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Using an rf solenoid magnet, we studied the depolarization of a stored 104.1 MeV vertically polarized proton beam. The two primary rf depolarizing resonances were properly centered around the protons{close_quote} circulation frequency f{sub c}, at f{sub c}(3{minus}{nu}{sub s}) and f{sub c}({nu}{sub s}{minus}1), where {nu}{sub s} is the spin tune; moreover, each resonance was roughly consistent with the expected width of about 720 Hz. Each primary rf resonance had two synchrotron sideband resonances at the expected frequencies. The two {nu}{sub s}{minus}1 sidebands were deep dips while the two 3{minus}{nu}{sub s} sidebands were very shallow; this was not expected. Moreover, all four sideband resonances were unexpectedly wider than the two primary resonances. {copyright} {ital 1998} {ital The American Physical Society}

We formed the first ``atomic-optics'' beam of electron-spin-polarized hydrogen atoms using a quasiparabolic polished copper mirror coated with a hydrogen-atom-reflecting film of superfluid $^{4}\mathrm{He}$. The mirror was located in the gradient of an 8-T solenoidal magnetic field and mounted on an ultracold cell at 350 mK. After the focusing by the mirror surface, the beam was again focused with a sextupole magnet. The mirror, which was especially designed for operation in the magnetic field gradient of our solenoid, increased the focused beam intensity by a factor of about 7.5.

We measured the analyzing power A out to ${\mathit{P}}_{\mathrm{\ensuremath{\perp}}}^{2}$=7.1 (GeV/c${)}^{2}$ with high precision by scattering a 24-GeV/c unpolarized proton beam from the new University of Michigan polarized proton target; the target's 1-W cooling power allowed a beam intensity of more than 2\ifmmode\times\else\texttimes\fi{}${10}^{11}$ protons per pulse. This high beam intensity together with the unexpectedly high average target polarization of about 85% allowed unusually accurate measurements of A at large ${\mathit{P}}_{\mathrm{\ensuremath{\perp}}}^{2}$. These precise data confirmed that the one-spin parameter A is nonzero and indeed quite large at high ${\mathit{P}}_{\mathrm{\ensuremath{\perp}}}^{2}$; most theoretical models predict that A should go to zero.

A recent experiment in the IUCF cooler ring studied the adiabatic turn-on of a partial Siberian snake at 370 MeV, where the spin tune, ${\ensuremath{\nu}}_{\mathit{s}}$ is 21/2 for all snake strengths. The snake consisted of two rampable warm solenoid magnets in series with a superconducting solenoid; this combination allowed varying the snake strength between about 0 and 25% at 370 MeV. We measured the beam polaraization after varying the snake either 1, 2, or 10 times; we found with good precision that no polarization was lost. This supports the conjecture that a Siberian snake can be ramped adiabatically at an energy where the spin tune is a half integer.