1. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 1 Charm Baryon Spectroscopy at Belle (1)Introduction to charmed baryons at Belle (2)Observation of  c (2800) in e + e - continuum (3) Improved measurement of  c 0 and  c + masses (4) Study of excited states  c (2645) (preliminary) (5) Observation of new charmed baryons decaying into  c + K -  + and  c + K 0 S  - (preliminary) (6) Search for the SELEX double charm baryon decaying into  c + K -  + (preliminary) (7) Summary Ruslan Chistov (ITEP, Moscow) Charm 2006 Bejing 5-7 June, 2006

2. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 2 Introduction to Charm Baryons at Belle Charmed baryon spectroscopy is an excellent laboratory to study the dynamics of light diquark in the environment of heavy C-quark.  Many theoretical predictions and approaches could be tested. History: ARGUS(1993) observed first excited charmed baryon  c (2625) +, then CLEO(1993) confirmed it and observed  c (2593) +, E687 and ARGUS subsequently confirmed the latter. Next observations came from CLEO:  c (2520) +,  c (2765) +,  c (2880) +. Belle(2005): Observation of first orbital excitation of  c :  c (2800). This year recent results from Belle include also *observation of new charm baryons in  c + K -  + and  c + K 0 S  - final states *and study of excited states  c (2645)

3. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 3 Signal  c + sideband Feeddown from  c(2880)+ Observation of  c (2800): (PRL 94, 12202 (2005)) c+-c+-c+-c+- c+0c+0c+0c+0 c++c++c++c++ ISOTRIPLET!

4. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 4 Theoretical models predict a rich spectrum of excited charmed baryons in the vicinity of the  c (2800) [L.A.Copley, N.Isgur and G.Karl, Phys. Rev D 20, 768 (1979)]. One of the candidates is a  c2 doublet with J P =3/2- and 5/2- (subscript 2 denotes the total angular momentum of light diquark.)  c2 is expected to decay principally into  c +  in D-wave. The predicted mass is close to the measured but the predicted width is only 15 MeV. But the  c2 (3/2-) can mix with the nearby  c1 (3/2-) which would produce a wider physical state. Observation of  c (2800): Discussion

5. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 5 Introduction to Charm Baryons at Belle Improved measurement of  c 0 and  c + masses PLB 605, 237 (2005) The  c ’s are reconstructed in 7 decay modes K-+K-+ pK-K-+pK-K-+ KS0KS0 pKS0KS0pKS0KS0 K-++K-++ -+-+ -++-++

6. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 6 Introduction to Charm Baryons at Belle Improved measurement of  c 0 and  c + masses PLB 605, 237 (2005), Erratum PLB 617, 198 (2005) +0.2-1.4 Due to the mass scale

7. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 7 Study of excited states  c (2645) Mass( c +  - ) Mass( C 0  + )  C (2645) 0  C (2645) + Reflection from  C (2790) 0   c ’+  -,  c ’ +   c +  (verified with MC) Reflection from  C (2790) +   c ’0  + (verified with MC)  c ’ 0   c 0  C+  - ++C+  - ++ C0  - +C0  - + L 450 fb -1 First confirmation

8. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 8 Study of excited states  c (2645): mass measurements Belle (2006): PDG(2005): Preliminary

9. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 9 New Charmed Baryons from Belle  cx (2980) + and  cx (3077) + Near threshold in Mass(  c + K -  + ) two new charmed baryons  cx (2980) + and  cx (3077) + were observed  cx (2980) +  cx (3077) + wrong-sign  c + K +  -  cx (3077) + : 9.7  N=326.0 ± 39.6 events M=3076.7 ± 0.9 ± 0.5 MeV  =6.2 ± 1.2 ± 0.8 MeV  cx (2980) + : 6.3  N=405.3 ± 50.7 events M=2978.5 ± 2.1 ± 2.0 MeV  =43.5 ± 7.5 ± 7.0 MeV Preliminary L 450 fb -1

10. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 10 New Charmed Baryons from Belle  cx (3077) 0 To get more information about the properties of found states we searched for their isopartners in Mass(  c + K 0 S  - ) and observe  cx (3077) 0  cx (2980) 0  cx (3077) 0 wrong-sign  c + K +  - High mass state -  cx (3077) 0 N=67.1 ± 19.9 M=3082.8 ± 1.8 MeV  =5.2 ± 3.1 MeV Significance=5.1  Low mass state -  cx (2980) 0 N= 42.3 ± 23.8 M=2977.1 ± 8.8 MeV  =43.6 MeV FIXED Significance=2.0  Preliminary L 450 fb -1

11. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 11 Recent Results from Belle Belle searched for the SELEX double charm baryon  cc (3520) +   c + K -  + null result Preliminary N=8.3 ± 37.3 < 69.1 @ 90% CL L 450 fb -1

12. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 12 Recent Results from Belle: upper limit on the production of the SELEX double charm baryon Preliminary  (  cc (3520) + )  Br(  cc (3520) +  c + K -  + | p*(  c + )>2.5 GeV) <1.5  10 -4  (  c + | p*(  c+)>2.5 GeV) @ 90% CL We reconstruct 835360 ± 13748  c +  pK -  + decays BaBar observes NO SIGNAL ALSO in a similar decay mode (hep-ex/0605075)

13. Ruslan Chistov (ITEP, Moscow) Charm Baryon Spectroscopy at Belle Charm 2006 13 Summary (1)NEW Isotriplet of Charmed Baryons is observed by Belle:  c (2800) (2) Belle measured with high accuracy the masses of  c 0  c +  c 0 and  c +  c (2645) 0 and  c (2645) + (3)  Belle searched for the SELEX double charm baryon  cc (3520) +, found no signal and set an UL on its production cross-section Belle observed three new charm baryons  Belle observed three new charm baryons  cx (3077) +   c + K -  +  cx (2980) +   c + K -  +  cx (3077) 0   c + K S 0  - Studies of their properties are ongoing