COMPTON SCATTERING IN FORWARD DIRECTION IN PRIMEX DATA

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COMPTON SCATTERING IN FORWARD DIRECTION IN PRIMEX
DATA
PAWEL AMBROZEWICZ

• NORTH CAROLINA AT STATE UNIVERSITY
• FOR
• PRIMEX COLLABORATION

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• GOAL
• STUDY ? ? e ? ? ? e AT 5 GeV

• INTRODUCTION
• PRIMARY GOAL
• EXPERIMENTAL SETUP

• DATA ANALYSIS HIGHLIGHTS
• YIELD EXTRACTION

• PRELIMINARY RESULTS
• CROSS SECTIONS

• SUMMARY

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PRIMARY GOAL OF PRIMEX
TEST FUNDAMENTAL SYMMETRY PREDICTION OF LOW
ENERGY QCD AXIAL ANOMALY

• THE ANOMALY IS MANIFEST IN
• ?0 RADIATIVE DECAY AMPLITUDE/WIDTH
• EXACTLY CALCULABLE IN THE CHIRAL LIMIT
• ???? 7.7250.044 eV
• CORRECTIONS NEEDED FOR NON-VANISHING
• QUARK MASSES / MESON MIXING
• ???? 8.100.08 eV - NEXT TO LEADING ORDER
• PREDICTION
• PRECISION MEASUREMENT OF ?0 RADIATIVE WIDTH
• NEEDED (see ERIC CLINTONS TALK)
• DESIGN REQIUREIMENT
• PRECISION WITH DISCRIMINATIVE POWER
• COHERENT ?0 PHOTOPRODUCTION
• IN COULOMB FIELD OF A NUCLEUS

• DECAY WIDTH AND CROSS SECTION DIRECTLY
  PROPORTIONAL
• CROSS SECTION DEPENDS ON SMALL NUMBER OF
  PARAMETERS

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PRIMARY GOAL OF PRIMEX
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EXPERIMENTAL SETUP

• C, Pb TARGETS
• JLAB HALL B PHOTON
• TAGGING FACILITY
• HIGH INTENSITY,
• HIGH RESOLUTION DEVICE
• (FIRST EXPERIMENT USING
• TAGGED PHOTONS PRIMAKOFF EFFECT)
• STATE-OF-THE-ART
• CALORIMETRY HyCal
• PAIR SPECTROMETER

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COMPTON SCATTERING
MEASURED QUANTITIES

• ENERGY OF INCIDENT PARTICLES
• POSITIONS AT HyCal FOR BOTH PARTICLES
• ENERGIES OF SCATTERED PARTICLES

EVENT SELECTION

• COINCIDENCE TIMING
• ENERGY-MOMENTUM CONSERVATION
• CO-PLANARITY OF EMERGENT PARTICLES
• ?e OPENING ANGLE
• FIDUCIAL REGION OF HyCal

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COMPTON SCATTERING EVENTS

• MINIMAL OPENING ANGLE/
• MINIMAL SEPARATION CUT
• ADDITIONAL CUTS SERVE
• TO MINIMIZE
• SIGNAL-TO-NOISE RATIO

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YIELD FIT DOUBLE GAUSSIAN SIGNAL FLAT
BACKGROUND
DATA
SIMULATION
TYPICAL DATA YIELD FIT
DATA / MONTE CARLO SIGNAL SHAPE COMPARISON
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YIELD FIT DOUBLE GAUSSIAN SIGNAL FLAT
BACKGROUND
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COMPTON CROSS SECTION
(mb/atom)
PRELIMINARY
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FORWARD CROSS SECTION - NC AT/UNCW/ITEP/JLAB
GROUP
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• STATISTICAL ERROR lt 0.5

SYSTEMATIC ERROR ESTIMATION

• PHOTN FLUX
  1.8
• TARGET THICKNESS
  0.1
• BACKGROUND ESTIMATION
  3.5
• ACCEPTANCE
  2.0
• STABILITY (CALIBRATIONS)
  2.0
• TOTAL
  5

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DIFFERENTIAL CROSS SECTION - MIT GROUP
NO DISTINCTION BETWEEN DETECTED PARTICELS
FORCES CONSIDERING A SUM OF CROSS SECTIONS
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CONCLUSIONS

• HIGH QUALITY ?0 PHOTOPRODUCTION DATA TAKEN IN
  FALL 2004
• TO CONTROL SYSTEMATIC OF THE PRIMARY PROCESS
• COMPTON CROSS SECTION MEASUREMENT NEEDED
• PRELIMINARY ANALYSIS DONE AT FEW PERCENT LEVEL
  
• AGREEMENT WITH THEORY OF 5
• WORK IN PROGESS TO REDUCE THE SYSTEMATICS TO
  1-2 LEVEL

This project was in part supported by grants NSF
MRI PHY 0079840 and NSF PHY-060252