Research Perspectives at Jefferson Lab

1
Research Perspectives at Jefferson Lab

• Kees de Jager
• Jefferson Lab
• Duality05 Workshop
• LFN Frascati
• June 6-8, 2005

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CEBAF _at_ 12 GeV, WHY?

• Gluonic Excitations and the Origin of Confinement
  
• Developing a Unified Description of Hadron
  Structure
• Valence Quark Structure and Parton Distributions
  
• Form Factors Constraints on the GPDs
  
• The Generalized Parton Distributions (GPDs) as
  Accessed via Deep(ly) Exclusive Reactions
  
• Other Topics in Hadron Structure
  
• The Physics of Nuclei
  
• The Quark Structure of Nuclei (resolving the EMC
  effect)
• The Short-Range Behavior of the N-N Interaction
  and Its QCD Basis
• Quark propagation through Nuclear Matter
  (hadronization)
• Symmetry Tests in Nuclear Physics
  
• Precision Tests of the Standard Model
• Spontaneous Symmetry Breaking
  

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Enhanced Kinematical Access to the DIS Regime
12 GeV will access the regime (x gt 0.3), where
valence quarks dominate
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with enough luminosity to reach the high-Q2,
high-x region
Counts/hour/ (100 MeV)2 (100 MeV2) for L1035
cm-2 sec-1
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Gluonic Excitations
from Alex Dzierba
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Gluonic Excitations and the Origin of Confinement
The quarks in a meson are sources of a color
electric flux which is trapped in a flux tube
connecting the quarks. The formation of the flux
tube is related to the self-interaction of gluons
via their color charge.
From G. Bali
linear potential

• Flux tubes result in a linear confining potential
• Do flux tubes apply to light-quark systems?
• Very little is known about gluonic (or flux-tube)
  excitations

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Photons Preferred for Flux Tube Excitations
Normal mesons JPC 0- 1- 2-
First excited state of flux tube has JPC1- or
1- combined with S1 for quarks results in
JPC 0- 0- 1- 1- 2- 2-
exotic (mass 1.7 2.3 GeV)
Double-blind Monte Carlo simulation 2 exotic
signal clearly visible
Photons couple to exotic mesons via g VM
transition (same spin configuration)
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Strategy for Exotic Meson Search

• Use photons to produce meson final states with a
  mass up to 2.5 GeV
• 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

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Hadron Structure
from Zein-Eddine Meziani and Volkert Burkert
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Unpolarized Neutron to Proton ratio

• Impact
• determine valence d quark momentum distribution
• extract helicity dependent quark distributions
  through inclusive DIS
• high x and Q2 background in high energy particle
  searches.
• construct moments of structure functions

• In the large x region (xgt0.5) the
• ratio F2n/F2p is not well determined
• due to the lack of a free neutron target

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Unpolarized Neutron to Proton ratio
DIS from A3 nuclei
Spectator tagging

• Mirror symmetry of A3 nuclei
• Extract F2n/F2p from ratio of 3He/3H structure
  functions and superratio R
• R ratio of EMC ratios for 3He and 3H
  can be calculated to within 1
• Most systematic and theoretical uncertainties
  cancel

• Nearly free neutron target by tagging
  low-momentum proton from deuteron at backward
  angles
• Small p (70-100 MeV/c)
• Minimize on-shell extrapolation (neutron only 7
  MeV off-shell)
• Backward angles (?pqgt 110o)
• Minimize final-state interactions

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Unpolarized Neutron to Proton Ratio
Hall C 11 GeV with HMS
Hall B 11 GeV with CLAS12
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Inclusive measurements of asymmetries
A1n at 11 GeV
A1p at 11 GeV
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Flavor decomposition
At RHIC with W production
Ee 11 GeV polarized NH3 and 3He
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Flavor decomposition polarized sea

• Predictions
• Instantons (cQSM)

• First data from HERMES
• ? 0

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Quark-gluon correlations and g2
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g2 at JLab with 11 GeV
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Moments of Structure Functions
target mass correction term
dynamical twist-3 matrix element
dynamical twist-4 matrix element

• Both d2 and f2 are required to determine the
  color polarizabilities
• To extract f2, d2 needs to be determined first

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Color Polarizabilities
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d2 with 11 GeV at JLab
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Charged Pion Electromagnetic Form Factor

• Where does the dynamics of the q-q interaction
  make a transition from
• the strong QCD (confinement) to the pQCD
  regime?
• It will occur earliest in the simplest systems
• the pion form factor Fp(Q2) provides a good
  starting system to
• determine the relevant distance scale
  experimentally

• In asymptotic region, F? ? 8??s ƒ ? Q-2

HMSSHMS (11 GeV) projection
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Proton Charge Form Factor
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CLAS 12 Neutron GMn
With 12 GeV Upgrade
eD en(ps) ep epn
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GPDs Deeply Virtual Exclusive Processes

handbag mechanism
Deeply Virtual Compton Scattering (DVCS)
x
g
x longitudinal quark momentum fraction
xx
x-x
2x longitudinal momentum transfer
t
xB
x

2-xB
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Kinematics Coverage of the 12 GeV Upgrade
JLab Upgrade
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DVCS SSA Measures phase and amplitude directly
DVCS at 11 GeV can cleanly test correlations in
nucleon structure (data shown 2000 hours)
DVCS and Bethe-Heitler are coherent ? can
measure amplitude AND phase
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DVCS/BH Transverse Target Asymmetry
Transversely polarized target
Ds sinfImk1(F2H F1E) df
AUTx Target polarized in scattering plane
AUTy Target polarized perpendicular to
scattering plane
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Exclusive ?0 production on transverse target
2D (Im(AB))/p
T
A 2Hu Hd
AUT -
r0
A2(1-x2) - B2(x2t/4m2) - Re(AB????2
B 2Eu Ed
A Hu - Hd B Eu - Ed
r
Asymmetry depends linearly on the GPD E, which
enters Jis sum rule.
CLAS12
K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001
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Physics of Nuclei
from Will Brooks
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Unpacking the EMC effect

• With 12 GeV, we have a variety of tools to
  unravel the EMC effect
• Parton model ideas are valid over fairly wide
  kinematic range
• High luminosity
• High polarization
• New experiments, including several major
  programs
• Precision study of A-dependence xgt1 valence
  vs. sea
• g1A(x) Polarized EMC effect influence of
  nucleus on spin
• Flavor-tagged polarized structure functions
  ?uA(xA) and ?dA(xA)
• x dependence of axial-vector current in nuclei
  (can study via parity violation)
• Nucleon-tagged structure functions from 2H and
  3He with recoil detector
• Study x-dependence of exclusive channels on
  light nuclei, sum up to EMC

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Hadronization
How do energetic quarks transform into hadrons?
How quickly does it happen? What are the
mechanisms?
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Expected Results on Hadronization
12
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Parity Violation
from Krishna Kumar
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Electron-Quark Phenomenology
V
A
A
V
C1u and C1d will be determined to high precision
by other experiments C2u and C2d are small and
poorly known can be accessed in PV DIS
New physics such as compositeness, new gauge
bosons
Deviations to C2u and C2d might be fractionally
large
Proposed JLab upgrade experiment will make it
possible to improve knowledge of 2C2u-C2d by more
than a factor of 20
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Parity Violating Electron DIS
e-
e-
?
Z
X
N
fi(x) are quark distribution functions
For an isoscalar target like 2H, structure
functions largely cancel in the ratio
Provided Q2 gtgt 1 GeV2 and W2 gtgt 4 GeV2 and x
0.2 - 0.4
Must measure APV to fractional accuracy better
than 1

• 11 GeV at high luminosity makes very high
  precision feasible
• JLab is uniquely capable of providing beam of
  extraordinary stability
• Systematic control of normalization errors being
  developed at 6 GeV

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2H Experiment at 11 GeV
?lab 12.5o
E 5.0 GeV 10
60 cm LD2 target
Ibeam 90 µA

• Use both HMS and SHMS to increase solid angle
• 2 MHz DIS rate, p/e 2-3

APV 217 ppm
xBj 0.235, Q2 2.6 GeV2, W2 9.5 GeV2

• Advantages over 6 GeV
• Higher Q2, W2, f(y)
• Lower rate, better p/e
• Better systematics 0.7

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Physics Implications
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PV DIS and Nucleon Structure

• Analysis assumed control of QCD uncertainties
• Higher twist effects
• Charge Symmetry Violation (CSV)
• d/u at high x
• NuTeV provides perspective
• Result is 3? from theory prediction
• Raised very interesting nucleon structure issues
  cannot be addressed by NuTeV
• JLab at 11 GeV offers new opportunities
• PV DIS can address issues directly
• Luminosity and kinematic coverage
• Outstanding opportunities for new discoveries
• Provide confidence in electroweak measurement

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Search for CSV in PV DIS

• u-d mass difference
• electromagnetic effects

• Direct observation of parton-level CSV would be
  very exciting
• Important implications for high-energy collider
  pdfs
• Could explain significant portion of the NuTeV
  anomaly

Sensitivity will be further enhanced if ud
falls off more rapidly than ?u-?d as x -gt 1
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APV in DIS on 1H
small corrections

• Allows d/u measurement on a single proton
• Vector quark current (electron is axial-vector)

• Determine that higher twist is under control
• Determine standard model agreement at low x
• Obtain high precision at high x

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d/u at High x
Deuteron analysis has nuclear corrections
APV for the proton has no such corrections
Must simultaneously constrain higher twist effects
The challenge is to get statistical and
systematic errors 2
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Large Acceptance Concept

• CW 90 µA at 11 GeV
• 40-60 cm liquid H2 and D2 targets
• Luminosity gt 1038/cm2/s

JLab Upgrade
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Add new hall
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6 GeV CEBAF
11
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Hall A w/ 2.2, 4.4, 6.6, 8.8 and 11 GeV Beam

• Retain High Resolution Spectrometer (HRS) pair
  for the continuation of research in which energy
  resolution comparable to nuclear level spacing is
  essential
• Use the hall infrastructure to support
  specialized large-installation experiments

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CLAS12 - Acceptance for DVCS
Occupancy of DVCS events
ep epg
Q2 gt 2.5 GeV2
E 11 GeV
Kinematic Limit
Central Detector
Forward Detector
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CLAS12
Preshower EC (not visible)
Forward EC
Low Threshold Cerenkov Counter (LTCC)
Forward Drift Chambers
Forward TOF
High Threshold Cerenkov (HTCC)
New Torus Coils
Central Detector
Beamline
Inner EC (not visible)
Reused CLAS element
Coil EC
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Hall C The SHMS and HMS
SuperHMS
HMS
SOS
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GlueX Detector
Lead Glass Detector
Barrel Calorimeter
Solenoid
Coherent Bremsstrahlung Photon Beam
Time of Flight
Note that tagger is 80 m upstream of detector
Tracking
Cerenkov Counter
Target
Electron beam from CEBAF
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DOE Critical Decisions
CD DOE Meaning Implications of CD Approval Time
CD-0 Approve Mission Need Formal CDR work begins using DOE funds RD for CDR begins PED funds can be requested Acquisition plan developed Serious search for non-DOE/NP funding April 2004
CD-1 Approve Preliminary Baseline Range Lehman review of CDR and approval PED funds can be spent August 2005
CD-2 Approve Performance Baseline Second Lehman review to establish budget, schedule and performance Long-lead procurements begin Request construction funding 2006/7 ??
CD-3 Approve Start of Construction Construction begins in earnest 2008/9 ??
CD-4 Approve Start of Operations Science begins! 2013 ??
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Status of 12 GeV project

• The 12 GeV JLab upgrade, a formal recommendation
  of the NSAC Long Range Plan, will permit a major
  step forward in the study of strong QCD and
  hadron structure
• Substantial progress has been made toward
  refining the experimental program and equipment
  designs
• DOE has provided a mission need statement (CD-0
  approval)
• A recent DOE review of the science program was
  highly supportive
• JLab is in the process of obtaining CD-1 approval
• International involvement is essential to move
  this exciting project forward rapidly

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Highlights of the 12 GeV Program

• Exploration of QCD in the Nonperturbative Regime
• Existence and properties of exotic mesons
• Detailed study of hadronic structure
• Revolutionize Our Knowledge of Spin and Flavor
  Dependence of Valence PDFs
• Revolutionize Our Knowledge of Distribution of
  Charge and Current in the Nucleon
• Totally New View of Hadron (and Nuclear)
  Structure
• GPDs, Determination of the quark angular momentum
• Nuclear Structure in Terms of QCD
• Spin and flavor dependence of EMC Effect
• Study quark propagation through nuclear matter
• Parity Violation in Deep Inelastic Scattering
• Factor 20 improvement in (2C2u-C2d)
• Sensitive tests of Charge Symmetry Violation
  valence region