Polarization observables in the photoproduction of mesons with

Polarization observables in the photoproduction of Φ mesons with linearly polarized photons Julian Salamanca* Philip Cole + The CLAS Collaboration **Ph. D Dec. 2009 (CLAS Analysis Note) NSTAR 2011 Newport News, VA May 19, 2011

OZI evading/respecting process Okubo Zweig Iizuka rule: In the strong interaction, processes with final state particles which can only be reached through quarkantiquark annihilation will be suppressed. 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 Ge. V 2) T. Mibe, “Measurement of meson photoproduction near production threshold with linearly polarized photons, ” Ph. D Thesis, Osaka University, Japan (2004), unpublished. T. Mibe et al. , Phys. Rev. Lett. 95, 182001 (2005).

Experiments SLAC: ~53 Events ---------------------Forward direction. No central region (Low “t ”) -0. 28 < t < -0. 12 Ge. V 2 Spring-8: ~5000 Events ---------------------Central region ( mid- to higher “t ” ) -1. 2 < t < -0. 24 Ge. V 2 g 8 b: ~8200 Events

CEBAF (Continuous Electron Beam Accelerator Facility) Hall B Hall C Hall A

CLAS

Coherent Bremsstrahlung Facility

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. 95 Ee implies Photon energy resolution is 0. 1% of the incident electron energy, Ee !

Φ-meson Photoproduction: g 8 b experiment Linearly Polarized Photon Beam p( ’, ϕ), K Target: Hydrogen

Event Selection Energy cut: 1. 68 to 1. 92 Ge. V 1. 88 to 2. 102 Ge. V 1. 9 Ge. V Coh. Edge 2. 1 Ge. V Coh. Edge

Φ-meson reconstruction was fitted by a Breit-Wigner convoluted with a Gaussian + 2 nd order polynomial (We fix ГΦ = 4. 26 Me. V from PDG) PARA Event Selection PERP 1. 9 Ge. V Coh Edge 2. 1 Ge. V Coh Edge

Results @ 2. 1 Ge. V Coherent Edge Parallel Perpendicular Results @ 1. 9 Ge. V 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

Acceptance SDMEs parametrization 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, 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-0555497