1. The Physics Program at an Upgraded Jefferson Lab
Cynthia Keppel
Hampton University / Jefferson Lab
DIS 2005
Madison, WI
Highlights of the 12 GeV Program
determination of spin and flavour structure in the valence region
exploration of the 3 dimensional picture of the nucleon
physics of nuclei
search for gluonic exitations

2. CEBAF @ JLab Today Main physics programs
nucleon electromagnetic form factors
strange form factors
N → N* electromagnetic transition form factors
(spin) structure functions of the nucleon
physics of nuclei and hypernuclei
Superconducting recirculating electron accelerator
max. energy 5.7 GeV
max current 200 mA
e polarization 80%
Simultaneous operation in 3 halls
2 high luminosity halls (L=1039)
large Acceptance Spectrometer for e and g induced reaction (L=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. Major Components to Achieve 12 GeV
upgrade of injector energy from 70 MeV to 130 MeV by adding recirculation
upgrade of linac energy from 0.6 GeV/linac to 1.1 GeV/linac by adding 5 new 100 MeV cryomodules to each linac
cryomodule technology advancements allow for doubling the acceleration in one-fourth the space via higher gradient and increased effective accelerating length
Original CEBAF: 20 MV achieved
Present CEBAF average: 28 MV (max=34MV) achieved
SL21 70 MV achieved
FEL3 80 MV achieved
Spec for Renascence 98 MV under construction
Required for 12 GeV 98 MV designed
build new cryogenics plant to double present capacity to 9kW
convert existing dipole magnets from C-magnets to H-magnets
result:
Continuous wave (CW) operation preserved
Minimize disruption to research program (~1 year)
Lower pass numbers also available with 12 GeV delivery (2.2/4.4/6.6/8.8 GeV)
Maximum beam current to Halls A and C (~80 mA), and Halls B and D (~5 mA)

5. Enhanced Equipment in Halls A, B, & C and a New Hall D
9 GeV tagged polarized photons and a 4 hermetic detector D C
Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles B
High Resolution Spectrometer (HRS) Pair,
and specialized large installation experiments A
CLAS upgraded to higher (1035) luminosity and coverage

6. Charged Pion Electromagnetic Form Factor
Where does the dynamics of the q-q interaction make a transition from
the strong (confinement) to the perturbative QCD regime?
It will occur earliest in the simplest systems
 the pion form factor Fp(Q2) provides our best chance to
determine the relevant distance scale experimentally
There are dozens of predictions…
Hall C E results, and E and 12 GeV projections

7. Proton & Neutron Electromagnetic Form Factors
(Polarization Experiments only)
Here shown as ratio of Pauli & Dirac Form Factors F2 and F1.
Taking orbital angular momentum into account  ln2(Q2/L2)Q2F2/F1  constant (Ji)

8. The Neutron to Proton Structure Function Ratio,
Extending DIS to High x
The Neutron to Proton Structure Function Ratio,
d(x)/u(x) pdf Ratio
current uncertainties quite large!
u(x)
d(x)
F2n / F2p
Add overlay of 6 GeV data obtained to date (need to “stretch” to get on graph properly) x
12 GeV will access the valence quark regime (x > 0.3)

9. An Effective Free Neutron Targetp n
Can also use 3H/3He mirror nuclei

10. Extending DIS to High x, continued..
The Neutron Asymmetry A1
The Proton Asymmetry A1
SU(6) breaking
pQCD
valence quark models
SU(6) symmetric
Add overlay of 6 GeV data obtained to date (need to “stretch” to get on graph properly) x

11. Flavor Decomposition using SIDIS
Sea quarks ?
Valence quarks
quark polarization asymmetries
Ee =11 GeV NH3+He3
Ee =11 GeV NH3+ND3
Unprecedented precision for valence quarks, discriminating power for sea quarks test models for quark polarization

12. kT-dependent parton distributions
Semi-Inclusive Deep Inelastic Scattering (SIDIS):
Probes orbital motion of quarks through quark transverse momentum distribution
Access to new PDFs not accessible in inclusive DIS.
Off-diagonal PDFs vanish if quarks only in s-state! In addition T-odd PDFs require FSI (Brodsky et al., Collins, Ji et al. 2002)
Mulders
Note mes
transversity
Sivers
Factorization of kT-dependent PDFs proven at low PT of hadrons (Ji et al)
Universality of kT-dependent distribution and fragmentation functions proven (Collins,Mets…)

13. Azimuthal Asymmetry – Sivers Effect
Originates in the quark distribution. Probes orbital angular momentum of quarks by measuring the imaginary part of s-p-wave interference in the amplitude.
f1T D1
AUT ~ k
sin(f-fs) T

14. quark flavor polarization
3D Images of the Proton’s Quark Content
M. Burkardt PRD 66, (2002)
b - Impact parameter T
u(x,b )
transverse polarized target
uX(x,b ) T
dX(x,b ) T
d(x,b ) T
quark flavor polarization
Accessed in Single Spin
Asymmetries. Hu Eu
Needs: Hd Ed

15. Beyond form factors and quark distributions –
Generalized Parton Distributions (GPDs)
X. Ji, D. Mueller, A. Radyushkin ( )
Proton form factors, transverse charge & current densities
Structure functions,
quark longitudinal
momentum & helicity
distributions
Correlated quark momentum
and helicity distributions in
transverse space - GPDs

16. Limiting Cases for GPDs
Ordinary Parton Distributions (D, t, x → 0)
H0(x,0) = Dq(x) polarized ~
H0(x,0) = q(x) unpolarized
Nucleon Form Factors (Sum Rules)
x P
(x-x) P
Dirac E H ~ ,
Axial vector P
PD
Pauli 2 D = t
Pseudoscalar
difference in momentum fraction between initial and final state parton
momentum transfer to the nucleon

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

18. 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
Many x, Q2 and t values measured simultanously !

19. …an unprecedented level of depth to nucleon structure studies….
Transverse Momentum Dependent GPDs (TMDs)
FFs F1pu(t),F2pu(t)..
x=0,t=0 dx
d2kT
(FT)
GPDs: Hpu(x,x,t), Epu(x,x,t),…
GPD
Measure momentum transfer to nucleon.
Probability to find a quark u in a nucleon P with a certain polarization in a position r and momentum k
Wpu(x,k,r) “Parent” Wigner distributions
TMD PDFs: fpu(x,kT),g1,f┴1T, h┴1L
d3r
d2kT
Measures momentum transfer to quark.
TMD
PDFs fpu(x), g1, h1
…an unprecedented level of depth to nucleon structure studies….

20. Quark Structure of Nuclei: Origin of the EMC Effect
Observation that structure functions are altered in nuclei stunned much of the HEP community 23 years ago
~1000 papers on the topic; BUT more data are needed to uniquely identify the origin: What alters the quark momentum in the nucleus? x
JLab 12
Jlab at 12 GeV
Precision study of A-dependence
Measurements at x>1
“Polarized EMC effect”
Flavor-tagged (polarized) structure functions
valence vs. sea contributions
Explain what the EMC effect is.
Point out the three regions and their conventional explanations.
Cannot be fully explained by conventional nuclear physics
Amazing that we still don’t know the answer after nearly a quarter of a century
Coverage extends at least to x=1.5

21. Nuclear effects in Hadronisation
h = p, K, h, w, f, p, .…
In general,
Significant dependence
of R on
Must measure
multi-variable dependence
for stringent model tests!
n (GeV) z
<z>= , <Q2>=
<n>= , <Q2>=
Introduce simpler form that represents primary measurements first
In parton model, ratio of sums of products of distribution function and fragmentation functions
These are the typical patterns of absorption
Discuss the simple interpretations of nu (time dialation) and z from gluon bremsstrahlung picture
Note that gluon emission = energy loss = attenuation in z
Second, discuss multivariable dependence.
Go into role of nu, z, pt, Q2 for nuclei :
z, gluon emission; nu,Lorentz boost; Pt, in-medium correlations, Q2, size of initial quark; Mention SSA
Explain that multi-variable dependence is needed to get hadronization mechanism, and to wring out models – 1D doesn’t do it
Don’t be negative about HERMES

22. Gluonic Excitations Gluonic Excitations predicted by QCD
crucial for understanding confinement
quantum numbers of the excited gluonic fields couple to those of the quarks to produce mesons with exotic quantum numbers
mass spectra calculated by lattice QCD
possibility for experimental search
From G. Bali

23. 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

24. Meson Map exotic nonets Lattice 1-+ 1.9 GeV 2+- 2.1 GeV 0+- 2.3 GeV
Radial
excitations
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
Meson Map
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)

25. 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
Perform partial-wave analysis
identify quantum numbers as a function of mass
check consistency of results in different decay modes

26. GlueX / Hall D Detector 12 GeV electrons Lead Glass Barrel Detector
collimated
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

27. Milestones and Timelines for 12 GeV
Development of Science Case and Exp.Equiment
April Recommendation by NSAC Long Range Planning
April DOE Approval of Mission Need (CD-0)
Development of Conceptual Design Report
Oct GlueX Detector Review
Jan Review of Spectrometer Options
April DOE Science Review of the 12 GeV Upgrade
(very positive response ! )
Sept Critical Decision on Prel. Baseline Range (CD-1)
Engineering and Design
Construction
Beam on Target

28. Summary
CEBAF 6 GeV has provided results with unprecedented precision on structure functions and form factors (including strangeness)
Upcoming years will highlight precision hypernuclear studies, standard model tests and . . .
The Upgrade to 12 GeV is essential to provide access
to new kinematic regions and will:
determine with extreme precision the spin and flavour structure
of the nucleon in the valence region
provide a totally new and complete view of the nucleon structure
access to quark angular momentum
finally (after > 30 years) determine the origin of the EMC effect
test our understanding of quark confinement
and much much more . . .

29. ELIC Layout IR IR IR IR IR
(Derbenev, Chattopadhyay, Merminga et al.)
One accelerating & one decelerating pass through CEBAF
(A=1-40)
Ion Linac and pre -
booster IR
Beam Dump
Snake
CEBAF with Energy Recovery 3
7 GeV
electrons 30
150 GeV light ions
Solenoid
Ion Linac and pre
Ion Linac and pre
Electron Cooling - -
booster
booster IR IR IR IR
Solenoid
Solenoid
Snake
Snake 3 3 - -
7 GeV
7 GeV
electrons
electrons 30 30 - -
150 GeV (light) ions
150 GeV light ions
Electron Injector
CEBAF with Energy Recovery
CEBAF with Energy Recovery
Beam Dump
Beam Dump

30. Luminosity Potential with eRHIC/ELIC
eRHIC: 10 GeV Electrons on 250 GeV Protons (up to Pb)
@SPIN2004 mention of 20 GeV Electrons in Linac-Ring Option
ELIC : 7 GeV Electrons on 150 GeV Protons (up to Ca)
25 GeV
TESLA-N
ELIC
ELIC Luminosity
LINAC-RING?
eRHIC
8x1034 cm-2sec-1
(per interaction point,
one day lifetime)
x100
EIC
x8,000
Precision
Frontier