1. Search for Exotic Hadrons at Jefferson Lab
Elton S. Smith, Jefferson Lab Q+ X+
X−− S5 N5
Strong interactions
quark model
Latest on Pentaquarks
Gluonic excitations
JLab 12-GeV upgrade

2. Families within families of matter
DNA
10-7 m
Molecule
10-9 m
Atom
10-10 m
Nucleus
10-14 m
Proton
10-15 m
Quark
<10-18 m

3. Interactions understood in terms of quarks
Very high energy
BUT… free quarks have been not found, only particles that contain quarks

4. Electromagnetic and color forces
±1 charge
O(a) ~ 0.01 g
±3 “color” charges
O(as) ~ 1
Color force in Quantum Chromo Dynamics (QCD)

5. Quarks are confined inside colorless hadrons
Quarks combine to “neutralize” color force q q q q q
mesons
baryons
glueball meson
hybrid meson
Configurations outside the standard quark model q
pentaquark
molecules

6. Families of quarks
S=+1
S= 0
I3 = Q ─ ½ (B+S) −½ +½
S=−1

7. Baryons built from meson-baryon, or qqqqq
Hadron multiplets K p
Mesons qq
Baryons qqq N S X W─
Baryons built from meson-baryon, or qqqqq Q+ X+
X−−

8. Quarks and QCD G~15 MeV s (ud) (uds) (ud) Spin ½+ antidecuplet L=1 L=1
Quantum Chromo Dynamics allows hadronic states with different quark configurations (e.g. 4q+q pentaquarks). When the antiquark has a different flavor than the other 4 quarks, the pentaquark has “exotic” quantum numbers.
G~15 MeV
Rotational excitations
of the soliton
[rigid core surrounded
by chiral (meson) fields]
Diakonov, Z.Phys. A359, 305 (1997)
L=1
(ud) s
JW hep-ph/
JM hep-ph/
SZ hep-ph/
L=1
(ud)
(uds)
I=1,S=0
I=0,S=1/2
Karliner, Lipkin, hep-ph/
Spin ½+ antidecuplet

9. Initial evidence for pentaquark states
Spring8
DIANA
JLab-d
ELSA
ITEP
SVD/IHEP
JLab-p
HERMES
ZEUS
pp  S+Q+.
COSY-TOF
CERN/NA49
Q0c H1
X--

10. The Q+ width Measured width dominated by experimental resolution
U. Meissner
Measured width dominated by
experimental resolution
Analysis of K+A data give limit of
few MeV.
K+D -> X
K+D , K+Xe → X
Sibirtsev et al.: GQ < 1 MeV
In most cases the observed width of the state is dominated by experimental resolution. Estimates of the natural width have to rely on estimates using the elastic K+n -> K+ n or K+-deuteron total cross section measurements. Several estimates show that the Q+ width cannot be more than about 1 MeV. The analysis of K+D total cross section data gives a width of 0.9 +/- 0.3 MeV. The data and fits are shown in here.
Very narrow for a hadronically
decaying particle with mass ~100 MeV
above threshold:
Q+(1540) -> nK+, pK0
From selected data sample
What can we say about event rates?
K+n → Q+ => G~1 MeV,
K-p → L* => G~16 MeV.
=> s(Q+)/s(L*) ~ 1.4% for formation.
GQ = 0.9 +/-0.3 MeV
W. Gibbs, Phys.Rev.C70, (2004)

11. Null Results

12. Pentaquark Scorecard (April 2005)
Negative Results
Positive Results
Experiment  (1520)  Lc
____________________________________ E
ALEPH
CDF
BaBar
HERA-B
SPHINX
HYPERCP
COMPASS
BELLE
SELEX ,800,000
 (1530) D D*
________________________________________________________ E
ALEPH
CDF
BaBar
HERA-B
ZEUS WA
FOCUS
Experiment signal backgrd  (1520)

Spring
Spring
SAPHIR
CLAS(d)
CLAS(p)
DIANA 
HERMES
COSY
ZEUS *
SVD
NOMAD
________________________________________
signal backgrd  D* NA H
* Estimate from cross section

13. Experimental evidence for Q+
Many experiments
New results from dedicated experiments
Examples from CLAS detector only
No attempt at completeness

14. Search for Pentaquarks at CLAS
A comprehensive program to search for pentaquarks in photoproduction experiments at Jeffeson Lab were approved in with the goal of confirming previous results and explore new kinematics with at least a factor 10 increase in statistics.
CLAS(d) g2
2003 Phys. Rev. Lett. 91,
SAPHIR
2003 Phys. Lett. B572, 127
NA49
2004 Phys. Rev. Lett. 92,
CLAS(p) g6
2004 Phys. Rev. Lett. 92,
Relevant Publication
g deuteron Eg ~ GeV
preliminary results
g proton Eg ~ GeV
hep-ex/ , accepted by PRL
eg deuteron Eg ~ GeV
data taken, analysis in progress
Super-g proton Eg ~ 3.8 – 5.7 GeV
planned for 2006

15. JLab accelerator CEBAF
Continuous Electron Beam
Energy 0.8 ─ 5.7 GeV
200 mA, polarization 75%
1499 MHz operation
Simultaneous delivery 3 halls

16. CEBAF Large Acceptance Spectrometer
Torus magnet
6 superconducting coils
Electromagnetic calorimeters
Lead/scintillator, 1296 photomultipliers
Liquid D2 (H2)target +
g start counter; e minitorus
Drift chambers
argon/CO2 gas, 35,000 cells
Gas Cherenkov counters
e/p separation, 256 PMTs
Time-of-flight counters
plastic scintillators, 684 photomultipliers

17. Quark lines for production of Q+g K− us us K+ Q+ n
ddu
ddu n
Q+ is composed of (uudds) quarks

18. gd → p K─K+ (n) in CLAS K+ p K- Sectors 3 & 6 Sectors 1 & 4

19. CLAS Cross Section Checks
gp  p w
g10 preliminary (3375A)
World data
CLAS g11
preliminary
SAPHIR
np-
1.05 < Eg < 1.15 GeV
ds/dWCM (mb/sr)
Different final states are measured
simultaneously in the CLAS detector
Cross section for known reactions
have been extracted to test the
accuracy of the analysis procedure
1% of statistics
gp  K+L
s(mb)
CLAS g11
preliminary
SAPHIR
cosqCM(p-)
Eg(GeV)

20. CLAS published data on gd → p K─K+ (n)Q+ p K–
Re-scattering
Events/10 MeV
MM(K-p) (GeV/c2)

21. New high Statistics CLAS(d) result
The statistical significance in the published data is an unlucky coincidence of a statistical fluctuation and an underestimate of the background in the mass region of 1.54 GeV/c2.
preliminary
M(nK+)(GeV)
Model-independent uppper limit 95% CL for Q+ is < 20nb.
With assumptions about the spectator, we can set a model- dependent upper limit to the cross section of < 4-5 nb.

22. Search for the Q+ (1540) on proton targetK0 K+ p+ g p Q+ p−
Counts KS
M (p+p-)(GeV)
The K0 is detected via its KS component decaying into p+ p-
Final state neutron is identified
using the missing mass technique
Strangeness is tagged detecting the K+
Using the full statistics (70 pb-1) a total of ~ events are selected
Counts n
Mx(p+p-K+ X)(GeV)

23. Upper Limit on the Q+ Yield
Counts/4 MeV
Counts/4 MeV
-0.8 < cosqCM < -0.6
Q+(1540) ?
no structure is observed at a mass of ~1540 MeV
the nK+ mass spectrum is smooth
M(nK+)(GeV)
Counts/4 MeV
0.6 < cosqCM < 0.8
M(nK+)(GeV)
M(nK+)(GeV)

24. Upper limit to the cross section gp→Q+K0
Absolute cross section
Detection efficiency computed for several Q+ production models
Br(Q+→nK+) = 50%
s < 1.3 nb

25. Pentaquark Status publ. Comments s/ b+s
Group Signal Backgr Significance
publ. Comments
SPring s 3.2s
SPring s
SAPHIR s 5.2s
DIANA s 3.4s
CLAS(d) s 4.4s
CLAS(p) s 4.7s
  s
HERMES  3.6s
ZEUS  s
COSY  s
SVD  s
SVD s Improved analysis
NA  s
H  s
SPring s L*(K+n)
STAR 2, , s Q++ candidate
s/ b+s
G11 CLAS-p
G10 CLAS-d
? BELLE Q+
This slide summarizes the remaining evidence for any pentaquark. The new CLAS results eliminated two signals one on hydrogen and one on deuterium. The two non-Theta+ signals at H1 and NA49 are highly questionable and contradict later results from ZEUS and HERA-B with higher sensitivity.
Finally, the very new CLAS data on deuterium, presented here for the first time, should be confronted with the LEPS deuterium results from SPring8 which have lower statistics.
On the side favoring pentaquark signal is some positive news: The SVD-2 improved analysis gives many more events with high significance. SprinG8 claims a signal in L*(K+n) with 5s, and there is a signal of a doubly charged Q++ from STAR at RHIC.
? BABAR X5
HERA-B, CDF, COMPASS
ZEUS, FOCUS, BABAR
Q0c
From V. Burkert EINN 2005, Milos Greece

26. Remarks on Pentaquarks - theory
All models have difficulty understanding the very narrow widths of the Q+ (~ 1 MeV).
Quark models do not naturally generate positive parity multiplets (s-wave configuration leads to negative parity).
Most calculations on the lattice do not predict bound states
Role and importance of diquark configurations has been highlighted during these investigations u d d

27. Remarks on Pentaquarks - experiment
Beware of statistics - Naïve estimates tend to overestimate significance of signal.
Empirical (smooth) background shapes do not always represent reality and need to be treated with special care.
Jefferson Lab has dedicated significant resources and priority to check initial results by running dedicated experiments proposed and analyzed in record times.
Summary: Pentaquark is not dead,
but it is on live support

28. Gluonic Excitations hybrid mesonq
hybrid meson
High mass requires higher energy beams
Predicted for heavy quarks by lattice QCD
Exotic JPC combinations do not mix with conventional mesons
Goal is to probe the dynamical role of glue in mesons

29. Normal Mesons – qq color singlet bound states
Spin/angular momentum configurations & radial excitations generate our known spectrum of light quark mesons.
Starting with u - d - s we expect to find mesons grouped in nonets - each
characterized by a given J, P and C.
Spin 0
Spin 1 K0 K+ K* r w f p0 h’ p− p+ h K− K0
JPC = 0– – – 1+ – 2++ …
Allowed combinations
JPC = 0– – 0+ – 1– – …
Not-allowed: exotic

30. Quark binding and configuration of gluons
Confinement arises from flux tubes and their excitation leads to a new
spectrum of mesons
From G. Bali

31. Hybrid Mesons
Hybrid mesons
1 GeV mass difference (p/r)
Normal mesons

32. Quantum Numbers of Hybrid Mesons
Excited Flux Tube
Quarks
Hybrid Meson
like
Exotic
Flux tube excitation (and parallel quark spins) lead to exotic JPC
like

33. exotic nonets 2 + – 2 + + 2 – + 1 – – 1– + 1 + – 1 + + 0 + – 0 – +
Radial
excitations
Meson Map
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
Each box corresponds
to 4 nonets (2 for L=0)
Mass (GeV)
exotic
nonets
0 – +
0 + –
1 + +
1 + –
1– +
1 – –
2 – +
2 + –
2 + +
0 + +
Glueballs
Hybrids
(L = qq angular momentum)

34. Reports of JPC exotics
p1(1400) and p1(1600) are likely four-quark (qqqq) mesons or generated by meson-meson interactions.
p1(2000) mass and decays are consistent with theoretical expectations, but need confirmation.
No families of exotics have been reported.

35. understood acceptance
Exotic signal in E852
Correlation of
Phase
&
Intensity
Exotic
signal
1(1600)
Leakage
From
Non-exotic Wave
due to imperfectly
understood acceptance
Result has also been challenged using a larger
statistics data sample with both p−p−p+ and p−p0p0
hep-ex/

36. Families of Exotics g  ,, 1-+ nonet K1 IG(JPC)= ½ (1-)
h’1 IG(JPC)=0+(1-+)
h1 IG(JPC)=0+(1-+)
K1 IG(JPC)= ½ (1-)
1-+ nonet
p1 IG(JPC)=1-(1-+) N g e X
Couple to vector meson
+ exchanged particle
p1  rp
h1  rb1 , wf
g  ,,
h’1  fw

37. Strategy for Exotic Meson Search
Use 8 – 9 GeV polarized photons (12 GeV electron beam)
Expect production of hybrids to be comparable to normal mesons
Dearth of experimental data
Use hermetic detector with large acceptance
Decay modes expected to have multiple particles
hermetic coverage for charged and neutral particles
high data acquisition rate to enable amplitude analysis
Perform partial-wave analysis
identify quantum numbers as a function of mass
check consistency of results in different decay modes

38. Upgrade magnets and power supplies
CHL-2
Upgrade magnets and power supplies 12
6 GeV CEBAF
add Hall D
(and beam line)
Enhance equipment in existing halls

39. GlueX collaboration

40. Architect’s rendering of Hall D complex
Service Buildings
Hall D
Cryo Plant
Counting House

41. Coherent Bremsstrahlung
12 GeV electrons
Incoherent &
coherent spectrum
flux
This technique provides requisite energy, flux and polarization
tagged
0.1% resolution
40%
polarization
in peak
photons out
collimated
electrons in
spectrometer
diamond
crystal
Hadronic
Backgrounds
photon energy (GeV)

42. Coherent Bremsstrahlung
GlueX / Hall D Detector
Lead Glass
Detector
Solenoid
Coherent Bremsstrahlung
Photon Beam
Tracking
Target
Cerenkov
Counter
Time of
Flight
Barrel
Calorimeter
Note that tagger is
80 m upstream of
detector
Detector Review
Oct 20-22, 2004
Electron Beam from CEBAF

43. Acceptance: high and uniform over PWA angles
 ~ 0.98
Acceptance
 ~ 0.99
cosGJ
GJ

44. Finding an Exotic Wave
An exotic wave (JPC = 1-+) was generated at level of 2.5 % with 7 other waves. Events were smeared, accepted, passed to PWA fitter.
Mass
Input: MeV
Width
Input: 170 MeV
Output: /- 3 MeV
Output: /- 11 MeV
Double-blind M. C. exercise
Statistics shown here correspond to a few days of running.

45. JLab 12 GeV Upgrade Project Status
Highlight in the 20-year plan of the Office of Science (2003)
What’s New: “New supercomputing studies indicate that force fields called “flux-tubes” may be responsible [for the mechanism that confines quarks], and that exciting these should lead to the creation of never-before-seen particles.”
Determination of “Mission Need” CD-0 (Apr 2004)
Review of Science program for the 12-GeV Upgrade (Apr 2005)
From the Executive Summary: “After a decade of research, we should know whether the formation of flux tubes by the gluon fields is the mechanism of confinement…”
Successful Project Review (Jul 2005), CD-1 expected soon
Four-year construction project planned to start in FY08

46. Summary of GlueX program
Mapping the spectrum of hybrid mesons provides essential experimental data on the physics of the strong interactions at low energies in the region of confinement.
This unique experimental program is possible now due to
to high quality electron beam at the 12-GeV CEBAF Upgrade
increases in computational power
new developments in detector readout technology
technology to produce thin diamond crystals
GlueX will establish the existence of exotic hybrids if they are present at the level of a few % of conventional mesons.

47. Conclusions
The spectrum of hadrons provides a means of probing QCD in the region of strong coupling.
The detailed study of pentaquarks has caused our field to reexamine our understanding of strongly interacting QCD and clarified the strengths and weaknesses of the quark model.
Mapping out the spectrum of hybrid mesons will confirm predictions of lattice QCD… or provide new insights into the dynamics of the complete theory.
models
lattice
experiment