Charmed Baryons at Belle

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International Workshop ee- Collisions from ? to
? Budker Institute of Nuclear Physics,
Novosibirsk, Russia (Feb 27-March 2, 2006)

• Charmed Baryons at Belle

• OUTLINE
• (1) Introduction
• (2) Brief experimental review of baryonic B
  decays
• (3) Recent results from Belle
• Observation of B decays to two charmed
  baryons
• ? B ? ?0c ?c (similar to B0 ?
  ?c- p)
• ? B ? ?c ?c- K
• Brief experimental review of charm baryon
  spectroscopy
• Recent results from Belle
• ? Observation of ?c(2800) in ee-
  continuum
• ? Improved measurement of ?c0 and
  ?c masses
• (6) Summary

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Introduction
Now B-factories Belle and BaBar are the reachest
sources of charmed baryons. They could provide
new knowledge about the spectroscopy, decay
modes and production mechanism of charmed baryons.
Charmed baryons in ee-? cc continuum
Study of baryonic B decays
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Experimental Review of Baryonic B Decays (1)
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Experimental Review of Baryonic B Decays(2)
Histograms are phase space expectation
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Experimental Review of Baryonic B Decays (3)
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B0 ? ?c- p and B ? ?0c ?c
PRL 90, 121802 (2003)
Belle
Br(2.190.56-0.49-0.32-0.57)x 10-5
Consistent with the pole model prediction
? but 100 times smaller than QCD sum rule
predictions and diquark models
One can expect Br 10-5
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Observation of B ? ?0c ?c
hep-ex/0510074
So, the naïve expectation is wrong
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Evidence for B ? ?-c ?c
hep-ex/0510074
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Observation of B- ? ?c ?c- K
hep-ex/0508015
The Brs of 2- and 3-body double charm baryonic
decays are approximately the same in contrast of
single charm baryonic decays.
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Observation of B0 ? ?c ?c- K0
hep-ex/0508015
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Experimental review of charm baryon spectroscopy
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).
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Observation of ?c(2800) Results (PRL 94, 12202
(2005))
Feeddown from ?c(2880)
Signal
?c sideband
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Observation of ?c(2800) Results (PRL 94, 12202
(2005))
Xp spectra of observed resonances
?p0.0780.021-0.017
?p0.0950.032-0.024
?p0.0690.015-0.012
Peterson parameters are similar to those for
other excited charm baryons in ee- annihilation
at ?s 10.6 GeV
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Observation of ?c(2800) Discussion
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 JP3/2- 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.
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Improved measurement of ?c0 and ?c masses
PLB 605, 237 (2005)
The ?cs are reconstructed in 7 decay modes
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Improved measurement of ?c0 and ?c masses
PLB 605, 237 (2005)
0.2-1.4
0.2-1.4
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Summary
(1) Belle observed new type of B decays B ?
?c0 ?c and B ? ?c ?c- K - decays to two
charmed baryons These are the b?ccs transitions
that have not been observed previously. The B
? ?c ?c- K have prominent Br but small energy
release. The Br(B ? ?c0 ?c) is presumably
100 times larger than the b?cud analog the B0 ?
?c- p decay. The question is to theoretically
understand these observations (coherent and
unified description of baryonic B decays).
(2) NEW Charmed Baryon is observed by Belle
?c(2800) (3) Belle measured the ?0c and ?c
masses with high accuracy ? Large statistics
collected by Belle opens a possibility for study
of B-baryons and new charmed baryons ?
understand underlying QCD effects in heavy hadron
system.
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KEKB asymmetric ee- collider

• Two separate rings
• e 3.5GeV
• e- 8.0GeV
• Crossing angle 22mrad
• Ecm 10.58GeV
• ??c? ? 200?m
• Beam size
• ?x 100?m
• ?y 3?m
• Luminosity
• design 1.0x1034 cm-2s-1
• achieved 1.07x1034 cm-2s-1

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Belle detector