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

The Γ ( η → γγ ) Experiment (E12-10-011) in Hall D/GlueX  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.  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 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 1

Statistics, Beam Time and Physics Results PAC35 Request PAC37 Request [ days ] [ days ] Setup calibration, 8 2 Tagger efficiency, 4 1 LH 2 target run 40 40 LHe4 target run 30 30  ( η - η ’) mixing angle Empty target run 6 6 Total 88 days 79 Estimated beam time request (1% statistical error on Primakoff events for each target.) Contributions Error Γ ( η → 3 π )= Γ ( η → γγ ) × BR(3 π )/BR( γγ ) Photon flux 1.0% meson mass Target thickness 0.5% ratio  Light quark mass ratio Γ ( η → 3 π ) α |A| 2 α Q -4 with Background subtr. 2.0% Event selection 1.7%  − 2 2 m m 1 = = + 2 s Q , whe re m ˆ ( m m ) Total Systematic 3.02% − u d 2 2 m m 2 d u Major Systematic errors H. Leutwyler PLB, 378,1996  Total estimated error on Γ ( η → γγ ) 3.2 % − ( m m ) Corr. + 0 e . m . K K A. Gasparian PAC37, Jan 10, 2011 2

Control of Overall Systematics:  Absolute cross section measurements are required for Γ ( η → γγ ) extraction  Forward Compton cross section will be measured by new CompCal detector in combination with FCAL  Compton cross sections are known on 1% level γ ′ ′ γ + → + e e  Will provide continuous control of overall systematic error in the experiment  CompCal calorimeter is16x16 (32x32 cm 2 ) relatively small PbWO 4 crystal detector  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. A. Gasparian PAC37, Jan 10, 2011 3