213 research outputs found
The Near-Threshold Production of Phi Mesons in pp Collisions
The pp->pp phi reaction has been studied at the Cooler Synchrotron
COSY-Juelich, 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 pp
omega-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.Comment: 4 Pages, 3 Figures, 1 Table, submitted to Phys. Rev. Let
First measurements of spin correlations in the np -> d pi^0 reaction
The transverse spin correlations Axx and Ayy in the np-> d pi^0 reaction have
been measured for the first time in quasi-free kinematics at the COSY-ANKE
facility using a polarised deuteron beam incident on a polarised hydrogen cell
target. The results obtained for neutron energies close to 353 MeV and 600 MeV
are in good agreement with the partial wave analysis of data on the
isospin-related pp-> d pi^+ reaction, though the present results cover also the
small-angle region, which was largely absent from these data
Measurement of the analyzing powers in pd elastic and pn quasi-elastic scattering at small angles
The analyzing powers in proton-deuteron elastic and proton-neutron
quasi-elastic scattering have been measured at small angles using a polarized
proton beam at the COSY storage ring incident on an unpolarized deuterium
target. The data were taken at 796MeV and five higher energies from 1600MeV to
2400MeV. The analyzing power in pd elastic scattering was studied by detecting
the low energy recoil deuteron in telescopes placed symmetrically in the COSY
plane to the left and right of the beam whereas for pn quasi-elastic scattering
a low energy proton was registered in one of the telescopes in coincidence with
a fast scattered proton measured in the ANKE magnetic spectrometer. Though the
experiment explores new domains, the results are consistent with the limited
published information.Comment: 10 pages with 8 figure
Resonance-like coherent production of a pion pair in the reaction in the GeV region
The reaction was studied at 0.8-2.0 GeV proton
beam energies with the ANKE magnetic spectrometer at the COSY synchrotron
storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8
GeV/, were detected at small angles with respect to the proton beam.
Distribution over the reaction missing mass reveals a local enhancement
near the threshold of the pion pair production specific for the so-called ABC
effect. The enhancement has a structure of a narrow bump placed above a smooth
continuum. The invariant mass of the system in this enhancement
region exhibits a resonance-like peak at GeV/
with the width GeV/. A possible interpretation of
these features is discussed.Comment: 14 pages, 16 figures, submitted to Eur. Phys. J. A. v2: Added
references [42,43] in section IV.A. v3: revised version according to referee
remarks v4: revised version according to referee remark
Coherent pion production in proton-deuteron collisions
Values of the proton analysing power in the
reactions at 350-360~MeV
per nucleon were obtained by using a polarised proton beam incident on a
deuterium cluster-jet target and with a polarised deuteron beam incident on a
target cell filled with polarised hydrogen. These results have a much larger
angular coverage than existing data. First measurements are also presented of
the deuteron vector analysing power and the deuteron-proton spin correlations.
Data were also obtained on the deuteron-proton spin correlation and proton
analysing power at small angles at 600~MeV per nucleon, though the angular
coverage at this energy was much more restricted even when using a deuteron
beam. By combining the extrapolated values of the spin correlations to the
forward or backward directions with published measurements of the deuteron
tensor analysing powers, the relative phases between the two non-vanishing
amplitudes were evaluated.Comment: 5 pages, 5 figure
Analysing powers and spin correlations in deuteron-proton charge exchange at 726 MeV
The charge exchange of vector polarised deuterons on a polarised hydrogen
target has been studied in a high statistics experiment at the COSY-ANKE
facility at a deuteron beam energy of Td = 726 MeV. By selecting two fast
protons at low relative energy E_{pp}, the measured analysing powers and spin
correlations are sensitive to interference terms between specific
neutron-proton charge-exchange amplitudes at a neutron kinetic energy of Tn ~
1/2 Td =363 MeV. An impulse approximation calculation, which takes into account
corrections due to the angular distribution in the diproton, describes
reasonably the dependence of the data on both E_{pp} and the momentum transfer.
This lends broad support to the current neutron-proton partial-wave solution
that was used in the estimation
Study of the charge-exchange reaction using a polarised deuterium target
The vector and tensor analysing powers, and , of the charge-exchange reaction have been measured at a beam energy
of 600 MeV at the COSY-ANKE facility by using an unpolarised proton beam
incident on an internal storage cell target filled with polarised deuterium
gas. The low energy recoiling protons were measured in a pair of silicon
tracking telescopes placed on either side of the target. Putting a cut of 3 MeV
on the diproton excitation energy ensured that the two protons were dominantly
in the state, here denoted by . The polarisation of the
deuterium gas was established through measurements in parallel of
proton-deuteron elastic scattering. By analysing events where both protons
entered the same telescope, the charge-exchange reaction was measured for
momentum transfers MeV/. These data provide a good continuation
of the earlier results at MeV/ obtained with a polarised
deuteron beam. They are also consistent with impulse approximation predictions
with little sign evident for any modifications due to multiple scatterings
Near-threshold production of omega mesons in the pn -> d omega reaction
The first measurement of the p n -> d omega total cross section has been
achieved at mean excess energies of Q = 28 and 57 MeV by using a deuterium
cluster-jet target. The momentum of the fast deuteron was measured in the ANKE
spectrometer at COSY-Juelich and that of the slow "spectator" proton p(sp) from
the p d -> p(sp) d omega reaction in a silicon telescope placed close to the
target. The cross sections lie above those measured for p p -> p p omega but
seem to be below theoretical predictions.Comment: 7 pages, 8 figures; second approach to describe the background has
been added; results changed insignificantly, EPJ in pres
Measurement of the analysing power in proton-proton elastic scattering at small angles
The proton analysing power in 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.Comment: 5 pages, 3 figure
The neutron-proton charge-exchange amplitudes measured in the dp -> ppn reaction
The unpolarised differential cross section and the two deuteron tensor
analysing powers A_{xx} and A_{yy} of the pol{d}p -> (pp)n charge-exchange
reaction have been measured with the ANKE spectrometer at the COSY storage
ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27 GeV, data were
obtained for small momentum transfers to a (pp) system with low excitation
energy. The results at the three lower energies are consistent with impulse
approximation predictions based upon the current knowledge of the
neutron-proton amplitudes. However, at 2.27GeV, where these amplitudes are far
more uncertain, agreement requires a reduction in the overall double-spin-flip
contribution, with an especially significant effect in the longitudinal
direction. These conclusions are supported by measurements of the
deuteron-proton spin-correlation parameters C_{x,x} and C_{y,y} that were
carried out in the pol{d}pol{p} -> (pp)n reaction at 1.2 and 2.27GeV. The
values obtained for the proton analysing power also suggest the need for a
radical re-evaluation of the neutron-proton elastic scattering amplitudes at
the higher energy. It is therefore clear that such measurements can provide a
valuable addition to the neutron-proton database in the charge-exchange region.Comment: 13 pages with 13 figure
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