80809 0890- Cornell University, Ithaca, New York 1/858 University of Florida, Gainesville, Florida M611 ' Harvard University, Cambridge, Massachusetts 02198 University of Illinois, Champaign Urbana, Illinois -61801 ' Ithaca College, Ithaca, New York 1/850 University of Kansas, Lawrence, Kansas 660)5 University of Minnesota, Minneapolis, Minnesota 55/55 State University of New York at Albany, Albany„New York 1M' (Received 24 June 1993) We observe the E+ baryon decaying to A, +ir and measure the mass diB'erence M(Z+) — M(A+) to be 168. 5 + 0.4 + 0. 2 MeV/c . We also measure the mass differences M(Z++) — M(A+) and M(Z, ) — M(A, +) with improved precision and determine the isospin mass splittings M(Z++) — M(Z ) 0031-9007/93/71 (20)/3259 (4) $06.00 1993 The American Physical Society 3259