Polarization of ${\Sigma }^{+}$ hyperons produced by 800 GeV/c protons on Cu and Be

We show that ${\Sigma }^{+}$ hyperons produced by 800 GeV/c protons on targets of Be and Cu have significant polarizations (15–20%). These polarizations persist at values of $p_t\approx 2\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{c}$ and a wide range of $x_F$. The polarizations from the Cu target are consistently less than from Be. The average ratio of the ${\Sigma }^{+}$ polarization from Cu to that from Be is $0.68\pm 0.08$.

Figure 1

Plan view (not to scale) shows the experimental apparatus and simulated events. Shown are the detectors, hyperon magnet and the M2 magnet. The major component of the magnets' fields are in the y-direction. Transition radiation detectors (TRD) were used to distinguish ${\Sigma }^{+}$ from lighter particles. Silicon strip detectors (SSD), proportional wire chambers (PWC), and vector drift chambers (VDC) were used to measure the spatial positions of the charged particles.

Figure 2

${\Sigma }^{+}$ effective mass ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{c}}^2$.

Figure 3

A summary of the ${\Sigma }^{+}$ polarization data from E781 and E761. The polarization is plotted as a function of $x_F$. The corresponding $p_t$ interval for each point is included in the legend.

Figure 4

${\Sigma }^{+}$ polarization ratio vs $x_F$.