**PhD Dec (CLAS Analysis Note)

OZI evading/respecting process 49.2 ± 0.6 % 34 ± 0.5 % Experimentally this decay mode is (15.3 ± 0.4) % mode is (15.3 ± 0.4) % ~84% of phi-meson decay is OZI respecting OZI respecting

Processes Yougseok Oh and H. C. Bhang, Phys. Rev. C (2001)

Previous Measurements J. Ballam, G.B. Chadwick et al., Phys. Rev. D (1972).

Spring-8 used a beam of linearly polarized photons (|t|<0.4 GeV 2 ) T. Mibe, “Measurement of  meson photoproduction near production threshold with linearly polarized photons,” PhD Thesis, Osaka University, Japan (2004), unpublished. T. Mibe, “Measurement of  meson photoproduction near production threshold with linearly polarized photons,” PhD Thesis, Osaka University, Japan (2004), unpublished. T. Mibe et al., Phys. Rev. Lett. 95, (2005). T. Mibe et al., Phys. Rev. Lett. 95, (2005). Previous Measurements

Experiments

Hall C Hall A Hall B

CLAS

PHOTON TAGGER There are 384 energy counter and 61 timing counters. The energy counters are 1/3 overlapping. This means we have effectivity doubled the number of channels to ~ 768 energy bins Because of hodoscope spans the energy region 0.20 ≤ E e’ ≤ 0.95E e implies Photon energy resolution is 0.1% of the incident electron energy, E e ! By conservation of energy: E γ =E e -E e’

Φ-meson Photoproduction: g8b experiment Linearly Polarized Photon Beam Target: Hydrogen p(  ’,  ϕ ), K 

2.1 GeV CohEdge 1.9 GeV CohEdge Energy cut: 1.68 to 1.92 GeV 1.88 to GeV Event Selection

Φ-meson reconstruction was fitted by a Breit-Wigner convoluted with Φ-meson reconstruction was fitted by a Breit-Wigner convoluted with a Gaussian + 2 nd order polynomial (We fix Г Φ = 4.26 MeV from PDG) a Gaussian + 2 nd order polynomial (We fix Г Φ = 4.26 MeV from PDG) PARAPERP 1.9 GeV Coh Edge 2.1 GeV Coh Edge

2.1 GeV Coherent Edge 1.9 GeV Coherent Edge Perpendicular Parallel

2.1 GeV Coherent Edge 1.9 GeV Coherent Edge Perpendicular Parallel

The Decay Angular Distribution Those are calculated in ϕ -meson rest frame (e.g. Helicity Frame) Linearly polarization gives access to six more density matrix elements

Density Matrix Elements

SDMEs parametrization Acceptance Acceptance effects cancels out

*Quantization axis is opposite the recoil proton in the cms of the proton and phi meson. We then boost along this quantization axis to the rest frame of the phi meson. The Kaon angular distributions are measured in this frame.

*Quantization axis is in the direction of the photon’s travel. We then boost along this quantization axis to the rest frame of the phi meson. The Kaon angular distributions are measured in this frame.

*Mibe et al., PRL 95, (2005)

 Natural-parity exchange mechanisms are larger than those for unnatural-parity exchange in both the s- and t-channels.  The relative contributions for natural- and unnatural-exchange processes are energy dependent in the t-channel and not in the s-channel  A small oscillation in W( ϕ ) suggests a small pseudoscalar-meson-exchange component and that no pomeron exchange is present in the t channel.

 Polarization ~70%  Over 8200 ϕ -meson events were analyzed. Highest ever at threshold with linearly polarized photons  Spin Density Matrix Elements (SDMEs) were extracted and are found to have non-VDM values.  Φ-meson azimuthal distribution has a considerable amplitude which suggests that one or more additional mechanisms beyond VDM are involved. **This work was made possible through a grant from NSF the National Science Foundation, NSF

Event Selection 1.9GeV CohEdge 2.1GeV CohEdge γ p → p ϕ →pK + K - Mode: pK + (X) → pK + (K - ) →

Event Selection 1.9 GeV CohEdge 2.1 GeV CohEdge π + background subtraction i.e. PERP i.e.PARA