Coherent Vector Meson Production Off the Deuteron

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Coherent Vector Meson Production Off the Deuteron
G. Dodge, S. Kuhn, S. Stepanyan
(co-spokesperson), L. Weinstein Old Dominion
University, Norfolk, VA 23529, USA H. Avakian,
W. Brooks, V. Burkert, D. Cords, H. Egiyan, L.
Elouadrhiri, Y. Sharabyan, E. Smith Jefferson
Lab, Newport News, VA 23606, USA F. Klein
(co-spokesperson) Catholic University of America,
Washington, D.C 20064, USA P. Ambrozewicz, A.
Gonenc, L.H. Kramer (contact person), R.
Nasseripour, M. Sargsian, B.A. Raue Florida
International University, Miami, FL 33199,
USA K. Griffioen The College of William and
Mary, Williamsburg, 23187-8795, USA M. Garçon,
J.-M. Laget, F. SabatiéDAPNIA/SPhN, CEA-Saclay,
F-91191 Gif-sur-Yvette, FranceM. Guidal
Institut de Physique Nucléaire, F-91406 Orsay,
France M. Holtrop University of New Hampshire,
Durham, NH 03824, USA M. Strikman Pennsylvania
State University, University Park, PA 16802,
USA L. Frankfurt Tel Aviv University, Tel Aviv,
69978 Israel H. Bagdasaryan, N. Dashyan, K.
Egiyan Yerevan Physics Institute, Yerevan, 375036
Armenia A. Stavinskiy Institute Theoretical and
Experimental Physics,117259 Moscow, Russia and
the CLAS collaboration
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Coherent Vector Meson Production Off the Deuteron
Jeopardy Update

• Goal Remain Unchanged
• Investigate the production of and its
  evolution into final hadronic state
• Study Color Transparency phenomena in the
  transition region
• Concurrent Running Complete
• Preliminary Analysis Shows Feasibility
• 10 of Total Data Request
• Active Field
• Recent Results Adds to Motivation

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Coherent Vector Meson Production Off the Deuteron

• Investigate the production of and its
  evolution into final hadronic state
• Study Color Transparency phenomena in the
  transition region
• Fully exclusive measurements of the reaction e d
  ? e V d at 6 GeV using CLAS
• Simultaneous measurement of r0, f, and w
• Detection of deuteron will insure dominance of
  rescattering at t gt 0.6 (GeV/c)2
• Large kinematic range
• 1 lt Q2 lt 4.5 (GeV/c)2
• 0.1 lt x lt 0.5 (0.4 lt lc lt 1 fm)
• 0.1 lt -t lt 1.0 (GeV/c)2
• Span range from VMD to QCD - Transition Region
• Establish the regime where quark-gluon
  degrees-of-freedom dominate (pQCD)
• Basis of broad experimental program for studying
  exclusive processes
• 12 GeV Program

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Small Size Neutral Objects

• Quantum Field Theory with Neutrality
• Small size objects have reduced interactions
• Charge Transparency
• p0 ? e e g (Perkins, 1955)

• Fundamental property of QCD
• Decreased interaction between quarks and gluons
  at small distances
• Small size configurations are produced in hard
  scattering processes
• Create small color neutral objects with reduced
  interaction
• Fundamental prediction of QCD
• - Color transparency (CT) -
• Nuclear matter becomes transparent to color
  singlet objects

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CT in vector meson electroproduction

• CT Experimentally Observed Through 2 Mechanisms
• Reduced Attenuation of Particles Passing Through
  Nucleus
• Decreased Production of Particles in 2-Stop
  Rescattering Process
• While the onset of CT should be observed earlier
  for meson production
• Easier to produce small than
• Focus on coherent vector meson production off
  deuteron
• Large photon-vector meson coupling
• The deuteron is the best understood nucleus
• Transition region (x gt 0.1 and Q2 gt 1 (GeV/c)2)
  remains unexplored experimentally
• The theoretical expectations are
• VDM picture will break down
• Transverse distance between will shrink as
  1/Q
• Important for emerging program of studying GPDs
  
• Complementary test of the onset of the
  factorization regime
• Dynamics of hard scattering process
• Measurement of the isosinglet contribution of
  GPDs

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Advantages of Coherent VM Production from
Deuteron

• 2 Dominant Diagrams
• Single Scattering
• Double Scattering
• Advantages
• YD Known to 5 (400 MeV/c)
• Deuteron is isoscalar
• No r / w mixing
• Other mechanisms suppressed
• Intermediate state must be isovector

SLAC Coherent r Photoproduction (1971)
Single Scattering
Double Scattering
Interference
t gt 0.6 (GeV/c)2 Rescattering dominant
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Production Mechanism

• Low Q2 Vector Dominance Model
• Photon fluctuates into intermediate VM
• Pomeron or meson exchange in t-channel
• Forms meson in final state.
• High Q2 Partonic Degrees of Freedom
• Photon fluctuates to
• (longitudinally polarized gs)
• Two Gluon Exchange
• Dominates at Small x / f
• Quark Interchange
• Handbag Diagrams

Small sized produced
Vanderhagen, Guichon, Guidal PRD 094017 (1999)
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Evolution of .

• Transverse size of produced object

Expand Rapidly Must detect object close to
production
Formation Length
Coherent VM Production of Deuteron Detect
Deuteron in Final State Studying Rescattering of
Off the Spectator Nucleon Major Experimental
Advantage
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Observables

• Measure t-dependence
• for 1 lt Q2 lt 4.5 (GeV/c)2
• Separate Longitudinal and
• Transverse Polarizations
• Main Focus
• RL is most sensitive (20)
• No Theoretical Normalization!

t1 -0.8, t2 -0.4
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Peak Seen in Nuclear Transparency

• Nuclear Transparency
• E834 and E850 measured peak at 9 GeV
• Interesting Physics

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Hall C Pion Electroproduction

• Earlier Onset for Mesons
• Hall C EXXXX 5.75 GeV
• Hall A E02-010

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E665 r0 Electroproduction

• Incoherent r0 Electroproduction on Nuclei

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Holding pen for figures
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What to include in review?

• E834/E850 peak at 9gev
• (Clas 94-019?)
• Hall C?
• E665?
• HERMES?
• E02110?
• E791?

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Experimental Situation of CT

• First Experiments A(e,ep)X at SLAC and JLab
• Not seen up to Q2 8 (GeV/c)2
• Slow moving small object expands rapidly
• Recent High Energy Experiments Clearly Establish
  CT
• Fermilab E791 absorption of dijets from C and
  Pt targets
• Found absorption of dijets 7 times smaller than
  is predicted without CT
• Fermilab E665 and New Muon Collaboration
• Incoherent r0 muon production at high Q2
• lc not constant CT or longitudinal interaction
  length effects?
• HERMES
• Incoherent r0 production
• lc not constant ? longitudinal interaction length
  effects
• Detector upgrade for coherent production
• COMPASS

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Other Physics Topics

• Compare Break-up and Coherent Channels
• Relative phases for neutron / proton scattering

• DVCS and p0 / h Coherent Production
• Complementary to proton / isosinglet / non-spin
  flip
• p0 / h amplitudes opposite sign for free proton
  neutron

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Experimental Objectives
Coherent Vector Meson Production at 6 GeV using
Modified CLAS
e d e d r0 e d e d f e d
e d w
Simultaneous measurement over large kinematic
range in Q2, x, and t

• CLAS has published data on r and f electro- and
  photoproduction off the proton.
• CLAS well suited to multi-particle final states
• Measured cross sections to lt10 systematic
  uncertainty

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Experimental Setup Optimized CLAS Configuration

• Replace the mini-torus
• shield with a solenoidal
• magnetic field.
• Higher luminosity
• 2 x1034cm-2s-1
• Move Target 60 cm Upstream
• Gain Forward
• Acceptance

Target
45o
8o
Solenoid
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• Kinematic coverage in Q2, W, and t

Generated s 1/Q6 t e-4t
d
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Kinematic coverage in lc and lc

• Vary both initial and final states independently
  
• Coherence Length
• Formation Length
• Average lf 1.5 fm
• Comparable to Deuteron

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Event Identification

• Standard techniques to identify final states
• Deuterons T gt 30 - 40 MeV (-t gt 0.15 (GeV/c)2)
• Vector Mesons reconstructed by decay products
• All final state topologies
• will be analyzed
• Focus on
• (edp) for r0 ? p p
• (edK) for f ? K K
• (edp g) for w ? p p p0

Data from E5 Run Period e d ? e h
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Sample Reconstructed Data
missing p
r0
Reconstructed (p p) final state Ee 3 GeV
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Analysis of Angular Momentum
VM Decay Angular Distribution Analysis to
Separate Longitudinal and Transverse
Polarizations

• Assume s-channel helicity conservation (SCHC)
• Decay angular distribution in helicity frame
  given by
• depends on W, Q2, and t
• For purely longitudinally (transverse) polarized
  VM ( )
• VM polarization is linked to the virtual photon
  polarization
• Check for SCHC with out of plane events

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Count Rate Estimates

• r0 Cross sections Frankfurt, Piller,
  Sargsian, and Strikman, Eur Phys J A 2 301
  (1998)
• For Q2 4 (GeV/c)2, lc 0.45, and t 0.8
  (GeV/c)2
• 483 counts in 50 days at L 2 x 1034 cm2 s1
• bins DQ2 0.4 (GeV/c)2, Dlc 0.1, and Dt
  0.2 (GeV/c)2
• 8 statistical accuracy for sL in 50 days
  (models vary by 20)
• Systematic uncertainties minimal in ratio
• f meson
• s 20 x lower
• Larger bins / Q2 3 (GeV/c)2
• Similar uncertainties

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Sensitivity

• Longitudinal separation from angular
  distribution of decays

• Simulation based
• on R 1.8

Crittenden, hep-ex/9704009

• Q2 4 (GeV/c)2

• 50 days of beam time
• L 2x1034 cm-2 sec-1

• t -0.4 (GeV/c)2
• Rext 1.8 0.007
• t -0.8 (GeV/c)2
• Rext 1.84 0.017

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Beam Request

• We propose to measure differential cross
  section of Coherent
• Vector Meson Production from Deuterium at 6 GeV
  using CLAS
• Kinematic Domain
• 1 lt Q2 lt 4.5 (GeV/c)2
• 0.1 lt x lt 0.5 (0.4 lt lc lt 1 fm)
• 0.1 lt -t lt 1.0 (GeV/c)2

• Ran concurrently with E6 run group January 2002
• 16 days L 1034 cm-2 sec-1
• 10 of data

• We request
• Remaining 50 days of new beam time
• Dedicated run with an optimized CLAS
  configuration
• L 2x1034 cm-2 sec-1
• For 8 stat. uncer. in sL _at_ Q2 4 (GeV/c)2, -t
  0.8 (GeV/c)2

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Conclusions

• First dedicated experiment on coherent
  electroproduction.
• High quality / high statistics over large
  kinematic range
• Deuteron is the standard source for neutron
  target. This will provide a large volume of data
  on e-n scattering at 6 GeV.
• Combined with CLAS photo- and electroproduction
  data from deuteron and proton targets will allow
  a systematic and complete study of dynamics of
  hard exclusive reactions in the transition
  region.
• Establishing existence of CT phenomena.
• Establishing regime when quark-gluon
  degrees-of-freedom are important (validity of
  factorization).

• Foundation for future studies at 12 GeV.

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Coherent Production Mechanism

• F1 IA / Single Scattering
• F2 Rescattering / Double Scattering

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Check SCHC Validity
Test Assumption with out of plane events

• Take F as angle between leptonic and hadronic
  scattering planes
• With
• SCHC RTT and RTL vanish, giving flat F
  angular distribution

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Simulated CLAS Acceptance
Target _at_ Z 60 cm / edp final state
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Simulated CLAS Acceptance
Target _at_ Z 60 cm / edp final state
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Sample Reconstructed Data
Reconstructed (K K) final state E 4 GeV
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Solenoidal Shielding Magnet
CVM
EG1
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Foundation for Future Studies

• Polarization
• Double scattering sensitive to tensor
  polarization of deuteron
• Increases sensitivity to smaller
  internucleon distances at same t
• Need frozen spin target
• Ultimately extend program to 12 GeV
• Part of Hadrons in Nuclear Medium / 12 GeV
  Whitepaper
• This work establishes foundation for future
  studies