301 research outputs found
Near threshold enhancement of the P anti-P mass spectrum in J/psi decay
No full textWe investigate the nature of the near-threshold enhancement in the pp̅ invariant-mass spectrum of the reaction J/Ψ→γpp̅ reported recently by the BES Collaboration. Using the Jülich NN̅ model we show that the mass dependence of the pp̅ spectrum close to the threshold can be reproduced by the S-wave pp̅ final state interaction in the isospin I=1 state within the Watson-Migdal approach. However, because of our poor knowledge of the NN̅ interaction near-threshold and of the J/Ψ→γpp̅ reaction mechanism and in view of the controversal situation in the decay J/Ψ→π0pp̅ , where no obvious signs of a pp̅ final state interaction are seen, explanations other than final state interactions cannot be ruled out at the present stage.A. Sibirtsev, J. Haidenbauer, S. Krewald, Ulf-G. Meißner and A.W. Thoma
Analysis of the p p-bar mass spectrum from J/psi decay
No full textThe near-threshold enhancement in the pp̄ invariant mass spectrum of the reaction J/→γpp̄, observed in an experiment by the BES Collaboration, is analysed. It is shown, within the Watson-Migdal approach to final state interactions, that the mass dependence of the pp̄ spectrum close to the threshold can be reproduced by the S-wave pp̄ interaction of the Jülich NN̄ model in the isospin I=1 state. Difficulties in the consistent interpretation of the pp̄ invariant mass spectrum of the reaction J/→π0pp̄, where there are no obvious signs for a final state interaction, are discussed. © 2005 American Institute of Physics.J. Haidenbauer, S. Krewald, U.-G. Meißner, A. Sibirtsev and A.W. Thoma
Hyperons in nuclear matter from SU(3) chiral effective field theory
No full textBrueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Λ and Σ hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Σ -nuclear potential and a weak Λ -nuclear spin-orbit force
Hyperon–nucleon interaction at next-to-leading order in chiral effective field theory
No full textResults for the Lambda N and Sigma N interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon-nucleon interaction while the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (pi, K, eta) is taken into account. An excellent description of the hyperon-nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon-nucleon interaction models
Weak strangeness production in nucleon-nucleon scattering
No full textUntil now the only way to study the strangeness changing baryon-baryon interaction has been through the decays of lambda hypernuclei. It would clearly be preferable to be able to study reactions such as pn→pΛ in free space. In order to provide some guidance concerning the feasibility of such a measurement, we investigate the energy dependence, parity violating asymmetry, and shape of the cross section for this reaction.J. Haidenbauer, K. Holinde, K. Kilian, T. Sefzick, A. W. Thoma
Neutral pion photoproduction at high energies
No full textA Regge model with absorptive corrections is employed in a global analysis of the world data on the reactions γ p → π0 p and γ n → π 0 n for photon energies from 3 to 18GeV. In this region resonance contributions are expected to be negligible so that the available experimental information on differential cross-sections and single and double polarization observables at - t 2 GeV2allows us to determine the reaction amplitude reliably. The model amplitude is then used to predict observables for photon energies below 3GeV. A detailed comparison with recent data from the CLAS and CB-ELSA Collaborations in that energy region is presented. Furthermore, the prospects for determining the π0 radiative decay width via the Primakoff effect from the reaction γ p → π 0 p are explored. © 2009 SIF, Springer-Verlag Berlin Heidelberg.A. Sibirtsev, J. Haidenbauer, S. Krewald, U. -G. Meißner and A. W. Thoma
p-wave pion production from nucleon-nucleon collisions
No full textWe investigate p-wave pion production in nucleon-nucleon collisions up to next-to-next-to-leading order in chiral effective field theory. In particular, we show that it is possible to describe simultaneously the p-wave amplitudes in the pn -> pp pi(-), pp -> pn pi(+), pp -> d pi(+) channels by adjusting a single low-energy constant accompanying the short-range operator that is available at this order. This study provides a nontrivial test of the applicability of chiral effective field theory to reactions of the type NN -> NN pi
KK-Bar photo production from protons
No full textWe study the contribution of the Drell mechanism driven by K^+ and K^- exchange to the reaction gamma N -> KKbar N. Our calculation implements the full KN and KbarN reaction amplitudes in the form of partial wave amplitudes taken from a meson-exchange model (KN) and a partial wave analysis (KbarN), respectively. Comparing our results to data of the LAMP2 collaboration we observe that the Drell mechanism alone cannot describe the large Lambda(1520) photoproduction rate observed experimentally. We argue that the discrepancy could be due to significant contributions from K*-meson exchange with subsequent excitation of the Lambda(1520) resonance. After adding such contributions to our model a good agreement of the LAMP2 experiment is achieved. When applying the same model to the recent SAPHIR data we find an excellent description of the K^+p spectrum and can determine the parameters of the Lambda(1600) P01 resonance, M_R = 1617 +/- 2 MeV and Gamma_R = 117 +/- 4 MeV, from the K^-p mass distribution.A. Sibirtsev, J. Haidenbauer, S. Krewald, U.-G. Meißner and A.W. Thoma
final-state interaction in the reactions and
No full textNear-threshold mass spectra for the reactions and are investigated with an
emphasis on the role played by the interaction in the system. As
guideline for the interaction a variety of
potential models is considered that have been established in the analysis of
data on in the past. Arguments why the
properties of the and interactions can be
expected to be very similar are provided. It is shown that the near-threshold
enhancement in the invariant mass observed for the reaction can be
reproduced quantitatively by the assumed final-state interaction
in the partial wave suggested by an amplitude analysis of the experiment. The
effect of the final-state interaction in other decays is
explored, including the recently measured reactions and . It is found that the final-state
interaction improves the description of the measured invariant mass near
threshold in most cases.Comment: 9 pages, 11 figure
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