Search

Developments in spin-polarized internal targets for storage rings have permitted measurements of 197 MeV polarized protons scattering from vector polarized deuterons. This work presents measurements of the polarization observables A_y, iT_11, and C_y,y in proton-deuteron elastic scattering. When compared to calculations with and without three-nucleon forces, the measurements indicate that three-nucleon forces make a significant contribution to the observables. This work indicates that three-body forces derived from static nuclear properties appear to be crucial to the description of dynamical properties., 8 pages 2 figures Latex, submitted to Phys. Rev. Letters

We describe an experimental setup for the measurement of polarization observables in pion production near threshold. Experiments carried out with this facility use a polarized proton beam in the Indiana University Cooler storage ring, and an internal, polarized hydrogen target. The detector system measures energy, direction and velocity of multiple outgoing charged particles that are within a forward cone of about 32° opening angle. An array of scintillators also allows the detection of neutrons. In addition to the technical details of the apparatus, we describe the procedure for data acquisition, as well as some aspects of the analysis.

A polarized internal atomic-hydrogen target and a stored, polarized beam are used to measure the spin-dependent total cross section {Delta}{sigma}{sub T}thinsp/{sigma}{sub tot} for {rvec p}{rvec p}{r_arrow} pp{pi}{sup 0} , as well as the polar integrals of the spin correlation coefficient combination A{sub xx}{minus}A{sub yy} , and the analyzing power A{sub y} at four bombarding energies between 325 and 400thinspthinspMeV. This experiment is made possible by the use of a cooled beam in a storage ring. The polarization observables are used to study the contribution from individual partial waves. {copyright} {ital 1998} {ital The American Physical Society }

We have demonstrated for the first time spin flipping of a polarized proton beam stored in a ring containing a nearly $100%$ Siberian snake; we did this using a ``snake'' depolarizing resonance induced by an rf solenoid magnet. By varying the rf solenoid's ramp time, frequency range, and voltage, we reached a spin-flip efficiency of about $91%$. This spin-flip efficiency was probably reduced because the horizontal stable spin direction was not perpendicular to the longitudinal field of the rf solenoid, and was possibly reduced by nearby synchrotron sideband resonances. The planned use of a vertical rf dipole may improve the spin-flip efficiency.

We have measured the $\mathrm{pp}$ spin correlation coefficients ${A}_{\mathrm{xx}},$ ${A}_{\mathrm{yy}},$ ${A}_{\mathrm{xz}}$ and the analyzing power ${A}_{y}$ at 250.0, 280.0, 294.4, 310.0, 350.0, 399.1, and 448.9 MeV over the laboratory angular range $3.5\ifmmode^\circ\else\textdegree\fi{}--43.5\ifmmode^\circ\else\textdegree\fi{}$ $({\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=7\ifmmode^\circ\else\textdegree\fi{}--90\ifmmode^\circ\else\textdegree\fi{}).$ The statistical accuracy is approximately $\ifmmode\pm\else\textpm\fi{}0.006$ for ${A}_{y}$ and $\ifmmode\pm\else\textpm\fi{}0.02$ for ${A}_{\mathrm{mn}}$ per $1\ifmmode^\circ\else\textdegree\fi{}$ angle bin, while the corresponding scale factor uncertainties are 1.3 and 2.5 %, respectively. The experiment makes use of a polarized hydrogen gas target internal to a proton storage ring (IUCF Cooler) and a circulating beam of polarized protons. The method of calibration relative to pp spin correlation coefficients and analyzing power at 197.4 MeV, the injection energy, involves up and down ramping of the energy of the polarized beam. The data are compared to recent $\mathrm{pp}$ partial waves analyses and $\mathrm{NN}$ potential models, emphasizing in particular the energy dependence in the region of the pion production threshold.

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}

Measurements of $\mathrm{pp}$ spin correlation coefficients ${A}_{\mathrm{xx}},$ ${A}_{\mathrm{yy}},$ and ${A}_{\mathrm{xz}}$ and analyzing power ${A}_{y}$ for $\mathrm{pp}$ elastic scattering at 197.4 MeV over the laboratory angular range 3.5 \ifmmode^\circ\else\textdegree\fi{}--43.5 \ifmmode^\circ\else\textdegree\fi{} $({\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=7\ifmmode^\circ\else\textdegree\fi{}--90\ifmmode^\circ\else\textdegree\fi{})$ have been carried out. The typical statistical accuracy per 1$\ifmmode^\circ\else\textdegree\fi{}$ angle bin is better than 0.02 for the ${A}_{\mathrm{mn}}$ and better than 0.005 for ${A}_{y}.$ Systematic errors are negligible except for an overall normalization uncertainty of 2.5% for ${A}_{\mathrm{mn}}$ and 1.3% for ${A}_{y}.$ The experiment makes use of a polarized hydrogen gas target internal to a proton storage ring (IUCF Cooler) and a circulating beam of polarized protons. The target polarization is switched in sign and direction $(x,y,z)$ every 2 s by reversing a weak guide field $(\ensuremath{\approx}0.3$ mT). Scattered and recoil protons are detected in coincidence by two sets of wire chambers, by scintillators, and by silicon-strip recoil detectors placed 5 cm from the proton beam. Analysis methods and comparison to recent $\mathrm{pp}$ partial-wave analyses and $\mathrm{NN}$ potential models are described.

We have measured the pd elastic scattering with an electron-cooled beam of a proton storage ring and an internal jet target operated with HD gas. The accurately known H/D ratio is used to transfer the precision of existing pp scattering data to the pd cross sections. Measurements were performed for proton energies between 200 and 300 MeV in the angular range 11°

With a storage ring synchrotron, two additional methods have become possible to establish polarization standards at arbitrary energies, making use of the ease with which the energy of the stored beam can be changed. Both methods yield the analyzing power of a reaction at one energy in relation to the known analyzing power at a different energy. One method involves ramping of the energy of a polarized beam up and down; the other requires a polarized target. The two methods have been demonstrated in an experiment with the Indiana Cooler, and their relative consistency has been established.

We have measured the time dependence of the polarization of a stored proton beam near an intrinsic depolarizing resonance. The distance to the resonance was varied by changing the vertical tune of the storage ring. The measurements are consistent with exponential decay and with a simple model for the change of the lifetime as the resonance is approached. It was originally expected that the presence of an internal target stimulates depolarization; however, we found no evidence for such an effect.

Measurements of the $\mathrm{pp}$ spin correlation coefficients ${A}_{\mathrm{xx}},$ ${A}_{\mathrm{yy}},$ and ${A}_{\mathrm{xz}}$ and analyzing power ${A}_{y}$ for $\mathrm{pp}$ elastic scattering at 197.8 MeV over the angular range $4.5\ifmmode^\circ\else\textdegree\fi{}$--$17.5\ifmmode^\circ\else\textdegree\fi{}$ have been carried out. The statistical accuracy is approximately $\ifmmode\pm\else\textpm\fi{}0.01$ for ${A}_{\mathrm{mn}}$ and $\ifmmode\pm\else\textpm\fi{}0.004$ for ${A}_{y},$ while the corresponding scale factor uncertainties are 2.4% and 1.3%, respectively. The experiment makes use of a polarized hydrogen gas target internal to a proton storage ring (IUCF Cooler) and a circulating beam of polarized protons. The target polarization $(Q=0.79)$ is switched in sign and in direction $(x,y,z)$ every 2 s by reversing a weak guide field (about 0.3 mT). The forward-scattered protons are detected in two sets of wire chambers and a scintillator, while recoil protons are detected in coincidence with the forward protons by silicon strip detectors placed 5 cm from the proton beam. The background rate from scattering by the walls of the target cell is $(0.2\ifmmode\pm\else\textpm\fi{}0.2)$% of the good event rate. Analysis methods and comparisons with $\mathrm{pp}$ potential models and $\mathrm{pp}$ partial wave analyses are described.

The spin asymmetries in the momentum distributions of the neutron and proton in He-3 are obtained from a Faddeev calculation of the ground state. Both two- and three-body configurations are found to be important. Using a PWIA model and measurements of the spin asymmetries in (3)((p) over right arrow,2p) and (3)((p) over right arrow,pn) quasielastic scattering at 197 MeV the asymmetries in the momentum distributions are experimentally determined. Good agreement between theory and experiment is found up to initial nucleon momenta of 300 MeV/c.

We report on recent developments of the internal supersonic gas jet target at IUCF. The emphasis has been on hydrogen jets that can be used as targets of ∼ 10 16 atoms/cm 2 thickness in high-luminosity experiments. A method of scanning jets with an ionizing 1 keV electron beam has been employed in order to study jet formation as a function of nozzle geometry and temperature. We summarize our results, obtained by scanning H 2 jets from 23 different nozzles, most of them made from glass capillaries. The present setup of the jet target in the Cooler storage ring is described.

We report measurements of spin correlations and analyzing powers in $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}(\stackrel{\ensuremath{\rightarrow}}{p}, 2p)$ and $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}(\stackrel{\ensuremath{\rightarrow}}{p}, pn)$ quasielastic scattering as a function of momentum transfer and missing momentum at 197 MeV using a polarized internal target at the Indiana University Cyclotron Facility Cooler Ring. At sufficiently high momentum transfer we find $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}(\stackrel{\ensuremath{\rightarrow}}{p}, pn)$ spin observables are in good agreement with free $p\ensuremath{-}n$ scattering observables, and therefore that $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}$ can serve as a good polarized neutron target. The extracted polarizations of nucleons in $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}$ at low missing momentum are consistent with Faddeev calculations.

We describe the first experiment to use a polarized internal gas target and polarized beam in a storage ring. A laser optically pumped polarized He internal gas target has been used with circulating beams of 197-414 MeV polarized protons to carry out an extensive set of measurements of spin dependent scattering. A large acceptance non-magnetic detector system consisting of wie-chambers, scintillators and microstrip detectors was used to detect protons, neutrons, deuterons, and He-3 nuclei from the beam-target interaction. It is demonstrated that these techniques result in low backgrounds (< 1%) due to scattering from species other than the polarized target gas and allow detection of low energy recoiling nuclei. Specific issues such as interfacing the experiment to the storage ring and monitoring the luminosity and polarizations are discussed in detail.

A storage cell has been constructed for use as an internal polarized gas target in the storage ring at the Indiana University Cyclotron Facility. The storage cell has thin teflon walls which allow for detection of low energy recoil particles. We report on nuclear polarization measurements of hydrogen atoms, produced by an atomic beam source, in this storage cell. The results indicate that a target polarization in excess of 0.70 is achieved. We discuss the design and construction details of a storage cell target and the polarization results which are based on low-energy pp spin correlation measurements using the University of Wisconsin tandem accelerator.

Measurements have been made in the Cooler ring at the Indiana University Cyclotron Facility (IUCF) of the mean lifetime of stored and electron-cooled proton beams in the presence of various target gas species at two ring locations differing in dispersion. A broad range of beam energy Tb, target atomic number Zt and thickness xt was employed. The loss (removal) cross sectionσL per target atom, extracted from the lifetime measurement, exhibits a minimum for small xt which is found to scale with ( Z t T b ) 2 . This behavior is expected because forward Coulomb scattering from target nuclei should be the dominant loss mechanism under the conditions of measurement. A marked increase in σL for larger xt is attributed to emittance growth arising from multiple scattering in competition with the transverse cooling rate. Lattice dispersion at the target increases the contribution to beam heating by electrons in the target atoms and introduces an additional loss mechanism. From the measured σL and beam lifetime, a time cycle may be selected which gives the optimum time-averaged luminosity for a given experiment. Scaling of σL allows prediction of the optimum luminosity over the full operating regime of the cooling ring.

The use of thin fibers as internal targets for nuclear physics experiments in storage rings is discussed. We have measured the lifetime and the energy spread of stored, electron-cooled beams in the presence of an internal carbon fiber target. Measurements have been carried out in the Indiana Cooler with proton beams between 100 MeV and 300 MeV. The effect of the inhomogeneous fiber target on the beam is the same as that of a homogeneous gas target of equivalent thickness within the accuracy of the measurement. The measurements are compared with a Monte Carlo simulation of the stored beam. It is demonstrated that charging of the fiber target can significantly affect the lifetime and energy spread of the stored beam.

The behavior of overlapping'' depolarizing resonances was studied using a stored 106.4-MeV polarized proton beam. We used an rf solenoid magnet to create an rf induced'' depolarizing resonance which was then forced to overlap with the [ital G][gamma]=2 imperfection depolarizing resonance. We found significant interactions between the two resonances by varying their frequencies and strengths; the frequency of the rf resonance strongly affected the response of the imperfection resonance to correction magnetic fields. The Siberian snake overcame all observable depolarization due to the overlapping resonances and maintained full polarization for all observed frequencies and strengths.

Stored ion beams offer the possibility to use polarized internal targets that consist of a source of polarized atoms in conjunction with a long, narrow, windowless target cell to enhance the target thickness. In this paper, we discuss the effect of such a cell on the performance of the storage ring, based on measurements carried out with the Indiana Cooler. A prototype target cell was constructed and was operated with a controlled flow of H2 target gas in a beam of stored protons. Detection of protons scattered at angles from 4° to 15° in coincidence with the associated recoil particles was used to identify elastic scattering. The results show that the presence of a 25 cm long target cell with a rectangular opening of 6.4 mm by 7.9 mm is compatible with operation of the Cooler ring. This demonstrates the feasibility of an important component of experiments with stored, polarized beams and carrier-free polarized, internal targets.

A recent experiment studied the effect of an rf solenoid magnet and a partial Siberian snake on a 120-MeV polarized proton beam. We measured the frequencies of the rf-induced''depolarizing resonance for different values of the snake strength; this frequency measurement determined the spin tune [nu][sub sp], which is the number of spin processions in one turn around the ring. A 4% snake increased the frequency of the rf-induced depolarizing resonance by the predicted 11 kHz and thus shifted the spin tune by the predicted [Delta][nu][sub sp]=0.006 88[plus minus]0.000 04; as expected the 4% snake also tilted the stable spin direction by more than 38[degree] from the vertical.

Making use of an electron-cooled beam in the IUCF storage ring, we have measured the total cross section σ tot for pp→pp π 0 at 31 bombarding energies between 285 and 325 MeV. At a level of about 5%, the data show no fluctuations that could be associated with the onset of other pion production channels. A calculation of the single-partial-wave cross section σ ss , including direct production only (no rescattering), falls short of the experiment by a factor of 5.2±0.3, but reproduces the observed energy dependence when scaled. This energy dependence is explained by contributions from the phase-space factor and the final-state interaction between the outgoing nucleons. The relative importance of higher partial waves is deduced from the energy dependence of σ tot as well as from the angular distributions of reaction protons.

The analyzing power {ital A}{sub {ital y}}({theta}) for {ital pp} elastic scattering at 185.4 MeV has been measured with a new technique in which the polarized beam in a storage ring was scattered from an internal H{sub 2} gas target. The measurement covered the angular range {theta}{sub c.m.}=5.45{degree}--21.36{degree}, where {ital A}{sub {ital y}} is dominated by interference between Coulomb and nuclear amplitudes. It is found that electromagnetic spin-orbit effects are required to explain the data. The present measurement demonstrates for the first time the feasibility and the advantages of nuclear physics experiments with polarized beams in storage rings.

The analyzing power ${\mathit{A}}_{\mathit{y}}$ for p+p elastic scattering at ${\mathrm{\ensuremath{\theta}}}_{\mathrm{lab}}$=8.64\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}0.07\ifmmode^\circ\else\textdegree\fi{} (${\mathrm{\ensuremath{\theta}}}_{\mathrm{cms}}$=18.1\ifmmode^\circ\else\textdegree\fi{}) and at a bombarding energy of 183.1\ifmmode\pm\else\textpm\fi{}0.4 MeV has been determined to be ${\mathit{A}}_{\mathit{y}}$=0.2122\ifmmode\pm\else\textpm\fi{}0.0017. The error includes statistics, systematic uncertainties, and the uncertainty in bombarding energy and angle. This measurement represents a calibration standard for polarized beams in this energy range. The absolute scale for the measurement has been obtained by comparison with p+C elastic scattering at the same energy at an angle where ${\mathit{A}}_{\mathit{y}}$ is very nearly unity.

Measurements of 20 vector and tensor spin observables in {ital d}-{ital p} elastic scattering at a deuteron bombarding energy of 1.6 GeV (800 MeV equivalent proton beam energy) are reported. Of these 10 are two-spin observables and the remaining ten are three-spin observables. The two-spin observables, six of which have been measured for the first time, were measured in the four-momentum-transfer range 0.12 to 0.85 (GeV/{ital c}){sup 2}. The three-spin observables, of which eight were measured for the first time, were measured in the momentum-transfer range 0.2 to 0.85 (GeV/{ital c}){sup 2}. The magnitude of the average vector polarization of the deuteron beam was 0.3, and of the average tensor alignment was 0.85. A frozen spin-polarized proton target was utilized for these measurements. These results are compared with previous measurements when possible, and show a general agreement. They are also compared with the predictions of the relativistic-impulse approximation, and its modified version, which takes into account a nontrivial off-mass-shell behavior of nucleon-nucleon scattering amplitudes.

The total cross section for the reaction pp\ensuremath{\rightarrow}pp${\mathrm{\ensuremath{\pi}}}^{0}$ was measured at nine center-of-mass energies from 1.5 to 23 MeV above threshold. The experiment was carried out with the Indiana Cooler, a recently constructed storage ring. The experimental advantages of an electron-cooled proton beam were utilized. The data cover an energy range where only the lowest possible angular momentum state contributes in the exit channel. The measured energy dependence of the total cross section is not compatible with that predicted by models of s-wave pion production and rescattering.

The use of microparticles for internal targets in storage rings is investigated. The design and construction of a specific microparticle target are described in detail. In the scheme used here, the particulate material is suspended in a carrier gas and accelerated in the flow of the gas through a capillary. The resulting microparticle beam is crossed with the stored ion beam. The target has been tested in a stored, cooled proton beam at the Indiana Cooler. Target thicknesses achieved range from 3×1013 to 2×1015 atoms/cm2.

The time dependence of the polarization of a stored proton beam was measured near an induced depolarizing resonance. The resonance was created by a magnetic field which oscillated along the beam axis. The distance to the resonance was varied by changing the frequency of the oscillating field. The resonance was approached from either side and the time dependence of the polarization was found to be symmetric with respect to the resonance, and in agreement with an earlier measurement that involved an intrinsic depolarizing resonance.

Using a 104MeV stored polarized proton beam and a full Siberian snake, we recently found evidence for a so-called {open_quotes}snake{close_quotes} depolarizing resonance. A full Siberian snake forces the spin tune {nu}{sub s} to be a half integer. Thus, if the vertical betatron tune {nu}{sub y} is set near a quarter integer, then the {nu}{sub s}=n{plus_minus}2{nu}{sub y} second-order snake resonance can depolarize the beam. Indeed, with a full Siberian snake, we found a deep depolarization dip when {nu}{sub y} was equal to 4.756; moreover, when {nu}{sub y} was changed to 4.781, the deep dip disappeared and the polarization was preserved. {copyright} {ital 1997} {ital The American Physical Society}

A recent experiment using a 160 MeV stored spin-polarized proton beam found clear evidence for a second-order intrinsic depolarizing resonance. With a 20% partial Siberian snake, we studied a first-order intrinsic depolarizing resonance; we then discovered and studied the second-order depolarizing resonance by changing both the horizontal and vertical betatron tunes. As expected, this second-order resonance is much weaker than the first-order resonance; it is probably due to sextupole fields plus coupling between the horizontal and vertical betatron oscillations caused by the 20% snake.

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.

The authors measured the photon beam polarization in the IUCF (Indiana University Cyclotron Facility) Cooler Ring at five energies. They found that the G/sub lambda /=2 imperfection depolarizing resonance occurred about 1.9 MeV below the expected resonance energy of 108.4 MeV. This energy shift could be due to a shift of about +0.0036 in the spin time, nu /sub s/, which is the number of spin rotations in each turn around the ring. It was then demonstrated that this spin tune shift is consistent with the cooler ring containing a partial type-3 Siberian snake, which is apparently caused by the magnets that confine the electron and proton beams in the cooling region. >

A measurement of the total cross section for the reaction pd → pdπ° very close to threshold has been carried out at the IUCF Cooler. The deuteron with its known "nuclear structure" is the simplest system where pion production on nuclei can be investigated and mechanisms other than the quasi-free production may become important. In this contribution the experimental setup and the data analysis are described. Total cross sections for pd → pdπ° in the range 0.1 < η < 1.0 are reported.

An internal water vapor jet target is used for the study of the 16 O(p, n) 16 F reaction in the Indiana University Cyclotron Facility Cooler storage ring. Water in a copper reservoir is heated to a temperature corresponding to the desired vapor pressure (typically 100 Torr), which determines the flow rate through a de Laval-type nozzle and thus the thickness of the target, typically 10 14 atoms/cm 2 7 mm from the nozzle, where the Cooler beam intercepts the jet. The presence of hydrogen in H 2 O allows for cross section normalization because pp elastic scattering has a relatively large and well known cross section.

We recently created a snake depolarizing resonance using an rf solenoid magnet in a ring containing a nearly 100% Siberian snake. We found that the primary snake rf resonance also had two weaker synchrotron sidebands, which are second-order snake resonances; they were probably caused by the energy-dependent strength of the solenoid snake due to the Lorentz contraction of its longitudinal ∫Ḃ dl. This was the first observation of an rf synchrotron-sideband depolarizing resonance in the presence of a nearly full Siberian snake.

A polarized proton beam with a large longitudinal polarization component of $0.545\ifmmode\pm\else\textpm\fi{}0.005$ (96% of the total polarization) was prepared in a storage ring (IUCF--Cooler). This was achieved by means of spin precession solenoids in two of the six straight sections of the ring. A polarized hydrogen storage cell target internal to the ring was used to measure the longitudinal spin correlation coefficient ${A}_{\mathrm{zz}}$ in $\mathrm{pp}$ elastic scattering over the laboratory angular range $5.5\ifmmode^\circ\else\textdegree\fi{}$--$43.5\ifmmode^\circ\else\textdegree\fi{} ({\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=11.5\ifmmode^\circ\else\textdegree\fi{}$--$90\ifmmode^\circ\else\textdegree\fi{})$ with statistical errors of typically 0.025. The absolute normalization was determined to an accuracy of 2.0% by use of the identity ${A}_{\mathrm{yy}}\ensuremath{-}{A}_{\mathrm{xx}}\ensuremath{-}{A}_{\mathrm{zz}}\ensuremath{\equiv}1$ at ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=90\ifmmode^\circ\else\textdegree\fi{}.$ The identity also allows a reduction of the scale factor uncertainty of the previously published analyzing powers and spin correlation coefficients. The results are compared to recent $\mathrm{pp}$ partial wave analyses and $\mathrm{NN}$ potential models.

We have detected low energy protons from elastic proton-proton scattering at forward angles (θlab = 2.3° −10.6°) with silicon strip detectors mounted inside the Indiana University Cyclotron Facility “Cooler” storage ring. Detection of both protons reduces the coincident background to less than ≈ 1% of the elastic scattering rate.

Recent polarized proton beam experiments in the IUCF Cooler Ring found an evidence for a second-order snake depolarizing resonance, when the vertical betatron tune was inadvertently set near a quarter-integer. We have also studied the possibility of spin-flipping the beam polarization in the presence of a full Siberian snake using an RF solenoid. By varying the rf solenoid's ramp time and frequency range, we reached a spin-flip efficiency of about 97%.

The HERMES Laser-Driven Target Task Force (Argonne, Erlangen, Illinois and Colorado) is charged with developing a polarized H/D target for use in the HERA ring at DESY. Rapid progress was made in the beginning of 1996, leading us to the decision to test the target in a realistic experimental environment. In particular, polarizations of 0.6 and flows above 1018 atoms⋅s−1 have been achieved on the bench. The laser-driven target and a simple detector system are currently installed in Cooler storage ring at the Indiana University Cyclotron Facility in order to test its applicability to nuclear physics experiments. Target polarizations are being measured using the H(p,p) and D(p,p) reactions. Initial tests were reasonably successful and the target is well along toward becoming viable for nuclear physics.

A laser driven source of polarized hydrogen and deuterium has been installed in the Cooler Ring at the Indiana University Cyclotron Facility. Polarized nuclei from the source are injected into a storage tube, and the resulting target has been used in a scattering experiment with 200 MeV proton beam. This paper discusses the performance of the source, including measurements of atomic fraction and electron polarization.

We recently accelerated a polarized proton beam from 95 to 380MeV through both the {ital G}{gamma}=2 imperfection depolarizing resonance and the {ital G}{gamma}=7{minus}{nu}{sub {ital y}} intrinsic depolarizing resonance. The imperfection resonance flipped the spin, while the intrinsic resonance initially caused partial depolarization. We then pulsed a vertical kicker magnet for about 500ns to increase the beam{close_quote}s vertical betatron amplitude; this made the intrinsic resonance much stronger. By varying the strength and start time of the kicker, we observed a sharp spin flip due to the now very strong intrinsic depolarizing resonance. {copyright} {ital 1996 The American Physical Society.}

A polarized internal H gas storage cell target has been successfully operated in the IUCF cooler ring. A target thickness for atomic hydrogen has been measured to be 3.5±0.3×1013/cm2 in a single spin state. Target polarization (0.75±0.01) showed no sign of deterioration after two weeks of operation with an average beam current of 100 μA. Detection of p‐p elastic events at 200 MeV bombarding energy has been demonstrated by use of coincidences between silicon detectors near the beam and a forward detector array. This target is presently being used to measure p‐p elastic scattering spin correlation coefficients at 200 MeV.

Measurements of analyzing powers and spin correlation parameters for 3He(p↘,2p) and 3H↘e(p↘,pn) quasielastic scattering have been carried out using a polarized internal 3He target and a stored, polarized proton beam. They were made over a wide kinematic range with a proton energy of 197 MeV and a large acceptance detector system which allowed the simultaneous measurement of both reactions. At momentum transfers sufficiently high to minimize rescattering effects, the (p,pn) results are in agreement with PWIA calculations. The (p,2p) results were found to be less sensitive to kinematic conditions and are also in agreement with calculations.

We recently studied the first acceleration of a spin‐polarized proton beam through a depolarizing resonance using a partial Siberian snake. We accelerated polarized protons from 95 to 140 MeV with a constant 10% partial Siberian snake obtained using rampable solenoids. The 10% partial snake suppressed all observable depolarization during acceleration due to the Gγ=2 imperfection depolarizing resonance which occurred near 108 MeV. However, 20% and 30% partial Siberian snakes apparently moved an intrinsic depolarizing resonance, normally near 177 MeV, into our energy range; this caused some interesting, although not‐yet‐fully understood, depolarization.

A recent experiment in the IUCF cooler ring studied the spin flip of a stored vertically polarized 139 MeV proton beam. This spin flip was accomplished by using an RF solenoid to induce an artificial depolarizing resonance in the ring, and then varying the solenoid’s frequency through this resonance value to induce spin flip. We found a polarization loss after multiple spin flips of about 0.00±0.05% per flip and also losses for very long flip times. This device will be useful for reducing systematic errors in polarized beam‐internal target scattering asymmetry experiments by enabling experimenters to perform frequent beam polarization reversals in the course of the experiment.

We recently studied the spin flipping of a vertically polarized, stored 139-MeV proton beam. To flip the spin, we induced an rf depolarizing resonance by sweeping our rf solenoid magnet's frequency through the resonance frequency. With multiple spin flips, we found a polarization loss of 0.0000[plus minus]0.0005 per spin flip under the best conditions; this loss increased significantly for small changes in the conditions. Minimizing the depolarization during each spin flip is especially important because frequent spin flipping could significantly reduce the systematic errors in stored polarized-beam experiments.