1. PrimEx Preliminary Result (short status)
A. Gasparian
NC A&T State University, Greensboro, NC

2. Three groups analyzed the data independently
0 Event selection
Three groups analyzed the data independently
A. Gasparian
JLab, October 31, 2007

3. 0 Differential Cross section
12C→012C Preliminary
GEANT:
acceptances;
efficiencies …
Experimental Yield
per 
Diff. cross section
A. Gasparian
JLab, October 31, 2007

4. Fit to Extract 0 Decay Width
Theoretical angular
distributions smeared with
experimental resolutions
are fit to the data
Primakoff
Coherent
Incoherent
Interference
Combined average from
three groups:
Γ(0)  7.93 eV  2.10%(stat.)
A. Gasparian
JLab, October 31, 2007

5. Estimated Systematic Errors (preliminary)
Photon flux
1.0%
Target thickness (+impurity)
0.4%
Background subtraction
Theoretical model error
‹1.0%
Event selection
0.5%
HyCal Response function
Beam energy (+parameters)
11/30/20075Acceptance
0.3%
Total
2.03%
A. Gasparian
JLab, October 31, 2007

6. PrimEx Preliminary Result
() = 7.93eV2.1%2.0%
0 Decay width (eV)
±1.%
A. Gasparian
JLab, October 31, 2007

7. Summary to perform precision test of chiral symmetry and anomaly
PrimEx collaboration has developed an experimental program
to perform precision test of chiral symmetry and anomaly
effects in the light pseudoscalar meson sector.
A state-of-the-art high resolution experimental setup has been
designed, developed and constructed in less than 5 years.
The first experiment, the 0 lifetime measurement has been
successfully performed in fall of 2004.
Our preliminary result:
Γ(0)  7.93 eV  2.10%(stat.)  2.0%(syst.)
improves the uncertainty in PDG average by 2.5 times
A. Gasparian
JLab, October 31, 2007

8. Summary (cont.) The proposed 1.4% accuracy in Γ(0) can be reached
with more stable data.
Reach experimental program in η, η’ widths and transition
form factors at 12 GeV with upgraded setup is being developed.
A. Gasparian
JLab, October 31, 2007