The paper describes the commissioning of the experimental equipment and the machine studies required for the first spin-filtering experiment with protons at a beam kinetic energy of 49.3 MeV in COSY. ...The implementation of a low-β insertion made it possible to achieve beam lifetimes of τb=8000s in the presence of a dense polarized hydrogen storage-cell target of areal density dt=(5.5±0.2)×1013atoms/cm2 . The developed techniques can be directly applied to antiproton machines and allow the determination of the spin-dependent p¯p cross sections via spin filtering.
We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement ...of the spin-flip cross section in low-energy electron–proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.
The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon ...near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.
With the ANKE spectrometer at the COoler SYnchrotron COSY Juelich the mesonic structure of the nucleon will be studied in polarized proton-proton and proton-deuteron collisions. The identification ...and tracking of low energy protons permits using deuterium as an effective neutron target. For this purpose, modular self-triggering tracking telescopes built up by double-sided silicon strip detectors inside the accelerator ultra-high vacuum have been developed. Their basic features are /spl Delta/E/E proton identification from 2.5 40 MeV and particle tracking over a wide dynamic range, either 2.5 MeV spectator protons or minimum ionizing particles. By the use of self-triggering read-out chips, the telescopes identify a particle passage within 100 ns and therefore allow the possibility of a fast hit pattern recognition. In combination with a read-out pitch of /spl sim/200 /spl mu/m, they provide a high rate capability. The recent development of very thick (/spl ges/5 mm) double-sided microstructured Si(Li) and very thin (/spl les/65 /spl mu/m) double-sided Si-detectors provides the use of the telescopes over a wide range of particle energies.
A Polarized Internal gas Target (PIT) has been developed for the ANKE spectrometer at COSY. After its first installation at the ANKE target position in summer 2005, commissioning studies were carried ...out. In March 2006, first single polarization measurements with the polarized hydrogen beam from an Atomic Beam Source (ABS) were performed. The beam was injected into a storage cell made from aluminum foil. The data analysis showed that the events from the extended gas target can be clearly identified in the ANKE forward detection system. Using unpolarized nitrogen, the background from the cell walls could be determined as well. The thickness of the gas in the storage cell with the hydrogen atoms in hyperfinestate |1⟩ was measured as 2×1013 atoms/cm2. The ABS jet target thickness was 1.5×1011 atoms/cm2. In November 2006, the commissioning of a Silicon Tracking Telescope (STT) was successfully finished. In the following beam time in January 2007, a new storage cell from aluminum coated with teflon was used together with the STT. The Lamb-shift polarimeter (LSP) was mounted below the target chamber to allow for online tuning of the transition units and monitoring of the ABS jet polarization. A first double-polarized experiment was performed, the results will be presented.
A new technique for manufacturing double-sided structured Si(Li) detectors has been established. The position-sensitive structure on the implanted p/sup +/-contact can be made smaller than 100 /spl ...mu/m by photolithography followed by plasma etching of grooves to separate the position elements. By modifying this technique position-sensitive structures on a thin (/spl sim/30 /spl mu/m) Li-diffused contact were created. Areas of 50 mm /spl times/ 50 mm were divided into 50 or 100 strips with a pitch of 1 mm or 500 /spl mu/m, respectively. The strips were separated by /spl sim/35-/spl mu/m-deep and /spl sim/50-/spl mu/m-wide grooves. Measurements of the electrical resistance of the grooves and reverse current of the strips are presented. Charge splitting on the adjacent strips shows practically no charge loss through the groove. Small pixel effects are demonstrated on a Li-diffused contact (100 strips with the pitch of 500 /spl mu/m) and on the first double-sided Si(Li) detector (50 /spl times/ 50 strips with a pitch of 1 mm). By measuring the relative time distribution of the signal from both contacts it is possible to obtain some three-dimensional imaging capability.
The vector (Pz ) and tensor (Pzz ) polarizations of a deuteron beam have been measured using elastic deuteron–carbon scattering at 75.6 MeV and deuteron-proton scattering at 270 MeV. After ...acceleration to 1170 MeV inside the COSY storage ring, the polarizations of the deuterons were remeasured by studying the analyzing powers of a variety of nuclear reactions. For this purpose a hydrogen cluster target was employed at the ANKE magnetic spectrometer, which is situated at an internal target position in the ring. The overall precisions obtained were about 4% for both Pz and Pzz . Though all the measurements were consistent with the absence of depolarization during acceleration, only an upper limit of about 6% could be placed on such an effect.
Spin observables in proton deuteron breakup reactions at low energies offer a rich testing ground for the modern theory of nuclear forces, the chiral effective field theory (EFT). In the ...three-nucleon continuum the experimental data and the theoretical predictions are today at variance. At the PAX facility at COSY we plan to make an extensive study of analyzing powers and spin correlation parameters in pd breakup reactions at low energies between 30 and 50 MeV, an energy range where previous measurements are scarce and limited while three-nucleon effects are expected to be significant. Furthermore it is an ideal energy for the predictive power of chiral EFT to be tested. The longstanding physics question of the nature of three-nucleon forces will be studied with large coverage provided by an optimized silicon detector barrel, and flexibility utilizing the sampling method, a technique for direct comparison between experiment and theory developed specifically for the complex analysis of three-particle final states. The proposed experiment will yield an independent determination of the low-energy constants D and E and enable tests of appearing three-nucleon interactions in chiral EFT, with possible implications also for the spectra of light nuclei.
The ratio of forward
K
+ production on copper, silver and gold targets to that on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as a function of the kaon momentum
p
K
using ...the ANKE spectrometer at COSY-Jülich. The strong suppression in the ratios observed for
p
K
<200–250 MeV/
c may be ascribed to a combination of Coulomb and nuclear repulsion in the
K
+
A system. This opens a new way to investigate the interaction of
K
+-mesons in the nuclear medium. Our data are consistent with a
K
+
A nuclear potential of
V
K
0≈20MeV at low kaon momenta and normal nuclear density. Given the sensitivity of the data to the kaon potential, the current experimental precision might allow one to determine
V
K
0 to better than 3 MeV.
A study of the deuteron breakup reaction pd→(pp)n with forward emission of a fast proton pair with small excitation energy Epp< 3 MeV has been performed using the ANKE spectrometer at COSY-Jülich. An ...exclusive measurement was carried out at six proton-beam energies Tp= 0.6, 0.7, 0.8, 0.95, 1.35 and 1.9 GeV by reconstructing the momenta of the two protons. The differential cross section of the breakup reaction, averaged up to 8° over the cm polar angle of the total momentum of the pp pairs, has been obtained. Since the kinematics of this process is quite similar to that of backward elastic pd→dp scattering, the results are compared to calculations based on a theoretical model previously applied to the pd→dp process.
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