Single \pi^- production in np collisions for excess energies up to 90 MeV

The quasifree reaction np\to pp\pim was studied in a kinematically complete experiment by bombarding a liquid hydrogen target with a deuteron beam of momentum 1.85 GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector $\mathbb{P}_n$ which differed from event to event. A range of almost 90 MeV excess energy above threshold was covered. Energy dependent angular distributions, invariant mass spectra as well as fully covered Dalitz plots were deduced. Sizeable $pp$ FSI effects were found as were contributions of $p$ and $d$ partial waves. The behavior of the elementary cross section $\sigma_{01}$ close to threshold is discussed in view of new cross section data. In comparison with existing literature data the results provide a sensitive test of the spectator model.Comment: 21 pages, 9 figures, 4 tables, submitted to EPJ

Measurement of Spin Correlation Parameters ANN_{NN}, ASS_{SS}, and A_SL{SL} at 2.1 GeV in Proton-Proton Elastic Scattering

At the Cooler Synchrotron COSY/J\"ulich 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$^o$ and 90$^o$. Our data on A$_{SS}$ -- the first measurement of this observable above 800 MeV -- clearly disagrees with predictions of available of 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.Comment: 4 pages, 4 figure

Determination of Deuteron Beam Polarizations at COSY

The vector and tensor 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 ring, the polarizations of the deuterons were checked by studying a variety of nuclear reactions using a cluster target at the ANKE magnet spectrometer placed at an internal target position of the storage ring. All these measurements were consistent with the absence of depolarization during acceleration and provide a number of secondary standards that can be used in subsequent experiments at the facility.Comment: 12 pages, 13 figure

Spin manipulation of 1.94 GeV/c polarized protons stored in the COSY cooler synchrotron

We recently studied spin flipping of a 1.94 GeV/c vertically polarized proton beam at COSY in Julich, Germany. We swept an rf-dipole's frequency through an rf-induced spin resonance to flip the beam's polarization direction. After determining the resonance's frequency, we varied the dipole's strength, frequency range, and frequency ramp time. At the rf-dipole's maximum strength, and optimum frequency range and ramp time, we measured a spin-flip efficiency of 99.3% +/- 0.1%. This result indicates that an rf dipole may allow efficient spin flipping in high energy proton rings

Elastic pd scattering with 200–300 MeV protons

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°<~Θc.m.<~  29°. The results are compared to nonrelativistic Faddeev calculations with different nucleon-nucleon interactions and total angular momenta j<~5 in the NN subsystem. The impact of a genuine 3N force is investigated. The discrepancies between data and calculations increase with projectile energy

Reply to “Comment on ‘Spin manipulation of 1.94 GeV/c polarized protons stored in the COSY cooler synchrotron’ ”

It seems improper to publish a theoretical Comment about an experimental Article without mentioning the Article’s referenced theoretical paper, which derived the equation that the Comment claims is incorrect. Our experimental collaboration declines to offer any opinion about which factor of 2 is correct