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Register a new userBeam Asymmetry $mathbf{Sigma}$ for the Photoproduction of $mathbf{eta}$ and $mathbf{eta^{prime}}$ Mesons at $mathbf{E_{gamma}=8.8}$GeV
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We report on the measurement of the beam asymmetry $Sigma$ for the reactions $vec{gamma}prightarrow peta$ and $vec{gamma}p rightarrow peta^{prime}$ from the GlueX experiment, using an 8.2--8.8 GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Lab. These measurements are made as a function of momentum transfer $-t$, with significantly higher statistical precision than our earlier $eta$ measurements, and are the first measurements of $eta^{prime}$ in this energy range. We compare the results to theoretical predictions based on $t$--channel quasi-particle exchange. We also compare the ratio of $Sigma_{eta}$ to $Sigma_{eta^{prime}}$ to these models, as this ratio is predicted to be sensitive to the amount of $sbar{s}$ exchange in the production. We find that photoproduction of both $eta$ and $eta^{prime}$ is dominated by natural parity exchange with little dependence on $-t$.
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We present high-statistic data on charged pion emission from Au+Au collisions at $sqrt{s_{rm{NN}}}$ = 2.4 GeV (corresponding to $E_{beam}$ = 1.23 A GeV) in four centrality classes in the range 0 - 40$%$ of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion multiplicity per participating nucleon decreases moderately with increasing centrality. The polar angular distributions are found to be non-isotropic even for the most central event class. Our results on pion multiplicity fit well into the general trend of the world data, but undershoot by $2.5 sigma$ data from the FOPI experiment measured at slightly lower beam energy. We compare our data to state-of-the-art transport model calculations (PHSD, IQMD, PHQMD, GiBUU and SMASH) and find substantial differences between the measurement and the results of these calculations.
Precise measurements of the proton electromagnetic form factor ratio $R = mu_p G_E^p/G_M^p$ using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of $R$ with momentum transfer $Q^2$ for $Q^2 gtrsim 1$ GeV$^2$, in strong disagreement with previous extractions of $R$ from cross section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Labs Hall A measured $R$ at four $Q^2$ values in the range 3.5 GeV$^2 le Q^2 le 5.6$ GeV$^2$. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher $Q^2$ motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for $R$, improving the consistency of the polarization transfer data in the high-$Q^2$ region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis.
Measurements of the linearly-polarized photon beam asymmetry $Sigma$ for photoproduction from the proton of $eta$ and $eta^prime$ mesons are reported. A linearly-polarized tagged photon beam produced by coherent bremsstrahlung was incident on a cryogenic hydrogen target within the CEBAF Large Acceptance Spectrometer. Results are presented for the $gamma p to eta p$ reaction for incident photon energies from 1.070 to 1.876 GeV, and from 1.516 to 1.836 GeV for the $gamma p to eta^prime p$ reaction. For $gamma p to eta p$, the data reported here considerably extend the range of measurements to higher energies, and are consistent with the few previously published measurements for this observable near threshold. For $gamma p to eta^prime p$, the results obtained are consistent with the few previously published measurements for this observable near threshold, but also greatly expand the incident photon energy coverage for that reaction. Initial analysis of the data reported here with the Bonn-Gatchina model strengthens the evidence for four nucleon resonances -- the $N(1895)1/2^-$, $N(1900)3/2^+$, $N(2100)1/2^+$ and $N(2120)3/2^-$ resonances -- which presently lack the four-star status in the current Particle Data Group compilation, providing examples of how these new measurements help refine models of the photoproduction process.
The determination of the magnon diffusion length (MDL) is important for increasing the efficiency of spin Seebeck effect (SSE) based devices utilising non-metallic magnets. We extract the MDL at $50$ and $300,rm{K}$ in an $rm{Fe}_{3}rm{O}_{4}$ single crystal from the magnon dispersion obtained using inelastic neutron scattering (INS) and find them to be equal within error. We then measure the heat flux normalised SSE responses and in-plane magnetization of $rm{Fe}_{3}rm{O}_{4}$ thin films and normalise by the static magnetization contribution to the SSE before determining the MDLs from a fit of the thickness dependence. We find that the MDLs determined in this way are smaller than that measured from INS which maybe due to differences in magnon propagation between bulk and thin film $rm{Fe}_{3}rm{O}_{4}$.
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.
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