Measurement of the helicity asymmetry E for the reaction γ p → π 0 p : The CBELSA/TAPS Collaboration.

A measurement of the double-polarization observable E for the reaction γ p → π 0 p is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C 4 H 9 OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from E γ = 600 to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.

Observation of the pη

Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W=1748 MeV to W=2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη^{'} threshold [E_{γ}=1447 MeV (W=1896 MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N(1895)1/2^{-} nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.

Three-body nature of N(*) and Δ(*) resonances from sequential decay chains.

The Nπ^{0}π^{0} decays of positive-parity N^{*} and Δ^{*} resonances at about 2 GeV are studied at ELSA by photoproduction of two neutral pions off protons. The data reveal clear evidence for several intermediate resonances: Δ(1232), N(1520)3/2^{-}, and N(1680)5/2^{+}, with spin parities J^{P}=3/2^{+}, 3/2^{-}, and 5/2^{+}. The partial wave analysis (within the Bonn-Gatchina approach) identifies N(1440)1/2^{+} and the N(ππ)_{S wave} (abbreviated as Nσ here) as further isobars and assigns the final states to the formation of nucleon and Δ resonances and to nonresonant contributions. We observe the known Δ(1232)π decays of Δ(1910)1/2^{+}, Δ(1920)3/2^{+}, Δ(1905)5/2^{+}, Δ(1950)7/2^{+}, and of the corresponding spin-parity series in the nucleon sector, N(1880)1/2^{+}, N(1900)3/2^{+}, N(2000)5/2^{+}, and N(1990)7/2^{+}. For the nucleon resonances, these decay modes are reported here for the first time. Further new decay modes proceed via N(1440)1/2^{+}π, N(1520)3/2^{-}π, N(1680)5/2^{+}π, and Nσ. The latter decay modes are observed in the decay of N^{*} resonances and at most weakly in Δ^{*} decays. It is argued that these decay modes provide evidence for a 3-quark nature of N^{*} resonances rather than a quark-diquark structure.

N(1520) 3/2(-) helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions.

New data on the polarization observables T, P, and H for the reaction γp→pπ(0) are reported. The results are extracted from azimuthal asymmetries when a transversely polarized butanol target and a linearly polarized photon beam are used. The data were taken at the Bonn electron stretcher accelerator ELSA using the CBELSA/TAPS detector. These and earlier data are used to perform a truncated energy-independent partial wave analysis in sliced-energy bins. This energy-independent analysis is compared to the results from energy-dependent partial wave analyses.

First measurement of the helicity asymmetry for γp → pπ0 in the resonance region.

The first measurement of the helicity dependence of the photoproduction cross section of single neutral pions off protons is reported for photon energies from 600 to 2300 MeV, covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, and BnGa partial wave analyses. Strikingly large differences between data and predictions are observed, which are traced to differences in the helicity amplitudes of well-known and established resonances. Precise values for the helicity amplitudes of several resonances are reported.

[Surgical tactics in spontaneous pneumothorax]. / Khirurgicheskaia taktika pri spontannom pnevmotorakse.

219 cases of nonspecific spontaneous pneumothorax have been analysed. The bullous lung disease was the reason of pneumothorax in 55% of cases. Diagnostic and curative thoracoscopy is an important element of diagnosis. It was performed in 45 patients. Surgical operations were done in 56 patients. An active surgical policy in the treatment of spontaneous pneumothorax is advocated. Partial and subtotal pleurectomy plays an important role in surgery, especially in diffuse bullous lung disease.

Evidence for a parity doublet Delta(1920)P33 and Delta(1940)D33 from gammap-->ppi;{0}eta.

Evidence is reported for the existence of a parity doublet of Delta resonances with total angular momentum J=3/2 from photoproduction of the ppi;{0}eta final state. The two parity partners Delta(1920)P33 and Delta(1940)D33 make significant contributions to the reaction. Cascades of resonances into Delta(1232)eta, N(1535)pi, and Na0(980) are clearly observed.

Quasifree photoproduction of eta mesons off the neutron.

Quasifree 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 quasifree n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta production off the neutron shows a pronounced bumplike structure at W=1.68 GeV (E{gamma} approximately 1 GeV), which is absent for the proton.

Modification of the omega-meson lifetime in nuclear matter.

Information on hadron properties in the nuclear medium has been derived from the photoproduction of omega mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the omega-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic omega width is found to be 130-150 MeV/c(2) at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the rest frame of the omega meson, this inelastic omega width corresponds to a reduction of the omega lifetime by a factor approximately 30. For the first time, the momentum dependent omegaN cross section has been extracted from the experiment and is in the range of 70 mb.

Neutral-pion photoproduction off protons in the energy range 0.3 GeV

Single pi(0) 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 approximately 98% of 4pi. Differential cross sections dsigma/dOmega have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gammap-->N(*)(Delta(*))-->ppi(0). 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.

Photoproduction of eta mesons off protons for 0.75 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 peta. At medium energies we find evidence for a new resonance N(2070)D15 with (M,Gamma)=(2068+/-22, 295+/-40) MeV. At gamma energies above 1.5 GeV, a strong peak in the forward direction develops, signaling the exchange of vector mesons in the t channel.

Observation of in-medium modifications of the omega meson.

The photoproduction of omega mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium modifications of the omega meson via the reaction gamma + A --> omega + X --> pi(0)gamma + X('). Results obtained for Nb are compared to a reference measurement on a LH2 target. While for recoiling, long-lived mesons (pi(0), eta, and eta;(')), which decay outside of the nucleus, a difference in the line shape for the two data samples is not observed, we find a significant enhancement towards lower masses for omega mesons produced on the Nb target. For momenta less than 500 MeV/c an in-medium omega meson mass of M(medium) = [722(+4)(-4)(stat)+35-5(syst)] MeV/c(2) has been deduced at an estimated average nuclear density of 0.6rho(0).

[The use of a pedicled greater omentum in pneumonectomies for the prevention of bronchial fistulas]. / Ispol'zovanie bol'shogo sal'nika na nozhke pri pnevmonéktomiiakh dlia profilaktiki bronkhial'nykh svishchei.

Expanded (13) and combined (9) pneumonectomy with laparotomy and plastics of the bronchial stump with the greater omentum on a vascular pedicle were conducted on 22 patients in the period from 1988 (June) to 1990 (April). The omentum was used for the prevention of bronchial fistulas and correction of defects in the pericardium. Laparotomy and omentopexy did not aggravate the patients' condition essentially and did not affect the terms of treatment. A defect in the bronchial stump occurred only in 2 patients in the post-operative period and closed spontaneously in one of them.

Some problems of tracheobronchoplasty for lung cancer in a Regional Hospital in Russia.

Tracheobronchoplastic procedures formed part of the operation for lung cancer in 41 patients of a Regional Hospital in Russia over the past 2 and a half years. Twenty-nine patients underwent sleeve lobectomy; in a further 12 patients, right pneumonectomy was combined with resection of other mediastinal structures. In 16 patients, sleeve lobectomy was indicated by the high risk of pneumonectomy. Involvement of the carina in the tumour indicated its resection. High frequency jet ventilation was a particular feature of anaesthesia for carinal resection. Omentopexy was used in 10 patients to prevent dehiscence of the bronchial anastomosis. Postoperative complications were encountered in 10 patients. The most frequent, in patients, was dehiscence of the tracheobronchial anastomosis after resection of the carina. Five patients died after operation, the causes of death being dehiscence of anastomosis, pneumonia, empyema, and acute heart failure. Despite the frequency of complications, tracheobronchoplastic operations are often the only possible option in the surgery of extensive lung cancer.