The ( ) Experiment (E12-10-011) in Hall D/GlueX We propose to - - PowerPoint PPT Presentation

• A. Gasparian

PAC37, Jan 10, 2011 1

The Γ(η→γγ) Experiment (E12-10-011) in Hall D/GlueX

• Potentially solve collider/Primakoff discrepancy
• Significantly improve (η - η’) mixing angle
• Most model independent determination of light quark mass ratio
• Change whole decay widths of η-sector in PDG:

Γ(η→X) =Γ(η→γγ)*BR(X)/BR(γγ)

• Precision tests of Chiral symmetry and anomalies in QCD
• Direct tests of emerging lattice QCD simulations
• We propose to perform a new Primakoff type experiment with a precision of 3.2% using standard

GlueX setup including the photon tagger and FCAL. η

ρ,ω

• We propose to use 2 low A targets (LH2 and LHe4) to:

 Address the coherency issue in the reaction mechanism  minimize and control the nuclear effects (FSI)

• A. Gasparian

PAC37, Jan 10, 2011 2

Statistics, Beam Time and Physics Results

PAC35 Request [ days ] PAC37 Request [ days ]

Setup calibration, 8 2 Tagger efficiency, 4 1 LH2 target run 40 40 LHe4 target run 30 30 Empty target run 6 6 Total 88 days 79

Estimated beam time request

(1% statistical error on Primakoff events for each target.)

• Total estimated error on Γ(η→γγ) 3.2 %

Γ(η→3π)=Γ(η→γγ)×BR(3π)/BR(γγ)

• Light quark mass ratio

Γ(η→3π) α |A|2 α Q-4 with

) ( 2 1 ˆ re whe ,

2 2 2 2 2 d u u d s

m m m m m m m Q + = − − = 

Corr. ) (

. . m e K K

m m

+

−

meson mass ratio

• H. Leutwyler PLB, 378,1996
• (η - η’) mixing angle

Contributions Error Photon flux 1.0% Target thickness 0.5% Background subtr. 2.0% Event selection 1.7% Total Systematic 3.02%

Major Systematic errors

• A. Gasparian

PAC37, Jan 10, 2011 3

Control of Overall Systematics: e e γ γ ′ ′ + → +

• CompCal calorimeter is16x16 (32x32 cm2)

relatively small PbWO4 crystal detector

• Forward Compton cross section will be measured

by new CompCal detector in combination with FCAL

• Will provide continuous control of overall

systematic error in the experiment

• Absolute cross section measurements are required for Γ(η→γγ) extraction
• Compton cross sections are known
• n 1% level
• Due to experimental backgrounds,

simultaneous detection of scattered photon and recoiling e- is required for event selection

• High magnetic field in Solenoid will significantly

destroy the e-position on calorimeter, changing the kinematical variables

• Example: the reaction co-planarity
• Solenoid field off configuration requires dedicated run.