1. What are hadrons made of? Seoul National University
Stephen L. Olsen
Seoul National University

2. Some Background

3. 1963 “stable” hadrons meson resonances baryon resonances “flavors”X S L N X* K* K Y* w p r m e
K2* D
“flavors”
Two “classes” of hadrons
“non-strange:” n, p, p, r, …
“strange:” L, S, K, K*, …

4. 1st attempts at Classification
With the discovery of new unstable particles (L, k) a new quantum number was invented: Þ strangeness
Gell-Mann, Nakano, Nishijima realized that electric charge (Q) of all particles could be related to isospin (3rd component), Baryon number (B) and Strangeness (S):
Q = I3 +(S + B)/2= I3 +Y/2
hypercharge (Y) = (S+B)
Meson “octet”
all have same JP=0-
Interesting patterns emerge when I3 is plotted vs. Y Y I3 4

5. Vector mesons also form an octet
JP=1-
K*0
K*+ r- w r0 r+ f _
K*-
K*0 Y I3

6. Baryons are in octets & decuplets? Y
missing in 1961 I3

7. 1961: Gell-Mann, Nishijima & Nee’man: “The Eightfold Way”
The Eightfold Way appears in the Buddhist teaching:
"This is the noble truth that leads to the cessation of pain. This is the noble eightfold way."

8. Octets (and decuplets) are representations
of the SU(3) Lie group:
SU(2) group:
Angular Momentum in QM
SU(3) group:
Generalization of SU(2)
Gell-Mann Matrices
Pauli Matrices
Representations:
Representations: … …
Spin=1/2
Spin=1
octets
decuplets

9. SU(3) prediction for the W- mass
Gell-Mann Okubo mass formula
JP=3/2+
M=1232 MeV
D ≈ 153 MeV
M=1385 MeV
D ≈ 148 MeV
M=1533 MeV ?
M≈ MeV = 1683 MeV

10. 1965: W- discovery 1965: the W- was discovered at
the Brookhaven Lab in NY. USA
with S=-3 & M = 1672 MeV, very
near the Gell-Mann-Okubo prediction

11. 1964: triplet = the most fundamental representation of SU(3)
B = 1/3
Y=+1
n-1/3
p-2/3
Y=+1/3
Y=0
l-1/3
Y=-2/3
Y=-1
Fractional
charges!!
Q =-1/3
Q =+2/3
Y=-2
Quarks
Gell-Mann
Aces
Zwieg

12. Original Quark Model Λ= (uds)
1964 The model was proposed independently by Gell-Mann and Zweig
Three fundamental building blocks 1960’s (p,n,l) Þ 1970’s (u,d,s)
mesons are bound states of a of quark and anti-quark:
Can make up "wave functions" by combining quarks:
baryons are bound state of 3 quarks:
proton = (uud), neutron = (udd), L= (uds)
anti-baryons are bound states of 3 anti-quarks:
Λ= (uds) 12

13. Make mesons from quark-antiquark_ _ _ us ds s d _ u _ _ dd _ _ uu ud du u d _ ss s _ _ sd su _

14. Ground state mesons (today)
JP=0-
JP=1-
498
494
892
896
K*0
K*+
135
548
783
776
776
776 r- w r0 r+
139
139
958 f
1020 _
494
498
K*-
K*0
896
892
(p+,p0,p-)=lightest
(r+,r0,r-)=lightest
nr=0
nr=0
S-wave
S-wave

15. Adding 3 quarks8-tets & 10-plets
dud
uud
ddd
uud
dud
uud
sdd
sud
suu
sdd
sud
suu
sud
ssd
ssd
ssu
ssu
sss

16. Ground state Baryons JP=1/2+ JP=3/2+ 939 938 M=1232 MeV 1115
1189
1197
1192
M=1533 MeV
1321
1315
M=1672 MeV
JP=1/2+
JP=3/2+
all nr=0
all S-waves
all nr=0
all S-waves 16

17. Are quarks real objects? or just mathematical mnemonics?
Are quarks actually real objects?" Gell-Mann asked.
"My experimental friends are making a search for them
in all sorts of places -- in high-energy cosmic ray reactions
and elsewhere. A quark, being fractionally charged,
cannot decay into anything but a fractionally charged
object because of the conservation law of electric charge.
Finally, you get to the lowest state that is fractionally
charged, and it can't decay. So if real quarks exist, there is
an absolutely stable quark. Therefore, if any were ever
made, some are lying around the earth."
But since no one has yet found a quark, Gell-Mann
concluded that we must face the likelihood that quarks are
not real.

18. 1974: discovery of J/y and y’
stot(e+e-  hadrons) c c c c
nr=0
M=3.097 GeV
nr=1
M=3.686 GeV
S-wave
S-wave
J/y & y’ interpreted as charmed-quark anticharmed-quark mesons

19. Charmonium mesons formed from c- and c-quarks c c r
c-quarks are heavy: mc ~ 1.5 GeV
velocities small: v/c~1/4
non-relativistic, undergraduate-level QM applies

20. What is V(r)? c c r linear “confining” V(r) 2 parameters:
“Cornell” Potential r
linear “confining”
long distance
component
V(r)
slope~1GeV/fm
~0.1 fm r
1/r “coulombic”
short distance
component
2 parameters:
slope & intercept

21. Charmonium (cc) spectrum Positronium (e+e-)spectrum_ y’
J/y

22. Run the accelerator here
J/y y’

23. P-wave Charmonium states
y’g X e+ y’ e- y’
Crystal Ball expt: Phys.Rev.D34:711,1986. Eg
“smoking gun” evidence that
quarks are real spin=1/2 objects
J/y

24. What are hadrons made of?
Hadrons are made of quarks
Three quarks  baryons
quark-antiquarkmeson
The discovery of the charmonium states convinced everyone that quarks are real
Google hits for “quarks” = 1,760,000

25. The Nobel Prize in Physics 1969
"for his contributions and discoveries concerning the
classification of elementary particles and their interactions"
                        
This classification of the elementary particles and their interaction
discovered by Gell-Mann has turned out to applicable to all strongly
interacting particles found later and these are practically all particles
discovered after His discovery is therefore fundamental in
elementary particle physics.

26. End of story??
Not so fast!!!!
The end?

27. Problem with the quark model:
Violation of the spin-statistics theorem?
s-1/3
s-1/3
s-1/3
W-=three s-quarks
in the same
quantum state

28. W- have different strong
The strong interaction “charge” of each quark comes in 3 different varieties
Y. Nambu
M.-Y. Han W-
s-1/3
s-1/3 1 2
s-1/3 3
the 3 s-1/3 quarks in the
W- have different strong
charges & evade Pauli

29. Attractive configurations
Baryons:
Mesons:
eijk eiejek
i ≠ j ≠ k i j i
dij ei ej j k
same as the rules for combining colors to get white:
add 3 primary colors --or-- add color+complementary color
quarks: eiejek  color charges
antiquarks:  anticolor charges ei ej ek
eijk eiejek
dij ei ej
“Quantum Chromo Dynamics” QCD

30. Are there other, “exotic” color-singlet spectroscopies?
Other possible “white” combinations of quarks & gluons: u u d d
Pentaquark: H-dibaryon:
e.g. an S=+1 baryon tightly bound
5-quark state 6-quark state
Glueballs:
gluon-gluon color singlet states
Tetraquark mesons
qq-gluon hybrid mesons s _ u u d s s d _ c u _ u c _ _ c c

31. Pentaquarks & the H-dibaryon

32. quark + quark  antiquark?du
diquark
antitriplet _ 3 dd du ud uu d u d u ds us d u  dd ud uu  = = ds us su sd 6 s s s sd su ss _
3  3 = 6  3 ss

33. Pentaquarks? 10 _   _ _ = 3 3 3 _ 8  __ Exotics Q+ _ N0 N+ du du s
D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305.
R.Jaffe & F. Wilczek PRL 91, (2003) __ 10 Q+
S=+1 _ N0 N+
S=0 du du s S- S0
---- S=-1 S+ _   _ _ =
X-- X- X0 X+ 3
- S=-2 3 3  _ _ ds us ds us u u _
antitriplet
antitriplet
antitriplet N0 N+
S=0 8 S- S0 S+
-- S=-1 L0 X- X0
S=-2
See also: Y.S. Oh & H.C. Kim PRD 70, (2004)
Prediction: M(X- -) ≈ 1750~1850 MeV
X- - p-X very clean!! |
 p-L0 33

34. Q+ Pentaquark at Spring-8?
Q+ decay modes:
Q+  K+ n
need to deal with the neutron
Q+  K0 p
cannot tag the strangeness
gnK- K+n
Q+ photo-production K+ Q+
S=+1
u+2/3
s+1//3
d-1/3
u+2/3
d-1/3
need a neutron target
(1st experiment used 12C tgt) n

35. Results gnK- K+n CLAS-D (2005) gnK- K+n ??? Q+  K+ n ? Q+  K+ n ?
Width consistent with (11 MeV) resolution
T.Nakano et al (LEPS)
PRC 79, (2009)
B.McKinnon et al (CLAS)
PRL (2006)

36. X- - in NA49 Expt at CERN? L & X signals are very clean _ _
X-p- + X-p+ + X+p-+ X+p-
M(Xp)5 = 1862±2 MeV
G5<18 MeV
S = 4.2s

37. No sign of X- - in CDF X*(1530)  X-p+
No peaks around M(Xp) = 1860 MeV/c2 for X-p+ and X-p-

38. Positive pentaquark sightings since 2003

39. Negative pentaquark sightings since 2003

40. “The story of pentaquark shows how poorly we understand QCD” – F
“The story of pentaquark shows how poorly we understand QCD” – F. Wilczek, 2005

41. Pentaquarks in a gluon-rich environment
less complicated than:
(1S) anti-deuteron + X
(1S)X- - + X d p n p p b b
(1S)
(1S) b p b p
CLEO: Bf((1S) anti-deuteron + X)=3x10-5
an appropriate comparison process
A limit on Bf((1S)X- - + X) below 10-5 would be
“compelling evidence” that Pentaquarks do not exist.

42. H dibaryon?   _ _ _ 3 3 3 d u d u d u u s d s u s d s u s d s d u s
antitriplet
antitriplet
antitriplet d u s s
decays weakly!! d u
R.L. Jaffee, PRL 38, 195 (1977): S=-2 di-hyperon with M<2ML

43. The “Nagara” 6He emulsion eventLL
MH > 2ML-7.7 MeV
6He LL
5He L
H. Takahashi et al, PRL 87, (1977)

44. H dibaryon decay modes MH(MeV) H  n or LL strong decay probably wide
12C(K-,K+LLX)
M + MN
(2260 MeV)
H LL strong decay
2ML
(2223 MeV)
H L n weak decay
2215 MeV
Ruled out
by Nagara
C.J. Yoon et al (KEK-PS E522)
PRC 75, (2007)
most interesting

45. Production via gluons S=-2 B=+2 Need to:
produce 6 quark-antiquark pairs
(including two ss quark pairs)
very close in phase space d u s s d u
Is this likely???

46. Anti-deuteron production
Similar process!! p d p n

47. Experimental signatures
MH(MeV)
H  n or LL
M + MN
(2260 MeV)
H LL
2ML
(2223 MeV)
H L n weak decay
2215 MeV
H L n is hard, but H  L n is possible
advantage of gluon production
is equal rates for H and H

48. Pentaquark & H-dibaryon searches via gluonic systems with sensitivites below the d production rate should be conclusive.

49. The “XYZ” exotic meson candidates

50. The XYZ Mesons

51. B-factories e+e–→(4S) and nearby continuum: Ecms ~ 10.6 GeV
L ~ 1034/cm2/s
fb-1 in total
At KEK in Japan
At SLAC in California 51

52. cc production at B factories

53. Search for a meson that decays to a final state
Strategy:
Search for a meson that decays to a final state
containing a c and c quark, If it is a standard
qq meson, it has to occupy one of the unfilled
states indicated above. If not, it is exotic.
predicted
measured

54. The X(3872)

55. Study p+p-J/y produced in BK p+p- J/y decays
????

56. The X(3872) BK p+p-J/y y’p+p-J/y X(3872)p+p-J/y M(ppJ/y) – M(J/y)
S.K. Choi et al PRL 91,

57. Its existence is well established seen in 4 experiments
CDF
9.4s
11.6s
X(3872) D0
BaBar
X(3872)

58. X3872 JPC values Fit to M(pp) favors rp+p-
Angular correlation analysis by CDF:
JPC = 1++ or 2-+
hep-ex/
PRL96,102002(2006)
Fit to M(pp) favors rp+p-
JPC = 1++
CDF: PRL

59. BaBar: X3872 gJ/y & gy’ JPC = 1++ favored over 2-+ B+K+gJ/y
3.6s
G(XgJ/y)  1/10 G(Xp+p-J/y)
1++  g J/y or gy’  Allowed E1
2-+  gJ/y or gy’  Suppressed E2
M(gJ/y)
B+K+gy’
JPC = 1++ favored over 2-+
3.5s
PRL 102,132001
M(gy’)

60. If it is not the c’c1, what is it?
can it be the 1++ cc state?
1++cc1’
(the only
charmonium possibility)
M=3872 MeV is low,
Xp+p- J/y decay
is a forbidden decay
3872 g
Xg J/y is an allowed
E1 transition; should be
stronger than p+p-J/y,
not 10x weaker.
p+p-
(Isospin
violating)
If it is not the c’c1, what is it?

61. X(3872) looks like a D*0D0 molecule
Predicted by N.A. Tornqvist PLB (2004)

62. M X(3872) ≈ MD0 +MD*0 <MX>= 3871.46 ± 0.19 MeV
new Belle meas.
new CDF meas.
MD0 + MD*0
3871.8±0.4 MeV
dm = ± 0.41 MeV

63. X3872 couples to D*0D0 BaBar Belle X3872 D0D*0 X3872 D0D*0 D*→Dγ
& arXiv:
605 fb-1
D*→Dγ
D*→D0π0
414fb-1
D0D0p0

64. Molecular Picture Since the X couples to D0 D*0 in an S-wave:
at least some fraction of it
≥ 6 fermis!!
E. Braaten et al arXiv:

65. X(3872)-J/y relative sizes
drms(X3872) ≈ 6 fm
drms(J/y) ≈ 0.4 fm
Volume(J/y)
Volume(X3872)
≈ 10-3 _
Overlap of the cc necessary to form the J/y in X p+p-J/y decays is rare
Probability for forming such a fragile object in H.E. pp collisions is small _
-- arXiv : sCDF(meas)>3.1±0.7nb vs stheory(molecule)<0.11nb

66. Produced like the y’ in pp collisions_
Produced like the y’ in pp collisions
Fraction from B decays
Long-lived fraction
y(2S) :
28.3  1.0(stat.)  0.7(syst.) %
X(3872) :
16.1  4.9(stat.)  1.0(syst.) %
(drms ≈ 0.4 fm)
(drms ≈ 6 fm??)
X(3872) behaves similarly to y(2S).
X(3872) mostly prompt.

67. X(3872)=diquark-diantiquark ?
Expect SU(3) multiplets
Isospin partners
S=-1 partners
X-=
Xs-= d s
doublet of “X(3872)” states
DM=8±3 MeV
Maiani et al PRD71,

68. No multiplet partners seen
BaBar search for “X-(3872)”p-p0 J/y B0
X(3872)– B-
M(J/π–π0)
PRD 71,
Bf(B0K+X-)Bf(X-p-p0J/y)
< 0.4
Bf(B-K+X0)Bf(X-p-p-J/y)
(expect  2)

69. Lots of interest in the X(3872) line shape
C. Hanhart et al arXiv:
also E. Braaten et al PRD
Line shape and very precise mass
measurement only possible at FAIR

70. The 1- - Y states

71. produced by ISR must have JPC = 1- - at least 3, maybe 5
Y(4350) & Y(4660)
must have
JPC = 1- -
e+e-gISRp+p-y’
BaBar
Y(4260)
BaBar
e+e-gISRp+p-J/y
Belle
Belle
Y(4008)?
M(p+p-y’) GeV
e+e-gISRLcLc
Y(4630)
Belle
M(p+p-J/y) GeV
M(LcLc)
at least 3, maybe 5

72. Only one empty 1- - charmonium slot is available:
predicted
measured

73. Not evident in stot(e+e–→charm)y
(3770)
if R
uds
=2.285
0.03
Durham Data Base Y(
4008)
(4040)
(4160)
4260)
4325)
(4415) Y
(4660) ψ
ψ(4160)
4360)
R(s) = σ(e+e–→charmed hadrons)/σQED(e+e–→μ+μ-)
The established 1 - -
charmonum states

74. D*D* Not evident in any exclusive charmed hadron channel DDπ DD DD*π
Λ+c Λc
Charm Exotic 2009

75. S(exclusive channel measurements) nearly saturate stot
Only small room for unaccounted contributions
Limited inclusive data above 4.5 GeV

76. G(p+p-J/y) [G(p+p-y’)] are much larger than seen in ordinary charmonium
e.g. G(Y4260  p+p-J/y) > 508 keV (X-L Wang et al., PLB 640, 182(2007))
compared to:
G(y’  p+p-J/y) ≈ 89 keV (PDG tables)
&
G(y3770  p+p-J/y) ≈ 45 keV

77. Z(4430)p+y’ u c c d
Smoking gun for charmed exotic?

78. BK p y’ (in Belle) ??
M2(p+y’)
K*(1430)K+p-?
K*(890)K+p-
M2(K+p-)

79. The Z(4430)± p±y’ peak “K* Veto” Z(4430) BK p+y’ M2(p±y’) GeV2
M (Kp’) GeV
Z(4430)
M2(p±y’) GeV2
M(p±y’) GeV
M2(Kp’) GeV2
“K* Veto”

80. Could the Z(4430) be due to a reflection from the Kp channel?

81. Cos qp vs M2(py’) p qp +1.0 M2(py’) cosqp -1.0K
+1.0
22 GeV2
(4.43)2GeV2
0.25
M2(py’)
cosqp
16 GeV2
-1.0
M (py’) & cosqp are tightly correlated;
a peak in cosqp  peak in M(py’)

82. S- P- & D-waves in Kp can’t make a peak (+ nothing else) at cosqp≈0.25
not without introducing other, even more dramatic
features at other cosqp (i.e., other Mpy’) values.

83. But…

84. BaBar doesn’t see a significant Z(4430)+
“For the fit … equivalent to the Belle analysis…we obtain mass
& width values that are consistent with theirs,… but only ~1.9s
from zero; fixing mass and width increases this to only ~3.1s.”
Belle PRL: (4.1±1.0±1.4)x10-5

85. Reanalysis of Belle’s BKpy’ data using Dalitz Plot techniques

86. 2-body isobar model for Kpy’
Our default model
ky’
K*(890)y’
K*(1410)y’
K0*(1430)y’
K2*(1430)y’
K*(1680)y’
KZ+
K*y’ B
K2*y’
Kpy’
KZ+

87. Results with no KZ+ term2 1 1 2 3 4 5 C B A 3 4 A B 5 C
fit CL=0.1% 51

88. Results with a KZ+ term 2 1 B 1 2 3 4 5 A 3 4 C B C A 5
fit CL=36%

89. Compare with previous results
K* veto applied
With Z(4430)
Signif: s
Published results
Without
Z(4430)
Mass & significance similar,
width & errors are larger
BaBar:
Belle: = ( )x10-5
No big contradiction

90. Variations on a theme Z(4430)+ significance
Others: Blatt f-f term 0r=1.6fm4fm; Z+ spin J=0J=1; incl K* in the bkg fcn

91. XYZ Summary
States with distinct signatures in PANDA

92. What are hadrons made of?
40 years after Gell-Mann’s prize, we still don’t know
expected non-qq mesons &/or non-qqq baryons not seen
non-qq meson candidates that are seen defy any comprehensive theoretical understanding.
new ideas needed.
Most progress has been experimentally driven
Lots for PANDA to do.

93. Thank you