**PhD Dec. 2009 (CLAS Analysis Note) OZI evading/respecting process Okubo Zweig Iizuka rule: interaction, with which can be In the strong 49.2 ± 0.6 % 34 ± 0.5 % Experimentally this decay mode is (15.3 ± 0.4) % ~84% of phi-meson decay is OZI 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). Previous Measurements Spring-8 used a beam of linearly polarized photons (|t|<0.4 GeV2) 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photoproduction near production threshold with linearly polarized photons,” PhD Thesis, Osaka University, Japan (2004), unpublished.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, 182001 (2005). Experiments -----------------------------------------Forward direction. No central region (Low “t ”) -0.28 < t < -0.12 GeV2 ------------------------------------------Central region ( mid- to higher “t ” ) -1.2 < t < -0.24 GeV2 (Continuous Electron Beam Accelerator Facility) Hall B Hall C Hall A CLAS PHOTON TAGGER • By conservation of energy: Eγ=Ee-Ee’ 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 ! Φ-meson Photoproduction: g8b experiment Linearly Polarized Photon Beam p(’,ϕ), K Target: Hydrogen Event Selection Energy cut: 1 .68 to 1 .92 GeV 1 .88 to 2 .102 GeV 1.9 GeV CohEdge 2.1 GeV CohEdge Φ-meson reconstruction was fitted by a Breit-Wigner convoluted with a Gaussian + 2nd order polynomial (We fix ГΦ = 4.26 MeV from PDG) PARA Event Selection PERP 1.9 GeV Coh Edge 2.1 GeV Coh Edge Results @ 2.1 GeV Coherent Edge Parallel Perpendicular Results @ 1.9 GeV Coherent Edge Parallel Perpendicular Results @ 2.1 GeV Coherent Edge Parallel Perpendicular Results @ 1.9 GeV Coherent Edge Parallel Perpendicular The Decay Angular Distribution Linearly polarization gives access to six more density matrix elements Those are calculated in ϕ-meson rest frame (e.g. Helicity Frame) Density Matrix Elements IF VDM: All density matrix elements should be equal to except for two ρ11-1 and Im{ρ21-1} ρ11-1, Im{ρ21-1} = (1/2, -1/2 : Pomeron) ρ11-1, Im{ρ21-1} = (-1/2, 1/2 : Meson) If any of the other • Knockout processes taking place? • Interesting physics beyond VDM : Acceptance SDMEs parametrization Acceptance effects cancels out tests for s-channel helicity conservation is sensitive to single helicity-flip transitions, and we find that this SDME is small for both • 1.7 < Eg < 1.9 GeV • 1.9 < Eg < 2.1 GeV (this means the probability of finding the phi-meson with longitudinal polarization photoproduced by a transversely polarized photon in the s channel is small). *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. tests for t-channel helicity conservation has the same value – within error bars – for both • 1.7 < Eg < 1.9 GeV and • 1.9 < Eg < 2.1 GeV averaged over the the datasets (this means the probability of finding the phi-meson with longitudinal polarization in the t channel is high). *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. which suggests a small contribution from non-helicity conserving processes. Perhaps from a possible f2’ exchange as pointed out by A.I. Titov and T.-S.H. Lee, PRC 67, 065205 (2003). • For 1.7 < Eg < 1.9 GeV, the parallel and perpendicular datasets averaged over • For 1.9 < Eg < 2.1 GeV, averaged over the parallel and perpendicular datasets – this SDME agrees with the LEPS experiment* where at low t for 1.97 < Eg < 2.17 GeV *Mibe et al., PRL 95, 182001 (2005) (1.9 < Eg < 2.1 GeV) (1.7 < Eg < 1.9 GeV) (1.9 < Eg < 2.1 GeV) (1.7 < Eg < 1.9 GeV) • Nota Bene: says for natural-parity exchange for unnatural-parity exchange 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-0555497 Event Selection → γ p → pϕ →pK+KMode: pK+(X) → pK+(K-) 1.9GeV CohEdge 2.1GeV CohEdge Event Selection i.e. PERP 1.9 GeV CohEdge i.e.PARA 2.1 GeV CohEdge π + background subtraction