Transcript Calorimeter Group

International Workshop e+e- 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
(4) Brief experimental review of charm baryon spectroscopy
(5) Recent results from Belle:
 Observation of c(2800) in e+e- continuum
 Improved measurement of c0 and c+ masses
(6) Summary
Ruslan Chistov (ITEP, Moscow)
1
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.
Study of baryonic B decays
Ruslan Chistov (ITEP, Moscow)
Charmed baryons
in e+e- cc continuum
2
Experimental Review of Baryonic B Decays (1)
Ruslan Chistov (ITEP, Moscow)
3
Experimental Review of Baryonic B Decays(2)
Histograms are
phase space expectation
Ruslan Chistov (ITEP, Moscow)
4
Experimental Review of Baryonic B Decays (3)
Ruslan Chistov (ITEP, Moscow)
5
B0  c- p and B+  0c c+
Belle PRL 90, 121802 (2003)
Br=(2.19+0.56-0.49+-0.32+-0.57)x 10-5
Consistent with the pole model prediction
but 100 times smaller than QCD

One can expect Br ~ 10-5
sum rule predictions and diquark models
Ruslan Chistov (ITEP, Moscow)
6
Observation of B+  0c c+
hep-ex/0510074
So, the naïve expectation
is wrong
Ruslan Chistov (ITEP, Moscow)
7
Evidence for B+  -c c+
hep-ex/0510074
Ruslan Chistov (ITEP, Moscow)
8
Observation of B-  c+ c- K+
hep-ex/0508015
The Br’s of 2- and 3-body double
charm baryonic decays are
approximately the same in contrast
of single charm baryonic decays.
Ruslan Chistov (ITEP, Moscow)
9
Observation of B0  c+ c- K0
hep-ex/0508015
Ruslan Chistov (ITEP, Moscow)
10
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 :
Ruslan Chistov (ITEP, Moscow)
c(2800).
11
Observation of c(2800):
Results (PRL 94, 12202 (2005))
Feeddown from
c(2880)+
Signal
c+ sideband
Ruslan Chistov (ITEP, Moscow)
12
Observation of c(2800):
Results (PRL 94, 12202 (2005))
Xp spectra of observed resonances
p=0.078+0.021-0.017
p=0.095+0.032-0.024
p=0.069+0.015-0.012
Peterson parameters are similar to
those for other excited charm baryons in
e+e- annihilation at s ~ 10.6 GeV
Ruslan Chistov (ITEP, Moscow)
13
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 JP=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.
Ruslan Chistov (ITEP, Moscow)
14
Improved measurement of
c0 and c+ masses
PLB 605, 237 (2005)
The c’s are reconstructed in 7 decay modes
Ruslan Chistov (ITEP, Moscow)
15
Improved measurement of
c0 and c+ masses
PLB 605, 237 (2005)
+0.2-1.4
+0.2-1.4
Ruslan Chistov (ITEP, Moscow)
16
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.
Ruslan Chistov (ITEP, Moscow)
17
KEKB asymmetric e+e- 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
Ruslan Chistov (ITEP, Moscow)
18
Belle detector
Ruslan Chistov (ITEP, Moscow)
19