Simple relation between the γN→N(1535) helicity amplitudes
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2011
Authors
Ramalho, G.
Tsushima, K.
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Physical Review D: Particles, Fields, Gravitation and Cosmology, 2011; 84(5):051301-1-051301-4
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G. Ramalho and K. Tsushima
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Abstract
It is shown that the helicity amplitudes A1/2 and S1/2 in the γN→N(1535) reaction, can be well related by S1/2=-√1+τ/√2MS2-M2/2MSQA1/2 in the region Q2>2 GeV2, where M and MS are the nucleon and N(1535) masses, q2=-Q2 the four-momentum transfer squared, and τ=Q2/(MS+M)2. This follows from the fact that the Pauli-type transition form factor F2* extracted from the experimental data, turns up to show F2*≃0 for Q2>1.5 GeV2. The observed relation is tested by the experimentally extracted helicity amplitudes and the MAID parametrization (Mainz group). A direct consequence of the relation is that the assumption |A1/2|≫|S1/2| is not valid for high Q2. Instead, both amplitudes A1/2 and S1/2 have the same Q2 dependence in the high Q2 region; aside from that S1/2 has an extra factor, -1/√2MS-M/2MS. The origin of this relation is interpreted in a perspective of a quark model.
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©2011 American Physical Society