Electroproduction of η Mesons in the S₁₁(1535) Resonance Region at High Momentum Transfer

Abstract

The differential cross-section for the process p(e, e ′ p)η has been measured at Q 2 ∼ 5.7 and 7.0 (GeV/c) 2 for centre-of-mass energies from threshold to 1.8 GeV, encompassing the S11(1535) resonance, which dominates the channel. This is the highest momentum transfer measurement of this exclusive process to date. The helicity-conserving transition amplitude A 1/2 , for the production of the S11(1535) resonance, is extracted from the data. Within the limited Q 2 now measured, this quantity appears to begin scaling as Q −3 -a predicted, but not definitive, signal of the dominance of perturbative QCD, at Q 2 ∼ 5 (GeV/c) 2 .

$$N^*$$ N ∗ form Factors Based on a Covariant Quark Model

“…1, in comparison with the data from Refs. [4,44,45]. Both form factors vanish at Q 2 = 0 as a consequence of the relation F * i (Q 2 ) ∝ |q|.…”

Strong QCD Insights from Excited Nucleon Structure Studies with CLAS and CLAS12

“…The most detailed information on the electrocouplings is currently available for the N * states in the mass range W < 1.6 GeV from studies of πN , ηN , and π + π − p photo-/electroproduction for Q 2 up to 7.7 GeV 2 for the ∆(1232)3/2 + and for Q 2 up to 7 GeV 2 for the N (1535)1/2 − [37, 65,70,71], and for Q 2 < 5 GeV 2 for other resonances [37]. The electrocouplings for the N (1440)1/2 + and N (1520)3/2 − available from independent studies of πN and π + π − p electroproduction are shown in Fig.…”

“…These studies have demonstrated that the structure of the N (1440)1/2 + is defined by a core of three dressed quarks in their Fig. 11 Improvements in the description of the results on the γvpN * electrocouplings [37,71] achieved after accounting for the contributions of the meson-baryon cloud and the quark core. A description of the N (1535)1/2 − is shown for the relativistic quark model [16] accounting for the contributions from KΛ loops and the quark core (solid lines) and the quark core only (dashed line).…”

Structure of the orbital excited $N^*$ from the Schwinger-Dyson equations

“…Using the world data base of pion photo-and electroproduction and the data from Mainz, Bonn, Bates and JLab [2], available at the time, further analysis by MAID [3] extracted longitudinal and transverse helicity amplitudes of nucleon resonance excitation N * (1535) to Q 2 = 4.2 GeV 2 . In the JLab Hall C [4], electroproduction of η mesons in the N * (1535) resonance region was analyzed to extract A 1/2 for even higher photon virtuality, Q 2 ∼ 5.8, 7 GeV 2 , under the assumption that the S 1/2 contribution for the cross section is negligible 1 . A value of A 1/2 at Q 2 ∼ 0 is also reported by PDG [5].…”