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JLab Physics Overview

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Title: JLab Physics Overview


1
JLab Physics Overview
Xiaochao Zheng Univ. of Virginia April 17, 2009
  • The Standard Model of Particle Physics What are
    the Challenges?
  • Introduction to Electron Scattering
  • Thomas Jefferson National Accelerator Facility
    (JLab)
  • Recent Research Highlights from JLab
  • Parity Violation in Deep Inelastic Scattering
  • Summary and Outlook

2
What is the Visible World Made of?
3
And How Do They Interact with Each Other?
SU(3)C
SU(2)L X U(1)Y
4
Standard Model of Particle Physics
  • Success of the Standard Model
  • Electro-weak theory tested to very good precision
  • QCD tested in the high energy (perturbative,
    weak) region
  • Major Challenges within the Standard Model
  • Understand and test QCD in extreme conditions
    (RHIC, LHC)
  • Understand and test QCD in strong interaction
    region (non-perturbative)
  • Understand the nucleon structure, how quarks and
    gluons form the nucleon's mass, momentum, and spin

aS
energy (GeV) (1/distance)
5
Standard Model of Particle Physics
  • Success of the Standard Model
  • Electro-weak theory tested to very good precision
  • QCD tested in the high energy (perturbative,
    weak) region
  • Major Challenges within the Standard Model
  • Understand and test QCD in extreme conditions
    (RHIC, LHC)
  • Understand and test QCD in strong interaction
    region (non-perturbative)
  • Understand the nucleon structure how quarks and
    gluons form the nucleon's mass, momentum, and spin

typically studied by lepton scattering on the
nucleon/nucleus
6
Studying Nucleon Structure Using Electron
Scattering
  • Success of the Standard Model
  • Electro-weak theory tested to very good
    precisions
  • QCD tested in the high energy (perturbative,
    weak) region
  • Major Challenges within the Standard Model
  • Understand and test QCD in extreme conditions
    (RHIC, LHC)
  • Understand and test QCD in strong interaction
    region (non-perturbative)
  • Understand the nucleon structure how quarks and
    gluons form the nucleon's mass, momentum, and spin

typically studied by lepton scattering on the
nucleon/nucleus
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11
Current Knowledge of Nucleon Unpolarized
Structure
3.5 3 2.5 2 1.5 1 0.5 0
10 9 8 7 6 5 4 3 2 1 0
F2(x,Q2)c(x)
F2(x,Q2)c(x)
Phys. Rev. D 66, 010001 (2002)
0.1 1.0 10 102 103 104 105
106
0.1 1.0 10
102
Q2(GeV2)
Q2(GeV2)
12
Structure Functions in the Quark-Parton Model
in the infinite momentum frame (IMF) x fraction
of nucleon's momentum carried by a particular
quark
(P 8)
  • After 35 years of DIS experiments, the
    unpolarized structure of the nucleon is
    reasonably well understood (for moderate xBj
    region).

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Scientific Mission
  • How are hadrons constructed from quarks and
    gluons of QCD?
  • What is the QCD basis for the nucleon-nucleon
    force?
  • Where are the limits of our understanding of
    nuclear structure?
  • To what precision can we describe nuclei?
  • To what distance scale can we describe nuclei?
  • Where does the transition from nucleon-meson to
    QCD quark-gluon description occur?
  • To make progress toward these research goals we
    must address critical issues in strong QCD
  • What is the mechanism of confinement?
  • Where does the dynamics of the q-q interation
    make a transition from the strong (confinement)
    to the perturbative QCD regime?
  • How does Chiral symmetry breaking occur?
  • Symmetry Tests in Nuclear Physics

15
Scientific Mission
  • How are hadrons constructed from quarks and
    gluons of QCD?
  • What is the QCD basis for the nucleon-nucleon
    force?
  • Where are the limits of our understanding of
    nuclear structure?
  • To what precision can we describe nuclei?
  • To what distance scale can we describe nuclei?
  • Where does the transition from nucleon-meson to
    QCD quark-gluon description occur?
  • To make progress toward these research goals we
    must address critical issues in strong QCD
  • What is the mechanism of confinement?
  • Where does the dynamics of the q-q interation
    make a transition from the strong (confinement)
    to the perturbative QCD regime?
  • How does Chiral symmetry breaking occur?
  • Symmetry Tests in Nuclear Physics

16
CEBAF _at_ JLab Today
  • Main Physics Programs
  • nucleon electromagnetic form factors (including
    strange f.f.)
  • N -gtN electromagnetic transition form factors
  • spin structure of the nucleon
  • form factor and structure of light nuclei
  • nuclear medium effects (EMC effects)
  • Standard Model test (parity violation in electron
    scattering)
  • ... ...

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JLab Accelerator
Recirculation arcs
Helium Refrigerator
20 cryomodules
45 MeV Injector
0.4-GeV linac
20 cryomodules
End Stations
19
The Accelerator (CEBAF)
NORTH LINAC
SOUTH LINAC
INJECTOR
RECIRCULATION ARCs (Magnets)
C
A
B
EXPERIMENTAL HALLS
20
Three Experimental Halls
  • Hall A
  • pair of high resolution spectrometers (HRS), E'
    up to 4 GeV/c, 7 msr
  • luminosity up to 1039 cm-2 s-1
  • Hall B
  • CEBAF Large Acceptance Spectrometer (CLAS)
  • luminosity up to 1034 cm-2 s-1
  • Hall C
  • High Momentum (HMS and Short-Orbit Spectrometers
    (SOS)
  • luminosity up to 1039 cm-2 s-1

21
Recent Highlights of JLab Research (a very limit
number of)
22
Nucleon Form Factors
  • e-nucleon elastic cross section determined by the
    EM form factors
  • In the Breit (centre-of-mass) frame the Sachs FF
    can be written as the Fourier transforms of the
    charge and magnetization radial density
    distributions.
  • Two different methods have been carried out so
    far
  • Rosenbluth separation
  • Polarization transfer

23
JLab Data on the EM Form Factors Provide a
Testing Ground for Theories Constructing Nucleons
from Quarks and Glue
Neutron
Proton
Electric
Magnetic
24
JLab Polarization-Transfer Data
  • Polarization transfer data from JLab Hall A
  • E93-027 PRL 84, 1398 (2000)
  • E99-007 PRL 88, 092301 (2002)
  • Investigate possible experimental sources for
    discrepancy
  • optimized Rosenbluth experiment confirmed SLAC
    results
  • Investigate possible theoretical sources for
    discrepancy
  • ? two-photon contributions

25
Nucleon Spin Structure Experiments
  • Inclusive
  • Sum Rules GDH, Bjorken .. ...
  • Nucleon structure functions and asymmetries
  • spin asymmetry A1 at high x (valence quark
    structure)
  • structure function g2 at low Q2
  • test of the spin duality.

Longitudinal
  • Semi-inclusive.
  • Exclusive DVCS ... ...

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What Makes the Large x Region Interesting?
28
Pre-JLab Data on A1n
  1. Bag Model
  2. LSS(BBS)
  3. BBS
  4. Duality
  5. CQM
  6. LSS 2001
  7. Statistical Model
  8. SU(6)
  9. Chiral Soliton 1
  10. Chiral Soliton 2

29
A1n Results
  • First time A1n turns positive
  • Indicate the importance of quark orbital angular
    momentum to the nucleon spin

X. Zheng et al., Phys. Rev. Lett. 92, 012004
(2004) Phys. Rev. C 70, 065207 (2004)
30
Data for Dq/q
  • Before JLab
  • With JLab Data

31
Parity Violation Deep Inelastic Scattering (PVDIS)
32
Electroweak Interaction The Standard Model
  • Weak charged currents given by a SU(2)L group
    with weak isospin T
  • But the observed neutral current couples to
    right-handed fermions, while neutral current from
    SU(2)L does not.

33
Electroweak Interaction The Standard Model
  • Weak charged currents given by a SU(2)L group
    with weak isospin T
  • Combine neutral current from SU(2)L and QED
    UEM(1)g to construct

completes SU(2)L
U(1)Y, Y weak hyper charge
observable
theory
photon
Z0
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Challenges of the Standard Model
  • Standard Model works well at present energy
    range
  • But, there are many conceptual reasons for new
    physics

(250 GeV
5 x 1014 GeV 2.4 x 1018 GeV)?
  • Data exist cannot be explained by the SM ( mn,
    NuTeV anomaly...)

36
Challenges of the Standard Model
  • Standard Model works well at present energy
    range
  • But, there are many conceptual reasons for new
    physics

High energy direct searches LEP, LHC
indirect searches E158, NuTeV, Qweak, PVDIS
(250 GeV
5 x 1014 GeV 2.4 x 1018 GeV)?
  • Data exist cannot be explained by the SM ( mn,
    NuTeV anomaly...)

37
Test of The Standard Model
  • Direct searches (LHC)
  • Indirect searches
  • Search for forbidden processes (bb-decay, EDM ...
    ...)
  • New physics modify
    at low energies

(expected)
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Neutral Weak Couplings from Charged Lepton
Scattering
  • Asymmetries (ratios) in charged lepton-N
    scattering can be used to measure products

lepton charge conjugate-violating eL, eR cross
sections
parity-violating eL, eR cross sections
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PV DIS and Other SM Test Experiments
  • E158/Moller (SLAC)
  • NuTeV (FNAL)
  • Atomic PV
  • Weak CC and NC difference
  • Nuclear structure?
  • Other hadronic effects?
  • Purely leptonic
  • Coherent Quarks in the Nucleus
  • - 376C1u - 422C1d
  • Nuclear structure?
  • Qweak (JLab)
  • PVDIS (JLab)

Different Experiments Probe Different Parts of
Lagrangian, PVDIS is the only one accessing C2q
  • 2 (2C1uC1d)
  • Coherent quarks in the proton
  • (2C1u-C1d)Y(2C2u-C2d)
  • Isoscalar quark scattering

Cartoons borrowed from R. Arnold (UMass)
43
PVDIS Experiment Past, Present and Future
  • 1970's, result from SLAC E122 consistent with
    sin2qW1/4, established the Electroweak Standard
    Model

C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978)
  • PVDIS asymmetry has the potential to explore New
    Electroweak Physics etc ...... However, hasn't
    been done since 1978.
  • (Re)start PVDIS at JLab 6 12 GeV

44
JLab 6 GeV Experiment 08-011
Co-spokesperson contact X.
Zheng Co-spokesperson P.E. Reimer, R.
Michaels Grad. students Xiaoyan Deng, Diancheng
Wang, Huaibo Ding. (Hall-A Collaboration
Experiment, approved by PAC27, re-approved by
PAC33 for 32 days, rated A-)
  • Use 85mA, 6 GeV, 80 polarized beam on a 25-cm
    LD2 target
  • Two Hall A High Resolution Spectrometers detect
    scattered electrons
  • Measure PV asymmetry Ad at Q21.10 and 1.90 GeV2
    to 2.7 (stat.)
  • Ad at Q21.10 will investigate the possible
    higher twist effects
  • If HT is small, can extract 2C2u-C2d from Ad at
    Q21.90 to 0.04 (or with reduced precision if
    higher twists are un-expectedly large)
  • Schedule to run Nov-Dec. 2009.

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Outlook Research Opportunities at JLab 2010-
  • 6 GeV (2010-2014)
  • Hall A
  • Nuclear physics short-range correlations,
  • Deeply Virtual Compton Scattering (DVCS),
    measurements of Generalized Parton Distributions
    (GPD).
  • Hall B Analysis of nucleon resonance data
  • Hall C
  • Qweak test of the Standard Model

Compton polarimeter (laser, detectors)
  • 12 GeV (2015 - )
  • Hall A PVDIS program using a large solenoid
    device

47
Outlook Research Opportunities at JLab 2010-
  • 6 GeV
  • Hall A
  • Nuclear physics short-range correlations,
  • Deeply Virtual Compton Scattering (DVCS),
    measurements of Generalized Parton Distributions
    (GPD).
  • Hall B Analysis of nucleon resonance data
  • Hall C
  • Qweak test of the Standard Model

Joint-training students can participate in all
these experiments
Compton polarimeter (laser, detectors)
  • 12 GeV
  • Hall A PVDIS program using a large solenoid
    device

As a group, can pursue detector development
48
Existing Chinese Collaborations
  • Hall A
  • Neutron spin structure experiments
  • University of Science and Technology of China,
    Prof. Yunxiu Ye, Dr. Hai-jiang Lu, Ph.D. student
    Yi Zhang (with Dr. Jian-ping Chen, JLab)
  • China Atomic Energy Institute, Prof. Shuhua Zhou,
    Prof. Xiaomei Li (with Dr. Jian-ping Chen, JLab)
  • Neutron transversity experiments
  • Beijing University, Prof. Bo-qiang Ma, Prof.
    Yajun Mao (with Prof. Haiyan Gao, Duke Univ.)
  • Hall B (with Prof. Liping Gan, Univ. of North
    Carolina-Wilmington)
  • PrimEx (Primakoff Experiment to measure ?0
    lifetime)
  • CIAE, Prof. Xiaomei Li,
  • Hall C (with Dr. Li-guang Tang, Hampton Univ.)
  • Hyper-nuclear experiments
  • Lanzhou University, Prof. Bitao Hu

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PVDIS Experiment Past, Present and Future
  • 1970's, result from SLAC E122 consistent with
    sin2qW1/4, established the Electroweak Standard
    Model

C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978)
  • PVDIS asymmetry has the potential to explore New
    Physics, study hadronic effects/CSV ......
    However, hasn't been done since 1978.
  • Do a first measurement at JLab 6 GeV
  • If observe a significant deviation from the SM
    value, it will definitely indicate something
    exciting
  • Indicate either electroweak new physics, or
    current understanding of strong interaction is
    worse than we thought.
  • New electroweak Physics
  • Non-perturbative QCD (higher-twist) effects
  • Charge symmetry violation

At the 6 GeV precision
Likely to be small, but need exp confirmation
Small from MRST fit (90 CL 1)
51
PVDIS Experiment Past, Present and Future
  • 1970's, result from SLAC E122 consistent with
    sin2qW1/4, established the Electroweak Standard
    Model

C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978)
  • PVDIS asymmetry has the potential to explore New
    Physics, study hadronic effects/CSV ......
    However, hasn't been done since 1978.
  • Do a first measurement at JLab 6 GeV
  • If observe a significant deviation from the SM
    value, it will definitely indicate something
    exciting
  • Indicate either electroweak new physics, or
    current understanding of strong interaction is
    worse than we thought.
  • At 12 GeV, a larger, well-planned PVDIS program
    could separate all three New Physics, HT, CSV,
    important information for both EW and Strong
    interaction study.

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Apparatus Needed for PVDIS
Large Acceptance and High Luminosity
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Plan View of the Spectrometer
BaBar Solenoid?
56
Shashlyk (Shashlik) Calorimeter
  • pi/e rejection 10(-2-3) at E0.44 GeV/c based
    on energy resolution
  • dE/E 1.46.7/sqrtE(GeV)
  • time resolution 1ns
  • radiation hard
  • can work in mag fields

can cut/isolate detector here to form a
double-layer struct. for improved PID
NIM A320, 144 (1992)
57
Shashlyk (Shashlik) Calorimeter
58
Scaling Violation in QCD
  • Bjorken limit , xBj fixed, (strict) one
    photon exchange

no scale (Q2 )dependence, scaling
  • High , soft gluon emission,

logQ2 dependence
  • Low , hard gluon emission

1/(Q2)(t-2) dependence higher-twist effects
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JLab Hall A

62
Hall B CLAS

63
Hall C View

64
Medium and High Energy Physics Facilities in
Europe and U.S.
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