**PhD Dec. 2009 (CLAS Analysis Note)

OZI evading/respecting process

49.2 ± 0.6 %

34 ± 0.5 %

Experimentally this decayExperimentally this decay mode is (15.3 mode is (15.3 ± 0.4) %± 0.4) % ~84%~84% of phi-meson decay is of phi-meson decay is

OZI respectingOZI respecting

Processes

Yougseok Oh and H. C. Bhang, Phys. Rev. C 64 055207(2001)

Previous Measurements

J. Ballam, G.B. Chadwick et al., Phys. Rev. D 7 3150(1972).

Spring-8 used a beam of linearly polarized photons (|t|<0.4 GeV2)

T. Mibe, “T. Mibe, “Measurement of Measurement of meson photoproduction near meson photoproduction near production threshold with production threshold with linearly polarized photonslinearly polarized photons,” ,” PhD Thesis, Osaka University, PhD Thesis, Osaka University, Japan (2004), unpublished.Japan (2004), unpublished.

T. Mibe T. Mibe et al.,et al., Phys. Rev. Lett. Phys. Rev. Lett. 95, 182001 (2005).95, 182001 (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 ≤ Ee’ ≤ 0.95Ee implies

Photon energy resolution is 0.1% of the incident electron energy, Ee !

• By conservation of energy: Eγ=Ee-Ee’

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 GeV1 .68 to 1 .92 GeV1 .88 to 2 .102 GeV1 .88 to 2 .102 GeV

Event Selection

Event Selection Φ-meson reconstruction was fitted by a Breit-Wigner Φ-meson reconstruction was fitted by a Breit-Wigner convoluted with convoluted with a Gaussian + 2a Gaussian + 2ndnd order polynomial (We fix order polynomial (We fix ГГΦΦ = 4.26 MeV from = 4.26 MeV from PDG)PDG)

PARA PERP

1.9 GeV Coh Edge

2.1 GeV Coh Edge

Results @ 2.1 GeV Coherent Edge

Results @ 1.9 GeV Coherent Edge

Perpendicular PerpendicularParallel Parallel

Results @ 2.1 GeV Coherent Edge

Results @ 1.9 GeV Coherent Edge

Perpendicular PerpendicularParallel 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 A

ccep

tanc

e

Acceptance effects cancels outAcceptance 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, 182001 (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 the National Science Foundation, NSF-0555497NSF-0555497

Event Selection

1.9GeV CohEdge 2.1GeV CohEdge

γ p → pϕ →pK+K- Mode: pK+(X) → pK+(K-)

→→

Event Selection

1.9 GeV CohEdge

2.1 GeV CohEdge

π + background subtraction

i.e. PERPi.e. PERP

i.e.PARAi.e.PARA