1. The 12 GeV Upgrade of the CEBAF Accelerator at Jefferson Lab
Elton S. Smith
Jefferson Lab
SESAPS 2004
Oak Ridge, TN
Gluonic Excitations
3-dim view
of the Nucleon

2. CEBAF @ JLab Today Main physics programs
nucleon electromagnetic form factors (including strange form factors)
N → N* electromagnetic transition form factors
spin structure functions of the nucleon
form factors and structure of light nuclei
Superconducting recirculating electron accelerator
max. energy 5.7 GeV
max current 200 mA
e polarization 80%
Simultaneous operation in 3 halls L[cm-2s-1]
2 High Resolution Spectrometers (pmax=4 GeV/c)
2 spectrometers (pmax=7 and 1.8 GeV/c) + special equipment 1039
Large Acceptance Spectrometer for e and g induced reactions 1034

4. 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

5. Gluonic Excitations
Dynamical role of Glue
Confinement

6. Confinement arises from flux tubes and their excitation leads to a new
Lattice QCD
Flux tubes realized
Confinement arises from flux tubes and their excitation leads to a new
spectrum of mesons
→ Flux Tube Model
From G. Bali

7. Understanding Confinement
The Ideal Experiment
The Real Experiment

8. 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.
JPC = 0– – – 1+ – 2++ …
Allowed combinations
JPC = 0– – 0+ – 1– – …
Not-allowed: exotic

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

10. 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

11. exotic nonets Lattice 1-+ 1.9 GeV 2+- 2.1 GeV 0+- 2.3 GeV 2 + – 2 + +
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
Lattice
GeV
GeV
GeV
(L = qq angular momentum)

12. Exotic Signal JPC=1─ + E852 p1(1600) → h p ↳ h pp ↳ gg
M =1.60  0.05
G = 0.34  0.06
E852 PRL 86, 3977 (2001)

13. 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
g  ,,
p1  rp
h1  rb1 , wf
h’1  fw
Couple to V.M + e

14. Strategy for Exotic Meson Search
Use photons to produce meson final states
tagged photon beam with 8 – 9 GeV
linear polarization to constrain production mechanism
Use large acceptance detector
hermetic coverage for charged and neutral particles
typical hadronic final states: f1h KKh KKppp b1p wp pppp rp ppp
high data acquisition rate
Perform partial-wave analysis
identify quantum numbers as a function of mass
check consistency of results in different decay modes

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

16. 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

17. 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.

18. 3-dimensional view
of the Nucleon
Deep Exclusive Scattering

19. 1-dim view from Deep Inclusive Scattering
What have we learned?
nucleon has a substructure made of quarks
quarks are spin ½ objects
Longitudinal momentum distribution of quarks q(x), Dq(x)
50% of the nucleon momentum is carried by quarks, the remainder by gluons
less than 25% of the nucleon spin is carried by quark helicity

20. Generalized Parton Distributions
GPD’s provide access to fundamental quantities such as the quark orbital angular momentum that have not been accessible

21. GPDs Contain Much More Information than DIS
DIS only measures a cut at =0
Quark distribution q(x)
Antiquark distribution q(x)
qq distribution

22. Key experimental capabilities include:
Measuring the GPD’s
Key experimental capabilities include:
CW (100% duty factor) electron beams (permits fully exclusive reactions)
modern detectors (permit exclusive reactions at high luminosity)
adequate energy (~10 GeV to access the valence quark regime)
Measurements of the GPD’s are now feasible

23. Interpretation of the GPD’s
Analogy with form factors
Charge ↔ Form Factor å ò = × - M r m R to
relative
measured e d q F i cm ) ( 3
Parton Distribution ↔ GPD’s
Ref. Burkardt CM i b iq R
from
distance a at x
fraction
momentum
with
quarks of
density
parton is f
where r to
relative
measured e d q H ^ × - = å ò ) , ( @ 2

24. 3-dim picture Elastic Scattering Deep Inelastic Deep Exclusive
from Belitsky and Mueller
Elastic Scattering
Deep Inelastic
Deep Exclusive

25. Deep Exclusive Scattering
Inclusive Scattering Compton Scattering
Deeply Virtual Compton Scattering (DVCS)
Probes the nucleon quark structure and correlations
at the amplitude level

26. ) ( DVCS Bethe-Heitler + 2 Beam Spin Asymmetry e e’ p g dydtd dx d = T
GPD’s B
dydtd dx d = ( ) BH
DVCS T * 2 + Q e y x 3 1 8 p a f s
Beam Spin Asymmetry ~

27. DVCS Single-Spin Asymmetry
Q2 = 5.4 GeV2
x = 0.35
-t = 0.3 GeV2
CLAS experiment
E0 = 11 GeV
Pe = 80%
L = 1035 cm-2s-1
Run time: 2000 hrs
CLAS Collaboration
PRL 87, (2001)
Measure interference
between DVCS-BH e e’ p
GPD’s g

28. Meson Production as a Filter
Use quantum numbers of meson to select appropriate combinations of parton distributions in nucleon.
Pseudoscalers (polarized)
p0: Duv - ½ Ddv
h : Duv - ½ Ddv + 2Dsv
Vector Mesons (unpolarized)
rL0: u + u + ½ (d + d); g
wL0: u + u - ½ (d + d); g
fL0: s + s; g g*
Y(z)GjY(y)
Y(z)GiY(y) p p

29. Kinematics for deeply exclusive experiments
no overlap with other
existing experiments
compete with other
experiments

30. JLab 12 GeV Upgrade Project Status
Developed by CEBAF User Community in collaboration with JLab
Nuclear Science Advisory Committee 5-year Long Range Plan
Highlight in the 20-year plan of the Office of Science
Plan presented to Department of Energy
CD-0 (determination of ‘mission need’) April 2004
Preparations underway for CD-1 review in mid 2005
Construction
construction start expected in FY2008 (October 2007)
4 year construction project

31. Exciting Compelling Timely Physics Program at 12 GeV
Gluonic Excitations
3-dim view of the Nucleon
…and a whole complement
of other physics
Compelling
In view of recent progress
in lattice calculations
Timely