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Register a new userPartial-wave analyses of $gamma p rightarrow eta p$ and $gamma n rightarrow eta n$ using a multichannel framework
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This paper presents results from partial-wave analyses of the photoproduction reactions $gamma p rightarrow eta p$ and $gamma n rightarrow eta n$. World data for the observables DSG, $Sigma$, $T$, $P$, $F$, and $E$ were analyzed as part of this work. The dominant amplitude in the fitting range from threshold to a c.m. energy of 1900 MeV was found to be $S_{11}$ in both reactions, consistent with results of other groups. At c.m. energies above 1600 MeV, our solution deviates from published results, with this work finding higher-order partial waves becoming significant. Data off the proton suggest that the higher-order terms contributing to the reaction include $P_{11}$, $P_{13}$, and $F_{15}$. The final results also hint that $F_{17}$ is needed to fit double-polarization observables above 1900 MeV. Data off the neutron show a contribution from $P_{13}$, as well as strong contributions from $D_{13}$ and $D_{15}$.
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Results from a partial-wave analysis of the reaction $gamma p rightarrow K^+ Lambda$ are presented. The reaction is dominated by the $S_{11}(1650)$ and $P_{13}(1720)$ resonances at low energies and by $P_{13}(1900)$ at higher energies. There are small contributions from all amplitudes up to and including $G_{17}$, with $F_{17}$ necessary for obtaining a good fit of several of the spin observables. We find evidence for $P_{11}$(1880), $D_{13}$(2120), and $D_{15}$(2080) resonances, as well as a possible $F_{17}$ resonance near 2300 MeV, which is expected from quark-model predictions. Some predictions for $gamma n to K^0 Lambda$ are also included.
The polarization observables $T, E, P, H$, and $G$ in photoproduction of $eta$ mesons off protons are measured for photon energies from threshold to $W=2400,$MeV ($T$), 2280 MeV ($E$), 1620 MeV ($P, H$), or 1820 MeV ($G$), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, JuBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the $Neta$ decay of nucleon resonances. A $Neta$-branching ratio of $0.33pm 0.04$ for $N(1650)1/2^-$ is found, which reduces the large and controversially discussed $Neta$-branching ratio difference of the two lowest mass $J^P=1/2^-$-resonances significantly.
High-statistics differential cross sections for the reactions gamma p -> p eta and gamma p -> p eta-prime have been measured using the CLAS at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The eta-prime results are the most precise to date and provide the largest energy and angular coverage. The eta measurements extend the energy range of the worlds large-angle results by approximately 300 MeV. These new data, in particular the eta-prime measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.
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.
u007fA search for radiative decays of the $P$-wave spin singlet charmonium resonance $h_c$ is performed based on $4.48 times 10^{8}$ $psi$ events collected with the BESIII detector operating at the BEPCII storage ring. Events of the reaction channels $h_{c} rightarrow gamma eta$ and $gamma eta$ are observed with a statistical significance of $8.4 sigma$ and $4.0 sigma$, respectively, for the first time. The branching fractions of $h_{c} rightarrow gamma eta$ and $h_{c} rightarrow gamma eta$ are measured to be $mathcal{B}(h_{c} rightarrow gamma eta)=(1.52 pm 0.27 pm 0.29)times10^{-3}$ and $mathcal{B}(h_{c} rightarrow gamma eta)=(4.7 pm 1.5 pm 1.4)times10^{-4}$, respectively, where the first errors are statistical and the second are systematic uncertainties.
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