# GlueX Physics Photoproduction

## Photoproduction

### Linear Polarization

In GlueX, the linearly polarized photons will be produced by coherent bremstrahlung. In this process, the photons in the coherent scattering peak from the crystal radiator are polarized. The direction of the polarization vector (in the lab) depends on the orientation of the crystal, but is fixed (in the lab). The degree of polarization of the coherent peak depends on the ratio of the photon energy to the end-point energy.

In the photo-production of mesons (via t-channel processes), the relevant

#### Reference Frames

The lab frame is typically taken with the z-axis along the incoming photon direction and the y-axis normal to the surface of the Earth. The x-axis is then taken ${\hat x}={\hat y}\times {\hat z}$. Related to the lab frame is the center of mass frame. The coordinate directions are the same, but the two frames are connected by a boost along the z-axis with $\beta =E_{{\gamma }}/(E_{{\gamma }}+m_{{p}})$ and the total energy in the center of mass is ${\sqrt {s}}={\sqrt {m_{{p}}^{{2}}+2m_{{p}}E_{{\gamma }}}}$.

In t-channel photo production, a particle X is produced recoiling against an out-going proton. The Mandelstam t is given as $t=(p_{{X}}^{{\mu }}-k^{{\mu }})(p_{{\mu X}}-k_{{\mu }})$ where k is the photon momentum and $p_{{X}}$ is the 4-momentum of the produced particle $X$.

### References

#### Experimental Papers

##### CLAS Publications
• First Measurement of the Polarization Observable E in the p⃗ (γ⃗ ,π+)n Reaction up to 2.25 GeV, S. Strauch et al. (CLAS Collaboration) arXiv.
• Data analysis techniques, differential cross sections, and spin density matrix elements for the reaction γp → φ p B. Dey et al., (CLAS Collaboration), Phys. Rev. C89, 055208 (2014), DOI
• Differential Photoproduction Cross Sections of the Σ0(1385), Λ(1405), and Λ(1520), K. Moriya et al. (CLAS Collaboration), Phys. Rev. C88 045201 (2013), DOI.
• Cross sections for the γp → K∗+Λ and γp → K∗+Σ0 reactions measured at CLAS, W. Tang et al. (CLAS Collaboration), Phys. Rev. C87 065204, (2013), DOI.
• Beam asymmetry Σ for π+ and π0 photoproduction on the proton for photon energies from 1.102 to 1.862 GeV, M. Dugger et al. (CLAS Collaboration), Phys. Rev. C88, 029901 (2013), DOI.
• Differential cross sections and recoil polarizations for the reaction γ p → K+ Σ0, B. Dey, et al., Phys. Rev. C82, 025202 (2010), DOI.
• Differential cross section and recoil polarization measurements for the γ p → K+ Λ reaction using CLAS at Jefferson Lab, M.E. McCracken et al (CLAS Collaboration), Phys. Rev. C85, 025201 (2010), DOI.
• Differential cross sections and spin density matrix elements for γp → ω p, M. Williams, et al., (CLAS Collaboration), Phys. Rev. C80, 065208 (2009), DOI, arXiv.
• Partial wave analysis of γ p → ω p and the search for nucleon resonances, M. Williams, et al., (CLAS Collaboration), Phys. Rev. C80, 065209 (2009), DOI, arXiv.
• Differential cross sections for the reactions γ p → η p and γ p → η' p, M. Williams, et al., (CLAS Collaboration), Phys. Rev. C<80>, 045213 (2009), DOI, arXiv.
• π+ photoproduction on the proton for photon energies from 0.725 to 2.875-GeV, M. Dugger et al. (CLAS Collaboration), Phys. Rev. C79, 065206 (2009),DOI.
• Search for the photo-excitation of exotic mesons in the π+ π+ π- system, M. Nozar et al., Phys. Rev. Lett. 102, 102002 (2009), DOI.
• Photoproduction of π+π- meson pairs on the protonM. Battaglieri et al., Phys. Rev. D80, 072005 (2009), DOI.
##### Other Publications
• First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Proton near Threshold, P. Levi Sandri et al. (GrAAL), submitted to Eur. Phys. J. C, (2015), arXiv.
• The polarization observables T, P, and H and their impact on γ p → p π 0 multipoles, J. Hartmann et al. (CBELSA/TAPS), Submitted for publication (2015), arXiv.
##### Older Publications
• On the apparent shift of the rho meson mass in photoproduction, P. Soeding, Phys. Lett. 19, 702, (1966), DOI.
• Interference Effects in Photoproduction of ρ0 Mesons, Allan S. Krass, Phys. Rev. 159, 1496 (1967), DOI
• On the Analysis of Vector-Meson Production by Polarized Photons, K. Schilling, P. Seyboth and G. Wolf, Nucl. Phys. B15 (1970), 397-412, DOI, pdf
• Bubble-Chamber Study of Photoproduction by 2.8 and 4.7 GeV Polarized Photons. I. Cross-Section Determination and Production of ρ0 and Δ++ in the Reaction γp → pπ+π- J. Ballam et al., Phys. Rev. D5 (1972), 545-589, DOI, pdf.
• Vector-Meson Production by Polarized Photons at 2.8, 4.7 and 9.3 GeV, J. Ballam et al., Phys. Rev. D7 (1973), 3150-3177, DOI, pdf.
• Spin-Parity Analysis of ρ' in the reaction γ p → π+ π+ π- π-p at 9 to 18 GeV, Joseph C.H. Park, Nucl. Phys. B58, (1973), 45-54, DOI, pdf.
• High-Energy Production and Decay of vector and Tensor Mesons, A.C. Irving and C. Michel, Nucl. Phys. B82, (1974), 282-325, DOI, pdf.
• The Reaction γ p → π+ π- π+ π- p at High-energy and dissociation into 4π, M. Davier, et al., Nucl. Phys. B58 (1973), 31-44, DOI, pdf.
• A Search for B and ρ'(1250) Production in the Reaction p π+π- + Neutrals at 2.8, 4.7 and 9.3 GeV, J. Ballam, et al., Nucl. Phys B76, 375-399 (1974), DOI, PDF.
• S-P Wave Interference in K+K- in Photoproduction Near K+K- Threshold, D.C. Fries et al., Nucl. Phys. B143, 408, (1978), DOI.
• The hadronic properties of the photon in high-energy interactions , T.H. Bauer, R.D. Spital, D.R. Yennie, and F.M. Pipkin Rev. Mod. Phys 50, No. 2, (1978) 261, DOI.

#### Theoretical Papers

• Polarization observables in the longitudinal basis for pseudo-scalar meson photoproduction using a density matrix approach B. Dey et al., Phys. Rev. C83, 055208 (2011), DOI.
• Vector meson photoproduction studied in its radiative decay channel, Qiang Zhao, J. S. Al-Khalili, and P. L. Cole, Phys. Rev. C71, 054004 (2005), DOI.
• Constraints on vector meson photoproduction spin observables W. M. Kloet and Frank Tabakin, Phys. Rev. C61, 015501 (1999), DOI.
• Spin information from vector-meson decay in photoproduction, W. M. Kloet, Wen-Tai Chiang and Frank Tabakin, Phys. Rev. C58, 1086 (1998), DOI.
• Completeness rules for spin observables in pseudoscalar meson photoproduction Wen-Tai Chiang and Frank Tabakin, Phys. Rev. C55, 2054 (1997), DOI.

#### Generalized Parton Distributions (GPD)

• Timelike Compton scattering: exclusive photoproduction of lepton pairs, E,.R. Berger et al., Eur.Phys.J.C23:675-689,2002 or hep-ph/0110062 pdf
• Photoproduction of a π ρ pair with a large invariant mass and transversity generalized parton distribution, M. El Beiyad et al., hep-ph/1001.4491 pdf

==Other==