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Register a new userBackward-angle photoproduction of $pi^0$ mesons on the proton at $E_gamma$ = 1.5--2.4 GeV
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Differential cross sections and photon beam asymmetries for $pi^0$ photoproduction have been measured at $E_gamma$ = 1.5--2.4 GeV and at the $pi^0$ scattering angles, --1 $<$ cos$Theta_{c.m.} <$ --0.6. The energy-dependent slope of differential cross sections for $u$-channel $pi^0$ production has been determined. An enhancement at backward angles is found above $E_gamma$ = 2.0 GeV. This is inferred to be due to the $u$-channel contribution and/or resonances. Photon beam asymmetries have been obtained for the first time at backward angles. A strong angular dependence has been found at $E_gamma >$ 2.0 GeV, which may be due to the unknown high-mass resonances.
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Differential cross sections for eta photoproduction off protons have been measured at E_gamma = 1.6 - 2.4 GeV in the backward direction. A bump structure has been observed above 2.0 GeV in the total energy. No such bump is observed in cross sections for eta, omega and pi0 photoproductions. It is inferred that this unique structure in eta photoproduction is due to a baryon resonance with a large portion of ss-bar strongly coupled to the etaN channel.
Differential cross sections for $gamma p to K^+Lambda(1405)$ and $gamma p to K^+Sigma^0(1385)$ reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of $0.8<cos(Theta)<1.0$ for the $K^+$ scattering angle in the center-of-mass system. This data is the first measurement of the $Lambda(1405)$ photoproduction cross section. The lineshapes of LamS measured in $Sigma^+pi^-$ and $Sigma^-pi^+$ decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the $Sigmapi$ scattering amplitudes. The ratios of LamS production to SigS production were measured in two photon energy ranges: near the production threshold ($1.5<E_gamma<2.0$ GeV) and far from it ($2.0 <E_gamma<2.4$ GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.
We report the measurement of differential cross sections for $omega$ and $eta$ photoproduction from protons at backward angles ($-1.0<cosTheta_{C.M}^{X}<-0.8$) using linearly polarized photons at $E_{gamma}=$$1.5-3.0$ GeV. Differential cross sections for $omega$ mesons are larger than the predicted $u$-channel contribution in the energy range $2.0leqsqrt{s}leq2.4$ GeV. The differential cross sections for $omega$ and $eta$ mesons become closer to the predicted $u$-channel contribution at $sqrt{s}>2.4$ GeV. A bump structure in the $sqrt{s}$ dependence of the differential cross sections for $eta$ mesons was observed at $sqrt{s}sim$2.35 GeV.
We report measurements of the photon beam asymmetry $Sigma$ for the reactions $vec{gamma}pto ppi^0$ and $vec{gamma}pto peta $ from the GlueX experiment using a 9 GeV linearly-polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Labs Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous $pi^0$ measurements and are the first $eta$ measurements in this energy regime. The results are compared with theoretical predictions based on $t$-channel, quasi-particle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models.
We report a measurement of the $pi^-$ photoproduction beam asymmetry for the reaction $vec{gamma} p rightarrow pi^- Delta^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2--8.8 GeV. The asymmetry $Sigma$ is measured as a function of four-momentum transfer $t$ to the $Delta^{++}$ and compared to phenomenological models. We find that $Sigma$ varies as a function of $t$: negative at smaller values and positive at higher values of $|t|$. The reaction can be described theoretically by $t$-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy.
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