A complete set of polarization-transfer observables has been measured for quasifree (p→,n→) reactions on H2, C12, and Ca40 at a bombarding energy of 495 MeV and a laboratory scattering angle of 18°. The data span an energy-loss range from 0 to 160 MeV, with a corresponding momentum transfer range of qc.m.=1.7–1.9 fm−1. The laboratory observables are used to construct partial cross sections proportional to the nonspin response and three orthogonal spin responses. These results are compared to the transverse spin response measured in deep inelastic electron scattering and to nuclear responses based on the random phase approximation. The polarization observables for all three targets are remarkably similar and reveal no evidence for an enhancement of the spin-longitudinal nuclear response relative to the spin-transverse response. These results suggest the need for substantial modifications to the standard form assumed for the residual particle-hole interaction.
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The analyzing power A N of proton-proton, proton-hydrocarbon, and antiproton-hydrocarbon, scattering in the Coulomb-nuclear interference region has been measured using thhe 185 GeV/ c Fermilab polarized-proton and -antiproton beams. The results are found to be consistent with theoretical predictions within statistical uncertainties.
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Data from hydrocarbon target.
Data from hydrocarbon target.
The analyzing power (spin-dependent azimuthal asymmetry) has been observed for the first time in the nuclear Coulomb coherent production process, the ‘‘Primakoff process,’’ with the use of the newly constructed 185-GeV/c Fermilab polarized proton beam. We have observed a large asymmetry of this process in the regions of ‖t’‖<0.001 (GeV/c)2 and 1.36<M(π0p)<1.52 GeV/c2, where the Coulomb process is predominant. The measured asymmetry is consistent with the analyzing power of the existing low-energy γ+p→π0+p data.
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The quasifree $\overrightarrow{\gamma} d\to\pi^0n(p)$ photon beam asymmetry, $\Sigma$, has been measured at photon energies, $E_\gamma$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 to 148$^\circ$. In this kinematic region, polarization observables are sensitive to contributions from the $\Delta (1232)$ and $N(1440)$ resonances. The extracted values of $\Sigma$ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID, and Bonn-Gatchina analyses; while a revised SAID fit, including the new $\Sigma$ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $\pi^0n$ photoproduction observables, based on fits to published data in the channels $\pi^0p$, $\pi^+n$, and $\pi^-p$.
Photon beam asymmetry Sigma at W= 1.2711 GeV
Photon beam asymmetry Sigma at W= 1.2858 GeV
Photon beam asymmetry Sigma at W= 1.3003 GeV
We have made, for the first time, a direct reconstruction of the pp elastic-scattering matrix at 579 MeV from a series of experiments performed at the Schweizerisches Institut für Nuklearforschung polarized-beam line. Fifteen observables consisting of the polarization, two-spin correlation and transfer parameters, and three-spin parameters were measured at seven angles between 66° and 90° (c. m.). The experimental results and reconstructed amplitudes are presented and compared to phase shift analysis.
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VALUES OF PRECESSION ANGLE O. OBSERVABLES ARE RELATED BY THE FORMULA, (OABC) = (S'ABC)*COS(O) + (K'ABC)*SIN(O).
Tensor polarization observables (t20, t21 and t22) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)^2. The experiment was performed at the Jefferson Laboratory in Hall C using the electron HMS Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q^2 the deuteron charge form factors G_C and G_Q. They are in good agreement with relativistic calculations and disagree with pQCD predictions.
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The differential cross section and deuteron analysing powers of the dp -> {pp}n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using a deuteron beam of energy 1170 MeV, data were obtained for small momentum transfers to a {pp} system with low excitation energy. A good quantitative understanding of all the measured observables is provided by the impulse approximation using known neutron-proton amplitudes. The proof of principle achieved here for the method suggests that measurements at higher energies will provide useful information in regions where the existing np database is far less reliable.
Differential cross section for the unpolarized DEUT P --> P P N reaction integrated over momentum transfer Q < 100 MeV.
Unpolarized differential cross section for the DEUT P --> P P N reaction of (P P) excitation energies < 3 MeV.
Spherical tensor analysing powers t20 and t22 for EPP 0.1 to 1.0 MeV and cos(theta) > 0.5.
We report measurements of the photon beam asymmetry $\Sigma$ for the reactions $\vec{\gamma}p\to p\pi^0$ and $\vec{\gamma}p\to p\eta $ from the GlueX experiment using a 9 GeV linearly-polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Lab's 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.
Measurement of the beam asymmetry $\Sigma$ for $\pi^0$ photoproduction on the proton at $E_\gamma = 9$ GeV. The uncorrelated systematic errors (syst) are given in the table below along with a correlated normalization uncertainty (norm) of 3.6% due to the beam polarization.
Measurement of the beam asymmetry $\Sigma$ for $\eta$ photoproduction on the proton at $E_\gamma = 9$ GeV. The uncorrelated systematic errors (syst) are given in the table below along with a correlated normalization uncertainty (norm) of 3.6% due to the beam polarization.
We report the measurement of the $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_{\gamma}=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_{\gamma}=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $\Lambda$ in the whole observed energy range. A lack of similar feature for $\Sigma^{0}$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{*}$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.
Differential cross sections for the GAMMA P --> K+ LAMBDA reaction as a function of photon energy Egamma for the kaon c.m. production polar angle 0.6 < cos(theta) < 0.7.
Differential cross sections for the GAMMA P --> K+ LAMBDA reaction as a function of photon energy Egamma for the kaon c.m. production polar angle 0.7 < cos(theta) < 0.8.
Differential cross sections for the GAMMA P --> K+ LAMBDA reaction as a function of photon energy Egamma for the kaon c.m. production polar angle 0.8 < cos(theta) < 0.9.
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.
Beam asymmetry $\Sigma$ vs. $|t|$ compared to theoretical predictions. The uncertainty on $|t|$ is the rms of values in the $\Delta^{++}$ signal region. The uncertainties on $\Sigma$ are statistical and systematic (uncorrelated across t bins), respectively. There is an additional fully correlated systematic uncertainty of 1.5% on the magnitude of $\Sigma$.
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