Transcript "Pentaquarks: Theory & Experiment"(ppt 1.59M)

Pentaquarks: 五夸克态
Bo-Qiang Ma (马伯强)
PKU (北京大学物理学院)
?
August 14, 2004
talk at CCAST Wokshop on QCD and RHIC Physics
In Collaboration with B. Wu
Hep-ph/0312041, PRD69(2004)077501
Hep-ph/0312326, PLB586（2004）62
Hep-ph/0311331, Hep-ph/0402244
Hep-ph/0408121
all to appear in PRD
Also HERMES Collaborators (Y.Mao et al.): PLB585(2004)213.
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A Break Through of Hadron Physics in 2003：
Pentaquark
•
五夸克态
Second Item of Top 10 Physics News in 2003
In News:
Nature Science Update: “…could have important
implications for understanding of the early
universe”
• BBC News: “should have far-reaching
consequences for understanding the structure of
matter”
• MSN: “a new classification of matter…”
•
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Search for Exotic Baryon States
• Standard Quark Model
– classifies hadrons as
• mesons ( qq )
• baryons (qqq )
– also allows “non-standard” or exotic
hadron states
• multiquark mesons ( qqqq )
• multiquark baryons ( qqqqq )
-> appear as baryon resonances
• hybrid states ( qqg or qqqg )
• dibaryons ( qqqqqq )
• glueballs
-> no convincing previous evidence for exotic baryon states
before 2003.
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Baryon States
•All baryons observed before
– classified as singlets, octets and decuplets of SU(3) flavor group
-> constructed of 3 quarks only,
- may have higher orbital angular momentum
– have strangeness from S=-3 to S=0
Y
baryon octet with JP=½+
0
baryon decuplet with
• Exotic Baryons with S=+1
– cannot be formed from only 3 quarks
– belong to higher SU(3) multiplet
IZ
JP=(3/2)+
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Previous Searches for Exotic Baryons
• Ideally: kaon-nucleon (KN) scattering
• started in 1966 at BNL
-> “clear” resonance peak found in K+p at
M=1.91 GeV and G=180 MeV
• searches: partial wave analyses in KN scattering
R. Cool et al., PRL 17, 102 (1966)
BNL 1966
– candidates: isoscalar Z0(1780) and Z0(1865)
-> give poor evidence (PDG)
• dropped from PDG listings after 1986
• reasons for failure:
– KN (in)elastic scattering at p(K) corresponding
to 1.74  MZ  2.16 GeV
– resonance widths large: 70  GZ  845 MeV
– MIT bag model predictions: MZ  1.7 GeV
• L(1405): molecular meson-baryon state uudsu ?
– interpretation problematic: could be
-> ambiguity remains
uds
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L(1405) as 5-quark state
Jue-Ping Liu, Z.Phys.C 22(1984)171
• Using QCD sum rule method to calculate
the 5-quark component of L(1405)
• But cannot rule out miminal uds
component in the state
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Pentaquark States
• Predictions of
pentaquark states with
both strange and charm
(by Lipkin et al.),
no evidence found in
experimental searches
for more than ten years.
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Prediction in Chiral Soliton Model
D. Diakonov, V.Petrov, M.Polyakov, Z. Phys. A 359, 305 (1997)
• all baryons are rotational excitations of a rigid object
• reproduces mass splittings witin 1% of
– baryon octet (JP=½+) and decuplet (JP=3/2+)
• predicts new anti-decuplet (among many Ncd artifacts)
• “only one” free parameter
Based on older predictions:
Manohar(1984); Chemtob (1984); Praszalowicz (1987)
the 3 corners
are exotic
pK0 or nK+
Identifying P11(1710) as
member of anti-decuplet:
prediction for Q+:
M=1.53 GeV, G  15 MeV
I=0
S=+1
JP=½+
with
X-p- or S-K-
X0p+ or S+K0
Q+  K0 p or K+n
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Suggestion for the existence of higher multiplets
M.-L.Yan and X.-H.Meng, Commun. Theor. Phys. 24 (1995) 435
• The corrections to the Gell-Mann-Okubo relations of
baryons masses in SU(3) Skyrmen model are
considered.
• The results could be regarded as a signal for the
existence of the SU(3) rotation excitation states of
baryons: 27-plet, 10*-let, and 35-let.
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Nothing is “Exotic” in the Chiral Solition Picture
• Baryons are “solitons” in the chiral fields.
• No baryon is “exotic” except that it has
different quantum numbers compared to other
baryons.
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“Exotic”-baryon (Pentaquark) Defination
H.Gao and B.-Q. Ma
Mod. Phys. Lett. A 14 (1999) 2313
• A pentaquark qqqqq state can be clearly
distinguished from the conventional qqq-baryon
state or their hybrids if the flavor of q is different
from any of the other four quarks:
minimal Fock state of pentaquark
-
• Possible existence of uudds and uuuds states are
suggested.
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Suggestion for search of pentaquark uudds state
in physics process
H.Gao and B.-Q. Ma Mod. Phys. Lett. A 14 (1999) 2313
• Suggested:
*n  K- Θ+
missing mass method to construct Θ+
• SPring8 and CLAS experiments: sub-process
 n  K- (K+n)
an additional K+ is detected to reduce background for the missing
mass spectrum and real photon is used instead of virtual photon.
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What is a Pentaquark
A pentaquark is a hadron that is composed of 4 valence quarks and
one valence antiquark. It has strangeness S=+1 and is tightly bound
by the strong hadronic force.
-> constitutes a new form of matter
HERMES Experiment
Decay Mode:
Q+  Ks p or K+n
 * D  X Q+  XpK 0
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HERMES Result: Talk by Yajun Mao at Tokyo
Resonance is observed at
1528  2.6  2.1 MeV
Width is
FWHM = 19  5  2 MeV
Naïve significance
56 / 144 ~ 4.7s
True significance
59/16 ~ 3.7s
Ns
in ±2s
Nb
Ns
N s
Unbinned fit is used: result doesn’t depend on bin size and starting point
Yajun Mao for HERMES Collaboration,
YITP Multi-quark Workshop, Feb. 17-19, 2004
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Where else to look for Q+ Production
• ideally: K0p and K+n
– mass range too low for kaon beams
high for f factory of kaons
• less ideal: collision of non-strange particles
– many particles in final states
– some are neutral -> complex detectors need
D. Diakonov,priv. commun. (May 2003)
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Summary of recent experiments
world-average:
M(Q+): 15322.4 MeV
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Summary of recent Evidence for
Experiments
Results
Mass
(MeV)
SPring8
DIANA
CLAS
SAPHIR
ITEP (n)
HERMES
KN elastic
1540 10 5
One theory
1530 MeV
(cQSM)
1539 2 “few”
1542 2 5
1540 4 2
1533 5
1526 2 2
I=0
S=+1
Width
(Mev)
G  25
G 8
FWhM = 21
G  25
G < 20
G  13
G  few MeV !
s ( = N s / Nb )
4.61
4.4
5.30.5
4.8
6.7
5.60.5
G15 MeV
JP=½+
Next:
• Determine width, other quantum numbers (parity!).
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Summary of Null Results
0 null results published, only 3 on arXiv so far
⇒ need null results to be published
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no evidence for Q++  K+p in HERMES
Suggesting
Q+ Being Isosinglet
I=0 is likely
I=2 is ruled out
I=1 is unlikely, but cannot be
ruled out
X.Chen, Y.Mao, and B.Q.Ma,
hep-ph/0407381
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Pentaquark States from Theory:
anti-decuplet in chiral soliton models-1st version
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Prediction of Diquark model
S
R.L. Jaffe and F. Wilczek, PRL91 (2003) 232003
[ud]2s
Q+(1530)
1
I3
-1
X*-
[ds]2u
1
S*0
-1
X*0
[us]2d
X3/2(1750)
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Evidence for New Pentaquark?
NA49 at CERN
s = 17,2 GeV
pp  X*-- X, X*0 X,
 X- p-  X- p+
cSM:
C. Alt et al., hep-ex/0310014
M(X*--) = 2070 MeV
[qiqj]2q: M(X*--) = 1750 MeV
But: It is not what theory
predicted !
D. Diakonov et al., hep-ph/0310212
1,862  0,002 GeV
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Anti-Decuplet in Chiral Soliton Model - Version 2
S
D. Diakonov and V. Petrov hep-ph/0310212
B. Wu and Ma, hep-ph/0311331, PRD
uud ds
Q+(1539)
1
sdu..
-1
duu(dd+ss)
sdd..
sdu..
X*-
ssd du
1
S*0
ssd (uu+dd)
I3
N(1647)
108 MeV
suu(dd+ss)
-1
S(1754)
X*0
ssu..
ssu ud
X3/2(1862)
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Where are the missing members of antidecuplet?
•
For baryons with spin ½ and + parity, there is no N around, and a weak
evidence for S(1770),
so Diakonov and Petro (hep-ph/0310212) suggeted a missing N around
1650-1690 MeV;
the position of N(1710) is not at M=1710 MeV, but some where
around M=1650 to 1690 MeV, suggested by Arndt et al(nucl-th/0312126) .
•
We noticed ( hep-ph/9311331) that there are candidates of N(1650) and S(1750)
with spin ½ and negative (–) parity, in PDG
This may suggest a negative parity for antidecuplet members in the
chiral soliton model:
parity in chiral solition has two parts: quantized part with positive
parity and classical part with unknown parity;
the collective coordinate quantization can not inevitably fix the
parity of the corresponding baryons.
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The width formula and the widths in the case of negative parity
decay width is excellent for S(1750), but poor for N(1650) , possible solution:
SU(3) breaking for baryons with strangeness,
or there is a missing N resonance around 1650 with narrow width.
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Theories of positive parity for Q+
• Chiral Soliton Models (old version)
Diakonov-Petrov-Polyakov, ZPA359(1997)305
• Analysis in Quark Model
Stancu-Riska, PLB575(2003)242
• Diquark Cluster Model
Jaffe-Wilczek, PRL91(2003)232003
• Diquark-Triquark Model
Karliner-Lipkin, PLB575(2003)249
• Inherent Nodal Structure Analysis
Y.-x.Liu, J.-s.Li, and C.-g. Bao, hep-ph/0401197
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Theories of negative parity for
Q+
• Naive Quark Model
Jaffe (1976)
• Some Quark Models
Capstick-Page-Roberts, PLB570(2003)185
Huang-Zhang-Yu-Zhou, hep-ph/0310040，PLB
• QCD Sum Rules
Zhu, PRL91(2003)232002, Sugiyama-Doi-Oka, hep-ph/0309271
• Lattice QCD
Sasaki, hep-ph/0310014, Csikor et al, hep-ph/0309090,
but we heard difference voices recently
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Where is the answer? Experiment!
• Many suggestions on detecting the parity
Oh-Kim-Lee, hep-ph/0310019
Zhao, hep-ph/0310350
Liu-Ko-Kubarovsky, nucl-th/0310087
Nakayama-Tsushima, hep-ph/0311112
Thomas-Hicks-Hosaka, hep-ph/0312083 ……
• Measurement of parity is crucial to test theories
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/ or S=1/2
/
What else if I=0
• Answer: Most theories would need revision!
Would be a new surprise!
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Predictions of New Pentaquarks -27-plet
Figure from Wu & Ma, PRD69(2004)077501.
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The mass splitting of the 27-plet from
chiral solitons
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The widths of the 27-plet baryons
SU(3) Symmetric Case
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The picture of the 27-plet baryons:
non-exotic members are well established
We suggest that the quantum numbers of X(1950) is JP=(3/2)+
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Many new pentaquarks
to be discovered
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Predictions of Q*
• Walliser-Kopeliovich, hep-ph/0304058
mass=1650/1690 MeV
• Borisyuk-Faber-Kobushkin, hep-ph/0307370
mass=1595 MeV, width=80 MeV
• Wu-Ma, PLB586(2004)62
mass=1600 MeV, width less than 43 MeV
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Predictions of New Pentaquarks -35-plet
Figure from Wu & Ma, PRD, to appear .
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Mass splitting of 35-plet from chiral solitons
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The widths of the 35-plet baryons
SU(3) Symmetric Case
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Prediction of Pentaquarks
in SU(4) Chiral Solition Model
B.Wu and B.-Q.Ma, hepph/0402244, PRD to appear
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Experiment Evidence at H1
hep-ex/0403017
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_
The pentaquark uuddc
• Prediction of the mass of the ground uuddcbar:
m=2704 MeV, as pD state
Wu-Ma, hep-ph/0402244
• Observation by H1 Collaboration: m=3099 MeV
hep-ex/0403017
can be considered as pD* state
• From M(D*-D)~300 MeV, the observed uuddcbar can be
considered as an excited state (chiral partner) of the
predicted ground pentaquark state
M. Nowak et al, TPJU-4/2004, BNL-NTBNL-NT-04/10
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Conclusions
• The discovery of pentaquark Q+，if confirmed,
opens a new window to understand the basic
structure of matter.
• Measurement of the parity, isospin and spin of Q+
is crucial to test different theories
• There could be new pentaquark states waiting for
discovery
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