PrimEx at 12 GeV with GlueX

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PrimEx at 12 GeV with GlueX

• A. Gasparian
• NC AT State University, Greensboro, NC

• Outline
• PrimEx Physics _at_ 12 GeV
• FCAL/PbWO issues
• Beamline issues
• Institutions and manpower

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The PrimEx Project at 12 GeV

• Experimental program
• 1) Precision measurements of
• Two-Photon Decay Widths G(?0???), G(????),
  G(????)
• Transition Form Factors at low Q2 (0.001-0.5
  GeV2/c2) F(??? ?0), F(?? ??), F(?? ???)

2) The ? rare neutral decays
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Physics Motivation

• Fundamental input to Physics
• precision test of chiral
• anomaly predictions
• determination of light quark
• mass ratio
• ?-? mixing angle
• ?0,? and ? interaction
• electromagnetic radius
• is the ? an approximate
• Goldstone boson?

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Primakoff Method
12C target
Primakoff
Nucl. Coherent
Nucl. Incoh.
Interference
Challenge Extract the Primakoff amplitude
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PrimEx _at_ 12 GeVPrecision Measurement of ????
decay width

• All ?? decay widths are
• calculated from ???? decay
• width and experimental
• Branching Ratios (B.R.)
• G(?? decay) G(????) B.R.

• Any improvement in
• G(????)
• will change the whole
• ?- sector in PDB

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Physics Outcome from ???? Experiment

• light quark mass ratio

• ? - ? mixing angle

G(??3?)G(????)B.R.
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Primakoff Method
12C target
Primakoff
Nucl. Coherent
Interference
Nucl. Incoh.
Challenge Extract the Primakoff amplitude
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???? Experiment with GlueX

• Advantages
• High energy tagged photon beam
• E?10 11.5 GeV
• High acceptance electromagnetic calorimeter
• (FCAL)
• Solenoid detector to veto charged particles,
• and reduce background on FCAL
• Targets (1-5 R.L.)
• LH2,
• LHe4,
• solid 12C

• Challenges
• Photon flux stability and control
• possible solutions
• ee- pair spectrometer
• Compton scattering
• High resolution FCAL needed for
• precision experiments
• possible solution
• Pb-glass PbWO4 crystals

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FCAL/PbWO Issues (prod. Angle Resol.)

• Precision Primakoff
• measurement requires
• high resolutions in
• luminosity (flux target)
• production angle (for fit)
• invariant mass (background)

FCAL with all Pb-glass
FCAL PbWO4(35x35 blocks (70x70 cm2)
FCAL PbWO4(75x75 blocks (150x150 cm2)
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FCAL/PbWO Issues (inv. Mass resol.)
FCAL with All Pb-glass
FCAL PbWO4(35x35 blocks (70x70 cm2)
FCAL PbWO4(75x75 blocks (150x150 cm2)
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2) The ? Rare Decays
(from B.Nefkens)
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Study of the ???0?? Decay

• A stringent test of the ?PTh prediction at ?(p6)
  level
• The first sizable contribution comes at ?(p6)
  level

A long standing ? puzzle is still un-settled.
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GAMS Experiment on ???0?? at Protvino

• Experimental result was first published in 1981
• The ?s were produced with 30 GeV/c ?- beam in
  the ?-p??n reaction
• Decay ?s were detected by lead-glass wall

Final result (D. Alde et al.) 40 of ???0??
events BR(???0??)(7.11.4)x10-4 ?(???0??)0.840
.17 eV

• Major Background
• ?-p? ?0?0n
• ? ??0?0?0

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What can be improved?

• Tagged ? to reduce non-resonance ?0?0 background
• Higher beam energy to reduce the background
• FCAL with PWO4 insertion
• Higher energy resolution ? improve ?0??invariance
  mass
• Higher granularity? better position resolution
  and less shower
• pile-up
• Large statistics to provide a precision
  measurement of Dalitz plot

KLOE
CB
GAMS
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Improvement on the ?0?? invariant mass
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Readout of PbWO in Magnetic Field

• FCAL with PbWO4 insertion is critical for our
  physics

• Required Modifications
• change the G10 housing
• to sift ion housing and
• extend it (2)
• insert optical extension
• extend the brass strips
• reassemble modules

The optical wrapping of Crystal should not change
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Time for PbWO Installation

• disassemble HYCAL - 3 months
• (2
  person)
• reassemble PbWO modules
• 3-4 months (3-4 person)
• assemble 1200 PbWO bloks in FCAL
• 3 months (2 person)
• Total estimated time from HYCAL to
• FCAL lt 12 months

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Beam Line Requirements

• Energy interval the 10 higest
• tagged range (10.5 - 11.5 GeV)
• Resolution 10-3
• Photon flux stability 1
• Collimation ??

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HYCAL (Crystal part)
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PrimEx Hardware Expertise Beam Profile/Position
Monitor
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Institutions/Manpower

• UMass (R. Miskimen, )
• ISU (D. Dale, )
• UNCW (L. Gan, )
• NC AT SU (A. Gasparian, R. Pedroni, )
• ITEP, Moscow group (in progress)

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The End
A. Gasparian
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Experimental Resolutions (production angle vs.
beam spot size)
Photon beam size up to 5 mm, as it is designed,
seams reasonable
A. Gasparian
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Experimental Resolutions(production angle vs.
target length)

• Reaction vertex can not be reconstructed
• in this experiment
• (recoil energies are too small Tlt 1 MeV)

• Large size of the FCAL calorimeter
• provides longer target to FCAL distance
• That makes less sensitivity from the
• target length up to designed 30 cm
• liquid targets

A. Gasparian
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