We present results on $\pi^+$-p interactions at 500 MeV from an experiment performed with the Saclay 35 cm hydrogen bubble chamber. A total of 1840 events have been observed. The branching ratio for elastic events is equal to 0.883$\pm$0.008. Eight events are unambiguously attributed to the reaction $\pi^+p\to\pi^+p\gamma$. Cross sections for the various reactions are given. The elastic angular distribution has been determined up to cos$\theta$ = +0.975 and shows evidence for S, P, D waves in good agreement with the results obtained in other experiments. For the one-pion production reactions, the ratio of $\pi^0$ production to $\pi^+$ production is found equal to 4.1$\pm$0.8. This result and the corresponding distributions for momentum and angle of the secondaries are compared with the predictions of the isobaric models.
No description provided.
Measurements of π±p elastic differential cross-sections have been performed in the forward direction, using a missing-mass spark chamber spectrometer. The films have been seanned by an automatic apparatus. A phase-shift analysis of the experimental data has been done, leading to three solutions. Various experiments are proposed in order to resolve the ambiguities.
No description provided.
No description provided.
No description provided.
The interactions of 720 MeV negative pions with protons were investigated using pictures from the 35 cm Saclay hydrogen bubble chamber. Partial cross-sections were determined with the following results: σ(elastic)=13.2±0.5) mb, σ(π−pπ0)=(5.25±0.30) mb, σ(π−π+n)=()7.17±0.35) mb σ (neutrals)=(9.9±0.7) mb, σ (2π production)=(1.03±0.13) mb. The elastic-scattering angular distribution was fitted with a fifth-order polynomial in cos θ* π which shows the effect of a significantF 5/2-D 5/2 interference contribution and predicts a value for (dσ/dΩ) (0°) in agreement with dispersion theory. For both single-π production channels, the two-body effective mass plots and c.m. angular distributions are presented, discussed and compared with the predictions from phase-space, the Olsson-Yodh isobar model and the pole model of isobar production. TheN *(3/2, 3/2) isobar is seen to play an important role in the ππN final states, but the agreement of the data with the existing isobar models and their assumptions is not satisfactory. A comparison of the different two-pion production cross-sections π−pπ−π+, π−pπ0π0 and π−π+nπ0 suggests a strong contribution of π−p→η0n to the π−π+nπ0 final state. An upper limit for σ(π−p→η0n) of (3.0±0.4) mb was obtained.
No description provided.
Total and differential cross sections for $\eta$ and $\eta ^\prime$ photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The $\eta$ mesons are detected in their two neutral decay modes, $\eta\to\gamma\gamma$ and $\eta\to 3\pi^0\to 6\gamma$, and for the first time, cover the full angular range in $\rm cos \theta_{cm}$ of the $\eta$ meson. These new $\eta$ photoproduction data are consistent with the earlier CB-ELSA results. The $\eta ^\prime$ mesons are observed in their neutral decay to $\pi^0\pi^0\eta\to 6\gamma$ and also extend the coverage in angular range.
Differential cross section for ETA production at incident photon energy 0.850 to 0.900 GeV.
Differential cross section for ETA production at incident photon energy 0.900 to 0.950 GeV.
Differential cross section for ETA production at incident photon energy 0.950 to 1.000 GeV.
The reaction $\gamma p\to p\pi^0\eta$ has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from $\Delta^+(1232)\eta$, $N(1535)^+\pi^0$ and $pa_0(980)$ as intermediate states. A partial wave analysis suggests that the reaction proceeds via formation of six $\Delta$ resonances, $\Delta(1600)P_{33}$, $\Delta(1920)P_{33}$, $\Delta(1700)D_{33}$, $\Delta(1940)D_{33}$, $\Delta(1905)F_{35}$, $\Delta(2360)D_{33}$, and two nucleon resonances $N(1880)P_{11}$ and $N(2200)P_{13}$, for which pole positions and decay branching ratios are given.
Total cross section for GAMMA P --> P PI0 ETA.
Differential cross sections as a function of the angles of the individual final state particles for the W range 1.7 to 1.9 GeV.. Errors shown are statistical only.
Differential cross sections as a function of the angles of the individual final state particles for the W range 1.9 to 2.1 GeV.. Errors shown are statistical only.
Quasi-free photoproduction of eta-mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta-mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasi-free n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta-production off the neutron shows a pronounced bump-like structure at W=1.68 GeV (E_g ~ 1 GeV), which is absent for the proton.
Measured value of the quasi-free eta cross section off protons and neutrons as a function of incident photon energy.
Ratio of the measured quasi-free neutron to proton cross sections as a function of incident photon energy.
Measured angular distribution for an incident photon energy of 0.700 GeV.
Single pi0 photoproduction has been studied with the CB-ELSA experiment at Bonn using tagged photon energies between 0.3 and 3.0 GeV. The experimental setup covers a very large solid angle of about 98% of 4 pi. Differential cross sections (d sigma)/(d Omega) have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gamma p --> N* (Delta*) --> p pi0. A combined analysis including the data presented in this letter along with other data sets reveals contributions from known resonances and evidence for a new resonance N(2070)D15.
Total cross section for GAMMA P --> P PI0 obtained by integration of the angular distributions and extrapolation into the forward and backward regions using the PWA result.
Differential cross section as a function of c.m. angle for the photon energy range 300 to 425 GeV.
Differential cross section as a function of c.m. angle for the photon energy range 425 to 550 GeV.
Total and differential cross sections for the reaction p(gamma, eta)p have been measured for photon energies in the range from 750 MeV to 3 GeV. The low-energy data are dominated by the S11 wave which has two poles in the energy region below 2 GeV. Eleven nucleon resonances are observed in their decay into p eta. At medium energies we find evidence for a new resonance N(2070)D15 with (mass, width) = (2068+-22, 295+-40) MeV. At photon energies above 1.5 GeV, a strong peak in forward direction develops, signalling the exchange of vector mesons in the t channel.
Total cross section determined by summing the angular bins and extrapolating outside the angular range of the experiment.
Differential cross section as a function of c.m. angle for the photon energy range 750 to 950 GeV.
Differential cross section as a function of c.m. angle for the photon energy range 950 to 1150 GeV.
The reaction γp → K 0 Σ + has been measured with the SAPHIR detector at the electron stretcher ring ELSA. The total cross section rises up to a peak value of 1.1 μ b at a photon energy of 1.4 GeV. The differential cross sections dσ/dΩ are consistent with being flat throughout the measured energy range. The first measurement of the Σ + polarization in photon induced reactions was obtained.
Total cross section for the reaction GAMMA P --> K0 SIGMA+. Errors include statistics and the uncertainty on the acceptance calculation and photon flux.
Differential cross section for the reaction GAMMA P --> K0 SIGMA+. Errors are dominated by statistical uncertainties.
Measure of SIGMA+ polarization in the reaction GAMMA P --> K0 SIGMA+.
Associated strangeness production in the reactions γp → K + Λ and γp → K + Σ 0 was measured with the SAPHIR detector at the electron stretcher ring ELSA at Bonn. Data on total and differential cross sections and on hyperon polarizations are presented. The total cross section for Λ production shows a strong threshold enhancement whereas the Σ 0 data have a maximum at about E γ =1.45 GeV. Along with the angular decomposition of the differential cross section into polynomials, this suggests resonance production. However, the angular distributions of both hyperon polarizations vary only slightly with the photon energy. Λ and Σ 0 polarizations show opposite signs and change sign over the angular range.
Total cross section for the reaction GAMMA P --> K+ LAMBDA.
Total cross section for the reaction GAMMA P --> K+ SIGMA0.
Differential cross section for the reaction GAMMA P --> K+ LAMBDA in the GAMMA energy range 0.90 to 1.10 GeV in three energy bins.
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