108 research outputs found
The energy dependence of the pp->K+ n Sigma+ reaction close to threshold
The production of the Sigma+ hyperon through the pp->K+nSigma+ reaction has
been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and
2.020 GeV. At low energies, correlated K+pi+ pairs can only originate from
Sigma+ production so that their measurement allows the total cross section for
the reaction to be determined. The results obtained are completely consistent
with the values extracted from the study of the K+-proton correlation spectra
obtained in the same experiment. These spectra, as well as the inclusive K+
momentum distributions, also provide conservative upper limits on the Sigma+
production rates. The measurements show a Sigma+ production cross section that
varies roughly like phase space and, in particular, none of the three
experimental approaches used supports the anomalously high near-threshold
pp->K+ nSigma+ total cross section previously reported [T. Rozek et al., Phys.
Lett. B 643, 251 (2006)].Comment: Submitted to PR
Observation of inverse diproton photodisintegration at intermediate energies
The reaction pp->{pp}_s\gamma, where {pp}_s is a proton pair with an
excitation energy E_{pp}<3 MeV, has been observed with the ANKE spectrometer at
COSY-Juelich for proton beam energies of T_p=0.353, 0.500, and 0.550 GeV. This
is equivalent to photodisintegration of a free 1S_0 diproton for photon
energies E\gamma ~ T_p/2. The differential cross sections measured for c.m.
angles 0 deg.<\theta_{pp}<20 deg. exhibit a steep increase with angle that is
compatible with E1 and E2 multipole contributions. The ratio of the measured
cross sections to those of np->d\gamma is on the 10^{-3}-10^{-2} level. The
increase of the pp->{pp}_s\gamma cross section with T_p might reflect the
influence of the Delta(1232) excitation.Comment: 4 pages + 4 figure
Measurement of the isospin-filtering dd -> 4He K+ K- reaction at Q=39 MeV
The total cross section for the dd -> 4He K+ K- reaction has been measured at
a beam momentum of 3.7 GeV/c, corresponding to an excess energy of 39 MeV,
which is the maximum possible at the Cooler Synchrotron COSY-J\"{u}lich. A
deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed
inside the storage ring, have been employed in this investigation. We find a
total cross section of sigma(tot) < 14 pb, which brings into question the
viability of investigating the dd -> 4He a0(980) reaction as a means of
studying isospin violation.Comment: Five pages with three eps figure
The Slow Control System of the Atomic Beam Source at ANKE/COSY: An Industrial Approach Based on WinCC and S7 PLCs
Toward polarized antiprotons: Machine development for spin-filtering experiments
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 MeV in COSY. The implementation of a
low- insertion made it possible to achieve beam lifetimes of
s in the presence of a dense polarized hydrogen
storage-cell target of areal density . The developed techniques can be directly
applied to antiproton machines and allow for the determination of the
spin-dependent cross sections via spin filtering
New determination of the mass of the eta meson at COSY-ANKE
A value for the mass of the eta meson has been determined at the COSY-ANKE
facility through the measurement of a set of deuteron laboratory beam momenta
and associated 3He center-of-mass momenta in the d+p -> 3He+X reaction. The eta
was then identified by the missing-mass peak and the production threshold
determined. The individual beam momenta were fixed with a relative precision of
3 x 10^-5 for values around 3 GeV/c by using a polarized deuteron beam and
inducing an artificial depolarizing spin resonance, which occurs at a
well-defined frequency. The final-state momenta in the two-body d+p -> 3He+eta
reaction were investigated in detail by studying the size of the 3He momentum
ellipse with the forward detection system of the ANKE spectrometer. Final
alignment of the spectrometer for this high precision experiment was achieved
through a comprehensive study of the 3He final-state momenta as a function of
the center-of-mass angles, taking advantage of the full geometrical acceptance.
The value obtained for the mass, m(eta)=(547.873 +- 0.005(stat) +- 0.027(syst))
MeV/c^2, is consistent and competitive with other recent measurements, in which
the meson was detected through its decay products.Comment: 11 pages, 11 figures, 3 tables, published versio
Evidence of kaon nuclear and Coulomb potential effects on soft K+ production from 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-Juelich. The strong suppression in the ratios observed for p_K<200-250
MeV/c can 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~20 MeV 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 to better than 3 MeV.Comment: 9 pages, 3 figures; changed conten
Absence of spin dependence in the final state interaction of the d(pol) p --> 3He eta reaction
The deuteron tensor analysing power t_{20} of the d(pol) p --> 3He eta
reaction has been measured at the COSY-ANKE facility in small steps in excess
energy Q up to Q = 11 MeV. Despite the square of the production amplitude
varying by over a factor of five through this range, t_{20} shows little or no
energy dependence. This is evidence that the final state interaction causing
the energy variation is not influenced by the spin configuration in the
entrance channel. The weak angular dependence observed for t_{20} provides
useful insight into the amplitude structure near threshold.Comment: 5 pages, 4 figure
Inclusive K^+ meson production in proton-nucleus interactions
The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been
investigated at the COoler SYnchrotron COSY-J\"ulich for beam energies T_p =
1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward
angles theta < 12 degrees as well as the target-mass dependence of the K^+
momentum spectra have been measured with the ANKE spectrometer. Far below the
free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of
collectivity in the target nucleus. From the target-mass dependence of the
cross sections at higher energies, the repulsive in-medium potential of K^+
mesons can be deduced. Using pN cross-section parameterisations from literature
and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X)
/ sigma(pp -> K^+ X) ~ (3-4).Comment: Accepted for publication in EPJ A; 17 pages, 10 figures, 11 table
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