43 research outputs found
Search for the Hypothetical pi -> mu x Decay
The KARMEN collaboration has reported the possible observation of a hitherto
unknown neutral and weakly interacting particle x, which is produced in the
decay pi -> mu + x with a mass m(x) = 33.9 MeV. We have searched for this
hypothetical decay branch by studying muons from pion decay in flight with the
LEPS spectrometer at the piE3 channel at PSI and find branching ratios BR(pi-
to mu- anti-x) < 4e-7 and BR(pi+ to mu+ x) < 7e-8 (95\% C.L.). Together with
the limit BR > 2e-8 derived in a recent theoretical paper our result would
leave only a narrow region for the existence of x if it is a heavy neutrino.Comment: 10 pages, TeX (uses epsf), 3 Postscript figures uu-encode
Exclusive measurement of coherent eta photoproduction from the deuteron
Coherent photoproduction of eta mesons from the deuteron has been measured
from threshold up to incident photon energies of 750 MeV using the photon
spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI.
For the first time, differential coherent cross sections have been deduced from
the coincident detection of the eta meson and the recoil deuteron. A missing
energy analysis was used for the suppression of background events so that a
very clean identification of coherent eta-photoproduction was achieved. The
resulting cross sections agree with previous experimental results except for
angles around 90 deg in the photon-deuteron cm-system where they are smaller.
They are compared to various model calculations.Comment: 4 pages, 4 figure
Photoproduction of pi0-mesons from nuclei
Photoproduction of neutral pions from nuclei (carbon, calcium, niobium, lead)
has been studied for incident photon energies from 200 MeV to 800 MeV with the
TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI
accelerator. Data were obtained for the inclusive photoproduction of neutral
pions and the partial channels of quasifree single pi0, double pi0, and
pi0pi+/- photoproduction. They have been analyzed in terms of the in-medium
behavior of nucleon resonances and the pion - nucleus interaction. They are
compared to earlier measurements from the deuteron and to the predictions of a
Boltzmann-Uehling-Uhlenbeck (BUU) transport model for photon induced pion
production from nuclei.Comment: 15 pages, 22 figures, accepted for publication in EPJ
Threshold enhancement in eta photoproduction from 2H and 4He
The photoproduction of eta-mesons from 2H and 4He has been studied for
energies close to the production thresholds. The experiments were carried out
with the tagged photon beam of the Mainz MAMI accelerator. The eta-mesons were
detected via their two photon decays with the electromagnetic calorimeter TAPS.
Total cross sections, angular and momentum distributions of the eta-mesons have
been determined for both reactions. The total cross sections in the threshold
region show a large enhancement over the predictions of a participant -
spectator model, indicating significant final state interaction effects. The
results are compared to recent model calculations taking into account
nucleon-nucleon and nucleon-eta final state interaction effects on different
levels of sophistication.Comment: 8 pages, 6 figure
Coherent \pi^\circ photoproduction from ^4He
Differential cross sections and beam asymmetries for coherent \pi^\circ
photoproduction from ^4He in the \Delta energy-range have been measured with
high statistical and systematic precisions using both decay photons for
identifying the process.The experiment was performed at the MAinz MIcrotron
using the TAPS photon spectrometer and the Glasgow/Mainz tagged photon
facility. The differential cross sections are in excellent agreement with
predictions based on the DWIA if an appropriate parametrization of the
\Delta-nuclear interaction is applied. The beam asymmetries are interpreted in
terms of degrees of linear polarization of collimated coherent bremsstrahlung.
The expected increase of the degree of linear polarization with decreasing
collimation angle is confirmed. Agreement with calculations is obtained on a
few-percent level of precision in the maxima of the coherent peaks.Comment: 22 pages, 6 figure
A dressed bag model study of the final-state interaction in photoproduction processes off the deuteron
The impact of the short-range interaction on the pion
photoproduction processes off the deuteron in the -resonance region is
studied in the framework of recently proposed dressed-bag model. A common
dressing procedure for bare three- and six-quark states is used to describe
both the pion decay widths of baryon resonances and the effective (or
) interaction at short ranges related to the inner dressed-bag
states. It is shown that the effect of short-range interaction for
the forward-angle photoproduction off the deuteron cannot be
neglected. The prospects for further development of the model to describe the
short-range (or ) correlations in the lightest nuclei are
discussed
Dynamical properties of algebraic systems : a study in closed geodesics
To a great extent, rigidity theory is the study of boundaries of semisimple groups. Here we investigate the action of a lattice on such a boundary. While we can construct topological factors for real rank 1 groups we show the nonexistence of such factors in higher rank for some cases.
We also study the geodesic flow on a compact locally symmetric manifold of the noncompact type. He calculate metric and topological entropies and see that the Liouville measure is a measure or maximal entropy. This leads to a study of compact maximal flats. We give a new proof of their density in the space of all flats. We prove specification and expansiveness theorems for the geodesic flow and apply them to determine a growth rate for compact maximal flats. Finally, we give an example of a space with infinitely many closed singular geodesics
Exclusive measurement of quasi-free eta-photoproduction from deuterium
Quasi-free photoproduction of eta -mesons from the deuteron has been measured at the tagged photon facility of the Mainz microtron MAMI with the photon spectrometer TAPS for incident photon energies from the production threshold at 630 MeV up to 820 MeV. In a fully exclusive measurement eta -mesons and recoil nucleons were detected in coincidence. At incident photon energies above the production threshold on the free nucleon, where final-state interaction effects are negligible, an almost constant ratio of sigma /sub n// sigma /sub p/ = 0.66 +or- 0.10 was found. At lower incident photon energies the ratio rises due to re-scattering effects. The average ratio agrees with the value extracted from a comparison of the inclusive d( gamma , eta )X cross section to the free-proton cross-section via a participant-spectator model for the deuteron cross-section ( sigma /sub n// sigma /sub p/ = 0.67 +or- 0.07). The angular dependence of the ratio agrees with the expected small deviation of neutron and proton cross-section from isotropy due to the influence of the D/sub 13/(1520)-resonance. The energy dependence of the ratio in the excitation energy range of the S/sub 11/(1535)-resonance disfavors model predictions which try to explain this resonance as K Sigma bound state
Exclusive measurement of quasi-free eta -photoproduction from deuterium
Quasi-free photoproduction of eta -mesons from the deuteron has been measured at the tagged photon facility of the Mainz microtron MAMI with the photon spectrometer TAPS for incident photon energies from the production threshold at 630 MeV up to 820 MeV. In a fully exclusive measurement eta -mesons and recoil nucleons were detected in coincidence. At incident photon energies above the production threshold on the free nucleon, where final-state interaction effects are negligible, an almost constant ratio of sigma /sub n// sigma /sub p/ = 0.66 +or- 0.10 was found. At lower incident photon energies the ratio rises due to re-scattering effects. The average ratio agrees with the value extracted from a comparison of the inclusive d( gamma , eta )X cross section to the free-proton cross-section via a participant-spectator model for the deuteron cross-section ( sigma /sub n// sigma /sub p/ = 0.67 +or- 0.07). The angular dependence of the ratio agrees with the expected small deviation of neutron and proton cross-section from isotropy due to the influence of the D/sub 13/(1520)-resonance. The energy dependence of the ratio in the excitation energy range of the S/sub 11/(1535)-resonance disfavors model predictions which try to explain this resonance as K Sigma bound state