e-Article
Measurement of Spin-Density Matrix Elements in $\Delta^{++}(1232)$ photoproduction
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Working Paper
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Afzal, F.; Akondi, C. S.; Albrecht, M.; Amaryan, M.; Arrigo, S.; Arroyave, V.; Asaturyan, A.; Austregesilo, A.; Baldwin, Z.; Barbosa, F.; Barlow, J.; Barriga, E.; Barsotti, R.; Barton, D.; Baturin, V.; Berdnikov, V. V.; Black, T.; Boeglin, W.; Boer, M.; Briscoe, W. J.; Britton, T.; Cao, S.; Chudakov, E.; Chung, G.; Cole, P. L.; Cortes, O.; Crede, V.; Dalton, M. M.; Darulis, D.; Deur, A.; Dobbs, S.; Dolgolenko, A.; Dugger, M.; Dzhygadlo, R.; Ebersole, D.; Edo, M.; Egiyan, H.; Erbora, T.; Eugenio, P.; Fabrizi, A.; Fanelli, C.; Fang, S.; Fitches, J.; Foda, A. M.; Furletov, S.; Gan, L.; Gao, H.; Gardner, A.; Gasparian, A.; Glazier, D.; Gleason, C.; Goryachev, V. S.; Grube, B.; Guo, J.; Guo, L.; Hernandez, J.; Hernandez, K.; Hoffman, N. D.; Hornidge, D.; Hou, G.; Hurck, P.; Hurley, A.; Imoehl, W.; Ireland, D. G.; Ito, M. M.; Jaegle, I.; Jarvis, N. S.; Jeske, T.; Jing, M.; Jones, R. T.; Kakoyan, V.; Kalicy, G.; Khachatryan, V.; Kourkoumelis, C.; LaDuke, A.; Larin, I.; Lawrence, D.; Lersch, D. I.; Li, H.; Liu, B.; Livingston, K.; Lolos, G. J.; Lorenti, L.; Lyubovitskij, V.; Ma, R.; Mack, D.; Mahmood, A.; Marukyan, H.; Matveev, V.; McCaughan, M.; McCracken, M.; Meyer, C. A.; Miskimen, R.; Mitchell, R. E.; Mizutani, K.; Neelamana, V.; Ng, L.; Nissen, E.; Orešić, S.; Ostrovidov, A. I.; Papandreou, Z.; Paudel, C.; Pedroni, R.; Pentchev, L.; Peters, K. J.; Prather, E.; Rakshit, S.; Reinhold, J.; Remington, A.; Ritchie, B. G.; Ritman, J.; Rodriguez, G.; Romanov, D.; Saldana, K.; Salgado, C.; Schadmand, S.; Schertz, A. M.; Scheuer, K.; Schick, A.; Schmidt, A.; Schumacher, R. A.; Schwiening, J.; Septian, N.; Sharp, P.; Shen, X.; Shepherd, M. R.; Sikes, J.; Smith, A.; Smith, E. S.; Sober, D. I.; Somov, A.; Somov, S.; Stevens, J. R.; Strakovsky, I. I.; Sumner, B.; Suresh, K.; Tarasov, V. V.; Taylor, S.; Teymurazyan, A.; Thiel, A.; Viducic, T.; Whitlatch, T.; Wickramaarachchi, N.; Wunderlich, Y.; Yu, B.; Zarling, J.; Zhang, Z.; Zhou, X.; Zihlmann, B.
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Abstract
We report the measurement of spin-density matrix elements of the $\Delta^{++}(1232)$ in the photoproduction reaction $\gamma p \to \pi^-\Delta^{++}(1232)$ with the GlueX experiment in Hall D at Jefferson Lab. The measurement used a linearly polarized photon beam with $E_\gamma=8.2-8.8$~GeV and the statistical precision exceeds the previous measurement from SLAC by three orders of magnitude for the momentum transfer squared region $-t < 1.4$ GeV$^2$. The data are sensitive to the previously undetermined relative sign between couplings in existing Regge exchange models. Linear combinations of the extracted SDMEs allow for a decomposition into natural and unnatural exchange amplitudes, which shows that the unnatural exchange plays an important role in the low $-t$ region.