Heavy hadron spectroscopy atBelleKenkichi Miyabayashi(Nara Women’s University)
Hadrons and Hadron Interactions inQCD 2015
2015 Mar. 2nd1

Outline	• Advantage with heavy flavors in hadron spectroscopy• KEKB e+e- collider and Belle detector• Variety of recorded reactions• Quarkonium(-like) states– X, Y and Z states in charmonium and bottomonium sectors• Charm baryons• Summary2

Advantage of heavy flavors	
• Light flavors (u,d,s) may mix;
example：	→η→η’• Heavy, well-separated masses: relation between
observed states and constituent quarks would bestraight-forward.
• J/ψ, ψ(2S) → e+e- or µ+µ-, Υ(1S or 2S or 3S)→µ+µ- :clean signature.
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Variety of recorded reactions	
There are various
processes to produce
charmonium(-like)particles.	
In two-body B-decays,
JPC=0-+, 1− −, 1++ infactorization limit. 	

Initial state radiation	
JPC=1− −	

Allowed/favoredquantum numbers aredifferent depending on
production processes.	
γγ collision	
JPC=0±+, 2±+,3++	

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KEKB/Belle : world highest
luminosity as e+e- at Υ region	
e+	e-	KEKB
8GeV×3.5GeV@Υ(4S)

BelleHigh resolution 4π
spectrometer with particle
identification capability

5Belle recorded more than 1 ab-1!	
772M BB6	

Detector performance:
great benefit	
• Originally designed/constructed/operated for timedependent CP violation measurement in B system.
• 4π general purpose spectrometer with
– High momentum resolution, σp/p = 0.3%@1GeV/c.
– Ability to detect γ down to 30 MeV.
– Good γ energy resolution, σM =5MeV for π0→γγ.
– Lepton identification capability, ε>0.9, fake<0.01.
– K/π/p separation capability, ε~0.9, fake<0.1.
– Excellent B decay vertex reconstruction, σΔz =80µm.

All these features led us to a lot of discoveries	

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First sensation was already12 years ago; X(3872)
B+ → J/ψ π+π- K+ψ(2S)“landmark”

Look this system invariant mass.
Very narrow peak is there, above DD
threshold!
Many things have been done, still
actively discussed object.

Mππll - Mll (GeV)

Belle, 152M BB,PRL91,261801(2003)
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More information about X(3872)	
PRD81, 031103(2010)	

PRL110, 222001(2013)	

X(3872)→D0D*0 seen.
Br(X(3872)→D0D*0) is aboutBr(X(3872)→J/ψ π+π-)×10.
Determined to be JPC=1++ (Belle,BaBar, CDF, LHCb) by J/ψ π+πangular distribution.
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LHCb visited radiative decay 	
LHCb	
NPB886, 665(2014)	
M(J/ψ γ) (GeV)	

LHCb	
Taken from Polyakov Ivan’s slides
in Moriond QCD	M(ψ(2S) γ) (GeV)	

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Admixture : most plausible
interpretation for X(3872)	
X(3872)	

Ar nucleus	

No signature for~ 7 fm	
•charged partner in J/ψ π+π0.
cc core	•C=-1 partner in J/ψ η and χc1 γ.
→ most likely, isospin=0.
D0D0*	→ disfavor tetraquark hypothesis.
S.Takeuchi, K.Shimizu and M.Takizawa, arXiv:1408.0973	

D±D∓*	

DD* molecule is mixing with the same JPC cc, χc1(2P) (yet unseen).
→can explain Br(X→D0D*0)/Br(X→J/ψ π+π-) is about 10.
(pure molecule case, to be about 1000).
→pure molecule is too fragile to be produced in Tevatron/LHC.
→another χc1(2P) dominant state would become broad.
Reaching such an interpretation is remarkable progress.
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Additional recent knowledge	
PRD 90, 112009 (2014)	

B0 → X(3872) K-π+ has been observed in X(3872)→J/ψ π+π-.
Fraction of B0 → X(3872) K*0 is small, different feature fromordinary JPC=1++ charmonium = χc1.	
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Z(4430)+ in ψ(2S)π± final state	

Clear peak at
4.43 GeV/c2
5.28GeV/c2	

Reconstructing B → ψ(2S) π± K,
M(ψ(2S) π±) is looked back.
It is charged and contains cc, at least
4 constituents are necessary.

PRL100,142001(2008)
PRD 80, 031104(2009)
PRD 88, 074026(2013)13

Situation at current B-factories
Belle : 660M BB
PRL100,142001BaBar : 455M BB
PRD79,112001

Significant signal at Bellev.s.
Only hint with 1.9σ at BaBar
Belle’s Dalitz plot analysis
confirmed a resonance at4430 MeV;PRD80 031104, (2009).
Statistically, both are notcontradicting with each other,but clear answer is to be given
by higher statistics data.
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LHCb confirmed Z(4430)+	Fit withZ(4430)+	Fit withoutZ(4430)+	

4D fit(M(ψ(2S)π±), M(Kπ), cosθψ(2S), φ), PRL112, 222002(2014)
Z(4430)+ interpretation is not as established as X(3872).	

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J/ψ π+ system in B0→J/ψπ+K-	
PRD90, 112009 (2014)	

4200	
4430	
One more charged state observed,
JP=1+	16

Surprise in bottomonium sector	At Υ(5S)(@10880MeV), Υ(ns) π+π- (n=1,2,3)
production rate is 2 order of magnitude larger
than Υ(4s) state.
PRL100,112001(2008)	

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Energy scan performed	
arXiv:1501.01137	
Υ（1S）ππ	Υ（2S）ππ	Υ（3S）ππ	Υ(nS) π+π- also show peakaround 10880 MeV.
Different feature from aroundΥ(4S) (10580 MeV).

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• MM(π+π-) after background subtraction.
PRL 108, 032001 (2012)	

Υ(2S)→Υ(1S)ππ	Observation of hb(1P, 2P) in
Ecms=10880 MeV data	
11.2σ	
Υ(3S)→Υ(1S)ππ	5.5σ	

M(hb(1P))= 9898.3 ±1.1 +1.0/-1.1 MeV
M(hb(2P))=10259.8 ±0.6 +1.4/-1.0 MeV
R(hb(nP)π+π-)/R(Υ(2S) π+π-)=0.46±0.08 +0.07/-0.12, higher than expected.
(For example, no hb(nP) signal in Υ(4S) data.)
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Two charged states,Zb(10610)+ and Zb(10650)+	

PRL108,122001(2012)

Υ(1S)π±	Υ(2S) π±	hb(1P)π±	Υ(3S) π±	Hb(2P)π±	20Molecule picture works	Decays to Υ and hb
can co-exist.
Signature in B*B(*)
partial recon. seen.

A.E.Bondar et al., PRD84,054010(2011)	

JP=1+ is supportedby Dalitz analysis.
arXiv:1403.0992.

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Neutral Partner of Zb0 	
PRD88, 052016 (2013)	

First observation of
ϒ(5S) → ϒ (nS)π0π0
Rates: about half of ϒ (nS)π+π-

Neutral partner in ϒ (nS)π0π0	

6.5σ stat. significance	
Mass 10609±4±4 MeV	

IG=1+, first example to observe isospin partner among “XYZ”.	 22

Back to charmonium(-like) by ISR	Y(4260)→J/ψπ+π↓Z(3895)+ in J/ψπ+ 	Initial State Radiation	
BES III also confirmed
the peak at 3885 MeV in(DD*)+.
PRL110,252002(2013)
PRL112,022001(2014)

PRL110,252002(2013)

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Charm baryon to check “di-quark”	
• Thought to be a good place tocheck if “di-quark” is behaving as agood degree of freedom to form
hadrons.
• One of the constituent quark isheavy, correlation between theremained light quarks wouldbecome clear. 	
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Reconstructed states with Λc	Reconstruct Λc→pK-π+ and add one pion.	
PRD89,091102(2014)	

Σc++ → Λc+π+	2455	

Σc0 → Λc+π-	2455	

2520	

2520	

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Reconstructed states with Λc(cont.)	
Select Σc(2455) π to see Λc+π+π-	Λc(2880)+ 	
PRL98,262001(2007)	

Λc(2880)+ 	
J=5/2
J=3/2

Λc(2940)+ 	

M(Λc+π+π-) [GeV]	

pion angular distribution
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Reconstructed states with Λc(cont.2)	
PRD89,052003(2014)	

Σc(2445)++ 	Λc+K-π+ final state
has been visited.	

Σc(2520)++ 	Ξc(2980)+ 	Ξc(3080)+ 	Ξc(3055)+ 	Ξc(3080)+ 	

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Reconstructed states with Ξc0(cont.)	
Ξc0 is reconstructed in Ξ– π+, pK-π+K- and ΛK-π+ 	
PRD89,052003(2014)	

Ξc0 π+ has been visited.	

Ξc0 → Ξ-π+	Ξc0 → ΛK-π+	Ξc0 → pK-π+K-	28

0Reconstructed states with Ωc 	
PLB672,1(2009)	

Ω-→ΛK-	Ωc0→Ω-π+	29

00
Ωc (2770) →Ωc γ	
PLB672,1(2009)	

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States seen in ΛD mode 	31Note for charmed baryons	• For many states, mass and width were poorly known, Bfactory results have been updating them.
• In Λc+π+K- case, only Ξc(3080)+ appears in Σc(2445)++ K- andΣc(2520)++ K-, while Ξc(2980)+ and Ξc(3055)+ appear only inΣc(2445)++ K-. Can resolving intermediate states help to see
if di-quark is a good picture?
• For most of cases, branching fractions are also poorlyknown. To get information from the production rate, decay
from higher states (feed-down) would become a problem• Even PDG Br(Λc→pKπ), several underlying assumptions.
New model-independent approach published from Belle.
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(*)+
Tag D p π to get M
PRL113,042002(2014)	

miss	Detect only these	33

Then explicitly reconstruct pK-π+	
PRL113,042002(2014)	

PDG was 5.0±1.3%	

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Summary	• Because of superb detector performance with excellent
accelerator luminosity, we got many exciting surprises, so far
mainly quarkonium(-like).
• Some of those reached very plausible interpretation.
– X(3872) as admixture of molecule and charmonium(χc1(2P))– Zb(10610)+ and Zb(10650)+ as B*B(*) molecule.
– For the state close to the threshold, molecular state turned out to beplaying important role.

• Extension to charmed baryons to test “di-quark” picture.
• Still unsettled interpretation for many states (ex. Z(4430)+, etc).
• Searches for new decay modes, partner states, attempt for JP
determination with higher statistics data to cheer up relevant
theorists to come up with convincing interpretation is a Belle II
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mission in hadron spectroscopy.