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Register a new userEta photoproduction in a combined analysis of pion- and photon-induced reactions
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The $eta N$ final state is isospin-selective and thus provides access to the spectrum of excited nucleons without being affected by excited $Delta$ states. To this end, the world database on eta photoproduction off the proton up to a center-of-mass energy of $Esim 2.3$ GeV is analyzed, including data on differential cross sections, and single and double polarization observables. The resonance spectrum and its properties are determined in a combined analysis of eta and pion photoproduction off the proton together with the reactions $pi Nto pi N$, $eta N$, $KLambda$ and $KSigma$. For the analysis, the so-called Julich coupled-channel framework is used, incorporating unitarity, analyticity, and effective three-body channels. Parameters tied to photoproduction and hadronic interactions are varied simultaneously. The influence of recent MAMI $T$ and $F$ asymmetry data on the eta photoproduction amplitude is discussed in detail.
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The production of eta mesons in photon- and hadron-induced reactions has been revisited in view of the recent additions of high-precision data to the world data base. Based on an effective Lagrangian approach, we have performed a combined analysis of the free and quasi-free gamma N -> eta N, N N -> N N eta, and pi N -> eta N reactions. Considering spin-1/2 and -3/2 resonances, we found that a set of above-threshold resonances {S_{11}, P_{11}, P_{13}}, with fitted mass values of about M_R=1925, 2130, and 2050 MeV, respectively, and the four-star sub-threshold P_{13}(1720) resonance reproduce best all existing data for the eta production processes in the resonance-energy region considered in this work. All three above-threshold resonances found in the present analysis are essential and indispensable for the good quality of the present fits.
We study $eta$ photoproduction off the deuteron ($gamma dtoeta pn$) at a special kinematics: $sim 0.94$ GeV of the photon beam energy and $sim 0^circ$ of the scattering angle of the proton. This kinematics is ideal to extract the low-energy $eta$-nucleon scattering parameters such as $a_{eta N}$ (scattering length) and $r_{eta N}$ (effective range) because the $eta$-nucleon elastic scattering is significantly enhanced. We show that if a ratio $R$, the $gamma dtoeta pn$ cross section divided by the $gamma ptoeta p$ cross section convoluted with the proton momentum distribution in the deuteron, is measured with 5% error, ${rm Re}[a_{eta N}]$ (${rm Re}[r_{eta N}]$) can be determined at the precision of $simpm$0.1 fm ($simpm$0.5 fm), significantly narrowing down the currently estimated range of the parameters. The measurement is ongoing at the Research Center for Electron Photon Science (ELPH), Tohoku University.
The reactions $gamma ptopi^0 p$ and $gamma ptopi^+ n$ are analyzed in a semi-phenomenological approach up to $Esim2.3$ GeV. Fits to differential cross section and single and double polarization observables are performed. A good overall reproduction of the available photoproduction data is achieved. The Julich2012 dynamical coupled-channel model -which describes elastic $pi N$ scattering and the world data base of the reactions $pi Ntoeta N$, $KLambda$, and $KSigma$ at the same time - is employed as the hadronic interaction in the final state. The framework guarantees analyticity and, thus, allows for a reliable extraction of resonance parameters in terms of poles and residues. In particular, the photocouplings at the pole can be extracted and are presented.
In this work, we study the production of strange quarkoniums, the $phi(2170)$, also named $Y(2175)$, and the $eta(2225)$, via a kaon induced reaction on a proton target in an effective Lagrangian approach. The total and differential cross sections of the reactions $K^{-}prightarrow phi (2170)Lambda $ and $K^{-}prightarrow eta (2225)Lambda $ are calculated by the Reggeized $t $-channel Born term under an assumption that the $phi(2170)$ and $eta(2225)$ are $Lambdabar{Lambda}$ molecular states. At the center of mass energies of about 4.2 GeV, the total cross section for the $phi(2170)$ production is predicted to be about 1 $mu $b. The numerical results indicate that it is feasible to produce the $phi (2170)$ via kaon beam scattering at the best energy window near 4.2 GeV. The total cross section for the $eta(2225)$ production is smaller than that for the $phi(2170)$ production and it may reach an order of the magnitude of 0.1 $mu$b. The differential cross sections for both reactions at different center of mass energies are also presented. It is found that the Reggeized $t$ channel gives a considerable contribution at forward angles. As the energy increases, the contribution from the $t$-channel almost concentrates at extreme forward angles. From these theoretical predictions, the relevant experimental research is suggested, which could provide important information to clarify the internal structure and production mechanism of these two strange quarkoniums.
The isobar model EtaMAID has been updated with new and high precision data for eta and etaprime photoproduction on protons and neutrons from MAMI, ELSA, GRAAL and CLAS. The background is described in a recently developed Regge-cut model, and for the resonance part the whole list of nucleon resonances has been investigated with 21 N* states contributing to eta photoproduction and 12 N* states contributing to etaprime photoproduction. A new approach is discussed to avoid double counting in the overlap region of Regge and resonances. A comparison is done among four newly updated partial waves analyses for observables and partial waves. Finally, the possibility of a narrow resonance near W=1900 MeV is discussed, that would be able to explain unexpected energy and angular dependence of observables in p(gamma,etaprime)p near etaprime threshold.
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