PR-05002:

1
PR-05002

• Dipangkar Dutta
• TUNL/Duke University

Hall A Collaboration Experiment
Dipangkar Dutta, Haiyan Gao and Roy Holt
Spokespersons
2
Outline

• Introduction
• Motivation
• Proposed Experiment
• Projected Results
• Summary

• Oscillatory Scaling
• Nuclear Filtering/ Color Transparency

• Only three different Linac energies

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Introduction
Map out the transition from the quark and gluon
degrees of freedom of QCD to the Nucleon-meson
degrees of freedom.
What is the Energy/Momentum Threshold for the
Transition?
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The Constituent Quark Counting Rule
Exclusive two body reactions (AB ?CD) at large
momentum transfers should scale as
s c.m. energy sq.
n of constituent fields

• First derived based on dimensional analysis
  (Brodsky, Farrar,.)
• Confirmed within short distance pQCD framework
  (Brodsky, LePage)
• Recently, derived from anti-de Sitter/Conformal
  Field Theory correspondence or string/gauge
  duality ( Polchinski, Strassler ..)

Many exclusive processes exhibit global scaling
behavior such as
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Pion-photoproduction
Recent JLab data (E94104) on photo-pion
production show scaling behavior at large C.M
. angles.
quark counting rule predicts
L. Y. Zhu et al., PRL 91, 022003 (2003)
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Hadron Helicity Conservation
Short distance pQCD predicts helicity
conservation in exclusive two-body processes
(AB?CD)

• Based on quark helicity conservation, neglecting
  quark orbital angular momentum.
• Experimental data tends not to agree with HHC.

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Quark Counting Rule vs HHC

• Global scaling behavior has been observed
• But experimental data do not support HHC.
• Short-distance physics may not be the full
  picture.

• Detailed investigation of the agreement with
  quark counting rule
• is necessary.

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Oscillations are Not Unique to p-p Scattering
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Oscillatory Scaling Behavior
The large spin correlation and oscillations in
the scaled cross-section explained as

• Resonance state production near the charm
• threshold (Brodsky, Schmidt , .).

• restricted locality'' of quark-hadron duality
  results
• in oscillations (Zhao Close).

• Interference between short distance (Born) and
  long
• distance (Landshoff) amplitudes, (Ralston
  Pire and
• Carlson, Myhrer, .)

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Born vs Independent ScatteringAmplitude in p-p
Scattering
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The Latest Idea to Explain Oscillatory Scaling
Behavior
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Generalized Counting Rule pp Elastic Scattering
Using their Generalized Counting Rule Ji et al.
predict the s dependence of the helicity
flipping amplitudes in pp elastic scattering as
and
D.Dutta and H. Gao, hep-ph/0411267
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How About Photo Reactions?

• Lacks two hadrons in the initial state, but
  Landshoff terms can contribute at sub-leading
  order.
• - can also contribute due to
  fluctuations to a vector-meson.
• Oscillations can be due to final state
  interactions.
• Similar oscillations predicted in deuteron
  photo-disintegration.

• Hints of oscillation seen in pion-photoproductio
  n.

Are oscillations a general feature of QCD ?
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What Happens to Oscillations in the Nuclear
Medium?
Nuclear filtering effect predicts that they are
filtered out in the nuclear medium. One
explaination for the BNL A(p ,2p) data
However, Brodsky and de Teramond explain the same
data in terms of excitation of charm resonance
states.
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Nuclear Filtering with Photo-pions
12
-
12
-
T
-

• Large oscillations in photo-pion transparency
  predicted by
• Jain, Kundu and Ralston PRD 65, 094027 (2002).
• Amplitude depends on an additional nuclear
  phase.
• Can be tested with photo-pion production from
  Carbon.

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The Complementary Color Transparency Phenomena
CT refers to the vanishing of the h-N interaction
for h produced in exclusive processes at high Q

• Nuclear filtering uses the medium actively to
  suppress the long-distance amplitude.
• In CT the large momentum transfer selects the
  short distance amplitude which is then free to
  propagate through the passive medium.
• The onset of CT is expected to be sooner on
  lighter nuclei, while nuclear filtering effect
  is bigger in heavier nuclei

There is no unambiguous, model independent,
evidence for CT in qqq systems.
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Recent Transparency Data

• Small size is more probable in 2 quark system
  such as pions. Onset
• of CT expected at lower Q in qq system.
• Photo-pion production data from E94104 show CT
  like behavior.

D.Dutta et al., PRC 68, 021001R (2003)
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Proposed Experiment

• 50 muA CW beam on 6 copper radiator
• LH2, LD2, He4 targets and 2 solid C target
• HRS-L for pi detection (for LH2 target)
• HRS-R for pi- and HRS-L for proton detection
• (for LD2, He-4 and Carbon targets)
• Gas Cerenkov detector for e/pi separation
• combination of aerogels A1 and A2 for p/pi
• separation.

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Proposed Experiment

• just two body kinematics
• for LD2, He4 and C target we need
• momentum and angle of both proton and
• pion to reconstruct the photon energy.
• The technique has been well established in
• experiment E94-104 in Hall-A .

Reconstructed photon energy spectrum for
from E94-104
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Proposed Experiment

• Same technique as E94104, use 100 MeV
• window.
• Transparency will be extracted using

Simulated photon energy spectrum for
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Rates and Backgrounds

• The H,D,He4 rates determined from observed
  E94-104 rates.
• The Carbon rates were obtained by comparing He-4
  rates from E94-104 to
• Monte Carlo simulations of He and carbon and
  an estimate of the relative
• transparency of carbon.
• Singles rates and e/pi ratios all estimated from
  observed E94-104 rates.

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Beam Time Request
Need 7 different energies but with just 3
different linac energies
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Projected Results
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Summary

• Studying the details of the agreement with quark
  counting rule is crucial to understand the exact
  mechanism behind the onset of scaling in
  exclusive processes.
• These studies are also important to learn about
  the contribution of helicity non-conserving
  amplitudes and quark orbital angular momentum.
• E94104 data show hints of oscillations about the
  scaling behavior.
• A fine scan of the scaling region for photo-pion
  production is needed to confirm and quantify
  these oscillations.
• This can be performed with 7 different energies
  (3 linac energies)
• The photo-pion transparency for Carbon can be
  used to test the nuclear filtering effect. While
  the same on Helium-4 can help look for CT.
• The E94104 data on Helium-4 show hints of CT
  like behavior.