1. Physics Prospects with the JLab 12 GeV Upgrade
Elton S. Smith
Jefferson Lab
PANIC02
Osaka
Gluonic Excitations
3-dim view
of the Nucleon
Valence Structure

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

3. 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

4. Gluonic Excitations
Dynamical role of Glue
Confinement

5. 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

6. Understanding Confinement
The Ideal Experiment
The Real Experiment

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

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. 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

10. 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)

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

12. Families of Exotics g  ,, 1-+ nonet p1 IG(JPC)=1-(1-+)
h’1 IG(JPC)=0+(1-+)
h1 IG(JPC)=0+(1-+)
K1 IG(JPC)= ½ (1-)
p1  rp
h1  rb1 , wf
h’1  fw
Couple to V.M + e

13. 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

14. 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)

15. 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
Electron Beam from CEBAF

16. 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.

17. 3-dimensional view
of the Nucleon
Deep Exclusive Scattering

18. Generalized Parton Distributions
GPD’s provide access to fundamental quantities such as the quark orbital angular momentum that have not been accessible
and the GPD’s unify the description of inclusive and exclusive processes, connecting directly to the “normal” parton distributions:

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

20. 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

21. 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

22. 3-dim picture Elastic Scattering Deep Inelastic Deep Exclusive
from Belitsky and Mueller
Elastic Scattering
Deep Inelastic
Deep Exclusive

23. 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

24. Program to determine GPD’sep ep r H 2 , E 2 ↳ p + p - ~ ~ en p + H 2 , E 2 ~ ~ e p g H 2 , E 2 , H 2 , E 2 r ~ ~ e p ep g H , E , H , E r H ~ ~ e p en p + * E
Other Channels r e p eN
(h,p) e D p e Nw e (L,S) K

25. Deep Virtual Compton Scattering: A Window on Quark Correlations
DIS is limited by the fact that it can only measure longitudinal distributions averaged over all quarks in the nucleon
DIS corresponds exactly to the imaginary part of the Deep Compton Scattering amplitude
Add determination of the final state (by exclusive reactions such as DVCS) and we can (finally!) probe nucleon quark structure and correlations at the amplitude level

26. 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

27. Hard Meson Electroproduction (ro)
Physics issue: map out GPD’s (need to isolate sL)
Technique: determine sL from r →pp decay angle distribution
CLAS at 11 GeV
400 hrs at L = 1035 cm-2s-1 e’ p r
GPD’s e
sL ~ Q -6
sT ~ Q -8

28. Valence Quark Structure
of the Nucleon
Parton Distributions at large x

29. Enhanced Access to the DIS Regime
12 GeV will access the valence quark regime for x > 0.3
where constituent quark properties are not masked by the sea quarks

30. Predictions for large xBj
Proton Wavefunction (Spin and Flavor Symmetric) 1 ) ( 3 2 18 = - + S uu d ud u p
Nucleon Model
F2n/F2p
d/u
A1n
A1p
SU(6)
2/3
1/2
5/9
Valence Quark
1/4 1
pQCD
3/7
1/5

31. Valence Quark Distribution
Physics issue:
compare behavior of u and d quarks as xBj → 1
Experimental problem:
extract information from comparison of hydrogen and deuterium data
need to correct for nuclear effects in D
Solution for CEBAF upgrade:
compare DIS off 3He and 3H (nuclear effects ~ same)
SU(6)
Valence Quark
pQCD

32. The Neutron Spin Asymmetry A1n
Study of spin structure functions has been limited to the low-x region
JLab at 12 GeV with its high luminosity is a prime facility for measurements at large x
Jlab E (3He)
preliminary

33. Flavor Decomposition: (e,e’+)/(e,e’-)

34. 12 GeV Upgrade Project Status
Developed by CEBAF User Community in collaboration with JLab
Nuclear Science Advisory Committee, NSAC
plan presented during last 5-year Long Range Plan
recommended by NSAC for new construction
Plan presented to Department of Energy
presently waiting for CD-0 (determination of ‘mission need’)
Detailed report is being prepared to be reviewed by Jlab PAC in January
Construction
construction start expected in FY2007 (October 2006)
3 year construction project

36. CLAS++ Detector Forward Cerenkov Forward EC Forward DC Inner Cerenkov
Forward TOF
Preshower EC
Forward EC
Forward Cerenkov
Forward DC
Inner Cerenkov
Inner Calorimeter
Torus Cold Ring
Central Detector

37. SHMS - HMS Spectrometers After Upgrade
Max. Central Momentum 11 GeV/c GeV/c
Min. Scattering Angle deg deg
Momentum Resolution % -.2%
Solid Angle msr msr
Momentum Acceptance % %
Target Length Acceptance cm
Opening Angle with HMS 25 deg 16 deg
Configuration QQ(DQ)
Bend Angle deg

38. Exciting Compelling Timely Physics Program at 12 GeV
Gluonic Excitations
Valence Structure
of the Nucleon
3-dim view
Compelling
In view of recent progress
in lattice calculations
Timely

39. Electron-Light Ion Collider Layout
Ion Source
RFQ
DTL
Snake
CCL
Snake
Solenoids IR IR
5 GeV electrons
100 GeV light ions
Injector
5 GeV CEBAF with Energy Recovery
100 MV cryomodules
Beam Dump
Luminosity = 1035cm-2s-1
Lia Merminga