η and η’ meson photoproduction on nucleons

First measurement of the $\Sigma$ beam asymmetry in $\eta^{\prime}$ photoproduction off the proton near threshold

“…4 together with the calculations of [25][26][27][28]. As one can see, the asymmetry is positive at forward angles and negative at backward angles.…”

“…As one can see, the agreement is excellent. GeV (corresponding to a total center-of-mass energy W of 1.903 and 1.912 GeV, respectively) as a function of the meson production angle in the center-of-mass system compared to theoretical calculations: red dotted line [26], blue dashed line [25] green dot-dashed [28], orange long-dashed [27]. The solid black line is the result of a fit performed with a function f (θ) = a · sin 2 (θ) cos(θ).…”

“…From the theoretical point of view, four approaches are available in the literature: a relativistic meson-exchange model of hadronic interactions [24,25]; a reggeized model for η and η photoproduction [26]; a chiral quarkmodel [27] and an isobar model [28].…”

Study of η and η′ Photoproduction at MAMI

“…So far, the existing experimental data for η 0 photoproduction, provided by CLAS [4,15] and CBELSA/TAPS [5], are quite scarce, especially in the near-threshold region. Recently, the threshold region attracted more attention after the first results for the beam asymmetry Σ were presented by GRAAL [16], which, although limited in statistics, could not be reproduced by any of the existing models describing η 0 photoproduction [17][18][19][20][21]. The threshold at W ¼ 1896 MeV for the γp → η 0 p reaction is located in a mass region that plays a key role for our understanding of the nucleon spectrum.…”

Energy-dependent analysis of eta-meson photoproduction on protons and neutrons without background in the energy region up to 3.4 GeV

“…The resonances entering the latest version of our model are listed in Table 1. In the columns 4 and 5 of the table we give adjustable parameters γ E and γ M , which are the product of hadronic and electromagnetic vertices of the corresponding resonance states [25]. They are related to the helicity amplitudes A λ (λ = 1/2, 3/2) which in turn are related to the quantities ξ λ :…”