The d+d->alpha+eta reaction has been investigated near threshold using the ANKE facility at COSY-Juelich. Both total and differential cross sections have been measured at two excess energies, Q=2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q=-2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition into partial amplitudes and their consequences for determination of the s-wave eta-alpha scattering length are discussed.
Measured cross sections. Systematic (DSYS) error does not include the luminosity uncertainty.
Experimental angular distribution at excess energy 2.6 MeV.
Experimental angular distribution at excess energy 7.7 MeV.
The pp->pp phi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the proton-proton final state interaction. Taken together with data for pp omega-production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.
K+ K- invariant mass distribution.
Total cross sections.
Differential decay distribution of the K+ in the rest frame of the PHI-meson w.r.t. the beam.
The neutral π0 and η mesons are studied in 197Au−197Au collisions at an incident energy of 800AMeV, substantially below the threshold for η production in N−N collisions. While the gross π0 multiplicity increases almost linearly with the number of participant nucleons, the multiplicities of η and hard π0 mesons show a stronger than linear dependence. The nonlinearity is governed by the average transverse-mass excess 〈mt〉−(s−2mN) of the mesons and is insensitive to their final-state interaction in the nuclear medium.
No description provided.
No description provided.
No description provided.
The quasi-free pn->dphi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the K+K- decay of the phi-meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with s-wave production, the kaon angular distributions show the presence of p waves at quite low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the eta-meson.
Differential cross section dependence on the angle of the K+ from the PHI decay in the PHI rest frame.
Differential cross section dependence on the polar angle of the PHI in the overall rest frame.
Total cross section as a function of the excess energy.
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.
Only statistical errors are presented.
Only statistical errors are presented.
Only statistical errors are presented.
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.
Total inclusive photoproduction cross sections. Statistical errors only.
Angular distributions of ETA mesons from the Deuterium target in the photon-nucleus cm system. Statistical errors only.
Angular distributions of ETA mesons from the Deuterium target in the photon-nucleus cm system. Statistical errors only.
Differential cross sections for Compton scattering from the free proton at Θ γ ′ lab =130.7° in the energy region from 200 MeV to 410 MeV and for quasi-free Compton scattering from the proton bound in the deuteron at Θ γ ′ lab =148.8° in the energy region from 200 MeV to 290 MeV have been measured. The free proton data are in agreement with dispersion-theory predictions based on standard parameters. The difference of the proton polarizabilities has been extracted from the quasi-free data. Our result, α ̄ − β ̄ =[9.1±1.7( stat+syst )±1.2( mod )]×10 −4 fm 3 , is in reasonable agreement with the world average of the free proton data if the backward spin polarizability γ π is taken to be −37.6×10 −4 fm 4 as predicted by dispersion theory in agreement with many theoretical calculations. This implies that quasi-free Compton scattering may also be used to determine the electromagnetic polarizabilities of the neutron. No indication has been found of a recently suggested new contribution to γ π .
No description provided.
The reaction pp->d K+ Kbar0 has been investigated at an excess energy of Q=46 MeV above the (K+ Kbar0) threshold with ANKE at COSY-Juelich. From the detected coincident dK+ pairs about 1000 events with a missing Kbar0 were identified, corresponding to a total cross section of sigma(pp->d K+ Kbar0)=(38 +/- 2(stat) +/- 14(syst)) nb. Invariant-mass and angular distributions have been jointly analyzed and reveal s-wave dominance between the two kaons, accompanied by a p-wave between the deuteron and the kaon system. This is interpreted in terms of a0+(980)-resonance production.
Total cross section for P P --> DEUT K+ KBAR0.
Centre of mass angular distribution of the deuteron with respect to the direction of the incoming proton.
Centre of mass angular distribution of the vector joining the K+ and KBAR0 with respect to the direction of the incoming proton.
Interaction cross sections and charged pion spectra in p+C interactions at 31 GeV/c were measured with the large acceptance NA61/SHINE spectrometer at the CERN SPS. These data are required to improve predictions of the neutrino flux for the T2K long baseline neutrino oscillation experiment in Japan. A set of data collected during the first NA61/SHINE run in 2007 with an isotropic graphite target with a thickness of 4% of a nuclear interaction length was used for the analysis. The measured p+C inelastic and production cross sections are 257.2 +- 1.9 +- 8.9 mb and 229.3 +- 1.9 +- 9.0 mb, respectively. Inclusive production cross sections for negatively and positively charged pions are presented as a function of laboratory momentum in 10 intervals of the laboratory polar angle covering the range from 0 up to 420 mrad. The spectra are compared with predictions of several hadron production models.
The total inelastic cross section and production cross sections. The latter are obtained from the former by subtraction of the quasi-elastic contribution.
The differential PI+ PI- production cross section in the lab. system for the angular range 0 to 20 mrad.
The differential PI+ PI- production cross section in the lab. system for the angular range 20 to 40 mrad.
Proton-proton elastic scattering has been measured by the TOTEM experiment at the CERN Large Hadron Collider at {\surd}s = 7 TeV in dedicated runs with the Roman Pot detectors placed as close as seven times the transverse beam size (sbeam) from the outgoing beams. After careful study of the accelerator optics and the detector alignment, |t|, the square of four-momentum transferred in the elastic scattering process, has been determined with an uncertainty of d t = 0.1GeV p|t|. In this letter, first results of the differential cross section are presented covering a |t|-range from 0.36 to 2.5GeV2. The differential cross-section in the range 0.36 < |t| < 0.47 GeV2 is described by an exponential with a slope parameter B = (23.6{\pm}0.5stat {\pm}0.4syst)GeV-2, followed by a significant diffractive minimum at |t| = (0.53{\pm}0.01stat{\pm}0.01syst)GeV2. For |t|-values larger than ~ 1.5GeV2, the cross-section exhibits a power law behaviour with an exponent of -7.8_\pm} 0.3stat{\pm}0.1syst. When compared to predictions based on the different available models, the data show a strong discriminative power despite the small t-range covered.
The measured differential elastic cross section. Data from the tabulation in CERN-PH-EP-2012-239.
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