Transcript Some Theoretical Aspects of Pentaquarks

Possible Interpretations of
DsJ(2632)
Shi-Lin Zhu
Peking University
QWG2004
October 14, 2004
Collaborators: Y.-B. Dai, C. Liu, Y.-R. Liu
Hep-ph/0407157 (PRD in press)
Hep-ph/0408234
Advances in Hadron Spectroscopy
Since 2003
• BES: pp_bar near-threshold enhancement in
J/Psigamma pp_bar decays, I=0 channel; p
Lambda_bar threshold enhancement in J/Psi K p
Lambda_bar
• BABAR/CLEO/BELLE: narrow states DsJ(2317),
DsJ(2457) below threshold
• LEPS and others found evidence of Pentaquarks!
• BELLE/CDFII: new narrow state X(3872)
• E852: two exotic mesons with JPC=1-+ at 1709/2001MeV
• SELEX: narrow state DsJ(2632) above threshold with
abnormal decay pattern
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SELEX observed DsJ(2632) in
Ds+ eta and D0K+ modes 2 state in (1 , 2 )
+
+
+
doublet in HQET
49.3 events
7.2 sigma
14 events
5.3 sigma
BABAR, CLEO, FOCUS
didn’t see DsJ(2632)
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SELEX:
fixed-target hadroproduction
600 GeV Sigma- beam
which consists strange
quark explicitly
looks at very large Xf, not
available for e+e- colliders
Production: gluon-gluon
fusion
BABAR/CLEO:
• e+e- colliders , center of
mass close to Upsilon
• Production: e+e- annihilation
FOCUS:
• photoproduction
• doesn't see double-charm
hadrons but they exist!
Non-observation of a particular state in certain
experiments does not exclude its possible existence
The production ratios of different charm states could be quite
different between e+e- annihilation and gluon-gluon fusion
According to Evdokimov at SELEX: If DsJ(2632) really exists
 Special mechanism in hadroproduction at large Xf
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Three Puzzles of DsJ(2632) If Not Artifact
• Narrow decay width. 274 MeV above D0K+ and 116
MeV above Ds eta threshold, decay width less than
17 MeV. Naive expectation around (100~200) MeV
• Is DsJ(2632) a cs_bar state?
L=0:
[Ds(1968), D*s (2112)]
L=1, lP=1/2+:
[DsJ (2317), DsJ (2457)]
L=1, lP=3/2+:
[DsJ (2536), DsJ (2573)]
Too low for L=2 assignment
Is it the first radial excitation of D*s (2112)? (K.-T. Chao)
• Unusual decay pattern
SU(3)F symmetry + cs_bar assignment
SELEX
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DsJ(2632) As a Tetraquark
Version I: (Liu, Zhu, Dai, Liu)
•
• 0+ isoscalar member in 15 rep., the ratio of SU(3) C-G coefficients
naturally explains its anomalous decay pattern:
• Quark content:
• Mass:
• Decay pattern:
SU(3) C-G
Decay Momentum
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Weight Diagram of Heavy
Tetraquark Multiplets
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Version II: (Chen, Li; Gupta)
• Quark content:
 fluctuates into
Hence main decay mode is
• D0K+ requires

,
component, OZI
suppressed
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Version III: (Chao)
• Tightly bound diquark configuration
which has small mixing with
,
 narrow total width
• Mixing between
 unusual decay
pattern
Version IV: (Maiani;Nicolescu)
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Quark content:
D0K+ suppressed while
Decay pattern:
Prediction:
important
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Problems With Tetraquark Scheme
• There should be many other tetraquark
partners of DsJ(2632). Where are they?
• Its narrow width may require that quarks inside
DsJ(2632) form tightly bound clusters like
diquarks. Otherwise tetraquarks fall apart easily.
• The first three versions of tetraquarks predict the
same production rates for D+K0, D0K+ final states.
The fourth version predicts very large D+K0 mode.
• But SELEX didn't find any signal in the D+K0
channel!
DsJ(2632) as Radial Excitation
• First radial excitation of Ds(2112) with JP=1- (Chao;
Barnes et al.;Bereven, Rupp)
• The nodal structure of its radial wave function
ensures the narrow total width
• Different decay momentum in two channels leads to
anomalous decay pattern
• Dynamical calculation very desirable and missing
Future experimental search for: (Dai, Liu, Liu, Zhu)
• its SU(3) flavor partners DJ0,+(2530)
• its B-meson analogues BJ 0,+(5840), BsJ+(5940)
• S-wave two pion decay modes
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Large Nc And DsJ(2632) As A Hybrid
Meson: Version I (Dai, Liu, Liu, Zhu)
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In the large Nc limit, the
dominant decay mode is for the
gluon to split into a color-octet
recombines with
pair to
form
The Nc order of this decay
amplitude is
No abnormal decay pattern as
observed in SELEX 
This assignment not preferred!
Version II: Hybrid Scheme
(Dai, Liu, Liu, Zhu)
• Decay mode (b) into glueball is
dominant, Nc0, forbidden by
kinematics
• The subleading mode (c) into
becomes dominant; is mixture of
and
•  Ds eta dominant
• D0K+ can occur via mode (a)
• c s_bar is color-singlet, additional
1/Nc suppression from color
mismatch, its Nc order
•
But its mass and decay width needs dynamical calculation!
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Summary
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SELEX observed DsJ(2632) but BABAR,
CLEO, FOCUS didn’t see it.
It could be an artifact.
If it really exists, it could be
- Tetraquark
- Radial excitation
- Heavy hybrid meson
-…