We report on an exclusive and kinematically complete high-statistics measurement of the basic doublepionic fusion reaction pn ! d 0 0 over the full energy region of the ABC effect, a pronounced low-mass enhancement in the -invariant mass spectrum. The measurements, which cover also the transition region to the conventional t-channel ÁÁ process, were performed with the upgraded WASA detector setup at COSY. The data reveal the Abashian-Booth-Crowe effect to be uniquely correlated with a Lorentzian energy dependence in the integral cross section. The observables are consistent with a narrow resonance PRL

The ABC effect-a puzzling low-mass enhancement in the pipi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn-->dpi;{0}pi;{0} at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pipi)_{I=L=0} channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a DeltaDelta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.

The first measurement of the cross section of the quasifree pn→pn reaction has been carried out at the CELSIUS storage ring using a deuterium internal cluster jet target. The energy dependence of the cross section is extracted using a fixed incident proton energy of T p ϭ1350 MeV and exploiting the Fermi momentum of the struck neutron. The data cover a range of center-of-mass excess energies from 16 to 109 MeV. The shape of the excitation function is broadly similar to that of the pp→pp reaction, though with a cross section about a factor of 6.5 larger. ͓S0556-2813͑98͒02811-8͔

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The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to Tp = 1.36 GeV. Total and differential cross sections have been obtained for the channels pnπ + π 0 , ppπ + π − , ppπ 0 π 0 and also nnπ + π + . For intermediate incident energies Tp > 1 GeV, i.e. in the region which is beyond the Roper excitation but at the onset of ∆∆ excitation, the total ppπ 0 π 0 cross section falls behind theoretical predictions by as much as an order of magnitude near 1.2 GeV, whereas the nnπ + π + cross section is a factor of five larger than predicted. An isospin decompostion of the total cross sections exhibits a s-channel-like energy dependence in the region of the Roper excitation as well as a significant contribution of an isospin 3/2 resonance other than the ∆(1232). As possible candidates the ∆(1600) and the ∆(1700) are discussed.Two-pion production in nucleon-nucleon collisions is an outstanding subject, since it connects ππ dynamics with baryon and baryon-baryon degrees of freedom. There is increasing evidence that the puzzling ABC effect observed in doublepionic fusion reactions may possibly be traced back to an isoscalar resonance phenomenon as source for the peculiar pion pair production in the ππ scalar-isoscalar state [1,2,3,4]. By contrast the isovector ππ channel in double-pionic fusion be-haves regularily, i.e. shows no ABC effect and follows the expectations from conventional t-channel ∆∆ calculations [5].In view of the challenging explanation [2,3,4] offered for the ABC effect it is interesting to study for comparison the behavior of ππ production in isoscalar, isovector and isotensor ππ channels in those cases, where the two actively participating nucleons do not fuse into a final nuclear bound system. From previous work it is known that the 1

In 1984-86, a glaucoma survey was carried out in a municipality in central Sweden, comprising 760 subjects 65-74 years of age. Since 1988, a follow-up study of those 527 subjects who had normal and reliable visual fields has been in progress. A visual field defect was required for a diagnosis of chronic open-angle glaucoma. By December 1991, 10 cases of capsular glaucoma and 3 cases of chronic simple glaucoma had been found. The standardized relative risk for chronic open-angle glaucoma was 3.4 times (95% confidence interval: 1.1-11) greater in subjects with a baseline intraocular pressure > or = 21 mmHg, using the highest pressure in either eye, than in those with an intraocular pressure < 21 mmHg. Pseudoexfoliation increased the standardized relative risk 9.8-fold (95% confidence interval: 2.5-38). There was indication of effect modification between intraocular pressure and pseudoexfoliation. Optic disc haemorrhages were associated with a 4.8-fold (95% confidence interval: 0.63-37) increased unadjusted risk. The study supports the pressure theory of optic nerve damage in glaucoma. Pseudoexfoliation was recognized as an independent risk factor for the development of chronic open-angle glaucoma.

The nuclear and electronic magnetic dipole moments of 21Fr and the nuclear ground-state spin of 207Fr have been measured directly by on-line atomic-beam magnetic resonance techniques at the ISOLDE facility at CERN. The following results have been obtained: μI(211Fr) = 4.00(8) nm, gJ(Fr, 7s 2S1/2) = 2.00497(9) and I(207Fr) = 9/2. A large deviation of the electronic magnetic moment from the free electron value was found. Using the measured nuclear magnetic moment μI(211Fr), a comparison is made between different theoretical calculations of the magnetic dipole hyperfine constants and with the available experimental data in 211Fr. An analysis of the electric quadrupole interaction is also given. Nuclear magnetic dipole and electric quadrupole moments are deduced for the sequences 207-213Fr and 220-228Fr, using the data on 211Fr as reference values. The nuclear quantities are discussed within the framework of the shell model and the core-quasiparticle model, giving information on the nuclear single-particle structure and on the variation in deformation along the sequences of francium isotopes.