R. Stassen

New method for a continuous determination of the spin tune in storage rings and implications for precision experiments

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by ν(s)=γG (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970  MeV/c, the deuteron spins coherently precess at a frequency of ≈120  kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order 10^{-8}, and to 1×10^{-10} for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.

Search for η-mesic He4 in the dd→He3nπ0 and dd→He3pπ− reactions with the WASA-at-COSY facility

The search for 4He-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd->3He n pi0 and dd->3He p pi- processes. The beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined based on the dd->3He n reaction and quasi-free proton-proton scattering via dd->pp n_spectator n_spectator reactions. The excitation functions determined independently for the measured reactions do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes were determined taking into account the isospin relation between both the channels considered. The results of the analysis depend on the assumptions of the N* momentum distribution in the anticipated mesic-4He. Assuming as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in 4He, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for npi0 and ppi- channels respectively.

Measurements of branching ratios for

The WASA-at-COSY experiment has collected 3×107 events with η mesons produced via the reaction pd→He3η at T=1.0GeV. Using this data set, we evaluate the branching ratios of the decays η→π+π-γ, η→e+e-γ, η→π+π-e+e-, and η→e+e-e+e-. The branching ratios are normalized to the η→π+π-π0 decay. In addition an upper limit on a CP-violating asymmetry in η→π+π-e+e- is extracted.

\eta

Abstract.We report on a high-statistics measurement of the most basic double-pionic fusion reaction

decays into charged particles

\overrightarrow{n} p\rightarrow d\pi^{0}\pi^{0}

Measurement of the (n)over-right-arrowp -g d pi(0) pi(0) reaction with polarized beam in the region of the d(*)(2380) resonance

over the energy region of the d*(2380) resonance by use of a polarized deuteron beam and observing the double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d* resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.

Measurement of the analysing power in proton-proton elastic scattering at small angles

Abstract The proton analysing power in p → p elastic scattering has been measured at small angles at COSY-ANKE at 796 MeV and five other beam energies between 1.6 and 2.4 GeV using a polarised proton beam. The asymmetries obtained by detecting the fast proton in the ANKE forward detector or the slow recoil proton in a silicon tracking telescope are completely consistent. Although the analysing power results agree well with the many published data at 796 MeV, and also with the most recent partial wave solution at this energy, the ANKE data at the higher energies lie well above the predictions of this solution at small angles. An updated phase shift analysis that uses the ANKE results together with the World data leads to a much better description of these new measurements.

High precision beam momentum determination in a synchrotron using a spin resonance method

In order to measure the mass of the eta meson with high accuracy using the dp -> He-3 eta reaction, the momentum of the circulating deuteron beam in the Cooler Synchrotron COSY of the Forschungszentrum Julich has to be determined with unprecedented precision. This has been achieved by studying the spin dynamics of the polarized deuteron beam. By depolarizing the beam through the use of an artificially induced spin resonance, it was possible to evaluate its momentum p with a precision of Delta p/p < 10(-4) for a momentum of roughly 3 GeV/c.

COSY-SCL, the superconducting injector linac for COSY

The superconducting injector linac COSY-SCL is being designed and constructed at the Forschungszentrum Juelich. The train goal of the new injector is to fill the cooler synchrotron COSY with polarized protons as well as with polarized deuterons up to the space-charge limit at injection energy. COSY-SCL is characterized by a base frequency of 160 MHz, 25 kV ion-source extraction voltage, a pulse length of up to 500 /spl mu/s, a maximum repetition rate of 2 Hz, injection into the linac at /spl beta/=0.073 and injection into COSY at kinetic energies of 52 MeV for protons and 56 MeV for deuterons, respectively. The injector configuration is presented, and its main subsystems-ion source (CIPIOS from IUCF for polarized H/sup -/ and D/sup -/), RFQ (built in co-operation with the University of Frankfurt), linac (based on half-wave resonators operating at 160 and 320 MHz)- are described and discussed. The present status of the project is reported.

Acceleration of Polarized Protons and Deuterons at COSY

At the cooler synchrotron COSY, protons and deuterons are accelerated up to 3.65 GeV/c. Vertically polarized proton beams with more than 70% polarization have been delivered in recent years to internal as well as to external experiment areas at different momenta up to the maximum momentum of COSY. In a strong‐focusing synchrotron like COSY, imperfection and intrinsic resonances cause polarization losses during acceleration. The existing magnet system of COSY allows to overcome all imperfection resonances by exciting adiabatic spin flips without polarization losses. A tune‐jump system consisting of two fast quadrupoles has been developed to handle intrinsic resonances in COSY. This magnet system is being successfully utilized at all intrinsic resonances in the momentum range of COSY. For the acceleration of vertically polarized deuterons, additional correction provisions are not necessary to preserve polarization during acceleration because depolarizing resonances are not crossed in the momentum range of C...