1. First Observation of the Baryon; Properties of,,, and Baryons Andreas Warburton Cornell University CLEO Collaboration XXX th International Conference on High Energy Physics ICHEP 2000, Osaka, Japan July 27  August 2, 2000 PA01c50

2. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 2 Talk Overview l Charmed-Baryon Spectroscopy l CLEO Charmed-Baryon Reconstruction Techniques l Mass and Width Measurements of the and Baryons l Discovery of and Mass Measurement of the Baryon l First CLEO Observation of the Baryon All new results are preliminary!

3. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 3 The Charmed Baryons Charmed baryons consist of a heavy c quark and a light diquark  Many J P states To date, all L=0 states seen except and None of the J P quantum numbers has been measured! diquark antisymmetric under SU(3) diquark symmetric under SU(3)

4. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 4 and Spectroscopy Not yet observed

5. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 5 Data Set and CLEO II/II.V Detector e + e  Collisions near Resonance (~10.5 GeV) Charm-quark Production: B-meson decays e + e   cc jets Two Configurations: CLEO II (1989  1995) CLEO II.V (1996  1999)

6. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 6 Reconstructed Candidate Modes and  modes Mode found by E-687 Hyperon Channels

7. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 7 Event Selection and Background Suppression Principles  candidates are reconstructed in the CsI calorimeter barrel region u candidates are identified using time-of-flight and dE/dx info u Displaced vertices are used to identify candidates  Scaled Momentum criterion: x p > 0.5 or 0.6, where x p  p/p max and Y reduces combinatorial background  Note: charmed baryons with B-meson parents have x p < 0.4

8. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 8 15 Modes x p > 0.5 Signal region:  1.6  Yield ~ 58 000 candidates S:N ~ 1 : 1.2

9. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 9 Inclusive Hyperon Samples

10. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 10 and Mass and Width Fits Double-Gaussian resolution function (  ~ 0.6 MeV/c 2 ) Yields: ~ 2000 events Fit to p-wave Breit-Wigner convolved with resolution function x p > 0.5 Resolution Function Resolution Function

11. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 11 Mass Fits to p-wave Breit-Wigner convolved with resolution function x p > 0.6 First observation of resonance and Yields

12. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 12 CLEO Mass and Width Measurements PRELIMINARY CLEO results G. Brandenburg et al. (CLEO), Phys. Rev. Lett. 78, 2304 (1997) All quantities are in. First uncertainties are statistical; second are systematic.

13. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 13 Search Modes x p > 0.5 or 0.6

14. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 14 Sum of 5 Search Modes Wrong-Sign Daughter Combinations Hyperon-Sideband Distributions Total Fitted Yield: 40.4  9.0 (stat.) candidates

15. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 15 Summary of Preliminary Results Unbinned maximum likelihood fit mass:

16. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 16 u We present the most statistically accurate measurements of the,, and masses. u We have made preliminary measurements of the and widths. u We report the first observation of the baryon and measure its mass to be Conclusions

17. CLEO July 27 - August 2, 2000 ICHEP 2000 A. Warburton Cornell University 17 u CLEO has now, for the first time, observed a significant number of candidates. We present a preliminary mass measurement of u Supporting documentation can be found in u hep-ex/0007041 u hep-ex/00070 u CLEO continues to contribute to knowledge of the charmed baryon sector. Conclusions, cont’d