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 NΔN\Delta interaction in photoproduction processes off the deuteron

The impact of the short-range $N\Delta$ interaction on the pion photoproduction processes off the deuteron in the $\Delta$-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 $NN$ (or $N\Delta$) interaction at short ranges related to the inner dressed-bag states. It is shown that the effect of short-range $N\Delta$ interaction for the forward-angle $\pi^\mathrm{o}$ photoproduction off the deuteron cannot be neglected. The prospects for further development of the model to describe the short-range $NN$ (or $N\Delta$) 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