Download "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.
1
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…”
•
2
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.
3
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)+
4
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
5
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
6
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.
7
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
8
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.
9
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.
10
“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.
11
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.
12
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
13
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
14
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)
15
Summary of recent experiments
world-average:
M(Q+): 15322.4 MeV
16
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!).
17
Summary of Null Results
0 null results published, only 3 on arXiv so far
⇒ need null results to be published
18
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
19
Pentaquark States from Theory:
anti-decuplet in chiral soliton models-1st version
20
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)
21
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
22
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)
23
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.
24
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.
25
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
26
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
27
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
28
/ or S=1/2
/
What else if I=0
• Answer: Most theories would need revision!
Would be a new surprise!
29
Predictions of New Pentaquarks -27-plet
Figure from Wu & Ma, PRD69(2004)077501.
30
The mass splitting of the 27-plet from
chiral solitons
31
The widths of the 27-plet baryons
SU(3) Symmetric Case
32
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)+
33
Many new pentaquarks
to be discovered
34
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
35
Predictions of New Pentaquarks -35-plet
Figure from Wu & Ma, PRD, to appear .
36
Mass splitting of 35-plet from chiral solitons
37
The widths of the 35-plet baryons
SU(3) Symmetric Case
38
Prediction of Pentaquarks
in SU(4) Chiral Solition Model
B.Wu and B.-Q.Ma, hepph/0402244, PRD to appear
39
Experiment Evidence at H1
hep-ex/0403017
40
_
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
41
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
42