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تسجيل مستخدم جديدThe N(1520) 3/2- helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions
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New data on the polarization observables T, P, and H for the reaction $gamma p to ppi^0$ are reported. The results are extracted from azimuthal asymmetries when a transversely polarized butanol target and a linearly polarized photon beam are used. The data were taken at the Bonn electron stretcher accelerator ELSA using the CBELSA/TAPS detector. These and earlier data are used to perform a truncated energy-independent partial wave analysis in sliced-energy bins. This energy-independent analysis is compared to the results from energy-dependent partial wave analyses.
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Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector in the reaction $gamma pto ppi^0$ for photon energies between 0.85 and 2.50 GeV. The $pi^0$ mesons are observed in their dominant neutral decay mode: $pi^0togammagamma$.
For the first time, the differential cross sections cover the very forward region, $theta_{rm c.m.}<60^circ$. A partial-wave analysis of these data within the Bonn-Gatchina framework observes the high-mass resonances $G_{17}$(2190), $D_{13}$(2080), and $D_{15}$(2070).
An experiment designed to investigate the strangeness photoproduction process using a tagged photon beam in the energy range of 0.90 -1.08 GeV incident on a liquid deuterium target was successfully performed. The purpose of the experiment was to meas
ure the production of neutral kaons and the lambda particles on a deuteron. The generation of photo produced particles was verified by the measurement of their decayed charged particles in the Neutral Kaon Spectrometer 2. The reconstructed invariant mass distributions were achieved by selecting events where two or more particles tracks were identified. Preliminary results are presented here.
The transition helicity amplitudes from the proton ground state to the $N(1440)1/2^+$, $N(1520)3/2^-$, and $Delta(1620)1/2^-$ resonances ($gamma_vpN^*$ electrocouplings) were determined from the analysis of nine independent one-fold differential $pi^
+ pi^- p$ electroproduction cross sections off a proton target, taken with CLAS at photon virtualities 0.5 GeV$^2$ $< Q^2 <$ 1.5 GeV$^2$. The phenomenological reaction model employed for separation of the resonant and non-resonant contributions to this exclusive channel was further developed. The $N(1440)1/2^+$, $N(1520)3/2^-$, and $Delta(1620)1/2^-$ electrocouplings were obtained from the resonant amplitudes of charged double-pion electroproduction off the proton in the aforementioned area of photon virtualities for the first time. Consistent results on $gamma_vpN^*$ electrocouplings available from independent analyses of several $W$-intervals with different non-resonant contributions offer clear evidence for the reliable extraction of these fundamental quantities. These studies also improved the knowledge on hadronic branching ratios for the $N(1440)1/2^+$, $N(1520)3/2^-$, and $Delta(1620)1/2^-$ decays to the $pi Delta$ and $rho N$ final states. These new results provide a substantial impact on the QCD-based approaches that describe the $N^*$ structure and demonstrate the capability to explore fundamental ingredients of the non-perturbative strong interaction that are behind the excited nucleon state formation.
Photoproduction of $Lambda$(1520) with liquid hydrogen and deuterium targets was examined at photon energies below 2.4 GeV in the SPring-8 LEPS experiment. For the first time, the differential cross sections were measured at low energies and with a d
euterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K$^{+/0}$ angles. This suggests the importance of the contact term, which coexists with t-channel K exchange under gauge invariance. This interpretation was compatible with the differential cross sections, decay asymmetry, and photon beam asymmetry measured in the production from protons at forward K$^+$ angles.
Results are presented for the first measurement of the double-polarization helicity asymmetry E for the $eta$ photoproduction reaction $gamma p rightarrow eta p$. Data were obtained using the FROzen Spin Target (FROST) with the CLAS spectrometer in H
all B at Jefferson Lab, covering a range of center-of-mass energy W from threshold to 2.15 GeV and a large range in center-of-mass polar angle. As an initial application of these data, the results have been incorporated into the Julich model to examine the case for the existence of a narrow $N^*$ resonance between 1.66 and 1.70 GeV. The addition of these data to the world database results in marked changes in the predictions for the E observable using that model. Further comparison with several theoretical approaches indicates these data will significantly enhance our understanding of nucleon resonances.
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