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  • Beam-Recoil Polarization Measurement of π^{0} Electroproduction on the Proton in the Region of the Roper Resonance
    Štajner, S; Achenbach, P; Beranek, T; Beričič, J; Bernauer, J C; Bosnar, D; Böhm, R; Correa, L; Denig, A; Distler, M O; Esser, A; Fonvieille, H; Friedrich, J M; Friščić, I; Kegel, S; Kohl, Y; Merkel, H; Mihovilovič, M; Müller, J; Müller, U; Nungesser, L; Pochodzalla, J; Schlimme, B S; Schoth, M; Schulz, F; Sfienti, C; Širca, S; Thiel, M; Tiator, L; Tyukin, A; Weber, A; Yaron, I

    Physical review letters, 2017-Jul-14, Letnik: 119, Številka: 2
    Journal Article

    The helicity-dependent recoil proton polarizations P_{x}^{'} and P_{z}^{'} as well as the helicity-independent component P_{y} have been measured in the p(eover →,e^{'}pover →)π^{0} reaction at four-momentum transfer Q^{2}≃0.1  GeV^{2}, center-of-mass proton emission angle θ_{p}^{*}≃90°, and invariant mass W≃1440  MeV. This first precise measurement of double-polarization observables in the energy domain of the Roper resonance P_{11}(1440) by exploiting recoil polarimetry has allowed for the extraction of its scalar electroexcitation amplitude at an unprecedentedly low value of Q^{2}, establishing a powerful instrument for probing the interplay of quark and meson degrees of freedom in the nucleon.

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