Measurement of spin-density matrix elements in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>ρ</mml:mi><mml:mo>(</mml:mo><mml:mn>770</mml:mn><mml:mo>)</mml:mo></mml:mrow></mml:math> production with a linearly polarized photon beam at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mi>γ</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>8.2</mml:mn><mml:mo>–</mml:mo><mml:mn>8.8</mml:mn><mml:mo> </mml:mo><mml:mi>GeV</mml:mi></mml:mrow></mml:math>
S. Adhikari, F. Afzal, C. S. Akondi, M. Albrecht, M. J. Amaryan, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, Fernando Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, В. В. Бердников, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, Duane Byer, E. Chudakov, P. L. Cole, O. Cortes, V. Credé, M. M. Dalton, D. Darulis, A. Deur, S. Dobbs, A. Dolgolenko, R. Dotel, M. Dugger, R. Dzhygadlo, D. Ebersole, M. Edo, H. Egiyan, T. Erbora, P. Eugenio, A. Fabrizi, C. Fanelli, S. Fang, S. Fegan, J. Fitches, A. M. Foda, S. Furletov, L. Gan, He Gao, A. Gardner, A. Gasparian, C. Gleason, K. Goetzen, V. Goryachev, B. Grube, J. Guo, L. Guo, T. J. Hague, H. Hakobyan, J. Hernandez, Nathaniel Hoffman, D. Hornidge, G. Hou, G. M. Huber, P. Hurck, A. Hurley, W. Imoehl, D. G. Ireland, M. M. Ito, I. Jaeglé, N. S. Jarvis, T. Jeske, R. T. Jones, V. Kakoyan, G. Kalicy, V. Khachatryan, M. Khatchatryan, C. Kourkoumelis, A. LaDuke, I. Larin, David Lawrence, D. I. Lersch, H. Li, B. Liu, K. Livingston, G. J. Lolos, L. Lorenti, Valery E. Lyubovitskij, R. Ma, D. Mack, A. Mahmood, H. Marukyan, V. Matveev, M. McCaughan, M. McCracken, C. A. Meyer, R. Miskimen, R. E. Mitchell, K. Mizutani, V. Neelamana, L. Ng, E. Nissen
Abstract
The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\phantom{\rule{4pt}{0ex}}\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $\ensuremath{\rho}$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$ dependence of natural- and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $\ensuremath{\rho}(770)$ differ by two units are negligible for $\ensuremath{-}t<0.5\phantom{\rule{4pt}{0ex}}{\text{GeV}}^{2}/{c}^{2}$.