Signatures of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>d</mml:mi></mml:mrow><mml:mrow><mml:mo>*</mml:mo></mml:mrow></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:mn>2380</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> Hexaquark in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>d</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>γ</mml:mi><mml:mo>,</mml:mo><mml:mi>p</mml:mi><mml:mover accent="true"><mml:mrow><mml:mi>n</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">→</mml:mo></mml:mrow></mml:mover><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math>
M. Bashkanov, D. P. Watts, S. Kay, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, C. S. Akondi, J. R. M. Annand, H. J. Arends, R. Beck, M. Biroth, N. S. Borisov, A. Braghieri, W. J. Briscoe, F. Cividini, C. Collicott, S. Costanza, A. Denig, E. J. Downie, P. Drexler, S. Fegan, A. Fix, S. Gardner, D. Ghosal, D. I. Glazier, I. Gorodnov, W. Gradl, Michael Günther, D. Gurevich, L. Heijkenskjöld, D. Hornidge, G. M. Huber, A. Käser, V. L. Kashevarov, M. Korolija, B. Krusche, A. B. Lazarev, K. Livingston, S. Lutterer, I. J. D. MacGregor, D. M. Manley, P. P. Martel, R. Miskimen, E. Mornacchi, C. Mullen, A. Neganov, A. Neiser, M. Ostrick, P. B. Otte, D. Paudyal, P. Pedroni, A. Powell, S. Prakhov, G. Ron, A. Sarty, C. Sfienti, V. Sokhoyan, K. Spieker, O. Steffen, I. I. Strakovsky, Th. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, Yu. A. Usov, S. R. Wagner, N. K. Walford, D. Werthmüller, J. Wettig, M. Wolfes, N. Zachariou, L. Zana
Abstract
We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570 MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the d^{*}(2380) hexaquark.