We study the polarization with respect to the normal to the production plane for a very clean sample of 27217 Λ 0 / Λ 0 hyperons produced in 230 GeV/ c π − Cu interactions. In general we find P(Λ 0 ) ≈ P( Λ 0 ap; 0 except for x F > 0, p T > 1GeV/ c where P ( Λ 0 ) = −0.28±0.09(stat.)±0.02(syst.).
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High-statistics measurements of differential cross sections and recoil polarizations for the reaction $\gamma p \rightarrow K^+ \Sigma^0$ have been obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass energies ($\sqrt{s}$) from 1.69 to 2.84 GeV, with an extensive coverage in the $K^+$ production angle. Independent measurements were made using the $K^{+}p\pi^{-}$($\gamma$) and $K^{+}p$($\pi^-, \gamma$) final-state topologies, and were found to exhibit good agreement. Our differential cross sections show good agreement with earlier CLAS, SAPHIR and LEPS results, while offering better statistical precision and a 300-MeV increase in $\sqrt{s}$ coverage. Above $\sqrt{s} \approx 2.5$ GeV, $t$- and $u$-channel Regge scaling behavior can be seen at forward- and backward-angles, respectively. Our recoil polarization ($P_\Sigma$) measurements represent a substantial increase in kinematic coverage and enhanced precision over previous world data. At forward angles we find that $P_\Sigma$ is of the same magnitude but opposite sign as $P_\Lambda$, in agreement with the static SU(6) quark model prediction of $P_\Sigma \approx -P_\Lambda$. This expectation is violated in some mid- and backward-angle kinematic regimes, where $P_\Sigma$ and $P_\Lambda$ are of similar magnitudes but also have the same signs. In conjunction with several other meson photoproduction results recently published by CLAS, the present data will help constrain the partial wave analyses being performed to search for missing baryon resonances.
Differential cross section as a function of COS(THETA(K+,CM)) for the centre-of mass range 1.69 to 1.7 GeV.
Differential cross section as a function of COS(THETA(K+,CM)) for the centre-of mass range 1.7 to 1.71 GeV.
Differential cross section as a function of COS(THETA(K+,CM)) for the centre-of mass range 1.71 to 1.72 GeV.
We have mesured the polarization of 375-GeV/c Σ+ and Σ¯ − hyperons produced by 800-GeV/c protons incident on a Cu target. We find that the Σ+ polarization rises with increasing pt to a maximum of 16% at pt=1.0 GeV/c and then decreases to 10% at pt=1.8 GeV/c. We compare this Σ+ polarization with data at lower energies. The Σ¯ − polarization has been measured for the first time. It has the same sign as the Σ+ but smaller magnitude in a similar kinematical region.
Data from Horizontal targeting.
Data from Vertical targeting.
Data from Horizontal targeting.
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 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 $\Sigma$.
We report measurements of the photon beam asymmetry $\Sigma$ for the reaction $\vec{\gamma} p\to K^+\Sigma^0$(1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected using a linearly polarized photon beam in the energy range of 8.2-8.8 GeV incident on a liquid hydrogen target. The beam asymmetry $\Sigma$ was measured as a function of the Mandelstam variable $t$, and a single value of $\Sigma$ was extracted for events produced in the $u$-channel. These are the first exclusive measurements of the photon beam asymmetry $\Sigma$ for the reaction in this energy range. For the $t$-channel, the measured beam asymmetry is close to unity over the $t$-range studied, $-t=(0.1-1.4)~$(GeV/$c$)$^{2}$, with an average value of $\Sigma = 1.00\pm 0.05$. This agrees with theoretical models that describe the reaction via the natural-parity exchange of the $K^{*}$(892) Regge trajectory. A value of $\Sigma = 0.41 \pm 0.09$ is obtained for the $u$-channel integrated up to $-u=2.0$~(GeV/$c$)$^{2}$.
Beam asymmetry $\Sigma$ for the low $-t$ region where the horizontal error bars indicate the rms widths of the $t$ bin. The uncertainties on $\Sigma$ are statistical and systematic (uncorrelated across t bins), respectively. There is an additional fully correlated systematic uncertainty of 2.1% on the magnitude of $\Sigma$.
Average beam asymmetry $\Sigma$ for the low $-u$ region where the uncertainty on $\Sigma$ is the statistical and systematic (uncorrelated across t bins), respectively. There is an additional fully correlated systematic uncertainty of 2.1% on the magnitude of $\Sigma$.
We report on the measurement of the beam asymmetry $\Sigma$ for the reactions $\vec{\gamma}p\rightarrow p\eta$ and $\vec{\gamma}p \rightarrow p\eta^{\prime}$ 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 $s\bar{s}$ exchange in the production. We find that photoproduction of both $\eta$ and $\eta^{\prime}$ is dominated by natural parity exchange with little dependence on $-t$.
Values and errors for the photon beam asymmetry $\Sigma_{\eta}$ for the reaction $\gamma p \rightarrow \eta p$ with $\eta\rightarrow\gamma\gamma$. For the binning in $t$, we report the range of the data, the event-weighted mean of all $t$ values, and the RMS of that distribution. For $\Sigma_{\eta}$, we report the value, statistical error, and systematic error. The total error is the sum of the previous two in quadrature. Not reported here is the $2.1\%$ relative uncertainty due to the determination of the polarization of the photon beam.
Values and errors for the photon beam asymmetry $\Sigma_{\eta\prime}$ for the reaction $\gamma p \rightarrow \eta^{\prime} p$ with $\eta^{\prime}\rightarrow \eta\pi^{+}\pi^{-}$ and the $\eta\rightarrow\gamma\gamma$. For the binning in $t$, we report the range of the data, the event-weighted mean of all $t$ values, and the RMS of that distribution. For $\Sigma_{\eta\prime}$, we report the value, statistical error, and systematic error. The total error is the sum of the previous two in quadrature. Not reported here is the $2.1\%$ relative uncertainty due to the determination of the polarization of the photon beam.
Values and errors for the ratio of photon beam asymmetries $\Sigma_{\eta\prime}/\Sigma_{\eta}$ for the reported reactions. To form the ratio, the $\eta$ analysis is done with the same binning in $t$ as the $\eta^\prime$ analysis, and for each bin we report the range of the data, the event-weighted mean of all $t$ values, and the RMS of that distribution. For $\Sigma_{\eta\prime}/\Sigma_{\eta}$, we report the value, statistical error, and systematic error. The total error is the sum of the previous two in quadrature.}
We have measured the polarization of $\Lambda$ hyperons produced inclusively by a $\Sigma^-$ beam of 340 GeV/c momentum in nuclear targets. From a sample of 9.5 millions of identified $\Lambda$ decays, polarizations were determined in the range $x_F \gt 0.1$ and $p_t\leq 1.6$ GeV/c . The polarization w.r.t. the production normal is mainly positive for $x_F \geq 0.3$. At fixed values of $x_F$, it increases with $p_t$ to a maximum between $p_t = 0.5$ and $p_t = 1$ GeV/c , and then decreases to zero or even negative values, in sharp contrast to the plateau above $p_t = 1$ GeV/c observed in inclusive $\Lambda$ production by protons.
Measured values of the LAMBDA polarization as a function of PT in the XL range 0.1 to 0.2.
Measured values of the LAMBDA polarization as a function of PT in the XL range 0.2 to 0.3.
Measured values of the LAMBDA polarization as a function of PT in the XL range 0.3 to 0.4.
Analyzing powers for πp elastic scattering at bombarding energies below the Δ(1232) resonance were measured at TRIUMF using the CHAOS spectrometer and a polarized spin target. This work presents π− data at six incident energies of 57, 67, 87, 98, 117, and 139 MeV, and a single π+ data set at 139 MeV. The higher energy measurements cover an angular range of 72°<~θc.m.<~180° while the lower energies were limited to 101°<~θc.m.<~180°. There is a high degree of consistency between this work and the predictions of the VPI/GWU group’s SM95 partial wave analysis.
Analysing power measurements for a 139 GeV PI+ beam (standard track).
Analysing power measurements for a 139 GeV PI- beam (standard track).
Analysing power measurements for a 117 GeV PI- beam (standard track).
The elastic scattering of 600-MeV protons from light nuclei has been studied at the National Aeronautics Space Administration Space Radiation Effects Laboratory (SREL) synchrocyclotron. Differential cross sections have been obtained for the scattering of protons from hydrogen, deuterium, helium-3, and helium-4. Polarization was measured for deuterium and He4 nuclei. The p−p cross-section data are in excellent agreement with the predictions from the Livermore phase shifts. Small-angle p−D, p−He3 elastic scattering data are compared with calculations based on the multiple-scattering theories of Watson and Glauber.
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