P.D. Eversheim

Parity violation in proton-proton scattering at 13.6 MeV

Abstract Parity nonconservation in proton-proton scattering has been studied by measuring the angle-integrated longitudinal analyzing power A z . We found A z (13.6 MeV)=(−1.5±0.5)×10 −7 . The error includes uncertainties due to statistics and corrections, as well as upper limits on systematic effects. The experimental result is discussed with respect to recent theoretical calculations.

Excitation functions of the analyzing power in elastic proton-proton scattering from 0.45 to 2.5 GeV

Abstract.Excitation functions AN(plab,Θc.m.) of the analyzing power in elastic proton-proton scattering have been measured in an internal target experiment at the Cooler Synchrotron COSY with an unpolarized proton beam and a polarized atomic hydrogen target. Data were taken continuously during the acceleration and deceleration for proton kinetic energies Tlab (momenta plab) between 0.45 and 2.5 GeV (1.0 and 3.3 GeV/c) and scattering angles 30 ° ⩽ Θc.m. ⩽ 90°. The results provide excitation functions and angular distributions of high precision and internal consistency. The data can be used as calibration standard between 0.45 and 2.5 GeV. They have significant impact on phase shift solutions, in particular on the spin triplet phase shifts between 1.0 and 1.8 GeV.

Measurement of spin correlation parameters A(NN), A(SS), and A(SL) at 2.1-GeV in proton proton elactic scattering

At the Cooler Synchrotron COSY/Jülich spin-correlation parameters in elastic proton-proton (pp) scattering have been measured with a 2.11 GeV polarized proton beam and a polarized hydrogen atomic beam target. We report results for A(NN), A(SS), and A(SL) for c.m. scattering angles between 30 degrees and 90 degrees. Our data on A(SS)--the first measurement of this observable above 800 MeV--clearly disagrees with predictions of available pp scattering phase-shift solutions while A(NN) and A(SL) are reproduced reasonably well. We show that in the direct reconstruction of the scattering amplitudes from the body of available pp elastic scattering data at 2.1 GeV the number of possible solutions is considerably reduced.

The polarized ion source for COSY

The polarized ion source for COSY‐Julich has been set in operation. The source produces H− or D− ion beams by means of a charge exchange reaction. For the first time beam acceleration in the injector cyclotron and a first measurement of the beam polarization downstream of the cyclotron took place. The working scheme of this colliding‐beam source and the latest results are discussed.

Position sensitivity by light splitting in scintillator arrays

Abstract A novel detector design of overlapping plastic scintillator elements in cylindrical geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles: each particle traversing the detector from the axis outwards will produce light in several elements. The relative amounts of energy deposited in those elements allow one to interpolate on the particle trajectory beyond the resolution given by the granularity. The detector covers the angular range 10° ≤ Θ lab ≤ 72° and 0° ≤ ϕ ≤ 360° with an inner layer of scintillator bars of triangular cross section and an outer layer of rings. The material is BC408. Tests with minimum ionizing electron beams show that spatial resolutions of ΔΘ lab ≈ 1.5° and Δϕ 12 ≈ 1.5° (FWHM) can be obtained for electrons or proton pairs with energies in the GeV range. In the EDDA experiment the ultimate spatial resolution is then determined by the size of the interaction area rather than by the intrinsic pulse height resolution of the detector.

The α + α → 8Be double resonance at the 16.6 and 16.9 MeV levels

Abstract The elastic scattering 4 He(α, α) has been investigated in the energy range 32.6–35.4 MeV. The level parameters of the overlapping 2 + states in 8 Be at 16.6 and 16.9 MeV were obtained with a double resonance formalism. In R -matrix theory the level energies and widths are 16623 ± 3 keV, 107.7 ± 0.5 keV and 16925 ± 3 keV, 74.4 ± 0.4 keV, respectively. In complex-eigenvalue theory the resonance energies and widths are 16630 ± 3 keV, 108.5 ± 0.5 keV and 16918 ± 3 keV, 73.6 ± 0.4 keV, respectively. The relation between the parameter sets is discussed. The present results are compared with previous investigations where 8 Be is formed as a product nucleus. The isospin mixing of the doublet and the deduced charge-dependent matrix element are discussed with regard to theoretical predictions.

Precise analyzing power calibration in proton-carbon scattering at 71 MeV

Abstract We have calibrated the analyzing power A y in proton-carbon elastic scattering at 71.2 MeV via double-scattering with polarized beam. An accuracy of ±0.001 was achieved using a highly efficient setup (statistical uncertainty of ±0.0003) and a new type of analysis based on asymmetry ratios. Our result A y =0.986±0.001 may indicate the existence of a point with A y =1 near 65 MeV.

Excitation functions of spin correlation parameters ANN, ASS, and ASL in elastic pol.p pol.p scattering between 0.45 and 2.5 GeV

Excitation functions of the spin correlation coefficients A_{NN}(p_{lab},theta_{c.m.}), A_{SS}(p_{lab},theta_{c.m.}), and A_{SL}(p_{lab},theta_{c.m.}) have been measured with the polarized proton beam of the Cooler Synchrotron COSY and an internal polarized atomic beam target. Data were taken continuously during the acceleration for proton momenta p_{lab} ranging from 1000 to 3300 MeV/c (kinetic energies T_{lab} 450 - 2500 MeV) as well as for discrete momenta of 1430 MeV/c and above 2000 MeV/c covering angles theta_{c.m.} between 30 deg and 90 deg. The data are of high internal consistency. Whereas A_{SL}(p_{lab,}theta_{c.m.}) is small and without structures in the whole range, A_{NN} and even more A_{SS} show a pronounced energy dependence. The angular distributions for A_{SS} are at variance with predictions of existing phase shift analyses at energies beyond 800 MeV. The impact of our results on phase shift solutions is discussed. The direct reconstruction of the scattering amplitudes from all available pp elastic scattering data considerably reduces the ambiguities of solutions.

STATUS OF THE EDDA EXPERIMENT AT COSY

The EDDA experiment is designed to study p + p excitation functions with high energy resolution and narrow step size in the kinetic energy range from 250 MeV to 2500 MeV at the Cooler Synchrotron COSY. Measurements during the accelertion phase in conjunction with internal targets will allow to achieve a fast and precise energy variation. Prototypes of the detector elements and the fiber target have been extensively tested with proton and electron beams; the detector performance and trigger efficiency have been studied in Monte Carlo simulations. In this contribution, results concerning detector design, prototype studies, Monte Carlo simulations and the anticipated detector resolutions will be reported.

Depolarization in proton-6Li elastic scattering

We have measured the differential cross section dσ/dΩ, the analyzing power Ay and the depolarization parameter D for p-6Li elastic scattering at 72 MeV. The spin/isospin character of this transition and the large spinflip effects observed make p-6Li elastic scattering a good case to study the isoscalar spinflip component of the effective force. The data were fitted by a conventional optical-model potential which included a real, spherical spin-spin potential with surface form factor and Vss = 5.3 ± 1.0 MeV. A qualitative description of the data was also achieved with a “semi-microscopic” folding calculation based on the density-dependent Paris effective force, shell-model wave functions and a phenomenological optical-model potential.