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
Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia.
Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, DE-55128 Mainz, Germany.
Phys Rev Lett. 2017 Jul 14;119(2):022001. doi: 10.1103/PhysRevLett.119.022001. Epub 2017 Jul 13.
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(e[over →],e^{'}p[over →])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.
在四动量转移 (Q^{2}\simeq0.1,\text{GeV}^{2})、质心质子发射角 (\theta_{p}^{*}\simeq90^{\circ}) 以及不变质量 (W\simeq1440,\text{MeV}) 的 (p(e[\overrightarrow{]},e^{'}p[\overrightarrow{]})\pi^{0}) 反应中，测量了与螺旋度相关的反冲质子极化 (P_{x}^{'}) 和 (P_{z}^{'}) 以及与螺旋度无关的分量 (P_{y})。通过利用反冲极化测量法首次在罗珀共振 (P_{11}(1440)) 的能量域中对双极化可观测量进行精确测量，使得能够在前所未有的低 (Q^{2}) 值下提取其标量电激发振幅，从而建立了一种强大的工具来探测核子中夸克和介子自由度的相互作用。
