113 research outputs found
Line shape of the muH(3p - 1s) hyperfine transitions
The (3p - 1s) X-ray transition to the muonic hydrogen ground state was
measured with a high resolution crystal spectrometer. A Doppler effect
broadening of the X-ray line was established which could be attributed to
different Coulomb de-excitation steps preceding the measured transition. The
assumption of a statistical population of the hyperfine levels of the muonic
hydrogen ground state was directly confirmed by the experiment and measured
values for the hyperfine splitting can be reported. The results allow a
decisive test of advanced cascade model calculations and establish a method to
extract fundamental strong-interaction parameters from pionic hydrogen
experiments.Comment: Submitted to Physical Review Letter
Pionic Deuterium
The strong interaction shift and broadening in pionic deuterium have been
remeasured with high statistics by means of the (3p-1s) X-ray transition using
the cyclotron trap and a high-resolution crystal spectrometer. Preliminary
results are (-2325+/-31) meV (repulsive) for the shift and (1171+23/-49} meV
for the width, which yields precise values for the pion-deuteron scattering
length and the threshold parameter for pion production.Comment: Conf. Proc. Few Body 19 (FB19), August 31 - September 5, 2009, Bonn,
Germany 9 pages, 13 figure
Precision determination of the dpi -> NN transition strength at threshold
An unusual but effective way to determine at threshold the dpi -> NN
transition strength is to exploit the hadronic ground-state broadening in
pionic deuterium, accessible by x-ray spectroscopy. The broadening is dominated
by the true absorption channel dpi- -> nn, which is related to s-wave pion
production pp -> dpi+ by charge symmetry and detailed balance. Using the exotic
atom circumvents the problem of Coulomb corrections to the cross section as
necessary in the production experiments. Our dedicated measurement finds
(1171+23/-49) meV for the broadening yielding (252+5/-11) \mub.Comment: 4 pages, 2 figures, 1 tabl
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
Line shape analysis of the K transition in muonic hydrogen
The K transition in muonic hydrogen was measured with a
high-resolution crystal spectrometer. The spectrum is shown to be sensitive to
the ground-state hyperfine splitting, the corresponding triplet-to-singlet
ratio, and the kinetic energy distribution in the state. The hyperfine
splitting and triplet-to-singlet ratio are found to be consistent with the
values expected from theoretical and experimental investigations and,
therefore, were fixed accordingly in order to reduce the uncertainties in the
further reconstruction of the kinetic energy distribution. The presence of
high-energetic components was established and quantified in both a
phenomenological, i.e. cascade-model-free fit, and in a direct deconvolution of
the Doppler broadening based on the Bayesian approach.Comment: 22 pages, 21 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
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
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
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